The Morgan Classic Brake System (A Complete Overview)

The Brake System
by Lorne Goldman

The braking system is the most important system in your car. If they fail, the result can be disastrous. Brakes are actually energy conversion devices, converting kinetic energy (momentum) of your vehicle into thermal energy (heat). When you step on the brakes, you command a stopping force ten times as powerful as the force that puts the car in motion. So the braking system exerts thousands of pounds of pressure on each of the four brakes. Many electric cars now preserve that braking energy temporarily so as the release it immediately after for creating incredible start-off times! 

WATCHPOINT Since 1968 (Plus 8s) or 1978 (all cars) Morgans have been fitted with dual circuit master cylinder systems, with each the front and the rear wheels braked by a separate subsystem. That way, if one subsystem fails, the other can provide life-saving braking power. These are infinitely safer than earlier braking systems. I counsel you to ignore or caution anyone who suggests a single circuit system be maintained rather than replaced.

But the basic process of converting a vehicle's momentum into (wasted) heat energy has not changed since the days of the horse and buggy. To stop a horse drawn carriage, the driver would pull on a lever which would rub on the wheel. A good braking system reflects the mass of the vehicle as the needed braking energy is a function of of the size of that mass and balance. 

EDITORIAL NOTE: Outside of the simplicity and purity of their design, trad Morgans set themselves apart from most automobiles by their very low weight. HFS, a canny engineer of the Old School, knew that simplicity, low weight and potent engine could beat all comers on the racing and autocross competition. The early Morgan record in those fields is remarkable. Even today, in their class, the 1968-70 Plus 8s are the cars to beat in an all marque competition of that era!  

But today's flock of moggers have lost their way on the braking side, as they have in other areas. 

Very low mass means much less braking power is necessary. But that is ignored by today's community. Even rear disk brakes are added when they make no sense. They remind me of the true tale that Peter Morgan prominently added front dampers only because they pleased the sensibilities of the post-shock customers! (One day you should all remove the front dampers for a test ride. You will be surprised.)  Morgans don't need much braking. Front disks and rear drums are more than sufficient for any road-going trad going Morgan and MOST racers I have ever seen. The tedious expensive installation of rear disk brakes often unbalances the braking again, making the comportment of the car harder to control and often at the cost of a functional safety brake. We can also theorize that the weight distribution of the unsprung weight prejudices the perfect weight of the trad.

WATCHPOINT 1: The balance proportioning of the pre-1993 systems should be verified and corrected or click here as wellThe set up of the dual cylinder Girlings is incorrect for our cars. It was correct when Bill Beck had the later AC power assisted system installed in all the cars.

WATCHPOINT 2: The design of the front end creates an unsteady hard-to-control factor on hard braking. It so potent that eventually it bows the cross member!! It can be easily/cheaply rectified in two good and one bad. The bad one is ingenious and simple! One bangs old kingpins down the lower crossmember piece to stiffen it and prevent its bending. It also stops the unsteadiness on hard braking. However, it add LOTS of weight at the very periphery of the car, exactly where you DO NOT want putting a heavy case on the rear does.

WATCHPOINT 3: I HAVE found a potent improvement in merely choosing better brake pad and drum show improvement. Though those chosen by some local communities have a sad if any performance effect. Porterfields will change the effective braking of two pot braking (assuming the rear shoes are done as well) to the effectiveness of the later 4 pot calipers. I tried it out on our UK Morgan.

Why do so many new moggers adopt such stuff? In my humble opinion, it certainly involves a blind copying of what OTHER marques do. :(  I believe it is also vastly encouraged by a very fundamental, very charming human trait. Humans can't love anything with expressing that. Just as we buy our loved ones new silk ties and earrings, we find similar ways of expressing our love for our Morgans! It is analogous to fondling. :D Very satisfying emotionally but we too often betray the car and HFS' wonderful earth bound common sense.

And in my 25 year experience with our Community, involving many 1000s of individual and public interactions, the greatest incentive to such sadness is poor and/or absent maintenance. When it reaches a point where even an amateur notices something amiss with the car, they are now told by today's brethren to buy a completely new design from the new predatory aftermarket!!! :(

The GoMoG Law of Professional Servicing: Do not report or repair any adjacent anomalies observed when doing this task. It will unjustly give you a predatory reputation. Wait until the area fails and the owner asks for a repair. Repair is far more profitable than than prevention. You must create a clientele with deep bond of trust of you(difficult in a hyper-suspicious world) before you can take care of their Morgan properly.

Lastly, after 20 years of unsettled financial times from the Aero's development and today, and no in-depth in-house talent in control of development, the MMC designs cars to please its current market demographic rather the exigencies of logic. :(  Accordingly, today's fare is not susceptible to the home skills of owners and is MUCH heavier.  In a nutshell, Morgans changed because a new owner demographic was sought out from 2000 on. Sadly, it gave the company a negative value
(aside from the equity of the last government grant), and forced the Family to sell for no more than the value of that grant :( ending an over-100 year heritage and modern day miracle. We should never allow our love of our Morgan prejudice them! Focus on add-ons that do NOT add to the complexity of the car, its reliability, the ease of understanding it, owner interaction, weight or handling. Tweaking, polished metal or chroming fits that bill for me! :D

The brake system is composed of the following basic components: The "master cylinder" which is located under the hood, and is directly connected to the brake pedal, converts your foot's mechanical pressure into hydraulic pressure. Steel "brake lines" and flexible "brake hoses" connect the master cylinder to the "slave cylinders" located at the wheel. Brake fluid, specially designed to work in extreme conditions, fills the system. "Shoes" and "pads" are pushed by the slave cylinders to contact the "drums" and/or "rotors" (discs) thus causing drag, which (hopefully) slows the car.

