Topic: Whum-whum-whum sound when getting off throttle

[Main One]

Getting a noise when lifting off the throttle.  The frequency of the whum-whum changes with changes in vehicle speed.  I thought it might be the rear u-joint but after getting that changed it is still there.  Anyone else have experience with this?

[russiankid]

I think you're experiencing the same issue I have, at least it sounds like it based on your description like letting off the throttle. I have changed the rear axle bearings, u-joints, and redid the brakes. The noise is still there. In my case, it is either the differential carrier bearings, ring and pinion, or just the whole diff.

[oHIobellboy]

Tires in good shape? Blower belt?

[Main One]

I think you're experiencing the same issue I have, at least it sounds like it based on your description like letting off the throttle. I have changed the rear axle bearings, u-joints, and redid the brakes. The noise is still there. In my case, it is either the differential carrier bearings, ring and pinion, or just the whole diff.

Yeah, I got a response or two over at performancetrucks.net asking the same question suggesting bearings in the diff.  Will probably pay a mechanic to fix it as its a bit hard to do while using a walker to get around.   

[russiankid]

Yeah, I got a response or two over at performancetrucks.net asking the same question suggesting bearings in the diff.  Will probably pay a mechanic to fix it as its a bit hard to do while using a walker to get around.   

I would do it myself but I have never set te back lash on a gear set and do not feel like screwing anything up. I already set aside a grand for myself so when my rear does blow I will go to a Detroit locker. However, my mechanic who has been a Chevy tech for 15 years now(mostly trucks) said he wouldn't worry about the noise. If it gets worse, then start to collect the money, but otherwise it should be ok.

[Main One]

I would do it myself but I have never set te back lash on a gear set and do not feel like screwing anything up. I already set aside a grand for myself so when my rear does blow I will go to a Detroit locker. However, my mechanic who has been a Chevy tech for 15 years now(mostly trucks) said he wouldn't worry about the noise. If it gets worse, then start to collect the money, but otherwise it should be ok.

Mine's been getting worse pretty rapidly.  I think I was hitting boost a little too often on my trip over to Cincy a couple of weeks ago.  Guess I'll see what my mechanic thinks......

[MonstaMonsta]

Keep us updated!

[russiankid]

Yeah definitely keep us updated.

[Main One]

My mechanic also thought it was a bearing in the rear end, and suggested I have it worked on by a rear-end specialist, who I just got off the phone with.  He heard the noise, opened up the rear end to let it drain, and saw about a 3" crack in one of the rear-end internal pieces.  He said it was surprising to him because he'd never seen one in a rear end that hadn't blown up.  I'm guessing it wasn't the cause of the noise - just lucky I guess that the noise (and being laid up) prompted me to get someone experienced to take a good look at it.

This rear end specialist recommended an Eaton Detroit Truetrac.  The Truetrac by itself (not counting labor) he said was about $550.  I gave him the green light - should be ready Thursday afternoon.

[oHIobellboy]

I'm pretty sure that's the same setup CDWPowerhouse put in his 03 when his stock rear end grenaded into pieces.

[MyBigToy]

I'm sure you're aware the True-Trac seems to be the recommended limited slip.

Back on topic, have you looked at the front unit bearings?

[Main One]

Back on topic, have you looked at the front unit bearings?

No, I haven't myself.  I assume my mechanic considered that before assessing the problem to be in the rear end.  Since one of the rotating assemblies in the rear end is cracked, the rear end needs to be replaced anyway.