Front end vibration and alignment

[BesideTheBox]

My car is an '86 Turbolook Carrera with 84K miles.
I have reproducible and intermittent shaking of the steering wheel that I would like to resolve/eliminate.
I now have 17" rims with Kumho Ecsta SPT tires.
Tires are balanced with 29 psi front, 40 psi rear.
The right rear tire has been shown to have "excessive road force", and I believe this to be reflected in the "seat of pants" vibration that is only noticed at 80mph and above.
Service records show "shocks complete" at 52K miles on 3/24/97.
Last weekend, while cleaning out wheel wells, I noticed BOGE strut cartridges in front and Bilstein shocks in back. Any issues with that?
Also, while cleaning wheel wells, undercoat there is black on driver side of car and silver on passenger side of car. To me, it does look original, but color is clearly different.
I had turbo tie-rods installed last year, and the shop performed a 4-wheel alignment at the same time.

Here are the measurements after the alignment was performed:
Left Front: Camber: -0.8; Caster: 5.7; Toe: .13
Right Front: Camber: -1.1; Caster: 5.8; Toe: .13
Left Rear: Camber: -0.8; Toe: .14
Right Rear: Camber: -0.9; Toe: .14
Steer Ahead: 0.0
Thrust Angle: 0.0
There was a note on the right front camber measurement, "Can not adjust any closer without major work. Will not affect handling."

The steering wheel vibration issue:
After car sitting over night, wheel shake starts about 45mph. Over the first 10 minutes of driving (as tires warm up?), the speed at which the shake starts increases from about 45mph to 65mph. After 10 or 15 minutes, the shake at 65mph seems to be dependent on road surface, ambient temperature, and if there is rain. Above 65, the steering wheel vibration is generally gone, but there are times when I can feel vibration around 75.

I am wondering if the front left to right camber difference (-0.8 vs. -1.1) can cause the front suspension to be overly sensitive to road surface conditions. Perhaps the cold tire transmits more of the road surface imperfections into the wheel and that is why the shaking decreases as the tires warm up.

Sorry for all the info, I've probably bored you to tears by now. Any ideas where to look? I have an appointment Monday morning with the shop that performed the alignment last year. I'd like to go in with the collective experience of the group behind me, so thank you for any ideas you might have. I will definitely update the group Monday after the appointment.

Keywords: alignment, shake, vibration, balance, shocks

[Oh Haha]

First off-Sweet 911!!! Love the color.

Some soft compound tires tend to aquire flat spots while sitting for a few days. My Sumitomos seem to have this affliction. I have a similar issue with a vibration that will go away.

How many miles on your tires?

The different color undercoating MAY indicate damage repair at some point.

The different front and rear brands of shocks isn't a big deal unless they are worn out. If the records are correct, one set or all 4 are at least 10 years old. Again, that doesn't mean to toss them out but just something to look into.

I have KYB in front and Bilstein rear shocks.

Are the Cup wheels factory, requiring offset adapters/spacers or aftermarket versions that fit without adapters?

Hope this helps as I know that a vibration can drive you freakin' nuts!!!!


EDIT: You should look into having your car lowered to Euro specs or close.

Also, I think 40 psi in the rear is too high. I would rather see around 35 or 36 cold. The front should be fine at 29. Someone posted that you should only have ~5psi front to rear for optimum handling. Track use usually requires much different psi based on tire compound, track temp and other factors, including driving style. Yours is, I would believe, mostly street driven.

Sorry, I didn't mean to write a book as a reply, the thoughts just seemed to start flooding my brain as I typed.

[BesideTheBox]

Front tires are brand new, purchased, installed, balanced within the last few weeks, so maybe 600 miles on them.
Rear tires are probably 4 years old, but I'd bet no more than 3 or 4K miles on them. I'd put the tread remaining at 50%. I am considering new rears just to get rid of the "seat of pants" vibration above 80mph.
I had 16" Sumitomo's on my original Fuchs. I returned them because they flat spotted over night.
I drive my car daily, but sometimes it won't get driven on the weekend. The steering wheel vibration is no worse Monday morning after 2.5 days of sitting than any other morning.
The cup wheels are aftermarket. No spacer required for these wheels. I acquired them (along with the Kumho tires) toward the end of last driving season. I replaced the fronts just a couple weeks ago, the rears are what was on them when I bought the wheels.
The owner's manual recommends 29front and 44rear for a turbo bodied car. I lowered the back a bit to 40 from 44 to decrease the expansion joint slap, but it didn't make any difference in the steering wheel shake. The new front tires -did- help, but there is something else going on there.
Thank you so much for the reply!

[mca]

The first and most practical step is to have the front wheels balanced.

I was chasing similar vibration issues for months. I finally took my wheels to a shop that ONLY does tires and brakes - generally speaking this means that their balancing machines are properly calibrated and the techs know what they are doing. The THREE previous shops did not balance the wheels correctly.

