Ideas on cruise vibration?

[suprarx7nut]

Hi all, I'm trying to pick the brains of those more experienced than myself here.

I have an annoying and slowly worsening vibration in my '90 when cruising around 35-45 mph. Seems to go away beyond 50mph. It ONLY happens when I am NOT on the gas at all. When I give it any push on the accelerator the vibrations go away completely. There is no vibration or rumble when it is floored, ONLY when it is decelerating while in gear.

It is NOT rpm dependant. It makes the same frequency vibration whether it is in 5th, 4th or 3rd. I can be gliding along in Neutral with no noise and simply put the tranny into any gear and lightly let off the clutch and the vibrations start.

I have old rotors on the rear brakes which are warped and need replacement. I really doubt they have anything to do with this, but thought I'd mention it.


Could this be....
-bad driveshaft
-bad diff
-bad tranny (was rebuilt fully last year)
-bad axle
-bad _____?


The rumble seems to come from the rear of the car.

The car has had this slight rumble for a while now, but it is getting worse. Do I need to have Aamco look at it before my warranty expires?


Cliffs:
Vibration when decel-ing IN GEAR.
Noise goes away completely when accelerating or in Neutral
Happens at about 35-45 MPH, seems to go away at highway speeds.


Please help me out!!

Thanks all!

 

[gaboonviper85]

Hi all, I'm trying to pick the brains of those more experienced than myself here.

I have an annoying and slowly worsening vibration in my '90 when cruising around 35-45 mph. Seems to go away beyond 50mph. It ONLY happens when I am NOT on the gas at all. When I give it any push on the accelerator the vibrations go away completely. There is no vibration or rumble when it is floored, ONLY when it is decelerating while in gear.

It is NOT rpm dependant. It makes the same frequency vibration whether it is in 5th, 4th or 3rd. I can be gliding along in Neutral with no noise and simply put the tranny into any gear and lightly let off the clutch and the vibrations start.

I have old rotors on the rear brakes which are warped and need replacement. I really doubt they have anything to do with this, but thought I'd mention it.


Could this be....
-bad driveshaft
-bad diff
-bad tranny (was rebuilt fully last year)
-bad axle
-bad _____?


The rumble seems to come from the rear of the car.

The car has had this slight rumble for a while now, but it is getting worse. Do I need to have Aamco look at it before my warranty expires?


Cliffs:
Vibration when decel-ing IN GEAR.
Noise goes away completely when accelerating or in Neutral
Happens at about 35-45 MPH, seems to go away at highway speeds.


Please help me out!!

Thanks all!

Driveshaft....in the rear section of the DS (behind the support bearing) look at the u-joints and see if the rear is lined up with the front...the rear portions of the stock shaft is know to be full of fail as me how I know.

 

[suprarx7nut]

Update: Goddamn, that was an easy fix. The bolts holding the two sections of the driveshaft had come loose. Two were hand-tight/loose and the other two weren't far from hand-tight. I tightened them and problem is completely solved. The lock washers must be worn out after 283,000 miles and 18 years of service, so they will likely be replaced soon. They really didn't appear to have much of any bite to them, more like regular washers at this point.

I feel like a dumbass for looking so deep into such an elementary problem. Lesson learned: Keep It Simple Stupid.

 

[IJ.]

With a 7M I've found 262 loctite on steel and 243 on aluminium are your best friends!
(Mine tried to fall apart after spending a day on the dyno doing 8300 rpm and 30 Psi pulls)

 

[gaboonviper85]

its spelled "stooped"