Front Wheel Vibration

Front Wheel Vibration or shimmy is a very common complaint by Morgan owners. Identifying which of the various front suspension components is causing these vibrations can be very frustrating. To try to ease some of this frustration, I will talk you through the steps of isolating and fixing the problem.

Tires and Rims

CHECKING THE TYRE PRESSURE The first and easiest check is tire pressure. For earlier 4/4s, it should be 16 to 18 pounds, for Plus 8s 20-22  (add 3-4 pounds for high speeds driving.  If in doubnt, check your Manual.

CHECKING THE RIMS  Next comes the possibility that a is "out of round". This condition is more prevalent in the cars fitted with wire wheels but if a disk wheel has had a brush with a curb, it too can be warped. The procedure to check the tires and wheels is similar and simple. Jack up far enough to get the desired wheel off the ground.

Place the brick along side the wheel and move the pointer so it is perpendicular to the wheel. You want the pointer to just touch the rim where it rolls in - where the bead seats. Again spin the wheel and watch for variations in the gap between the pointer and the rim. If the gap is less that 1/8" the rim is OK. If the gap is greater than 1/8" the wheel will have to be trued - especially so for wire wheels. For disk wheels, the wheel is usually replaced.

CHECKING THE TYRES, place brick just in front of the tire. On the brick place a screwdriver (or something) to be used as a pointing device. Slide the pointer towards the tire, until it just touches. Now slowly rotate the wheel. As the tire passes the pointer watch the gap between the pointer and the tire. If there is a "hi" spot the tire will push the pointer back onto the brick. At the low spot on the tire, you will see the widest gap between the tire and the pointer. If this gap is less than 1/8" the tire is OK.

CHECKING THE BUSHES
from Greg Solow on eMog

With the car sitting on the ground at normal ride height, have a friend grab the top of the front wheel and push inward toward the center of the car and then pull outward away from the car. This must be done with some degree of force. While your friend is doing this, take a bright light and look carefully at the point where the spindle rests on the top of the rebound spring (that is the small lower spring at the bottom of the kingpin).

You are looking for side to side movement at this point. This is where most wear occurs on the kingpin. With unworn parts there will be no movement here, and the greater the usage the more the movement. More than 1/8 inch of play at this point is an indication of worn out bushings and probably kingpins also. 1/8 inch of wear at this point probably equals about 1/2 inch or more of movement at the edge of the tire.

Movement at the edge of the tire can also indicate play in the front wheel bearings. That is why it is important to look at the interface of the rebound spring and spindle to ascertain exactly where the play is located.

CHECKING THE WHEEL BEARINGS
from Lorne Goldman on eMog

With the car on the ground and front wheels facing straight ahead, grab the tread at the top of tyre with your fingers try to push and pull in and out.. Do you feel a significant movement (a slight click can be ok) . If the movement is excessive, you should check the adjustment of the castle nut holding the bearing. To adjust the castle nut, you remove its cotter pin and then tighten until it makes just contact with the bearing and then back OFF to first cotterpin hole. (WATCHPOINT: If you tighten the castlenut too tightly against the bearing, you will quickly burn the bearing.)
 

CHECKING THE DAMPER BLADES  To test for wear, with the car on the ground, grab the blade and push forward and back. If a click or movement can be heard or felt the shims need to be pushed tight against the blades to prevent that. However, there MUST be free movement in and out of the slot made by the shims. Push down on the blade to see if it can move in  and out.  

Wheel Cracks

There are two places where disc steel wheels "normally" crack, firstly,  at the lug nut and secondly, at the hub cap attaching stud. Cracking at the lug nut is not caused by over tightening the lug nut, but rather by the stress to the wheel induced  by the stiff sliding pillar suspension under racing conditions. The factory also introduces stresses at this location by stamping the wheel to provide full purchase for the sloped shape of the wheel lug nuts. Lastly, wheel stresses are also magnified by the fact that these wheels have only four lug nuts, a 20% increased loading factor on each nut over normal five studded wheels.

The crack at the hub cap studs is due to the factory induced stress when the curved portion of the wheel is flattened for insertion of the hub cap stud. These cracks then radiate to the ventilation holes in the wheel. An appropriate solution is to have a competent and experienced welder weld 1/8 inch flat plates  to the back side of the wheel with appropriate holes for the lug nuts and the center hub.