Even if you have had them recently balanced. Take the wheels to a specialty shop and have them tape over the weights so that the weights don't come off. This tends to happen after washing your car - soap and water can penetrate the sticky weights. The tape is just extra insurance.

[pete3799]

Jack the car up and place something against the tread of the tires ( spray can etc. ) and spin it.
You may have flat spots on the tires.
I had a vibration on mine when i bought it. Turns out the PO had locked em up at one time and flat spotted both frt. tires.
Check them all even your new fronts.

[DRACO A5OG]

I had crazy symptoms as well:

Alignment went bad: Loose Passanger side Camber

Wheel Wobble: Replaced Bearings yet still had vibration at 60-90 MPH. Found Passanger side Shock was loose, tightened it and it helped a little but now camber seems to be off. Will realign.

Went to a Performance Tire/Wheel Shop GLOBE TIRE and had them re-balance each wheel. Bought the tires from JUST TIRES (Goodyear) they really don't know how to balance tires.

B I N G O, no more vibration at 60-90+ MPH and found right rear wheel was bent.

[moneymanager]

All my front end vibration issues have been the result of poor balancing, or lost weights, at the front. Go to the Hunter Engineering site and look at their gsp9700. http://www.gsp9700.com/
Find a local shop that uses this machine and try it. You may indeed have another problem but there sure are a lot of people out there who can't adequately balance Porsche wheels.

[clexton1]

I had a similar problem with my car that drove me nuts since most of my driving is highway speeds. I ended up changing all the tires and also found the front wheel bearings were loose, that fixed it.

Something else very interesting happened. Shortly after the vibration was solved, I had to take the front wheels off to work on my sway bar. To my surprise, after this repair the car was vibrating in the front again. It turns out that the front left is sensative to the position it is installed on the hub. I rotated the wheel on the hub 2 studs and the vibration completely went away. I have since been careful to always put the wheels back on the hubs with the same orientation. I marked the end of the stud which aligns with the valve stem so it is easy to remember.

Paul

[BesideTheBox]

Got to the shop about 7:45 this morning. Described the issue to the shop manager, who then talked with the shop owner. The shop owner and I took the car out for a test drive.

During the test drive, he was able to cause the steering wheel to shake / vibrate by slowly coming up to 65 mph. At 75 mph or so, the shaking would stop and as he slowed to 65, the car did not begin shaking again. He was able to reproduce the steering wheel shake several times by slowly accelerating to 65 mph.

Back at the shop, they pulled both front wheels and inspected the suspension. All looked good with the exception of the RF strut housing. The front strut housings have a cap that holds the strut insert in place. This cap on the right front strut housing has 2 more exposed threads than the left front strut housing, and there is a very slight amount of play in this RF strut housing.

They checked the balance on the front wheels and the technician found the *left* front to be 1/4 oz. out of balance and declared that it wouldn't be an issue. Then the shop owner walked up and asked the tech what he found. The tech told him 1/4 oz. off and the owner said that it fit exactly with the steering wheel shake he experienced. So they pulled off the existing balance weights and corrected the *LF* wheel balance. The *RF* wheel balance was checked and found to be perfect. *Note that I have corrected the right/left information that I sent earlier, I had it backwards.

The shop owner and I again took the car out for a drive. At this time it appears that the vibration is gone. Time will tell. I've thought the vibration was gone before, only to have it show up again intermittently.

The shop owner's conclusion from all of this is that the front shocks are likely marginal and the slight imbalance in the wheel would interact with the marginal shock to produce an oscillating vibration that causes the steering wheel to shake. He reassured me several times that the left to right camber difference would not lead to the vibration that I (and now he) experienced.

The shop owner confirmed the seat of the pants vibration around 80 and felt that a new rear tire would eliminate that.

All of this took over two hours of the shop owners time and he only charged me about $50. Even if this doesn't take care of it, I really feel good about him taking the time to test drive, inspect, modify, and test drive again.

I will update again in a week or so. Thank you all for your suggestions and sharing your experience.

[mca]

Good stuff. Very thorough evaluation.

It would be a good idea to take pictures of the weight placement. If the wobble returns, compare the weights to your pics in order to determine if some fell off.

FWIW I had a bad passenger front insert ... it didn't cause any sort of wobble. This isn't to say that it doesn't cause wobble, but it didn't in my case.

[mpetry]

Cars with low unsprung weight are very susceptible to vibrations like this. I had a similar problem right at 55mph. Yes you should have the fronts balanced. Assuming that everything else is in order (ball joints and bushings tight, wheel offset correct, etc) then the ultimate fix if nothing else works is to have the tires buffed or trued - this can be done by a shop that does tire preparation for racing.

But first eliminate the stuff that's obvious and make sure there isn't something you have not thought of. One time I knew of a tire that could not be balanced - no matter what the shop did. Turned out there was water in the tire - it had been sitting outside, deflated.

Some shops I know that can do tire truing -

Long Beach - Nate Jones Automotive
SF Bay Area - Custom Alignment
Seattle - Group2 Motorsports

Mark Petry
Bainbridge Island, WA
81 SC