Disc brakes have been used for years for front wheel applications, (and on many older cars are fast replacing drum brakes on the rear wheels). This is generally due to their simpler design, lighter weight and better braking performance. The greatest advantage of disc brakes is that they provide significantly better resistance to "brake fade" compared to drum type braking systems. Brake fade is a temporary condition caused by high temperatures generated by repeated hard braking. It occurs when the pads or shoes "glaze" due to the great pressure and heat of hard use. Once they cool, the condition subsides. Disc brakes allow greater air ventilation (cooling) compared to drum brakes. Drum brakes are not internally ventilated because if they were, water could accumulate in them. Disc brakes can rapidly fling off any water that they are exposed to, and so they can be well ventilated. Morgan rotor (discs) are quite thick which requires higher temperatures to heat but are also difficult to cool for the same reason. High performance disc brakes have drilled or slotted holes through the face of the rotor, which helps to prevent the pads from "glazing" (becoming hardened due to heat).  Many suppliers sell ventilated discs for racing applications.

Disc Brakes
by Lorne Goldman

Disc brakes use a clamping action to produce friction between the "rotor" and the "pads" mounted in the "caliper" attached to the suspension members. Inside the calipers, pistons press against the pads due to pressure generated in the master cylinder. The pads then rub against the rotor, slowing the vehicle. Disc brakes work using much the same basic principle as the brakes on a bicycle; as the caliper pinches the wheel with pads on both sides, it slows the bicycle. Disc brakes offer higher performance braking simpler design, lighter weight, and better resistance to water interference than drum brakes.

Disc brakes, like many automotive innovations, were originally developed for auto racing, but are now standard equipment on the front wheels of all Morgans and the rear brakes are of the "drum" type. Drum brakes use two semi-circular shoes to press outward against the inner surfaces of a steel drum. The older cars have drum brakes on all four wheels. Libra Motive and other suppliers sell a rear disc brake conversion kit.

Because disc brakes can fling off water more easily than drum brakes, they work much better in wet conditions. This is not to say that water does not affect them, it definitely does. If you splash through a puddle and then try to apply the brakes, your brakes may not work at all for a few seconds! Disc brakes also allow better airflow cooling, which also increases their effectiveness.

Rotors (Discs)
by Lorne Goldman

The rotor (also called the disc) is clamped by the brake pads in order to slow the vehicle. The rotor is a heavy circular steel plate attached to the wheel providing a two sided braking surface. Pressurized fluid in the brake lines flows into one or more "slave" cylinders in each caliper. The fluid pressure is exerted against the slave pistons, which force the brake pads against the surface of the disc. As the pads clamp onto the rotor, intense heat is generated, which can in extreme conditions actually cause the rotor to glow red hot!

The surfaces of the rotor are "turned" (re-machined) whenever the brake pads are replaced in order to remove the "glazed" surface which forms on the rotors. The turning process also "trues" the disc (makes it perfectly flat) which eliminates the pulsations which are experienced when the rotor is warped. Warped rotors give a slight tugging when the brakes are applied, and send a pulsing sensation back through the brake pedal. Rotors have "minimum thickness" and if it is "turned" to resurface, it may become too thin to withstand heat as it warms, requiring replacement. Maximum runout on the rotor faces is only .002 inches (.0508 mm). The maximum permissible finish of the disc machining is 15-30 micro inches circumferentially and 50 micro inches measured laterally, one thin cut (if that) that might last a few hundred miles. Pre-1992 4/4 and Plus 4s arrive new at .375, later models and Plus 8 start at .500". Please note that Morgan Rotors are specially ordered by the Company, if you find a suitable replacement please email me.

(Semi metallic brake pads give better performance, longer replacement intervals and reduced "fade", but they also wear down the rotor more quickly than organic [non-metallic] pads.) Recently, I decided to try Carbon Kevlar pads and and rear shoes and I am very pleased with the difference. The braking has more "feel" and is far more effective in all conditions.... no squeaking either!


1. A brake disc is one of a vehicle's active safety components. Competence and constant technical updating is therefore essential for anyone dealing with it.

2. It is appropriate to regularly check the disc thickness and appearance. A change must be made before the disc thickness reaches its minimum value (thickness) [.450 inch on a Plus 8 or post-1992 4/4 or Plus 4], or whenever anomalies are noted on the disc surface. The thickness of the rotor indicates how resistant it will be to the high heat of its use. Below a certain point, it will not be able to stay true for any period.

3. The disc assembly instructions must be read and scrupulously followed at all times.

4. Discs on the same axle must always be changed together.

5. Brake pads must be changed together with the discs. The correct choice of pads is essential for braking efficiency and comfort.

