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.
The first and easiest check is tire pressure. It should be 16 to 18 pounds normally and add 6 pounds for high speeds driving. However, most of us start off at about 25 pounds.
Next comes the possibility that a tire or rim 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. (Do I have to remind you to use jack stands?)
TO CHECK THE TIRE, 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.
TO CHECK THE RIMS, 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 Bushings
(from Greg Solow on the Morgan List)
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.
(Greg also makes hard-chromed and centerless kingpins
which vastly outlast the standard.)
Webmaster Comment
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.
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.
| 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 |