Very smart backyard mechanic friend (rebuilds Jags) and I am in conflict. He claims I have a bad tranny. I think it is the drive shaft (U joints).

Background: My 90 GXL with 112,00 and impeckably maintained began to vibrate at 60MPH. Slowly lowered MPG to where it is now at starting out. It is a speed and not an RPM vibration. Vibrates more under load (accelleration).

I first had wheel balance checked and is OK. Jacked it up and played with the drive shaft when in neutral. It has play in it. Differential fluid is OK.

Checked for play in front wheel bearings found none and no noise when spun.

I then checked tranny fluid on freind's insistance. OOPS, it is down just under a quart and one half. So I refill. Did not solve vibration.

He is insistant that the low tranny fluid damaged one or more bearings. I say no cuz absolutely no sound from tranny itself.

Does the play in the drive shaft mean the U joints are the villan? Had to replace drive shaft on my first '90 and there was play and a "clunk" when put in gear. I am not getting a "clunk" this time on this car

Any peace maker out there with a sure fire answer??

 

If it is a speed thing, and not an RPM thing, I doubt it would be the trani - but then maybe not your driveshaft either. Check all the wheel bearings. Have you looked at the rear end? If the trani was low, then maybe the diff is too.

The way I look at it is that if there is play in the driveshaft - it should be fixed wether that's the problem or not. It is far cheeper to replace a U joint than a trani, so why don't you take the drive shaft out yourself, and get the U joint changed. If that fixes the problem - great! If not, well at least you know that it had to be done anyway.

 

so, that means what? There should be absolutely no play in the drive shaft? I have about 1/4 - 1/2 inch rotation. That bad?

 

If you have rotation(1/4 to 1/2) that's back lash which should only be minimal, but should not cause the vibration. Check driveshaft front and rear at "u" joints for movement. Could be many things as stated. Check trans/eng mounts for breakage.

 

Check if you can move either u-joint yoke at the transmission up&down or side2side. Then do the same at the differental. That should diagnose the problem.

 

Any thought on the low tranny fluid level causing vibration.. possible or not?

 

Its possible. If the main shaft carrier housing has bearings (wich most trannys have needle bearings) and they are run dry (because the oil is in the base of the sump, not by the shaft) then Yes, its Possible. However, I find worn trannys (at least on other makes) have a whining or squeeling sound. Not really a rumble, or vibration, just a whine. Rumbling/vibration and clunks indicate drive shafts or CV joints. Check your Diff and CV's by putting the car in gear with one wheel on the ground. Rotate the wheel (that is off the ground) back and forth, there should be no more than 1/3 rotation of the wheel from lash to lash.