6. The discs and pads being replaced are an important source of information. Always carefully inspect the disc condition (condition of the braking surfaces, colors, appearance, etc.). This may show anomalies in one or more components  (calipers, pads, bearings), and before changing the discs any such problems
should be identified and solved.

7. Clean the disc and most important the hub surface, and remove any traces of corrosion.

8. Properly tighten the bearing nut and replace the pin with a new one. Properly tighten the fastening bolts in a cross-wise order using a torque wrench to check to applied torque. The same instruction goes for installing the wheel.

9. Check the run-out of the brake disc, by using a run-out gauge attached to a fixed part of the suspension. 

10. In order to allow a perfect fit of the materials and guarantee top  performance, observe a short  running-in period (180-300 miles), using only regular and smooth braking action.


Here is the analysis.

imgSmooth Brake Rotors

thumbsup.jpgSlotted Brake Rotors

WATCHPOINT: Some dedicated slotted “racing” rotors employ a sharp edge on the slots to cut into the brake pad a small amount for better bite, but this can greatly accelerate brake wear.

thumbsdown.jpgCross Drilled Brake Rotors 

thumbsdown.jpgDrilled & Slotted Brake Rotors

CONCLUSION: Choosing the Right Brake Rotor

Brake Pedal
by Lorne Goldman

The brake pedal, (in case you're one of those people who don't use it), is located between the accelerator pedal and the clutch. The brake pedal is connected to the master cylinder via a push rod which has a "slack" adjuster fitting to properly adjust the brake pedal relationship to the push rod.

The brake pedal is solidly mounted to the firewall, and works as a force multiplying lever. Stepping on the brake pedal pushes a piston within the master cylinder, thereby pressurizing the hydraulic brake lines. The hydraulic pressure pushes the brake shoes and pads against the brake drums and rotors, thus slowing the wheels.

The brake pedal gives feedback to the driver which can be beneficial to good maintenance, and therefore potentially save your life. If the pedal pulses when pressed, the usual culprit is a warped rotor, which is potentially destructive to the caliper. If the pedal squishes down when pressure is applied, a dangerous leak is likely present (even if fluid does not drip out anywhere). Your brake pedal should not move more than a small amount when you press it, no matter how hard it is pressed. It should not feel sponge like: a spongy pedal spells trouble in the braking system. With the car parked, press the brake pedal firmly and hold the pressure. If the pedal sinks slowly, a leak is present.

A good rule of thumb is this: ANY changes in the "feel" of your brake pedal should be a cause for serious concern. Remember, with brakes, there is NO excuse for poor maintenance.

Brake Drums (generally)

The brake drum is a heavy flat-topped cylinder, which is sandwiched between the wheel rim and the wheel hub. The inside surface of the drum is acted upon by the linings of the brake shoes. When the brakes are applied, the brake shoes are forced into contact with the inside surface of the brake drums to slow the rotation of the wheels.

They are not cooled internally, because water could enter through the air vent cooling holes and braking would then be greatly impaired.

One advantage of drum brakes is that they can easily be set up to be mechanically activated by a pull cable (for use as parking brakes). Drum brakes are usually quite sufficient for rear brakes because most of the car's weight transfers to the front wheels during hard braking. The reduced weight on the rear wheels makes the higher performance of disc brakes somewhat unnecessary except in racing.

The working parts of a drum brake are contained inside the brake drum. The drum is attached to the hub of the wheel and revolves with it. Inside the drum are a pair of curved brake shoes that are held close to the drum by retractor springs. The shoes and actuator linkages are mounted to the backing plate behind the drum. When the brake pedal is pressed, fluid is pressurized in the wheel cylinders. Pistons in the wheel cylinders then push outwards against both shoes, overcoming the retractor spring tension and pressing the shoes against the drum. The friction of the shoes against the drum slows the wheel. When pressure is released from the brake pedal, the retractor springs force the shoes back to their normal (released) position. The springs force the brake shoes slightly back (inward) away from the drum when the brake is released. These springs, along with the other brake hardware, should be replaced every other time the brake shoes are replaced.

As the linings of the shoes wear down and become thinner, an adjustment screw must be used to keep the shoes close to the drum but without touching until applied.

Back Plate
by Lorne Goldman

The backing plate is a round, stamped steel disc, used to keep water out of the drum/rotor, and in drum brakes as a mount for the wheel cylinder. It is bolted to the end of the rear axle housing. The backing plate is the foundation for the wheel cylinder and brake shoe assembly. By the way, the racers prefer they older adjustable rear brakes (pre-7/1993) to the later self-adjusting brakes used after. 

Anchor Pins and Shoe Retainers

The anchor pin is a strong metal pin mounted to the backing plate, which prevents the shoes from turning along with the wheel when the brakes are applied. Shoe retainers are small spring clips of various designs used to hold the brake shoes against the backing plate. These pins insure shoe alignment and prevent them from rattling.

