greg928GTS

LOL. In a Ford Aspire.

worf928

Remote diagnosis is always problematic.

I don't know what you're running for exhaust and therefore don't know what the ambient noise level is in your car. In my '91 with the small resonators and an RMB I didn't clearly hear a 'bearing noise' at first. I just noticed the vibration. That's why I advised you to take out all the stuff from the hatch area.

It wasn't until I was in the passenger seat, with CarChick driving in stop-and-go-really-really-fast traffic, that I was able to concentrate on hearing what the car was saying. Once I'd tuned myself to the noise it was clear and I heard it all the time.

Once thing I noticed about my RWB syndrome was that it only clearly made noise after it had been run for a hour or so. Cold I couldn't hear it. But, once the car was run up to speed I could hear the noise even at slow speed. That's how I was eventually able to isolate it to the outside. The noise was a coming and going rhythmic 'thrumming' sound. At slow speeds it was low frequency - maybe 200 Hz - with a period of about 1 Hz. As speed increased the frequency and period increased. At about 50 mph the noise was drowned out by other ambient noises.

SharkSkin

Another possibility is CV joints. Usually they will make an audible clicking when they are going out, but not always. Get under there with the car in neutral, parking brake on & wheels chocked and give them a wiggle -- preferably without jacking. If the suspension hangs down the CVs will not be in their normal wear spot.

greg928GTS

This is good information. I assume that at lower speeds under 50mph you didn't feel much, if any vibration, you just noticed the noise.

I don't notice any vibration until I get on the highway. Your description of the vibration being a rythmic thrumming sound is exactly what I'm experiencing.

If I am having RWB issues, will I be able to tell by jacking the car and spinning the rear hubs? Or is this a sometimes maybe and then other times only while driving?

How would a Porsche mechanic diagnose the RWB issue? Would he bring an assistant out on the highway crawling around out back to try and locate a noise? It seems there's got to be a more concise way of determining the condition of the RWB's in the shop, no?

Thanks again. The help on this forum is just terrific.

worf928

Yes. In my case the vibration would get noticeable at 70 and very annoying by 90.

Actually, the noise was rhythmic and periodic until the period was high enough that it was a constant-seeming noise. The vibration was not rhythmic. It was constant with increasing amplitude.

greg928GTS

I drove the car about 50 miles today and the vibration has gotten a little worse. I didn't notice the rythmic part of the vibration this time, it was just steady and increased in intensity with speed. Really, very much like a tire balance issue. I was not able to go very fast because of all the X-mas shoppers. I ended up in hell. Well, actually it was a "Christmas Tree Shop" store with more people inside than should have been there, but that's pretty much the same as hell. I was being the good husband and offered to go with my wife so she didn't have to go alone. Afterwards I took her to Sears to look at tools. Heh heh.

I spent a few hours today working on the car. I jacked it up with the liftbars, which are fantastic by the way, and set it on jackstands. It was very stable, more so than I thought it would be.

I checked for any play on all 4 wheels and found only very, very slight play on the fronts. The rears were as tight as can be.

I did notice the upper A-arm bushing on one side of the front move a little when I pulled out on the top of the tire.

No funny noises when turning the wheels. Very smooth turning.

I did find a slight build-up of corrosion, brake dust, and ?? on the hubs where the wheels attach. There was a little corrosion on the back sides of the wheels where they attach too. So I spent the time to clean all of those surfaces up, and I cleaned the wheels too of course.

Visual inspection of everything seemed fine. If it wasn't for the fact that I recently had the wheels balanced, while I watched, and then immediately still had the vibration, I would say this vibration is a wheel balance issue. I guess I'll try again before looking further. I'm going to bring the wheels in to be balanced on Monday and first see if they are out of balance.

BC

I had a thought. I once took out the rear seat belts from a 928 5spd. This may seem mundane, but it was quite interesting all the (now very clear) noises I heard. It was because the transmission was JUST outside of that now open hole, and I could hear gear whine, some brake noises, I think some CV noises.

Maybe try that. Its sure as hell easier then taking the rear suspension and hubs apart for a wheel bearing that may not be bad. Depending on what your time is worth, parts changing could be more or less expensive then true diagnostistics.