Throttle-off rear rumble

[GregH]

At freeway speeds I am getting an on-again off-again rumble coming from rear of vehicle. It occurs only in off-throttle conditions and comes and goes with road undulations.

Rear driveshaft has almost new GBR/Spicer u-joints (less than 2k miles) and appear in good shape. I am pulling rear outer pinion bearing this weekend to check. Any other ideas?

 

[Nomar]

Did the rumbling start with the new driveshaft ? Mine did something similar but the pinion yokes were out of "phase"....

 

[Steve Rupp]

Pinion bearing preload may not be tight enough.

 

[Steve83]

The fact that it comes & goes suggests that it's in the diff carrier. The slight difference in tire diameters across an axle causes the spider gears to turn constantly; even in straight-line driving, although VERY slowly. If they're worn irregularly, they could cause a noise like you described.

Or it could be wheel bearings or even tire treads phasing in & out, but they wouldn't be affected by driveline load.

 

[Steve Rupp]

Steve, He is saying that the noise comes immediately after letting off the gas at high speeds. The vibe goes away after a second. I think he means that as long as he is on the gas there is no vibe. My 94 acted the same way. Unfortunately I didn't have it long enough to diagnose the problem.

 

[GregH]

Steve, He is saying that the noise comes immediately after letting off the gas at high speeds. The vibe goes away after a second. I think he means that as long as he is on the gas there is no vibe. My 94 acted the same way. Unfortunately I didn't have it long enough to diagnose the problem.

Yes and no. The rumble is noticeable only at freeway speeds and not at low speed. It only occurs when I let off the gas. Under power it goes away. When on long downhill stretches with foot off the gas it is very noticeable and is constant inless there is bumps in the road. When going over bumps or undulations in the road it will temporarily go away after cresting bump and weight of vehicle is off the suspension. It then returns when weight settles back onto suspension.

The noise is getting progressively worse during the last 500 miles. Rear driveshaft is not new but the original-just U-joints replaced. I suspected U-joints but since they are relatively new and I cannot see or feel any probs with them I am suspecting rear pinion bearing (also have 3" lift and stock trailing arms without additional shim/washers so may be running bearing too dry too-my bad as I have RTE replacements sitting on garage floor ). Hoping it's the outer bearing and not inner. No leaks from pinion seal but again may not be getting enough lube.

Any other ideas?

 

[Steve Rupp]

You might want to get those links on and get the proper pinion angle. If you're not running a double cardon rear, make sure that angles are 180 deg out of phase. (rear pinion perfectly horizontal)

 

[Steve83]

...180 deg out of phase...

Huh? The yokes attach at 180?, so that's still in phase. Do you mean 90?? I'd advise against that - it's always best to be in phase.