IndecisiveS197

I'm hoping Sam or Norm can chime in here but I'll take any advice.

after I swapped out my 7.5" rear end to an 8.8" I found that my car now dog tracks and I get vibrations around 100kmh(which I think is related).

I confirmed this by doing a rough check on the wheelbase and the passenger side is approximately 3/4" further back that the driver's side. I've checked the control arms to make sure they're not defective(J&M lower control arms) and everything is good.

Should I be concerned that I may have a bent axle housing? I've put the car up and let the car run and didn't see and weird wobbles so I think the axles themselves are okay.

I've had the suspension apart and back together multiple times now and I can't get things back into spec.

the solution in my mind is adjustable lower control arms, but is that a good idea or should I get a frame shop involved? I know that my car doesn't have frame damage as I've had that checked (was in a minor accident in the past). I know I can get an alignment and get them to set the front toe to counter the dog tracking but I'd rather fix my thrust angle.

Here are my suspension mods if they matter.
J&M lower control arms
Eibach lowering springs
Eibach anti-sway bars

The control arms I was thinking of going to were the UPR double adjustable street control arms.

Sam Strano

Ok, first if you need to get control arms and you were looking for my help, I'd appreciate if I had a shot at the business. I have a number of different adjustable control arms with various ends to help with noise and ride, etc.

Yes, the axles might be different, even stock by a big, but yours seems way, WAY off. And if you had no vibration before, and you just straight swapped axles (and the 8.8 is not tinkered with), then I suspect you did get one that maybe had a little poke at some point (always a danger with used parts you don't know). Because there is no way the car would track that badly with a box stock, undamaged axle from Ford.

Norm Peterson

If all of that 3/4" error is in the axle, I'd start looking for an axle tube to have twisted in the diff housing. That would also mess with the total U-joint angle even if it didn't tweak the "pinion angle" all that much.


Are the left and right rear toes roughly equal with one side 'in' and the other side 'out'. Is the left wheelbase the short one?


If you still have the 7.5", you may be able to use it to find differences that should not exist.




Norm

UPRSharad

I'd be happy to offer you a discount on the UPR control arms AND free shipping... but we need to resolve this problem first.

If you had the J&M arms before the 8.8 swap, and if you did not install LCA Relocation Brackets WITH the 8.8 swap, then you have a twisted housing. I've seen it several times. That's BAD. It would have to be removed and taken to a chassis shop to fix it properly.

Not that I wouldn't love to sell you LCAs, but you need to check that housing first. Then let me know.

IndecisiveS197

Thanks everybody. I'm not quite sure how I can find out the toe so I'll have to sort it out.

But sounds like i'll need to bring the car in to an axle shop before I start throwing parts in the mix. Now that it's been suggested that the axle tube may have spun I'll have to get back underneath to see if I can confirm.

Sam and UPRSharad, I'll be in the market for other suspension parts once this axle issue is sorted out so I'll definitely be in contact when I'm ready. Thank you guys very much.

tbear853

Measuring Toe:



On your Mustang's rear axle, toe should be "0" (zero).

Norm Peterson

You can check toe yourself by setting up parallel strings, one down each side of the car. Measure the distances between the strings and the wheel rims at the extreme forward and rearward longitudinal points on the wheel flanges. Measure with a scale graduated to 1/32" or finer.


You'll be interested in the individual left and right rear toe measurements, not so much in the total toe.

There is a commercially available product called "Smart Strings" that simplifies the setup for DIY toe measurements.


For checking axle twist . . . drop a plumb bob over the axle tube just inboard of the LCA bracket. Measure horizontally between the plumb bob string and the center of the LCA bolt at the axle bracket. Do this for both sides (your measurements should match). If it's easier to work on the outboard side of the LCA brackets, do both of them that way instead.


Double check by setting your 7.5" up on jack stands and doing the same thing, maybe use that axle for practice first.


Norm

Norm Peterson

Should be, yes. At least in theory or on the design drawings. But I'd bet on there being a fraction of a degree tolerance on both rear toe and rear camber.


Until fairly recently I had a car whose rear axle sat with -0.5° camber and almost +0.5° toe on both rear wheels. Zero thrust angle. Wish I'd tried a little harder to find a place where I could have traded most of that toe-in for a little more negative camber.




Norm

IndecisiveS197

looks like I'll need to buy myself a plumb bob and some string.

tbear853

One thing that will often tweak an axle is jacking a solid axle with a single jack under the pumpkin. I've seen even machanics do it, I've had some tell me I'm wrong .... "parts changers"? Also, anytime one takes a hit in the rear axle area it should be checked.


You're right, there's a small tolerance stated in about every manufacturer's shop manuals I've ever looked at. He was asking how to find out the toe so I thought a simple diagram might help and "0" is preferred on the rear of a solid axle car (where as the diagram shows some toe in as you'ld look for on a front end with steering linkage, control arms, bushings and their tolerances).

Later .....