Wheel (Slave) Cylinders

Wheel cylinders, also called the "slave" cylinders, are cylinders in which movable piston(s) convert hydraulic brake fluid pressure into mechanical force. Hydraulic pressure against the piston(s) within the wheel cylinder forces the brake shoes or pads against the machined surfaces of the drum or rotor. There is one cylinder for each wheel. Drum brake wheel cylinders are made up of a cylindrical casting, an internal compression spring, two pistons and rubber cups or seals. This type of wheel cylinder is fitted with push rods that extend from the outer  side of each piston through a rubber boot, where they bear against the brake shoes.  Only one of the Morgan rear wheel cylinders has a bleeder screw (right hand side)  (or bleeder valves) to allow the system to be purged of air bubbles.

As the brake pedal is depressed, it moves pistons within the master cylinder, pressurizing the brake fluid in the brake lines and slave cylinders at each wheel. The fluid pressure causes the wheel cylinders' pistons to move, which forces the shoes against the brake drums. Drum brakes use return springs to pull the shoes back away from the drum when the pressure is released.

N.B. See the note on master cylinders

Removing Rear Slave Cylinders (pre-1993)
by Lorne Goldman
Removing the Morgan wheel cylinders can be a trick at first. The little shims/clips and doodads are great fun. There are three of them holding the rear cylinder in its slot (but allowing it to move in the slot). The two bigger ones nearer to the back plate are U-shaped and (they come in from different ends) lock together at one end with two locking tabs holding them together. This is extremely hard to see the first time without 15 year old eyesight and an electron microscope. First remove the third one which is the obvious outer one applying the pressure. You may have to remove the parking brake lever to do this. After removing this pressure shim, use a good light, and possibly a magnifying glass to see the two locking pieces and the tabs..lifting the two apart at the locking tabs with a very small screwdriver or even an exacto knife and then sliding one (the lower?) back to disengage them.

Special Note on Wheel Cylinders!
by Lorne Goldman
 December 21, 2005

The Works has announced that the Girling rear brake cylinders are no longer available and has sent this information to their Agents. This crucial parts was/is used on the following Morgans

+4s 1958 to 7/1993
4/4s from 1960 to 7/1993
+8s from 1968 to 7/1993

In fact, there is a readily available OEM match sourced by an eMOG member at a retailer. Here are the details.

Pattern Rear Brake Cylinders manufactured by Past Parts, part no. 25-0146
They take Visa and are willing to ship worldwide.
Cost is GBP 15.08.

Special Note on Wheel Cylinders! (post-1993s)
by Lorne Goldman  June 2012
The wheel cylinders are Caparo AP Braking CW 15953 which are matched by Delphi Lockheed LW 15953.

Notes on Removing Morgan Brake Drums (Series V 4/4)
from Paul Helman

Those large screws on the drum alone are not what you are looking for.  All they do is retain the drum to the hub. You should also be looking at those quarter inch 27/inch threaded hex bolts.

Try backing off all the way on your adjuster screws then gentle tapping around the rim of the drum (using a piece of wood between hammer and drum rim) should get it off.  I assume your basic configuration is similar to mine (Series V 4/4) which I am currently redoing.

N.B. I suggest new retaining bolts to avoid shearing off the bolt when retightening the drum. (I did this twice recently necessitating removal of the hub and a bit of careful drilling to extract the body of the bolt with a stud extractor without damaging the thread of the mounting holes in the rim of the hub. These are hardened bolts so it did present a challenge.  I am getting somewhat adept at it just through repetition..

Removal of the the hub is easy once the drum is off by using a large gear puller. Hopefully your cotter pin has been installed in such a manor that straightening it will be no problem .  Once the cotter pin is removed, the removal of the castellated nut is no problem. This is what made removal of the sheared bolt relatively easy with the hub in hand and the careful use of a drill press.  This is not something to be tried with the hub still mounted.

by George Dow at the eMog Pub

Most old cars that I have worked on have a securing screw that is usually done up too tight. These screws are there to stop the drum coming off with the wheel when it is changed, therefore do not need to be done up tight "too" tight at all. If you have a suitably sized screwdriver that can take a hit on the handle,  put the driver in the screw head and give the screw a hit before you try to loosen it (if you have such screws fitted) If that don't impact driver might do the job. (Please remember to NOT use it to put them back on! Some anti-seize on the threads can help next time you decide to remove them.

First back off the adjuster (at the rear of the back plate) on these pre-1993 (Triumph rear brakes).

You can also borrow a brake drum puller. See method at the right

by Lorne Goldman years later

George's instructions above will pretty much do the trick. However, the post-1993 reardrums do NOT have a post adjuster at the rear of the back plate. (for this reason many racers move back to the earlier pre-1993 versions (if they are lucky enough to find a back plate!). At one point, Librands was looking into having a better rear drum system made. Check with them.

Aside from terminal furstration occasioned by amateurs fitting a new rear cylinder or shoes into this very fiddly system, many mistakenly remove the hub fittings. These are the huge slotted fittings that clear the drum and are visible from the outside. One would think that even a first time cursory examation would show that these things do not have anything to do with the drum at all, but this has not been obvious to everyone. LEAVE THEM ALONE unless you wish to remove the hub and drums off the axle, a very tough job needing a slide hammer.

To remove the drum, merely remove the little bolts and then bang the drum outward (from their interior edge) with a rubber hammer .

