Rear camber, too much negative.
 

So I have a 1984 GSL with 71,000 miles. And it has maybe 1.5 to 2 degrees of camber, Its even on both sides. I can't see any damage to the axle or anything. But it ate my new rear tires in about 4,000 miles, I don't autocross or do burnouts or anything. so this is an issue eating tires so fast.

I looked and there didn't seem like a way to adjust rear camber (i've done alignments before). Is there indeed a wy? or is there a bushing shot or anything?

Thank you.

straight axle car - someone might have jacked using the pumpkin and the stress bent the axles down?

Jacking a car by its pumpkin should be fine to do. I do it all the time.

Is it positive or negative camber?

Either way check the axle housing to make sure its straight. Then I would
pull the axles and see if they are straight and if the bearings are good.

+1 someone ran over something at sometime

Has the car ever belonged to someone who autocrossed it? If it is negative camber then it may have been done on purpose. You can heat the housing in such a way that the metal will srink, inducing camber. You may be able to use this technique to get it out.

I like bearings here...

I couldn't tell you if someone has autocrossed it (actually I ran it at one event just for fun, I usually run my miata), i doubt it, because nothing else on the car is set up for autocross, but then again I really don't know, I know some history on the car from what the previous owner told me and it doesn't sound like an autox history unless he lied :P I know the car sat with a tarp ontop of it due to scratches.... but that doesn't change anything.... anyway....

I've seen some things about heating it to change it. I feel competent enough to do that, I've got more searching to do on that, can you point me to any good references or starting points? I have access to a propane and an oxy/aceteline torch so I'm sure i can get enough heat.

I'll have to jack the car and start taking measurments, I'll do it today if I have time, or tommorrow.

I jacked it, and took the wheels off, and took the disk off of the passenger side. according to my level the camber is 0* to .5* negative, within tolerances as far as i'm concerned. The drivers side isn't striped down to the gub yet, but the disk is about .1* negative. So i'm lost, nothing looks out of place or anything. nothing looks like its been heated up at one time, and all the paint is intact and consistant. Wheel bent isn't the issue because the tire wear is too consistat.

When I try to move the passenger hub, sometimes I might think I might feel some play but its still pretty tight. I'd hate to replace two 40 dollar wheel bearings for no reason, I guess i'll have to pull the axles and do more exploring...

I wish I took some real camber measurments befor I jacked the car, but I ddidn't. vbut visually the rear wheels looked like they had more camber than my miata that has 1.5*

BTW, just to give an example about how bad the tire wear is, the inside edge is worn smooth and the outside edge is almost new, I knew I'd get uneven tire wear but I didn't expect this much...

In all honesty, rear ends are a cheap enough item I would just replace the housing with a used straight one. Use your pumpkin/axles/brakes/ect.

Isaac

posted the same time you did, disregard my suggestion if your housing is straight :)

Toe out will cause aggressive inner tire wear as well.

You may not have a camber problem but a toe in/out problem instead.

I read the technique of inducing camber in a book about high performance suspension tuning,I believe the author was Herb Adams, I will dig it up and provide more information when I can get a chance.

Edit: Chassis Engineering by Herb Adams

When you are checking the alignment make sure of the following,

All tires are aired up to the proper pressure.
The floor is perfectly level, a scale platform is the best.
You are in the car.
Use a true camber gage.
Make sure the gage and the surface it contacts are clean and free of rust.
Springs are properly seated.
Sway bars are disconnected.

My axle has about .75 - 1 degree of camber. Just enough for some decent grip for road racing. ;)

Yes, I may have a toe problem as well, but the camber can be seen when standing behind the vehicle.

I can tell you that the new to me 1982 RX7 that I had in 1983 with 20K miles on it wore out a pair of 205R13 BF Goodrich Comp TAs in about 12K miles. And the wear pattern on the rear tires was all on the inside - as in steel bands showing.

How wide are your tires?

to check for a bent axle, you need to support the rear of the car really well, remove the rear wheels. you then start the car and put it in 1st, and you can easily see if something is bent.

to check for a bent axle HOUSING is a little harder. you need to be able to measure from wheel hub to wheel hub.

send us some pics for kicks

and if the rubber bushings in the 4 link are real worn the axle housing will move all over the place causing odd tire wear.

Sounds like something most 1st gens guys would want!
A couple degrees of rear camber is what racers were shooting for when they intentionally bent their rear axles. 1-2 degrees is enough to help rear traction,but not ruin the bearings.

rwatson5651 is right,it sounds like toe is a bigger concern.Camber by itself doesnt cause inner or outer tire wear,its the camber COMBINED with toe that causes the localized scrubbing which eats only a small portion of the tread up.
Every car with IRS drives around with a couple degrees of camber all the time,let alone when they corner or hit a bump,and they dont eat tires up. Ever followed behind a BMW or a old VW? Even bone stock they have a visible,quite obvious tilt to the rear rubber. Now if those non-steering tires are angled out in either direction(toe) they are going to be grinding against the pavement each and everytime they go round.Id check the trailing arms for bends or damages bushings/mounts.

I had that exact same thing happen...
 

I had that exact same thing happen. It turned out that the car had gone over a cement parking stop and dented the driveshaft and bent the rear end so that the pumpkin was higher due to a bent rear housing so the wheels weren't square with the surface. It's easy enough to tell if that's your problem if it is as bad as mine was. Just looking at it and I could see the bend; you might need to measure but it shouldn't be hard to tell.

Although the fix is relatively easy, you have to swap the housing which means removing the pumpkin and the axles, brakes and lines, emergency brake cable.
That's the easy part. Next is the four links and the watts linkage. If you're lucky, you won't have rusted bolts in bushings. If you have to do all that work, you might as well either replace all the shafts (4 links and the 2 for the watts linkage) or at least all the bushings.

I think even with a bushing or two shot, the wheels should still be parallel with the pavement. Did you have even wear on the tires or only on one side? Were the wear patterns 'cup' shaped? If so, that usually means bad shocks as well.

Some answers to a few of the questions,

My tires are stock size, they have like 4 or 5000 miles on them. I could live with a 10000 mile treadlife but not 4 or 5.

The bushhings all look pretty good to me considering the car is already almost 30 years old.

Nothing looks bent...

My plan is to do what was suggested to check for axle being bent, then I'm going to check the wheels for trueness with my dial indicator, then i'm going to put it all back together, check tire inflation, and go to the levelest place I can find (using a water level to level a car in my garage is alot of work...) then i'm going to check all alignment parameters. (just some fyi, I've got experience with alignments from doing one on my miata in my garage.)

I'm going to attach a bunch of pics.

I'm not so sure what I should show pics of but heres some more....

and some more...

I checked runout on each side,

on the passenger side

Just the hub- .002 inch

at the rotor- (well, it went crazy and I couldn't get a good reading, it was even scraping on the caliper but it never did that before because i'd have noticed when I ran it without wheels last year, I tried hitting the rotor with a hammer to make it seat, but it just wouldn't so i'll have to seat it with the wheel I guess...)

at the rim of the wheel- .020" at the limit of wheel runout according to the haynes manual (alloy wheel)

Driver side

At the rotor -.005 ish i was in a hurry, i ran the car between sides to see the hubs/rotors rotating under power, rotary exhaust gases arent fun.

at the rim of the wheel- .01-.015


I'd say its fairly straight, I cant really see any movment just eyeballing it, only when I use the runout guage/dial indicator.