Cupping wear...

[donagain1]

While doing some undercar slithering recently in order to chase down an electrical issue, I noticed some minor cupping on the inner edge of my '85's front tires. After reading some notes on potential causes for this sort of wear I must admit to being slightly confused. Some mention bouncing, others mention wobble, tire balance, worn/loose wheel bearings, shocks/struts, or any of a myriad of suspension parts. With so many potential sources for such wear, what's the easiest/cheapest to start with... wheel balance? I'm not without my own particular skills in certain areas of things automotive, but tweaking suspension adjustments isn't one which I've finely honed. Will a "normal" alignment check reveal anything? If so, can a general automotive aligment shop diagnose it, or is there some things that are peculiar to these cars and require eyes that are Porsche-tuned (ergo $$$)?

If anyone can point me to things that are easily investigated with results that are obvious to we non-experts, please fire away with suggestions. One request... if your response is going to include too many suspensionspeak terms like "pittman-bushing-tie-end-swing-rods", please attach an 8X10 color glossy with circles and arrows showing where the... (sorry for the literary ripoff, Arlo)
Don~

[timmy2]

Take it to a shop that does corner balancing and alignments for an assessment.
They will tell you what it needs.

[Bob Kontak]

Originally Posted by donagain1

if your response is going to include too many suspensionspeak terms like "pittman-bushing-tie-end-swing-rods", please attach an 8X10 color glossy

If you are not aware of the oft discussed Frammitz-Georing thermo-couple adjusting clevis then why would you even ask?

Timmy is right. At least consider a decent independent alignment/chassis shop.

I do not think there are shortcuts like proper tire inflation. Lower cost tires will scallop faster given the same problem.

[KTL]

Abnormal wear can be caused by bad alignment and also by worn parts. Loose ball joints, worn shocks, or worn tie rods can cause the condition you're seeing. If you could post a picture that would be good too. Sometimes people call it cupping when it's something else.

Do you have an idea how old the shock absorbers are? I've found a lot of 911s with original shocks during replacement and when removed their damping effect was minimal at best.

You can check your wheel bearings very easy. With the car on the ground you grab the top of the tire (wherever you can get your hands in there) and shake it in & out, side-to-side. If You feel excessive rocking, then your wheel bearings are loose and need adjustment or replacement. You should feel a slight amount of play, as in a minor click. If you get major clunking by doing that test, there's some significant play going on that shouldn't be.

You can check your ball joints very easily. Jack up the car and remove a wheel. Put a jack stand under a sturdy part of the car in the front. Turn the steering wheel a bit so you can get behind the brake rotor. Grab the strut body at the bottom where it connects to the A-arm and firmly push-pull on it to feel for play. A bad ball joint will reveal itself pretty easy.

Thankfully the front end of the 911 is very simple in nature. The parts are all easily accessible and serviceable. The hardest part to deal with IMO is the ball joint. But a big ol hammer and chisel (and maybe some heat from a propane torch) will take care of that ring nut no problem.

[donagain1]

The beautiful part of all this is in that I paid a moderate amount of money to the local P dealer's service dept. for a "31-point" roadworthiness check earlier this year prior to taking a longish roadtrip this summer. One would think that ball joint / wheel bearing / thermo-coupling clevis (think one of my exes had that once) failures wouldn't be all that spontaneous, but things do happen. Kevin, thanks for the easy to follow tips, I'll do that. Dennis & Bob, thanks for affirming that a reputable alignment tech can detect and correct whatever issues there are just as well as a luftwaffe trained Porsche specialist is able. New tire time will be coming around next season (not necessarily due to tread wear, mostly due to age), so if I can wait without things falling off... well, you get it.
Don~

[KTL]

In all honesty any competent alignment tech can handle the front suspension of an old 911. It's very basic.

It's the rear that can throw them off. Those eccentric bolts that require careful attention to dial-in the camber and toe are tricky if someone's not fully aware of how the adjustments work.

[donagain1]

Yeah, I was thinking about that, Kevin. It seems to me that the rear wheels go over just as many potholes or other road bumps and such as the front wheels do, but it's only the fronts which show any alignment/suspension issues. The rear tires show no uneven wear or under/overinflation patterns, and seem to be riding flat, straight, and true. FWIW, the shocks have never been replaced during my 16 year term of ownership, and the ride is just fine.

[KTL]

Shocks are worth a look though. The fronts take a lot of abuse for some reason. I don't know why this is the case. But most of the 911s i've worked on have decent rear shocks and the fronts are toast.

Shocks are relatively cheap on these cars because they're nothing really special- typical of a shock absorber you'd find on many other cars. IMO one of those easy fixes to help restore the ride quality of the car. So they're an easy wear item to replace. Not trying to twist your arm or spend your money for you. Just saying that they're an easy fix. A jack and some basic hand tools are all you need for front or rear shocks on these cars.

Plus you need to consider your personal adjustment to the car. Its one of those things where you get accustomed to the gradual degradation and really don't notice the drop in performance/refinement/composure/whatever term you prefer. I equate it with how people react when they get a new set of tires. "Wow, these new tires are great. Way better than the old ones." Well, the old ones may not have been all bad when new. But with age and wear, their time has come to be replaced. Over time, you just don't detect the fall-off in quality.

That is, unless you drive someone else's car that has put new shocks and bushings in the car. Boy what a difference fresh shocks and bushings makes to "clean up" the feel of the car. I did it years ago and it was a very rewarding project in terms of how good the car felt

[donagain1]

Points well taken, Kevin. What I may be loving because of the "feel of driving a stiff suspensioned sportscar that corners like a dream ride", may well be indicators of bouncing/shimmying wheels and not know it. I don't race the car, and these days my big thrill is taking my local freeway cloverleaf ramp w/out wandering out of my lane at 55+ when the sign says slow to 25. Maybe if I get this stuff fixed I can hit 60. ;-)