Brake Calipers

The caliper works like a C-clamp to pinch the pads onto the rotor. It straddles the rotor and contains the hydraulic "slave cylinder" or "wheel cylinder" piston(s). One caliper is mounted to the suspension members on each wheel. Brake hoses connect the caliper to the brake lines leading to the master cylinder. A "bleeder valve" is located on each caliper to allow air bubbles to be purged from the system.

Morgan calipers contain two (and recently four) separate pistons. These calipers are fixed in place; i.e., there is no lateral movement like the newer floating caliper, the pistons take up the slack on each side of the rotor. These are called "dual cylinder" or "dual piston" calipers, and are standard equipment on many performance cars.

Brake Pads and Brake Shoes

Brake pads and brake shoes are composed of a friction lining material mounted onto metal backing plates. Brake linings are designed to have a specific coefficient of friction. The linings contact the drums and discs, create drag, and thereby retard the speed of the vehicle. The lining material is designed to wear down faster than the rotors and drums they rub against, so that they are the only part that usually has to be replaced. When worn out pads and shoes are replaced, the drums and rotors are re-machined or "turned" (a small amount of metal is removed from their surfaces) so that the brake shoes and pads will "break in" properly.

Because of intense friction and heat produced in braking, brake linings were first composed of heat resistant asbestos compound. When it was discovered that breathing dust containing asbestos fibers cause serious bodily harm, asbestos pads were replaced with other types. There are now three basic types of materials used in brake linings: (1) non asbestos organic, which is usually made from filler materials and high temperature resins; (2) metallic; and (3) semi metallic, which are composed of finely powdered iron or copper, graphite, and small amounts of inorganic filler and friction modifiers. The first and third types of brake lining are used for conventional brake service. Under extreme braking conditions (sports cars, ambulances, police cars), the metallic type of linings are used, because they provide more constant frictional characteristics (reduced brake fade) than the other two. Organic pads and shoes wear down the rotors and drums less than semi metallic or metallic pads, but also wear down quicker themselves, requiring more frequent replacement.

Most pads and shoes have "wear indicators" built into them, or into the hardware which holds them in place. The wear indicators cause a squealing noise when the linings wear down to the level of the indicator. Mechanical wear indicators (small metal tabs) allow the driver to know when their brakes are needing replacement before serious damage occurs. When the pads or shoes wear out completely (past the wear indicators) and the backing plates contact the drums or discs for extended periods of time, the damage which results can require replacement of the rotor or drum, which is MUCH more expensive than the shoes and/or pads! (Some advanced braking systems have electronic wear indicators built into the linings, which allow the driver to be warned by a light on the dash.)

Better Pads and Shoe Compound

As noted above, I decided to try carbon kevlar pads and and rear shoes and after search about a bit. I am very pleased with the difference. I have experience with five compounds used on Morgans.


These have the braking compound that will be provided by the MMC as original stock. They are the bottom of the list for feel and effectiveness but are serviceable. The have an infamous tendency to squeal. Available from your Morgan dealer or off


The UK community favors EBC Green Stuff Pads. I also tried THEM on our UK Plus 8. IMHO they are better than the stock pad as they act normally when cold. But other than that they seem to be nowhere near as performant as something made specifically for road going sports cars. On that point, I have never read anything noteworthy about them in performance applications and I removed them after a single season. However, they seem to wear well and make less noise than the stock pads. British Company


I first bought these 24 years ago at the suggestion of John Sheally II, the racer. I started with their Brake pads and then their shoes at the rear drums, using the same compound, 4 years after (their R4-S compound). I now swear by them. The braking has more "feel" and is far more effective in all conditions.... no squealing either. To give you an example, I found the 2 pots calipers had the same braking power as 4 pots when the Porterfields were put on! US Company. And the stuff seems to last forever!

Master Cylinder (pre-1993) 
by Lorne Goldman

The master cylinder displaces hydraulic pressure to the rest of the brake system. It holds THE most important fluid in your car, the brake fluid. It actually controls two separate subsystems which are jointly activated by the brake pedal. This is done so that in case a major leak occurs in one system, the other will still function. N.B. We do NOT recommend the use of single circuit masters used on pre-1978 cars. Their lack of any redundancy or safety measures make them dangerous.  The two sub-systems should be supplied by separate fluid reservoirs or they may be supplied by a common reservoir that is is split inside. The systems are divided front and rear. When you press the brake pedal, a push rod connected to the pedal moves the "primary piston" forward inside the master cylinder. The primary piston activates one of the two subsystems. The hydraulic pressure created, and the force of the primary piston spring, moves the secondary piston forward. When the forward movement of the pistons causes their primary cups to cover the bypass holes, hydraulic pressure builds up and is transmitted to the wheel cylinders. When the brake pedal retracts, the pistons allow fluid from the reservoir(s) to refill the chamber if needed. This is the system Morgan used from 1970s on.. a Girling unit from 1978-1993 and then a AP Racing system with an integrated booster.

