rosenfe

in my 79,i feel a vibration under my seat when i get above 80.car runs fine otherwise.no poblems up to 80,,good acceleration.new axle boots and tires.could this be the torque tube?

Adamant1971

Have the wheels been "road forced" or matched? If not I would start there.

Torque tube should produce vibration linked to rpm not speed.

Mrmerlin

Just a WAG , but did you take the CV joints apart ,
including removing the ***** and the bearing cage?

DID you use the WSM to reference how they are put together?

rosenfe

my local shop did them.ill ask them to look it over

Mrmerlin

FWIW if the CV joints are not put back together properly,
then meshing issues can happen./
Other things could be failed motor mounts and or trans mounts,
broken exhaust hangers and or heat shields hitting,
make sure to check the CV bolts for proper torque as the bolts could be coming loose,
check the wheels for lug nut torque,
and also the axle nut

Jerry Feather

When my 87 did that, exactly, it was a rear wheel bearing.

MainePorsche

When mine did something like that (speed not rpm related), it was the motor mounts.

OTR18WHEELER

A new set of front wheel bearings reduced the vibrations at high speeds in my car dramatically.
120 it gets a little shaky, but I have not ballenced the rear wheels. I usually don't run above 72.

The Deputy

If it's a vibration without any assoicated noises, like grinding, rubbing or such...and it starts at eight and stays constant afterwards and beyond...I'd start with the tires or look over my rims for defects. Also checking the lug nuts of course...since they probably had the wheels off while doing the axle shafts. They may have knocked off a wheel balancing weight, while doing so, too.

Did the problem exist before you had the axle shafts worked on, if not...I'd check that out. Might be loose retaining bolts, like mentioned, or put together incorrectly.

My motor mounts were shot, extremely shot actually, on my 84...and when accelerating...I had more of a vibration at certain RPM's (with no associated noise), mainly around 1800/2000, then the vibration would go away or be less noticable beyond that, trans would shift and no vibration until I got to mentioned RPM's again and fade, and repeat until in final drive.

Plus, I believe your 79 has solid motor mounts...so I'm not sure if they could even offer the same vibration.

I guess the first thing you should do...is make sure eveything is tight and secure...especially before driving it at those speeds again.

Good luck, finding your issue.

Brian.

The Deputy

Question...do you feel the vibration more in the seat of your pants or the steering wheel?

Knowing which one could make a difference in narrowing it down.

Information is key to solving issues with vehicles.

Whenever a driver comes in the garage complaining about a rattle...the first question I ask them is..."do you hear the noise more on the inside or the outside of your head."

Brian.

Adk46

I have had a vibration also. Moderate, felt not heard, not from any obvious source, constant above 80. Not affected by throttle. It was like this when I got it, and I still have it. In totality, it is not quite like any I have experienced before. In between, much has changed:

New shock absorbers all around, fronts first, then rears
New rims with tires mounted*
Redone CV joints, ***** apart
New Volvo motor mounts

* I got these from Adam, who told me he had not had them road-force balanced, and that he had been generally bedeviled by this sort of vibration with a variety of wheels/tires. My vibration remained. Had them balanced on regular machine, and checked for roundness. Vibration remained.

Adam also told me that he believes a "road force" balance includes procedures not always done. Done properly, it solved his problem. That will be my next step. Then transmission mounts, I guess.

It could be some sort of weird aerodynamic thing, which depends on exactly what we have installed underneath. I have gone with and without chin spoiler (no effect), and no belly pans.

FredR

If you feel the vibration through the seat then the problem is most likely in the rear end of the car.

Once the vibration starts does it get worse with more speed or does it die down again as you go faster still?

The sources of potential problems are not too many covering wheels/tires, half shafts, wheel bearings , suspension bushings and ultimately something in the transmission. If it was the torque tube then I might expect a rev dependent initiation rather than a speed based one but....?

Sad to say these sort of problems often get a bit fuzzy to resolve and trial and error is often the way - process of elimination.

Rgds

Fred

rosenfe

noise is felt in seat of the pants not steering wheel.gets worse as i accelerate past 80,not present before 80.after axle shaft boots were redone noise was not present.now about 300 miles later noise has begun.it feels like its coming from middle to the back of car.im ok driving under 80,but it would be nice to rule things out.engine mounts are ok,maybe trans mounts?

FredR

Vibration due to failed mounts tends to be noticed initially at specific engine frequencies when natural resonances are amplified.

Your case suggests something out of balance connected with road speed and at the rear so the obvious candidates to eliminate initially are the wheels/tyres.

Rear wheel bearing failure was characterised by a noticeable noise [whine] at low revs when my late S4 bearings started to fail. I dare say there could be some connection between replacing the rear axle boots and the problem appearing as mentioned by Stan, if you dismantled the joint and did not put everything back the same way and something might then have manifested itself- is this a possibility?

When I did my boots a few weeks ago I went to some lengths to ensure the joints stayed in-situ- maybe that was not possible if you have the older non welded design?

If it was a drive shaft issue I might have expected the problem to occur at specific engine speeds.

How old are your tires? Have you clouted anything with them or hit a big pothole recently? Rim damage is easy to spot but internal tyre damage is usually not visible- you just feel a problem and more so at speed as the out of balance forces increase.

Rgds

Fred