Drivetrain cruising vibration! - FIXED

[IncorpoRatedX]

I've been chasing down this strange intermittent vibration for a while now.

This vibration would happen while cruising at part throttle (think maintaining speed on a highway 55mph) and when i'd let off the throttle i'd get a pulsing vibration in the drivetrain, very faint, but strong enough to annoy the hell out of me. often while cruising it would a 2 pulse vibration whenever the slightest downgrade in the road began, meaning load was taken off the drive train. This was driving me bonkers.

I started with a tear down of the driveshaft, after replacing the lobre joint the car was smoother, but the intermittent vibration still existed
Swapped out transfer cases, no fix
swapped in my spare transmission, no fix
New front axles, no fix
Finally, swapped out my rear diff, suspecting a pinion bearing that might be wore, despite feeling no initial play in the pinion.
Swapping the diff fixed the problem, smooth as butter. However upon opening the old diff, this is the wear I found that was causing the vibration, it's only in this one spot, almost looks like pits from rust, or it chewed something up, or... i dont know, thoughts? /ubbthreads/images/graemlins/dunno.gif

 

[GSX_TC]

How many miles did that diff have before you pulled it?

 

[IncorpoRatedX]

No idea.

 

[AnotherNewb]

I saw something like this on an old truck rear end, and it was rust. Truck sat for a few years and had water in the diff housings

 

[cheekychimp]

I have something very similar in my daily. Ken says it's a rear axle but I'm worried that it might be the rear diff. He has a 3.909 rear diff and transmission he has promised me so I'm not too bothered at this stage, I'll have him swap those in and see if they cure the issue later.

 

[IncorpoRatedX]

I thought I should update this, it's not the rear diff. the problem wasnt fixed, i just didnt get it up to the right speed.

 

[cheekychimp]

Well that's bad luck Josh! Mine did turn out to be worn splines on the rear axle/axle cup. I ended up swapping in a 4.3 ratio transmission (yes they do exist, something Ken pulled off a rally car back in the day).

Josh I mentioned this in your other thread, but when you rebuilt the driveshaft did you check the bushings/mounts for the carriers? There are a couple of threads on here about wub wub noises during deceleration and some solutions involved shimming the carriers to get the correct angle on the shafts. It isn't unreasonable to suspect that if those bushings are worn (allowing the carrier to move more than it should) that the angle of the driveshaft can get deflected, especially when load is suddenly removed. I installed some of the solid bushings that Torque Solutions and Garfield sells and whilst they obviously didn't solve my vibration issues (which were caused by something unrelated) they did firm up the drivetrain nicely and you can definitely feel the difference as you release the clutch and load the drivetrain.