Rear alignment appears to have strayed out of spec

[450knotOffice]

Interesting development.

For the past month or so my car's rear end has gotten somewhat loose and twitchy in the twisty bits. I attributed this to my worn out rear SO-3's so I finally went out and replaced the rears two weeks ago. I've got 8's in back so I decided to buy 245's for extra grip. Immediately I noticed that the car had a tendency to tramline more and was downright scary in the twisty bits. The car was really loose and unsettled mid turn.

I figured OK, I guess I should have listened to those who have said that I needed 9's with the 245's and decided to swap the 245's with the original sized 225's. This helped a bit but not entirely. I still noticed a bit of looseness and instability mid turn, so I thought that I just needed to scrub in the tires.

Well, today I was out and about putting miles on the tires and happened to stop at the local Porsche dealer to pick up a few items and drool over the 997's (Btw, they had TWO Carrera GT's, Red and Silver. Sheesh! Show-offs.) Anyway, as I stepped outside to head back to the car I noticed that it appeared to me that my left rear wheel had zero camber. Odd, I thought. So I went to the other side and noted plenty of camber, probably over 2 degrees. Hmmm. Back and forth to check if my eyes were playing tricks on me. Nope.

So I called my mechanic and asked if I could come over to his place so he could have a look. No problem. Ten minutes later I've got it in their huge shop (Hergesheimer) and Mark's looking at it and says basically, Yup, looks like it's definitely out of whack. He told me that when the camber gets knocked out, the toe goes out with it, which can make the car quite unstable in corners. He said that some of his old race cars were really hard to keep aligned for any length of time.

Bingo!! This seems to have been my problem all along! I just had the car aligned six months ago when I rebuilt my suspension and would never have imagined that it could be knocked out so easily. I've never hit anything or even hit any bumps that hard.

Come to think of it, the car started acting up on the last big Mulholland Run with Jack and his crew. I wonder if the major thrashing on those super tight corners pushed the rear wheels out of alignment a bit.

Anyway, it goes back into their shop on Tuesday to be re-aligned on their laser rack. Until then it'll have to sit in the garage.

Has anyone else experienced stuff like this? It'd be interesting to hear similar stories.

[Oh Haha]

No problems here but maybe the question should be put to the experts here.
How often should the rear alignment be done? I had mine done when I lowered it last year but just did the front this year.

[Jeff Alton]

Just driving it hard on the street should not cause it to go out of alignment. Hitting a bump or other such thing will. Also, not properly tightening up the camber, toe and ride height adjustment nuts on the spring plate may cause a problem. Same goes for the two bolts that hold the trailing arm to the spring plate, infact those two are the most critical. Yes, your mechanic is right though, camber and toe will both be affected. My guess is the spring plate to trailing arm bolts were not torqued correctly...



cheers

[Zeke]

Hard as it is to believe, even a good shop can forget something. You will have to wait to see what they need to do. Then, the reason may become apparent.

Sorry that you're gonna miss the turkey day run.

[450knotOffice]

Thanks for the words of wisdom, Milt.

If I had your skills I'd just re-align it myself, but I don't. Considering that I see Porsche alignment as a black art, I am amazed that guys like you can align your own cars basically anywhere with just some crude tools at your disposal. It blows me away.

[450knotOffice]

bump.

[J Smith]

Scott - I also have a feeling that a few bolts were not tightened up completely.

It would be easy enough to jack up the car and throw a wrench a few of the nuts to see if any are loose. The two at the rear of the spring plate that hold it to the trailing arm are the most important. Those are the two that really hold the alignment setting. But those eccentrics should be tight also.

I would think you would have to hit a pretty serious pot hole or something to knock things out of whack on the rear if everything was tightened up to spec.

After my alignment, I came home to check everything underneath, and one of those rear bolts was loose......my wrench got sidetracked (probably form me gabbing in his ear the whole time). So it does happen.

Just my opinion.

[450knotOffice]

Thanks. I think I'll do a quick inspection after the alignment is done on Tuesday (just to be sure).

[Jeff Alton]

It would also be interesting to see the "before" specs when they first set the car up on the rack. Is it just the one side that is out?

Cheers

[450knotOffice]

I'm not really sure, to be honest. The rear was set up with about 1 1/4 degrees negative camber but my mechanic says it looks like the right side's got well over 2 degrees and the left side looks like zero degrees. I'm really eager to see where the toe has gone. I'm sure the toe issue is why my handling went bad.