I'm trying to help my friend Dave diagnose a problem with his recently purchased 03 WRX wagon. It is completely stock with 30k miles, with the exception of Deede's Tarmac 2s with some very well worn 225/45R17 Azenis which we installed last night.

A little bit of history: The car is a salvage, from what we can tell the front end was pushed in a bit, and the driver's side quarter panel has some bondo work. Everything else looks straight, nothing appears to be tweaked other than the front end where the bumper mounts up.

What we checked: The alignment was verified at Les Schwab, nothing has been modified from the stock settings. Everything checked out okay on their lazer alignment rack. We did a quick visual inspection last night when we installed the Tarmac 2's, and I didn't see any glaring problems. The gap between the sidewall of the tire and the strut was about a finger and a half on the right side, and I couldn't quite fit my finger in on the left side. Lugs are tight, tires are all air'd up to around 36psi.

Now the issue. While driving around, the car's rear end will get really light. I rode in the car this afternoon, and I noticed it sitting in the passenger seat. Dave said that he had the car up to about 120mph, and then all of a sudden the rear end got really loose. He said it got worse when he tried to brake, and he had to keep alternating the gas and the brakes to keep it in line. The car also acts odd over road gaps like expansion joints, but I can't really explain it.

We're both kind of stumped as to what the issue is. This is starting to go beyond my realm of suspension knowledge at this point. My thought is that there might be a shock problem.

Does anyone have any input?

 

Sounds like the exact same problem with my front end. Though it might be related to how I have the dampening, height and sway bars set at. From what I gathered about my problem, its an issue with the strut on one side being set too high and rubbing on one tire, where as there is no rubbing on my other tires. It might be an issue with the sway bar or sway bar mounts or endlinks being bent too. That's my best guess.

 

at what speed does the rear start to get light? It sounds (at first glance) like some more rear downforce (maybe some kind of gate spoiler) would help this. I'm not too surpised that getting on the brakes would aggravate the problem, since braking shifts weight forward which makes the rear even lighter (and more skittish).

If possible, maybe lower the front a tad to keep air from getting underneath the car.

 

The rear starts to wiggle oddly at lower speeds (20-30mph) too.

 

Could be related to the diffs...

 

tell him to put the spare back in the car

 

Hmm, interesting.

I also have a discussion going on, on SECCS. http://www.seccs.org/forums/showthread.php?t=4697

 

Maybe the tires are different sizes.

 

The varying gaps worry me a bit, as if the alignment is correct, that means the hub carrier or strut mounting tabs are bent/warped, if the subframe/diff carrier aren't tweaked. Waht's the fender clearance like, is it the same on both sides in the rear?

If there's something tweaked, and the geometry is different to one side, that could cause weird issues like what you're describing.

 

I'd have to double-check the fender clearances, but I'm leaning towards the same conclusion as you and Kevin.