©By: John T. Blair (WA4OHZ) 1133 Chatmoss Dr., Va. Beach, Va. 23464; (757) 495-8229 Originally written: circa 1996 Last update: June 13, 2009 - Reformatted page
Front Wheel Vibration or shimmy is a very common
complaints 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.
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 jackstands?) 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 pointing 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.
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.
The only item that is readily adjustable is the toe in. This can be done by the do it yourselfer easily and can be safer then letting a shop do IT to you!
For those Do-it-yourselfers, there is a great article on
aligning the front end.
Toe in should be set to 2 degrees (or 1/8-3/16") of toe in.. Camber angle should be 2 degrees positive camber (the top of the tires slant outward like this "\ /") for all 4/4 Series II through Vs and +4s with the TR engines. I don't have any information on the post 60 vintage model 4/4s, +4s or +8s. Castor angle should be 4 degrees for all 4/4 Series II through Vs and +4s with the TR engines. Kingpin inclination should be 2 degrees for all 4/4 Series II through Vs and +4s with the TR engines. These last 3 items are fixed by the design and assembly of the front suspension. While it is conceivable that they can be adjusted it is done with brute force. So stop and think about it before changing any of these settings unless the car has just been in an accident. (I would be remiss if I did not point out at this time that there is a "modification to the front suspension call a "negative camber" mod. This will change the tire stance from " \ /" to "/ \" ). However, this modification will take a little work and there is some discussion as to its applicability for street use. Fred Sisson as a nice write up about it in his book.
If none of the above has helped solve the front end vibrations, you
will have to come face to face with the mystique of the Morgan
front end.
There are 3 unique items to the Morgan suspension: the bushings, the dampener blades and the one-shot oilier. Replacing the bushings will require the rebuilding of the front end. (See the article by John T. Blair - Rebuilding the Front End - here on the Morgan Web page.) The dampener blades can replaced with out totally disassembling the front suspension and the oilier doesn't really contribute to our problems. Bob Nogueira's explanation of how the front end design can cause the front wheels to wobble and how the dampener blades help correct it is one of the best I've seen.
"The damper blades were not fitted to three wheelers I believe because the large wheels, light weight, and low speeds did not result in front wheel shimmy.
Most Morgan owners usually go 25,000 to 30,000 miles between front end
rebuild but some say they've found that 15,000 miles is the point where
the wear will start to cause the infamous shimmy. Other owners claim
to get 50,000 to 90,000 miles to a rebuild (but I think that's pushing
it).
Borrowing a section from Fred Sisson's book (Notes from a Morgan Garage), he discusses a problem with the tie rods:
"I found a source of play on my +4 steering. It is a simple adjustment to eliminate it. The Pitman arm (on the steering gear box) transfers it's motion to the tie rod (the rod between the front wheels transverse rod) via the drag link. The ball end on the drag link fits into a clamp-on fitting on the tie rod. The Morgan has had 3 or 4 different steering arrangements. The first 4/4s were similar to that on the Trikes. They simply had a reduction gear mounted on the steering column. This was quickly change and a Burman worm and nut box was installed. This was used up until the +8s when the steering box was changed to a Gemmer box. I'm of the understanding that the factory now uses a rack and pinion system. Note: This old Burman box is no longer available and has almost no adjustments. As it wears, it will have to be rebuilt. I do not know of any sources for parts nor have I tried to find any. It also has one very serious draw back. It does not collapse. It has the old type single shaft steering column which can impale the driver in a front end collision. The Burman box has an adjustment for loading the worm. Also check that the bolts on the top of the steering box have not vibrated loose. To check the worm loading, jack up the car and disconnect the Pittman arm (the big heavy steel arm coming from the bottom of the box) from the drag link (cross bar that connects to the tie rod). Carefully turn the steering wheel from lock to lock. There should be just a slight (ever so slight - about 12 in. pounds) increase in the force required to move the steering wheel through center. If not, loosen the locking nut on the screw adjuster located on the top of the steering box. Turn the adjusting screw slightly, tighten the locking nut and retest. Once there is some resistance felt, no further adjustment is required.
I currently have no information on the Gemmer box other than what is
in Fred's book and no information on the rack and pinion system. From
what I've been told by some Morgan owners is that they are replacing
the old Burman steering box with the newer Gemmer box. This will
require some modifications to the steering column which is beyond the
scope of this article. I've been told the Gemmer conversion will cost
about $1,000). The other possibility is to convert to the rack and
pinion system. Again, I have not done this and have no idea what it
entails.
I'd like to thank all those that have contributed their ideas and experiences with this problem: Jeremy Edwards, Bill Jouris, Dave McCoy, D. L. Rotman, Lloyd Shields and especially Fred Sisson and his Notes from a Morgan Gargage, Bob Nogueira. Enjoy your Morgan John
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