69 rear axle sits too far towards driver side
 

HI All,

I have been trying to solve why my rear tire scrapes on inner fender lip on one side. It's on a mostly stock 69 GTO with 255/60/15 tires scrapes over deep dips only on drivers side. It has been shaving rubber off the sidewall and probably time to change the tires because of this.

I had replaced all the control arm bushing w polygraphite 20 years ago and everything looks good there. Axle seems to sit about 1/2 inch more towards the driver side of the car. Pass side has the clearance. The driver side also sat 1 inch lower but I adjusted that even with Spohn SP1 coilovers and adjustable shocks set to stiffness of what is tolerable but it still scrapes.

Car has boxed lower control arms with factory sway bar.

Any thoughts on how to balance out the rear axle so it sits evenly?

Do you have a pic from the front and rear? If the bushing are installed correctly......is the frame straight? or does it dog track at all? You could try a 4 wheel alignment and see if it is square!

If you take it to a frame shop they will put the car on a rack and make measurements and be able to tell you exactly what the problem is. My guess its bent control arms due to poly bushings. Poly bushings are a really bad idea on the rear of A body cars. I found out the hard way. They destroyed my upper control arms. The A body rear suspension is designed for the give of rubber bushings as the suspension is compressed. The poly bushings don't give so something else has to.
Here is some good info https://www.umiperformance.com/home/...pros-and-cons/

This, you don't want polygrahite stuff in the rear control arms, it's too stiff. Rubber bushings or spherical bushings only.

Depending on how the boxing of the control arms was done, it's also possible heat may have warped/stretched/shortened one or more control arms which can pull the axle out of it's centerline.

My advise in all honesty would be to skip the frame shop first and order up some aftermarket control arms for the car and install. If at that point it's still out of whack, it's a good possibility there's something frame or body oriented going on. At that point, seek help from a frame specialist.

You might want to check to see if the body is centered on the frame. I have a similar issue and found that the body is not quite sitting perfectly centered on the frame, and could measure this in the gap between the inner fender and frame.

I agree with this as a place to start. When I installed my body on the frame using the alignment holes and pins, the body was parallel to the frame but over to the passenger side by at least 1/2".

I ended up using a wooden block as a spacer between the frame and inner rocker on both sides and things ended up much better.

Thanks for all the great ideas.

I did the poly bushings over 20 yrs ago when they were "the way to go". That was when I did all the suspension and power train. The boxed arms are factory and likely purchased on the PY classifieds.. There is less than 10000 miles on the car since then.

I have never removed/replaced the body mounts or checked for body centering on the frame. Good thing to check.

I'd prefer to keep from spending the $$ for aftermarket control arms and then finding out they didn't fix the issue..... Believe me I thought about it!

It feels and appears to track straight down the road and I just had an alignment a month ago so I'll call them and ask about being square if they checked that.

I know the car had been in a front pass corner accident b4 I got it. There are still slight wrinkles on top of radiator support panel.

I know I could go to 245/60/15 in rear and avoid this but I like the thicker skins.

FWIW, way back in 1974 I purchased a used 69 GTO that I know was never wrecked, as I stripped the body down to metal for a custom paint job. At the time I had L60 14 tires on the rear. They also rubbed the sidewall on one side because the lip on the quarter panel was closer on one side.

Just as you said about 1/2 inch difference side to side. Having owned a lot of Pontiacs with as much rubber as I could stuff in the rear wheelwells, it's not at all uncommon for one side to be a little closer than the other. Having lived through the late 60s early 70s when these cars were fairly new, it wasn't unusual at all to see a variance side to side, when trying to stuff the biggest possible tire under them.

Two options were rolling the inner lip up into the wheel well, or grinding some of the seam away. Just a variation in factory parts sometimes will give you different clearances, the frame and rear axle could be fine, just slight variances in assembled body panels.

My 73 T/A was closer on one side than the other too, just trimmed the edge back for enough clearance.

I
 

Yeah, I already put the grinder to the inside of the quarter panel lip and nibbled back some of the chrome trim to try to adjust that factory variation out of it!! Cut off about a third of inch but still not enough. I know wheels with a larger backspacing would be a solution but then I would have to buy new wheels all around and I like the old school all chrome Cragar copy look that I have..... And that would be expensive.

I was hoping I could just put a few larger heavy washers somewhere to adjust it over but I just didn't see anywhere I could do that.

