The Brake System
The braking system is the most important system in your car. If your brakes fail, the result can be disastrous. Brakes are actually energy conversion devices, which convert the 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. The braking system can exert thousands of pounds of pressure on each of the four brakes. Newer cars have dual systems, with two wheels' brakes operated by each subsystem. That way, if one subsystem fails, the other can provide reasonably adequate braking power. The newer brake systems are more complex, but also much safer than earlier braking systems.
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.
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 most 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). Libra Motive sells a ventilated rotor kit for racing applications.
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.
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 (.0508mm). 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!
THE TEN COMMANDMENTS OF DISC BRAKES
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 (min.TH) [.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. It should indicate less than 0,15 mm. If it exceeds this value, remove the disc, reinstall it in a different angular position and recheck it.
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.
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.
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 removed 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.
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.
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 pistons back away from the drum when the pressure is released.
N.B. See the note on master cylinders
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 aplying the pressure. You may have to remove the parking brake
lever to do this. After removing this pressure shim, use a good light,
and possibily 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!
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
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.
The Parking (Emergency) Brakes
The parking brake (sometimes called the emergency brake) is a cable activated system used to hold the brakes temporarily by hand (when stopped on a hill at a red light) or continuously in the applied position when parked. The parking brake activates the brakes on the rear wheels. Instead of hydraulic pressure, a cable (mechanical) linkage is used to engage the brake shoes or discs which does not need or use the brake master cylinder and hydraulic lines. When the hand lever is pulled, a cable draws the brake shoes firmly against the drums or rotors. The release lever or button slackens the cables and disengages the brake shoes.
The parking brake can be useful while driving up hills:
If you pull up to a stop on an incline, you might notice that you
don't have enough feet to operate the clutch, brake, and gas at the same
time. In other words, you will likely roll backwards slightly while getting
started again. If a someone pulls up right behind you, this can be a problem.
Your parking brake is useful in this situation: Apply the parking brake
after you stop. When you want to go, release the clutch while pressing
the gas, and release the parking brake. This keeps you from having to quickly
switch your left foot from the brake to the clutch, or your right foot
from the brake to the gas pedal. A little practice, and you'll be able
to do it smoothly. Also,
remember if you pull up behind someone who is stopped
on a hill, give them extra room to roll back a little. Especially if it's
a large and ugly truck.
All this being said, most Morgan parking brakes are less than performant. However, there is a trick that can increase the braking power of the rear adjusting models. After adjusting the cable tension, wind a expanding spring around the cable between the adjusting nut and axle brcaket. You will be quite pleasantly surprised. (courtesy of Maurice Owen through Bill Fink)
Remember, it's a good idea to test the parking brake periodically and keep it in good condition. It may save your life if the main braking system fails!
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 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 a 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.)
As noted above, I decided to try Carbon Kevlar pads and
and rear shoes and I am very pleased with the dfiiference. The braking
has more "feel" and is far more effective in all conditions.... no squeaking
either!
GoMoG Webmaster
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. The two systems may be supplied by separate fluid reservoirs, or they may be supplied by a common reservoir. Some brake subsystems are divided front/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.
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 FOR YOUR VEHICLE. Use of improper 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.
Leaks are not the only symptoms of a master cylinder problem. In the front and back brake system, fluid can also be forced from one section of the master cylinder into the other rather than down the brake lines. The effect here will be a loss of brake pressure after an initial effective pump. No leaks will show in the system but the cylinder should be replaced, or professionally completely rebuilt , or, in the case of absolutely perfect cylinder walls and pistons, a rebuild kit may be used (with your fingers crossed).
Difficulty in fitting brake lines to the master is due
to the ends of the steel flairs 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.
Attaching the Brake Lines to the Master and Brake Cylinders
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,
their ends closest to the flaired 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 overtightening.
That is the area that needs to be filed down so that its diameter is smaller
than the minor diameter of the threads. DO NOT FILE THE
ACTUAL FLAIRED 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 flaired 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.
Two closely fitted pistons are located inside the 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 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.
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 and bubbles into the fluid in which the other hose ends are submerged.
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.
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 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.
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.
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.
Since the brake system is filled with fluid, it must be occasionally "bled". (the old fluid is released in order to install new fluid). This is also done to remove any air bubbles that have gotten into the system (usually when any of the brake parts are changed). All hydraulic brakes have bleeder valves near the slave cylinders. These valves are opened while the brake pedal is pressed, causing the brake fluid to flow out as well as any air bubbles present. When the brake fluid comes out without any air bubbles, the mechanic seals the bleeder valve and tops off the brake fluid reservoir. Bleeder valves can also be found on the side of the master cylinder. These are used for the same purpose; getting air bubbles out of the master cylinder assembly. If you have air bubbles in your fluid, your pedal will feel softer than normal, and braking power will be reduced, so it is a good idea to have your brakes bled properly.
To bleed the brakes, it is easiest to have the tires removed, though it can be done with the tires still on. Ensure that the Master Cylinder supply tank is kept topped up with new (NEVER NEVER USED) brake fluid. This is to ensure that air cannot enter the system through the supply tank.
(Assuming always that your Master Cylinder is properly bled), commence the bleeding at the wheels with the near side rear drum brake if you have drums all around, but if the car has rear drums and front discs, start at the front near side wheel.
With someone at the brake pedal, unscrew the bleed screw one half a turn or so enough to allow the fluid to be pumped out, and close the screw after the last downward stroke of the brake pedal when the air bubbles no longer appear.
With the bleeder screw open, the pedal should be pushed by the person at the pedal through the full length of the stroke followed by three short little fast strokes after which the pedal should be allowed the rest. This action should be repeated until there is no air and only fluid expelled. Then it is repeated at each bleeder screw (nipple). (Each of us has different methods of bleeding the system, many ways will work, don't choose one that doesn't.
In many Morgans, there is a brake light which indicates a drop of pressure in the brake hydraulic system. If your light stays on continually, check the warning switch which has a wire attached to the top of it. If disconnecting the wire turns off the light, you have found the problem. What needs to be done is to center the shuttle piston in the switch. The shuttle has rear brake pressure on one end and front brake pressure on the other. It is supposed to tell you when there is pressure loss in one system and is usually turned on by someone bleeding the brakes.
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 alo 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 castelated 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.