bwoodry

Hello:

My car is a 1990 964 with build date of Dec 22nd 89.


I have a vibration between 68 and 80mph that is very evident in the gear shift ****.
The shift lever moves up and down some at a high frequency.
It is not severe but annoying.
I have checked tire pressure and balance and they are ok.

My concern is the drive shaft to the front differential. Any issues with the torque tube bearings in these cars ?.

I have already changed out the rear motor mounts and have yet to check the transmission mount.

Ideas?

Tks

Bob

springer3

High frequency vibration is common with a bearing is rough and nearing failure. Couple of things to consider:

It the vibration consistent with road speed or engine speed? What changes when the engine is pulling, retarding motion, or in between? Any change when you put the brakes on gently? Any gear where the problem goes away completely? How fast did this develop, and what is the current rate of change?

It could be a hard or loose transmission mount that is letting a resonance couple into the shift ****.

Larry Herman

My advice: don't screw around with it. Take it to the best Porsche trans guy that you know because it could be a precursor to a very expensive repair. I had a noise and mild vibration that suddenly appeared in my old Carrera between 55 & 65 mph. No one could find out what it was, heck some guys couldn't even feel it, but after about a year it finally let go at a club race. It was a carrier bearing in the rear, and when it failed the ring gear moved away from the pinion, and all hell broke loose. Crap & metal parts all through the trans. $3500 later it was all better.

The motto here is find it and fix it while it's still cheap to repair. A replacement of that bearing would have cost me only $600 or so.

KirkF

Curtis had this exact problem with his car. I went for a test drive with him and it was the damndest vibration. It was slightly evident at lower speeds but between 65-85 mph it was terrible.

It was his dif tube bearings.

Reference this thread:

https://rennlist.com/forums/showthre...ferrerid=10545


Kirk

Toddimus

I had some vibration at 70-80mph, but it seemed like it was more through the steering wheel. When I recently did my valve adjustment/tune up, I had the wheels off. I took that opportunity to put the wheels back on right with the red-tipped wheel stud lined up next to the valve stem. I remember reading that you should also install the extendo wheel lock lug nut back on this red stud.

I told the tire shop about this when I got tires a while ago, but they seemed to have lost that bit of instruction during my careful instructions about not jacking on the oil thermostat drain plug next to the jacking point.

Anyways, to make a long story a bit longer, wheels and lugs back on properly and the vibration is completely gone.

bwoodry

Thanks for the input:

I will check the transmission mount and take it to a shop for evaluation.


I hope it is not the Dif tube bearing as this sounds like a real PIA.

Bobw

Red rooster

Kirk,
Did Curtis get new tube bearings or another tube ? Be good to know if there is someone out there that can replace the bearings !

Thanks

Geoff

KirkF

I think he totalled (wrote off) his car before the repair was done.

Kirk

gross964

Springer3

I have a 1991 car with 108,000 miles. It has started to make a noise like wheel bearings going. Have had them all replaced, and the noise is still there. Mechanic and I aren't sure what to blame next!

Suspect it could be the torque tube bearings as at different speeds the sound can appear to be from the front (higher road speeds, and slightly variable on turning) or from the rear (lower speeds). It definately rumbles when braking gently at quite low speeds. You asked the other poster about that.

Sound is dependent on road speed, not engine speed.

If this gives you any clues then I'd be incredibly grateful. I guess you know how it feels when the car's gone sick, and you can't quite work it out!

All the best,

Graham

Youcef

I had a vibration in the car at 160kmhr, it was a failed engine mount.

springer3

Graham:

If you have done the wheel bearings, the only things left that are proportional only to road speed are brakes driveshaft bearings, and some bearings in the transmission. I am sorry your mechanic replaced the bearings. They can be checked for roughness. Replacement on suspicion after 16 years is not a terrible call.

I have no experience with the C4, but Garrett is the guru on those. Perhaps he can help.

To check a bearing, find a way to roll it under all different loading directions. Use "safe cracker" feel in your fingers to detect the microscopic bumps that are the first stage of bearing failure. If the bearing has just started making noise, it will not be easy to feel. The alternative is to drive it until the noise gets worse. It can take a long time.

Good luck

dfinnegan

Many years ago I worked in the plastics processing machinery business. We had a customer experiencing problems with one of our film winders. We brought in a vibration analysis expert who analyzed the frequency of the vibrations. In no time at all we isolated the problem to some rolls.

It may be that these services are far too expensive for us to use on our cars, but I'm sure they could pin-point the source of the vibration in very short order.

In searching the web I've found an interesting link to vibration analysis service companies around the country: Virbration Analysis Services

Phone calls are cheap and someone may just be able to help isolate the source.

Just a thought.

david@st ives

I too have a vibration issue at these speeds.

It only appeared when I changed my tyres, I have had them balanced 4 times now and they are balancing up ok , but still got the vibration.

I think your next move , the same as me is to swap wheels with someone for a couple of hours to see if the problem persists.

I am sure mine is tyre related.

Dave

DarrylH

If you can find someone with a Hunter Roadforce balancer, you may solve the problem. http://www.hunter.com/pub/company/ne.../prGSP9700.htm

bwoodry

Update:

After further consideration,, I had changed my wheels with Aftermarket cups and this is when the vibration occured. When I put the d90's back the vibration is gone,, so,, this is a Wheel balance or tire issue.

I have tracked the car 5 times in the last year and nothing has changed ,, when I run the cups ,, the vibration occurs,, when I run the orignial D90's ,, no vibration.


Bob