Maybe different tires of same size but ones that have less of a balloon bulge on the sidewalls would work... These are 20yr old Tiger Paws.

Maybe put it into assend slide into a curb would coax it back to the other side!!

Install a set of adjustable upper control arms. Skip to 2:25 in the video to see how to move the diff side to side.

https://youtu.be/H2uwqd90Pvc

The first thing the OP needs to do is to find out whether the rear axle is centered in the chassis, and that won't happen without a measuring tape, and crawling around under the car.

You don't want to be adjusting the rear axle to fit the sheetmetal, you adjust sheetmetal to fit the chassis.

If the body isn't seated square, and your body mounts are able to be backed out, you could loosen the bolts, and use a come-along to pull the body to where it needs to be. However the rear axle placement needs to be confirmed beforehand.

:2cents:

I will measure from frame to rear diff on each side to determine if it's centered tonight.
How many body mount bolts are holding it in place?
Also, where would be a safe place to pull from on the body if needed? Behind the rear rocker panel?

Thx Mike

I've actually have never tried it, but threw it out as an idea if the rear axle is centered and square, and the sheetmetal needed to be slid one way, or the other.

I've wrenched on cars as my living for roughly 50 years, so I tend to think of logical ways to solve problems, and that would be what I'd try if the body needed to be moved a fraction of an inch.

Since the rear, behind the rear axle kickup of an A body frame is pretty weak, I'd be looking for a place to pull in the rear axle area, or ahead of the rear axle, where the frame is much more robust. Get your body centered, and re-tighten the body mounts, and see where it ends up.

Most body, frame configurations have alignment holes that you put a round guide in to align them, it may prove to be off those guide holes. But you're going to have some type of manual, or a video of where those alignment holes are on your particular car. Maybe someone with more body shop background on the board will chime in?

I guess I meant to say pull behind the rear of the lower kick panel just in front of the rear wheel. Definitely not the rear rocker panel! Or, Maybe cut a block of wood with a slight angle to wedge in there between the panel and the frame.... Tap it with a light sledge to see if it moves it after body mount bolts are loose of course! Loosening the body bolts will be the big IF......

Body mounts

From that drawing, it looks as though the factory left enough clearance to move the bolts around enough to get your body shifted a slight bit. The tough part is will all the bolts loosen up without spinning the cage nuts inside of the body mounts. I know if it were a car from the rust belt the answer is, probably not, but a southern car would have a much better chance of the bolts loosening up.

Although the idea of moving the body on the frame seems like a reasonable suggestion and I like the spirit of it, the reality of attempting such a task might result in upsetting the panel gaps between the doors and the fenders, hood, etc. If we were talking about an unassembled car without the front clip, I'd say yeah go for it, but on a fully assembled car I'd be more hesitant. I did this on my car when I dropped the body back onto the frame, but it was a 100% bare shell with no interior, glass, etc. to weigh it down and make it harder to pull. Critically, I didn't have the doors, fenders, or hood installed yet, either.

I am running 275's on my 67 so you should be able to get 255's to fit in a 69 pretty easy with the right wheel offset.

I considered the gaps changing before I suggested it, but 1/2 inch at the rear of the body is less at the front. Unless someone has done it before, no one knows for sure. It may flex the metal enough that it all moves together. I guess weighing out whether the juice is worth the squeeze is what the OP has to do.

But we're putting the cart before the horse, gotta see if the if the rear axle is centered in the chassis first. It may be in the suspension, and not the body.

The rear axle is centered on the frame. Checked it this morning and measured from the inside of frame to center of upper side diff cover bolt and they were within 1/8th inch.

Every time I try to solve one of the issues with it, It fights back and says "Leave Me ALONE!!!" I love it and hate it at the same time :)

I'm also trying to lift this same side of the car to match pass side by adjusting the new rear coilovers. QA1 with 150lb springs. I started with a 1 inch lower difference on driver side (side that scrapes) at fender lip so I have tried to set the coilovers to raise it to reduce scrape. I set it to match pass side and every time I come back after test drive it settles back down to nearly same position. The difference between the sides is around 2 1/2 inches when measuring the amount of thread showing on the coilovers. I only wanted a 1 inch lift but that much diff at coilover seems excessive. Almost like something is locking into place and once it goes past that point, that is where it stays. I'm so frustrated!!


p.s. Had to temporarily remove tailpipes and will adjust location due to installing coilovers.