On later models. if the brake light comes on, the fluid level in the reservoir(s) should be checked. If the level is low, more fluid should be added, and the leak should be found and repaired as soon as possible. BE SURE TO USE THE RIGHT BRAKE FLUID (see brake fluids and the note on Silicone fluid)  FOR YOUR VEHICLE. Switching to or from silicone brake fluid can contaminate the system. If this occurs, ALL of the seals in the brake system will need replacement, and that is usually a VERY expensive operation. The tandem master cylinder  was devised to avoid the possibility of all the brakes of a vehicle being put out of action by a fracture in the pipe line leading to one brake cylinder. . There are two pistons in the master cylinder, in line with each other.

Difficulty in fitting brake lines to the master is due to the ends of the steel flares having been squashed by over tightening.  Girling calls for a tightening torque of 15 inch lbs.  The tube nuts should be able to be easily threaded all the way into the master cylinder ports by fingers alone.

Replacement for the Morgan Dual Master Cylinder (pre-1993)

Many with single master cylinders have switched, for safety reason, to Dual Masters. Sadly, the Girling unit used by Morgan from 1978 to 1993, is no longer available and was very expensive when it was. One option that has been tried and tested by many is the one used in the Subaru "BRAT" (aka the SHIFTER in the UK or the BRUMBY in Australia)..but other marques also adopted it and it is VERY hard to find now. If one is found It will require adapters and a bit of curving of the brake tubing and possibly relieving the entry hole into the car a bit but it is a close match to the Girling and much cheaper new. 

If anyone finds another suitable replacement, please advise me
by Lorne Goldman

By the way, this SUBARU MC was used on the following cars. (12) 1978-1981

1600  (2) 1978-1979
1979 H4-1595cc 1.6L 2 BBL Vin EA71
1978 H4-1595cc 1.6L 2 BBL Vin EA71

1600 DL  (2) 1978-1979
1979 H4-1595cc 1.6L 2 BBL Vin EA71
1978 H4-1595cc 1.6L 2 BBL Vin EA71
1600 FE  (1) 1979-1979

1979 H4-1595cc 1.6L 2 BBL Vin EA71
1600 GF  (2) 1978-1979
1979 H4-1595cc 1.6L 2 BBL Vin EA71
1978 H4-1595cc 1.6L 2 BBL Vin EA71

BRAT  (5) 1978-1981
1981 H4-1781cc 1.8L 2 BBL Vin EA81
1980 H4-1595cc 1.6L 2 BBL Vin EA71
1980 H4-1781cc 1.8L 2 BBL Vin EA81
1979 H4-1595cc 1.6L 2 BBL Vin EA71
1978 H4-1595cc 1.6L 2 BBL Vin EA71


AIMCO M900304
PROPORTIONING WATCHPOINT (1978-1993) : Savvy owners have discovered that the original Girling MC (1978-1993) provides a 50-50 division of hydraulic force to front and rear brakes. This is very unusual for a front disk/rear drum set up. We know of three cures. 

A. One can use a proportioning valve, (fitting it at one of the rear junctions seems easiest) and adjust the proportion until the car is under complete control (57-60 % bias in favor of the front)  or, if you are the mathematical sort, you can use a brake bias calculator.

B. One can use the later AP Caparo (originally Lockheed) 1993-on Master Cylinders which are proportioned correctly. However, these come with a booster which can make fitting difficult as the reservoir can abut the exhaust too closely requiring a remote reservoir.

C. Fit the Subaru MC above which comes with proper proportioning.

The result is a happy one. The rear brakes stop locking first making the rear end of the car more controllable under braking. Take note, brakes are not an area for mistakes. If you have ANY concerns, use the services of a competent professional. That being said, even a Morgan pro not be aware of the proportioning issue.

Master Cylinder Bore Size
by Lorne Goldman

The question of MC bore size has become more important as other Tandem master cylinders have being replacing the earlier (and dangerous) single cylinder brake systems Morgan used.

Decreasing MC bore size will decrease your pedal effort and increase your pedal travel. Conversely, a larger bore in your master cylinder will, all other components being the same, increase your pedal effort and decrease your pedal travel. As with some other brake parts purchases, this comes down to your preference for how the brakes "feel" under foot when you are driving...but Morgan owners want to retain the original feel all while significantly increasing their safety. The magic number is a bore size of .75" (3/4 inch)

Attaching the Brake Lines to the Master Cylinder

The ends of the NUTS that push the flares up against the sealing surfaces in the wheel and master cylinders are what get mushroomed out and that prevents the threads on the nut from getting in far enough to engage the threads in the cylinders.  If you look at the nuts, the ends closest to the flared end of the brake pipe have no threads. That portion of the nut is supposed to be smooth and straight. That is the area that normally gets mushroomed out from over tightening. That is the area that needs to be filed down so that its diameter is smaller than the inside diameter of  the threads.  DO NOT FILE THE ACTUAL FLARED END OF THE BRAKE LINE ITSELF.  If the end of the nut is the proper diameter and the threads on the nut and in the cylinder are in good shape, and the nut is carefully started STRAIGHT into the threaded hole of the cylinder, then it should screw right in with your fingers until it bottoms against the flared end of the brake pipe. Then just snug it down with a 7/16 line wrench and
check for leakage with pressure applied to the brake pedal.

