Vibration saga

[Peterofdevon]

The saga continues...

The 94Q spent the day at the shop and the tech says's the vib is in the drivetrain. He thought it may be the front of the drive shaft where that donut thing with all the rubber bushings is. Its a $750 stab in the dark and I may give it a shot.

Other owners have posted about vibration even after transmission mounts and EHs are done. I wonder if this is a common failure for this vintage Q?????

The transmission mount was done over a week ago and the car was perfect for 3/4 days. The start up vib is gone (when the car is cold) and the over all vib is reduced but the car still has a contining subtle vib. My tech thinks perhaps the transmission mount job shifted the shaft and when the mount settled in the vib returned.

Any input on drive shaft issues on your Qs?

Let me know.

Thanks,

Peter of the 3 Qs

[elwesso]

if you go for a new driveshaft, get one from powertrain industries, thats what i have in my Q... $450 shipped...

You can also replace the center bearing for like $100... however that flex disc that he's talking about really does suck..... it needs to go away, and the PTI driveshaft has all U joints and the driveshaft is completely rebuildable.

you could always try and shim the transmission mount to try and hike the back of the transmission up..... I suppose its worth a shot.

[96Qowner]

Is this vibration rpm dependent - at 2250 rpm? If it is, it really can't be the driveshaft.

If not, I know Wes did extensive work on his driveshaft, trying to isolate vibrations. He worked on the U-joints and other stuff. Ended up buying an aftermarket replacement:

zerothread?id=108553

[JohnPa]

My 90 Q45t has new motor mounts, transmission mount, and a new factory driveshaft. It still vibrates at around 60mph. I also have new tires with a 'dynamic balancing' job, new differential mounts, a new left rear wheel bearing, and a used replacement right half shaft.

My next step is to put the car up on railroad ties (for safety) and run it up to speed to try and find the culprit. I won't get to it for a couple of weeks, so if anyone has some other ideas to check out, I'm all ears. I actually suspect the transmission although I admit I haven't done the brakes yet.

John in Seattle

[Q45tech]

Vibrations at 60 mph [in any gear][depending on exact tire loaded radius] are almost always tire/rotor/wheel related because the periodicy falls in line for 2nd harmonic. The number of rotation per minute at 60 mph.......radial force pushes up the springs as the hard spot rotates around and shocks don't have time to dampen it out thus body vertically rise 13 times per second at 60 mph.

Jacking car up removes the load/changes tire diameter thus changes vibration.Make sure all 4 tires have a radial force imbalance under 10 pounds on a Hunter machine.

A tire can be perfectly balanced with rim weights and still have severe radial force problems.......the usual solution is to switch to Michelin and save the radial force testingretesting money.

There are so many modes and intensity levels that one must speak of vibration frequency [measured exactly] and amplitude.

A clue to tires is that the vibration frequency changes as the tires warm up as they change diameter as the pressure increases...........of course so do rotors as the warm up.........but most other things don't change much.

[Peterofdevon]

wes,

What exactly cured your vibration?

And Q45tech, what are your thoughts on it being the drave shaft?

The vib sets in at 30 to 40mph, the higher tourque zone. Its not horrible buts it there, plus it can come and go.

Thanks,

Peter

[elwesso]

the driveshaft sounds likely..... However, when i replaced mine i didnt have the likely causes... My car vibrated bad over 70MPH... but was pretty smooth under that.... now my car has an EVER SO SLIGHT vibration at 40, 60, and 90+...

my car is mostly smooth, except when i get above 90, im actually going to create another thread if a new transmission mount doesnt fix it..... I may also get one of those driveline inclinometers to try and optimize everything.....