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MG MGA - Wheelbase discrepancy

I discovered the other day that the wheelbase on one side is around 1/8 to 3/16 different than the wheelbase on the other side. The spec for both should be 94 inches.
Have any of you adjusted the wheelbase(s) on your MGAs to get both sides to the 94" specification? I'd like to correct mine, but am a bit hesitant on starting before getting some feedback.
How did you go about doing it and any pitfalls or steps to watch out for? Thanks.
Rick deOlazarra

That small a discrepancy could well be rear spring perch locations rather than accident damage. I'd probably ignore it, but you could always loosen the clamps, push the rear end along the spring and tighten them up again, if there is enough leeway there.
Bill Spohn

I would be surprised if this mattered. Factory tolerances were quite generous and our cars are so light on tyres that it should not be a problem (IMHO).
Barry
BM Gannon

I've repaired quite a few accident damaged cars in my lifetime and hydraulically straightened chassis members etc. now we always worked to plus or minus 1/8" for wheelbase for the final check so quite frankly I wouldn't worry about this.
Iain MacKintosh

Rick;

How did you measure this?
Del Rawlins

Thanks for all your comments; so much nicer to make a decision based on some info.
Del; I measured both sides by making sure the front wheels were straight ahead, then took a self-contained spring loaded metal tape measure and measured the distance from the front center of the front wheel rims (at axle height) to the front center of the rear wheel rims.
Rick deOlazarra

Unless you did it on a front end alignment machine, dialed in and centered, I wouldn't place a whole lot of faith in that measurement.
Del Rawlins

Del;
Thanks for the observation, but I don't understand.. with the front wheels straight, what error would the alignment machine eliminate? I'm not contesting your line of thought so much as wondering what is overlooked by the method I employed. Thanks.
Rick deOlazarra

Getting the front wheels straight is the key there. "Straight" is in reference to the rear wheels, and to set that accurately, you hang projectors from each front wheel (which have to be calibrated/adjusted to the wheel so they track true as the wheel is rotated), and targets on the rear wheels. By turning the wheels until both targets register the same value, you know that the steering is centered. All the while, the "wheelbase" measurement on each side is changing because the spindle moves fore and aft as the steering angle changes. All of this is done with the front wheels resting on "slip plates" which allow the suspension to unload any binding from the tires on the ground so you can get true readings.

The important thing is that your wheelbase measurement is going to change a lot, for relatively smaller changes in steering angle, to the point of being useless. If you could measure based on the relative positions of the king pins then that might give you some useful information. But if the car is otherwise aligned properly, and is steering and driving in a normal fashion, then I don't see what the point would be.
Del Rawlins

I think it is certainly possible to measure to an accuracy of less than 1/8" just by being careful. But the real point is what to adjust? To do that, then I think you need to have very accurate measurement. I expect there is quite a tolerance build up in all the components as well as a tolerance in the chassis. There are a lot of joints and a lot of rubber between the wheel rims and the chassis, so everything will have to be in perfect condition and completely "settled" before you could even start to decide what needs to move.
Certainly you would need to follow Del's advice.
Personally I would check that everything is tight and there is no wear in any suspension parts and then just see how the car drives and handles. Unless there was an obvious fault or problematic tyre wear I would not try to adjust anything.

Rear springs and inner fulcrum bushes would be the first thing I would check though
Neil McG

As a long term A owner and having read lots of articles about construction in the factory I wouldn't expect any better accuracy than this. Forget it, it isn't a problem. (At least its not a Renault 4 that were designed with a significant difference in wheelbase!)

Paul
P M Dean

Ignorance is what drives me to this site more often than not, and, as usual, shifts my perspective in a more constructive and realistic way. The wheelbase discrepancy still offends my sense of order, but wherever I go with it, if at all, will be done in a more insightful manner. Thanks for all your help and comments... :)
Rick deOlazarra

Neil, making the physical measurement from front to rear isn't the hard part. The difficulty lies in making sure that the wheels are straight ahead as they would be with the car going down the road, without specialized equipment.

My father's mechanical specialty was rebuilding front suspensions, which I used to help him with. He had the only wheel alignment rack in our small town, which I got to use quite a bit. Getting it done accurately is quite a bit more exacting than the string and tape measure crowd would have you think, and there are a number of things that will throw off the process, including a little bit of wear in the system. There's nothing like chasing your tail, trying to get the wheels centered and the toe set, only to have the whole thing shift out of tolerance as soon as you touch the wheel, due to some previously undetected slop.

If I was really worried about my car being out of whack, I would put it up on jack stands (under the suspension) on a flat, level floor, remove the wheels, and drop a plumb bob from each lower swivel link to the floor, marking the location. Then do the same from a chosen point at the rear. Measuring the points on the floor, if there is a significant discrepancy, work inward to the frame until you find the source.

I wouldn't bother with any of that absent some symptom in the way the car drives, but on the other hand, if Rick really wants to let his sense of order run free, this would be a good way of getting some meaningful measurements. It would only cost him his time unless he decides to act on anything he happens to discover. 8^)
Del Rawlins

This thread was discussed between 20/03/2014 and 22/03/2014

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