Flaring Brake Lines

I do not recommend single flares for brake lines. These will work acceptably for fuel lines but are a no-no for brake lines. The safest ends for brake lines use either a double flare or bubble flare. The problem with bubble flares are that they are considerably harder to make perfectly for the home garagiste and for this reason I am loathe to suggest that they be made by any other than a professional.

by Robert Robinette

Tools: I use a pipe cutter ($10) and a double-flare tool ($40-50) a table vice and a file.

Put the pipe cutter on the brake line where you want to cut it. Gently tighten the knob on the cutter and then spin the cutter around the pipe about three times and then tighten the knob a little more and repeat then repeat until the line breaks in two. Now immediately slide on the flare nut. REMEMBER TO PUT THE FLARE NUT ON THE PIPE BEFORE YOU FLARE IT OR YOU WILL HAVE TO CUT OFF YOUR NICE NEW FLARE AND START OVER! Once you can slide the flare nut on the tube enough to get a clamp on you're fine.

Now smooth out the outer edge of the pipe with a file and use a deburring tool (or hand use a large drill bit) to smooth out the inside edge of the pipe.

Double-flare tool with pipe clamped, ready to flare (note both flare nuts are in place on pipe)

Put the flare tool's pipe clamp on using the appropriate sized hole that matches your brake line. Expose the required amount of pipe, clamp it down, attach the correct adapter for the pipe you are using, screw it down on the pipe while watching the pipe to make sure it doesn't slide out of the clamp. Now back out the clamp and remove the adapter, then finish the double-flare by screwing down the flare tool into the pipe. It's easier than it sounds, just follow the directions that come with the tool. Repeat for the other brake line end. .

Blow some WD-40 or other solvent through your short line and then blow compressed air through the line to dry it out. Push the brake pedal a little to flush some brake fluid through the line coming from the master cylinder-this must be done to remove any debris that got into the line during cutting, sanding and flaring.

Here is an explanatory Video (If the video does not appear, please advise me)

WARNING You must torque the brake line nuts to 113-190 inch pounds! (about 10-15 foot pounds) If you don't, you run the risk of having a nut coming loose and dumping brake fluid with a loss of brake pressure and braking ability.

For the curious. Or those who wish to buy lines at their nearest auto store, Here is a image of a bubble flare.

Master Cylinder Pistons

Two closely fitted pistons are located inside the dual circuit master cylinder. The inner part of the piston is pressed against a rubber primary cup that prevents fluid from leaking past the piston. The outer end of the piston is pressed against a rubber secondary cup. This prevents the fluid from getting out of the master cylinder. The inner piston also has several little bleeder ports; these pass through the head to the base of the primary cup. Both of the piston assemblies are in the cylinder, and are kept there by a stop plate (or snap ring) in the end of the cylinder. A push rod, connected to the brake linkage, applies pressure to the pistons.

Though master cylinder kits are sold to repair leaking cylinders and replace all the rubber components, it is commonly accepted that the master cylinder is better completely rebuilt with the cylinders re-shaped or replaced as new when there is a problem. A Morgan master cylinder is normally good for 40,000 miles before a rebuild. have the MC sleeved with stainless steel and it will become a "forever" component requiring only rubber part replacement at long intervals.

Please note that when replaced the Master Cylinder itself MUST be "bled" of air bubbles. This is done with hoses attached to the cylinders brake lines and looped back into the reservoir. By pumping the brakes, the hoses will expel bubbles into the fluid in which the other hose ends are submerged.

Caliper Piston Seals

The caliper piston seals are designed to keep the fluid pressure behind the pistons, and to retract the pistons enough to allow the brake pads to just barely clear the rotor, thus reducing rolling resistance. The seals should NEVER leak. If a leak is detected, it must be repaired immediately, because the fluid which escapes can defeat braking power by getting on the disc, and the pressure loss can affect brake safety.

Brake Hoses

The master cylinder is connected to each wheel by brake lines and hoses. Brake hoses are specially constructed flexible tubes with metal ends for transmitting fluid under extreme pressure. These hoses are used to connect the calipers to the metal brake lines, allowing the caliper to move when the wheel turns or goes up and down. The entire hydraulic system is filled with brake fluid, which is pressurized by the movement of the master cylinder's pistons. This fluid is very important. Always use only the recommended fluid.

When you remove a wheel, these hoses are easily visible. If the hoses appear cracked or brittle, they should be replaced immediately. Close inspection of the brake hoses is a good way to prevent catastrophe!

Brake Fluid

Brake fluid is a special liquid for use in hydraulic brake systems, which must meet highly exact performance specifications. It is designed to be impervious to wide temperature changes and to not suffer any significant changes in important physical characteristics such as compressibility over the operating temperature range. The fluid is designed to not boil, even when exposed to the extreme temperatures of the brakes.

Different types of brake fluid are used in different systems, and should NEVER be mixed. Most cars use "DOT 3" or "DOT 4" brake fluid. Some newer cars use silicone brake fluids. Though Dot 3 and 4 are compatible, Dot 5 should NEVER be mixed together with either, because the seals in each car are designed to work with only their specific fluid types. For example, the mixing of "Silicone" brake fluid and conventional glycol based DOT 3 or DOT 4 fluids should be avoided at all costs, as the two fluid types are not miscible (they will not mix together). DOT 3 brake fluid and DOT 4 brake fluid CAN be mixed.


