Doug94968

I have a '94 968 cab with 90k on it. It has a bad shake or vibration at about 60 to 65 mph. I have been trying to get it fixed for about 9 months now with no luck.

Originally, I had very bad wear on the inside right rear tire only and old front tires were out of round.

Put on 2 new Bridgestone RE750 on rear only and had it aligned. The toe on that right rear was out just very little, despite wear into the steel cords.

Put matching RE750's on the front. Still vibrates as though tire imbalance.
tire shop said suspension was tight and ok. Replaced some of the tires and the vibration changed some but was still there. sometimes it is more in the rear (seat) sometimes in the front (steering wheel shake)

Had local Porsche dealer look the car over, road test and road force balance 4 tires. Maybe a little better but still not right by a long shot. Porsche said it was the tires.

Replaced more tires, checked wheels for trueness, until 12, yes twelve tires had been tried, all RE750 to no avail.

Got my money back from Firestone.

Put on goodrich Gforce sport tires. Much better grip and quieter, except same problem. Tires were meticously road forced balanced as I watched two techs take over an hour to do the four tires. Filled with Nitrogen which is std. The road force machine measured rim runout and none was worse than 0.018inches in any direction, radial or axial. The road force imbalance was 3-10 lbs for all tires. They allowed 16 lbs.

I put the 40lb damper weight back in the trunk, no change.

I love this car, but am at a total loss as to what to do.

Also, with the Goodrich tires the car wants to wander more and I wonder if the alignment is right or if the Firestone specs match the Porsche specs. I am considering getting the alignment specs from Porsche and getting it checked again. It steers like it is toed out in the front. The Gforce tires like to follow the pavement grooves and seams a little. The grip is awesome, treadwear is 340 too!

As far as I know all suspension components, including struts are original.

The vibration is very much in tune with the wheel speed, and does not change if I switch gears or let the engine idle with clutch in. It is severe enough that any technician driving it instantly confirms it is there.

The wheels are the stock 16 in Porsche wheels. The rotors are pretty well worn but no pulsating and I would have a hard time believing them to be out of balance due to age or wear. The wheels seem to turn true on the car.

Is it safe to run the rear at 60 -65 on jackstands? Of course suspension would be topped out.

What should I do? Please help. I have described this the best I can and have technical background.

Robby, in Knoxville, if you read this would you consider swapping wheels and tires to help figure this out??

Doug '94 968 Cab Red

Lord_Galva

I ran Potenza RE750's on my car and they were awsome.
They were great up till the accident.
I don't blame the tires.
I had a vibration and I discovered it was at 3000rpm's.
Check to see if its a certain rpm vs mph.

968rz

Have your brake rotors checked for warps, I've seen this cause the problem you have. also could be a loose wheel bearing. Just ideas.

Luis de Prat

Sounds like you need to get the rear axle aligned first, and not many tire shops are familiar with the procedure on the 944/968 cars.

Which parts of the suspension did they check? The typical items notorious for creating the 65 mph "shimmy" are lack of proper alignment, worn control arm ball joints, worn tie rod ends, busted caster block bushings, and even loose front wheel bearings. All of these items were checked? Is the steering wheel off center at all?

Lemming

Brake warping is pretty much a none issue on a street car. Uneven pad deposits are however very common. But given that he said no pulsing, not likely the cause of his problem.

Doug - I would not run the car at speed on jackstands with the wheels hanging (unloaded)!!!! Once you start to get some speed going they will begin to bounce quite violently.

Doug94968

Thanks. I'm going to start checking all the suggestions. The 65mph shimmy is exactly what it is. The alignment was done for caster, camber, and toe for all four wheels. But it has this wandering like it is toed out. I am going to go over the suspension and alignment again. My Dad had an s-10 blazer years ago that ate tires. found out that the tire shop alignment specs were different than the dealers, despite the alignment shop having it built into the software in the machine. On that note, any suggestions for alignment specs for normal street driving where I don't want to sacrifice tire wear. Any one run the Goodrich G-Force Sports? I'm impressed especially for the money.

RajDatta

If you have the factory manual, it tells you stock settings.
Raj

spieln

I run G-Force sports on my 968 and they work great. Quiet, good handling and a great price. Mine will tramline some if the pressure gets low. On my coupe I run them at 36 lbs. all the way around. No problems then. I have even used them on the track at DEs.

If I want a good alignment, I usually take it to the dealer. They will give you a before and after print out. I can get it done cheaper at other places but never really sure they do it correctly.

Doug94968

The dealer quoted me over $400.00 to align. I can talk him off some. I watched Firestone do it and was satisfied with the print out. But I don't like the handling and suspect the specs may not be right. Plus how can that right rear get ground down beyond the steel belt on the inside and only be out 1-2 degrees toed out? Further, they maxed out the adjustment to get it in that little bit. I wonder if they, and the porsche dealer missed a bad bushing or something on that corner. But I have seen correspondence on this board about that right rear corner wearing the inside. I don't have the manual or specs. Can we all agree that the factory specs are good for all around driving and tire life? I second the G-Force sports. Amazing grip, quiet, and $89. front $109. rear (16's) installed with nitrogen locally. the road force balance was $10. more per wheel. And 340 treadwear. Can't say enough about them. I liked the RE750's too, but for less money, I swear the GForce out grips it. Well I am gathering information and saving money. I won't drive it too much until spring anyway. If anyone has more ideas please chime in. Thanks,

Doug

RajDatta

Most places that do race support in our area charge around $250 for 4 wheels alignment with corner balancing. Your price seems high. I would call some of the local independents with PCA and see how much they charge.
Raj

spieln

Dealer her in St Louis charges $175 for 4 wheel alignment. That is with the PCA discount.

Doug94968

I'm going to start with a thourough inspection of all the suspension joints, then find a shop that can align it properly, and hopefully, for less than $250.00 I love this car and this is driving me nuts!!

Robby

DOUG!!!! Where have you been??? I tried calling & e-mailing, etc, & haven't been able to get in touch. It's been a BAD few months- I lost my little girl on December 18th, so I've sort of dropped off the face of the earth for awhile. I did just get my car back last week, finally, & it's at my parent's house until I figure out why I STILL have a fuel pump leak & get a few WG/boost probs fixed. Anyway, I could swap wheels w/you for a day if you need if you haven't already figured this one out. I know it's been going on a long time. Get in touch- my # & E-mail are both the same.... OR PM me & we can go from there, if you've lost my contact info...

Robby

Doug-

Yeah, I knew that weight was NOT the prob- btw- we can mount your battery back there if you'd like- I have the stuff to do it, but need to make a few decisions. Anyway, we can yank the 40lb battery from hte front of your car & replace it w/a 26lb battery in the right rear, all told, w/large gauge cable for less than $200 (unless you want fuses & then I'll have to source the ones Dan used). How does that sound?

I have Pilot Sport PS2's & they've lasted a LOOOONG time- the fronts are ~30k & going strong & THAT'S the way I drive...

I used AirCooled Classics for my alignment & it was ~$250- I'd bet they're a little higher now, but still, shouldn't top $300.

I know of SEVERAL local Boxsters that have had alignment probs, just as you're describing (steel radials exposed on inside of right rear) that have been aligned at dealer- not sure why, but it is interesting...

get in touch...

RajDatta

My condolences to you and your family on your loss. My heart goes out to you and your family.
Regards.
Raj