1/4" difference in wheel base side to side question - Ford Mustang Forum
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post #1 of 13 (permalink) Old 08-21-2018 Thread Starter
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1/4" difference in wheel base side to side question

Got the car back from having a front end alignment and they noted that the wheel base on the driver side was 1/4" longer than the passenger side. They said they compensated the alignment as best they could, but I may want to correct it and bring it back for a re-alignment. The car drives fine and if there is a problem, I don't feel it in the steering.

I pulled a tape measure from the lower ball joint zerk fitting to the center of the leaf spring axle mounting plate. I agree there is a 1/4" difference between the sides. To get the axle square to the car frame, it looks like I need to slide the driver side axle forward 1/8" and the passenger side to the rear 1/8". What I don't see is any adjustment for rotating the axle. The leaf springs are a matched set based on the part numbers stamped on them.

So is there an adjustment I don't see? If not, does 1/4" matter? Can you elongate the center hole of the axle mounting plate holes and tighten the U-bolts to hold it in place?


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post #2 of 13 (permalink) Old 08-22-2018
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I wouldn't worry about it. There aren't any easy adjustments so if it drives right, leave it alone. I don't now that Ford even specified what the wheelbase should be. Who says its your rear axle out of alignment; it could well be the front suspensions are attached differently?

I have two '66s. I knew the orignal owner so I have a complete history for the coupe and it has never been in any collisions other than a scraped fender. It has a wheel base of 108" on the passenger's side and 107 3/4" on the drivers side. You could never tell it by looking or driving the car and I have driven it all over the US. Our GT convertible has been smacked pretty hard in the right rear although it still has the original, straightened quarter panel. Its wheelbase measures 108 3/8" on both sides. The coupe with unequal wheelbase drives better than the one with equal numbers when both cars are aligned to the same spec.

I think most cars have some variation side to side. Most owners have never measured to know about it. Wheelbase also varies by fractions of an inch depending how you align the front end. Putting in more caster tilts the spindle forward at the bottom which increases wheelbase. Similarly, adjusting camber changes the track width of the front wheels.

Its simialar to the left-right deck height on a 289. Rarely were they the same from the factory. Its such a small 'defect' no one really knows about it until they measure.

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post #3 of 13 (permalink) Old 08-22-2018 Thread Starter
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Thanks Ivy. My thoughts exactly. It falls in the category of if it isn't broke, don't fix it. Since the front is aligned to the recommended OpenTracker radial tire settings, I feel like it's close enough.
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post #4 of 13 (permalink) Old 08-22-2018
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As long as it's not "dog tracking", leave it alone. I see Ford full sized vans doing that all the time. They've been making the same van chassis for decades and they still don't have it right.
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post #5 of 13 (permalink) Old 08-23-2018
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I think it's a frame issue. Your car was probably involved in an accident at one point. I say this because my passenger side wheelbase is I think 1/2" shorter at 107.5", while my driver's side is at the proper 108". It drives fine, but it causes some tire to fender alignment issues. Drives fine, though. If I were circle tracking it, I'd probably want it to go the other direction.

So, best you can do is take it to a collision shop and have them put it on a stretching table.

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post #6 of 13 (permalink) Old 08-27-2018
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1/4" doesn't sound like a lot, but if it's the rear axle that's not perpendicular to the frame, you should be able to correct it using a "thrust alignment plate" kit.
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post #7 of 13 (permalink) Old 08-27-2018 Thread Starter
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I did not know about an alignment plate. Looks like an option if I see an unusual tire wear pattern. Thanks.

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post #8 of 13 (permalink) Old 08-27-2018
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I'd loosen the rear axle on the leaf springs and see if it has shifted and can be shifted back again.
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post #9 of 13 (permalink) Old 08-27-2018 Thread Starter
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I got a printout of the alignment. The thrust angle is -.0.41*. Seems like being less than 1/2 degree would be considered minor, but maybe that's wishful thinking. Again, it doesn't pull to one side and the steering wheel is centered. I don't mind doing the work, but just don't want to fix something that is close enough for a 52 year old car.

GT - It looks like the centering stud on the leaf spring is very close in diameter to the bolting plate centering hole. I can't see much play. I am still considering your suggestion. I would put web straps on each side of the axle and pull in opposite directions. If there is any play in the hole sizes, then it may rotate slightly. I would try this before buying a thrust angle plate because it costs over $100 and raises the body 1/2" on the side it's installed.

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are you sure the difference lies in the rear axle? if so, the first thing I would check is the leaf spring mounts, it's been a long long time since I looked at one of those, but if I remember correctly, there are rubber bushings between the leaf and the mount bolt, which could be worn. it's also possible that the body of the car is 1/4 inch off, right from the factory. the body was a welded unibody, on a mass produced car. at the time, 1/4 inch off may have been perfectly acceptable. the other thing, the caster is adjusted by moving the lower control arm forward or backward, are you sure the 1/4 inch difference does not lie in the position of the lower ball joint? instead of measuring at the ball joint, try measuring from a fixed point on the body of the car, to see where the 1/4 inch difference actually is
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post #11 of 13 (permalink) Old 11-08-2018 Thread Starter
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Thanks 73, The alignment machine laser was the first to note the 1/4" difference between the front wheel and the rear wheels. The caster was set during the alignment so I pulled from the ball joint to leaf spring to confirm their finding. Since this thread was posted, I've inspected and see nothing wrong with the leaf spring supports or the centering bolt. The car tracks great. It may be 1/4" off, but I can't tell of any problems. I guess tire wear may show something in time.

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post #12 of 13 (permalink) Old 4 Weeks Ago
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post #13 of 13 (permalink) Old 4 Weeks Ago
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Without seeing the settings that the alignment shop used for camber, caster, and toe its hard to say if there was a compromise to the settings. There is at least an 1/8" of slop on the axle mounting pins that will allow the rear to shift one way or another.

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