Balancing Your Wheels

With these items checked it's time to head down to the local tire shop and have your wheels dynamically (spin) balanced. Most shops take the wheel and tire off the car to balance it.. It requires a special adapter, so check with the shop to ensure that they have the adapter.) The advantage here is that the wheel/tire unit can be moved around to any of the 4 axles and maintain its balance.

Sometimes the suspension components can add to the balancing problems. To try to balance the entire suspension you will have to find a shop that can still spin balance the wheels on the car. But this seem to have passed on to oblivion like so many other things. This method will give you a better balance at each corner but the wheels and tires can not be moved. When the tires are rotated, the suspension will have to be re-balanced.

Wheel Bolt Torque
 
Thread Size lbs  / ft  Kg / mtr 
3/8 UNF  38 - 40 5.2 - 5.5
7/16 UNF 53 - 55 7.3 - 7.6 
1/2 UNF 77 - 79 10.6 - 10.9 
M12 x 1.25  65 - 67  9.09 - 9.20 

Front Vibration (Curing it when all else fails)
Webmaster Note: There is plenty in these pages that will show how to sort ANY stock Morgan front suspension and rid it of vibration. In theory..and happily most often in practice, these pages can cure all issues in the original Morgan manner. However, for whatever the mysterious reasons, sometimes vibration will be beyond the skills of the owner or various addons or changes he may have made. It such cases the cars become a source of deep frustration. The point of this Manual is not to force you to sort your Morgan as it was originally meant to be. The priority is to help you reap enjoyment, not frustration from your mog. For those of you with front end vibration that resists your efforts, here is a quick fix to stop vibration and get you back on the road. You can always renew your efforts for the proper cure at your leisure. And if someone sees this non-Morgan solution and takes you to task, direct them here and beat them on the head with your knock-off hammer. That's what it's for. Enjoying your Morgan is more important than being correct. 

Lorne,
I wanted to wait until the traffic died down before I wrote. eMog was good to me and I thank you for it. I wanted to let you know that my St. Malvern's dance is gone. I made lower adjustable braces, but with them I was only able to limit the shake to a very narrow critical speed (about 45 MPH) or make it much worse depending on how I had them adjusted. At the worst, I was able to make the shake occur at 60MPH accelerating, and then shake again at 40MPH decelerating. I could not rid the car of the stroke of 5 1/4 inches (same as a VW beetle damper) and my car requires 5 3/4 inches for the steering to go fully right and left, so I have ordered a damper for a Mercedes SLK or Chrysler Crossfire which has a longer stroke. I should have that installed in the next month, but I'm in no hurry since I can now drive the old car. Caster certainly plays a part, but adding the damper worked like magic. I cannot detect it as far as steering effort goes, and the only side effects are the good feeling steering and no shake. I'll send you a picture of the Mercedes unit when I get it fitted. In the meantime, these are pics of the VW unit installed. I used some very stiff alloy 3/16" aluminum flatbar mounted to the lower rad mounts. The rad is still mounted as before on rubber with the nylock nuts only snugged up enough to compress the rubber a little, but the forward bolts are tight to hold the flatbar in place. When I install the Merc unit, I will have to mount it more to the right of the car, and about 1-1/2 inches forward so that it does not foul the steering rod on large bumps. I am now of the opinion that those old cars should have come with a damper. :-)

Three weeks later!!!

Lorne,
        I hope all is well with you. My aftermarket Mercedes SLK (also fits Chrysler Crossfire) steering damper arrived and I mounted it. As I predicted, I had to mount the fixed end slightly forwards of the aluminum plate to prevent the steering rod from contacting it on hard right hand bumps. This time I also mounted the damper correctly so that the dust cover would not collect water. The previous photos of the VW bus damper show how NOT to do it. This damper works even better than the VW unit. It has plently of travel with some to spare so that the wheels will turn fully to the steering stops. Also, this damper is slightly stiffer, but not so stiff as to be noticeable when turning the steering wheel, but stiff enough to completely damp the steering vibration. With the VW damper, the critical speed at which the St Malvern Dance occurred could be felt, although the dance never started. With the Mercedes damper, running the car up and down through that critical speed reveals no evidence that there is a critical speed at which vibration occurs. Here's a couple of pictures of the installation and the parts I used. Take care,  Meyle part number 026 046 0161


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