Girling has advised that  silicone based brake fluids DO CAUSE SEAL EXPANSION.OR THE CREATION OF A GOOEY SUBSTANCE THAT COLLECTS AROUNDS THE SEALS; In most cases, in street driven cars this is not a problem because the hydraulic cylinder seal fits into a groove in the piston. The groove is very deep, and the piston and the seal slide back and forth in the bore of the cylinder in which they are a close fit.  The 10% expansion of the seal, (this is the figure used by Girling), only makes for a tighter seal.   But in some older Girling master cylinders, the seal fits into a groove in the body of the cylinder and the piston, which is smooth, slides back and forth through the seal.  And experience has shown that in these cylinders, the expansion of the seal causes the seal to lose contact with the piston and the cylinder stops working.  In fact ALL pressure is lost and the pedal goes right to the floor!  The type of cylinder where this has occurred is used in all  Morgans up to about 1955.   All the sealing setup in most disc brake calipers is the same as this,  therefore the use of silicone should be restricted to clutch hydraulics and drum brake systems that use the later design master cylinder and where the cars are driven infrequently and are really "garage queens."

BRIEFLY IT IS NOT RECOMMEND TO USE  SILICONE FLUID FOR ANY DISC BRAKE CAR THAT IS EVER DRIVEN HARD.  As the temp of the fluid rises, the fluid becomes more and more compressible, and it becomes more susceptible to contributing to a sudden, total, and unpredictable lack of any pedal pressure and consequent brake failure. It is just not worth the risk.

If you are not racing your car or you are a Concours competitor then silicone brake fluid can be used. But for the reasons mentioned, it is wiser to stay away!

The other problem (not usually mentioned) with silicone fluid is that it is much more difficult to bleed the brakes.  Pumping the pedal vigorously as one does with glycol will cause air to dissolve into the silicone fluid and defeat the process.  One must be very gentle with the pedal action when bleeding or use a power bleeder.


Because we do a lot of restoration work, I thought it would be a good idea to try silicone fluid. We started using it for the first time about 15 years ago.  What we have found is that glycol based fluid does  NOT cause Girling or Lockheed seals to expand,  silicone based fluid DO CAUSE SEAL EXPANSION.  This has been confirmed by a press release that I have from Girling that they put out about ten years ago. In most cases, in street driven cars this is not a problem because in most hydraulic cylinders the seal fits into a groove in the piston,  The groove is very deep, and the piston and the seal slide back and forth in the bore of the cylinder in which they are a close fit.  The 10% expansion of the seal, (this is the figure used by Girling), only makes for a tighter seal. But in some older Girling master cylinders,  the seal fits into a groove in the body of the cylinder and the piston, which is smooth, slides back and forth through the seal. In our experience, in these cylinders, the expansion of the seal causes the seal to lose contact with the piston and the cylinder stops working. In fact you completely lose ALL pressure and the pedal goes right to the floor!  The type of cylinder where this has occurred is used in all Morgans up to about 1955. All the sealing setup in most disc brake calipers is the same as this, we have decided  to restrict the use of silicone fluids to clutch hydraulics and drum brake systems that use the later design master cylinder and where the cars are driven infrequently and are really "garage queens."

The other cars we use these fluids on are cars like MG T series and Morris Minors where the master cylinder is mounted under the floor boards and are therefore exposed to a lot of moisture as well as having the later design of cylinder.


As the temp of the fluid rises, the fluid becomes more and more compressible, and it becomes more susceptible to contributing to a sudden, total, and unpredictable lack of any pedal pressure and consequent brake failure. It is just not worth the risk. Regards, Greg Solow

One of the WORST things that can happen to your car is if the brake fluid becomes contaminated, because the seals are designed to work with only pure brake fluid. "System contamination" means that all of the piston seals and hoses are deteriorating, and therefore must be replaced, a MAJOR expense. So, be VERY careful what you put in the master cylinder reservoir!

It should be noted that brake fluid is highly corrosive to paint, and care should be used not to get it on your car's finish.

Brake fluid will become oxygenated over time and should be changed at intervals which are a function of time as well as mileage.

Brake Lines

Brake lines are small steel tubes with special internal coatings to prevent rust and corrosion. These tubes connect to the master cylinder, and then run under the car to each of the wheels. At the wheel, a "brake hose" connects the brake line to the caliper or wheel cylinder. As the brake pedal is pressed, the master cylinder forces the brake fluid throughout the brake lines and into the wheel (or brake) cylinders. This pressure causes the slave cylinder pistons to move, forcing the shoes and pads against the drums and rotors to slow the vehicle.

People use different materials for brake lines. Some are excellent and some are unwise. For flexible lines, into the calipers and from the rigid line tot the rear brake system, I  use Aeroquip, the best there is. Make sure you get the stainless steel braid version. It is available from Morgan specialists like John Worrall or Brands Hatch Morgans. For the rigid line, there is a perfect product called Cunifer or Kunifer. It is a UK product that has swiftly gathered praise in  the US as well. It has all the advantages of copper but is much stronger and enduring.