Humming on deceleration

[Stepbyrd]

99 K1500 Suburban 5.7L GU6/G80 Rear

I swear, I fix one thing on this truck and two other things pop up.

Trucks been inop for the past 6 weeks while I worked on upgrading the injectors and replacing front end components (ball joints, tie rods, and idler arm).

Drove it today for the first time to have it aligned. About 3 miles into my ten mile drive, I started hearing a humming noise but only when I let off the gas. As long as I was accelerating or holding the speed steady, I didn’t hear anything. Sound seems to be isolated to the rear of the truck.

Truck just turned 308,000 miles. I’m guessing that I’m looking at rebuilding the rear diff.

Is there something else that anyone recommends I check?

Fluid was changed in September 2023. Old fluid was dirty but no metal pieces found.

I’m planning on popping the cover off this weekend to check the condition inside.

This is another “new” repair for me and I would really like to do it myself. Doesn’t anyone have any advice or suggestions? Any good instructions out there?

Thanks in advance for anything you can recommend.

 

[HawkDsl]

My 89 hummed in the rear sense new. GM rears are usually indestructible with regular driving. Good idea to have a look, but I suspect it's nothing.

 

[Orpedcrow]

You can push up and down on the pinion yoke, that might show a worn bearing.

Did you use a friction modifier when you changed the fluid last?

 

[Stepbyrd]

You can push up and down on the pinion yoke, that might show a worn bearing.

Did you use a friction modifier when you changed the fluid last?

I’ll check that this weekend. As far as the fluid goes I don’t remember what I used specifically but I do remember it said no additives. GL-5 compatible comes to mind.

 

[Erik the Awful]

Check your U-joints and your pinion play.

 

[evilunclegrimace]

Most likely worn bearings in the rear differential.

 

[Stepbyrd]

Ok, so u-joints appear and feel ok. Tight but not overly so. Nice and smooth movement.

Pinion.....well let's just say it ain't good. It does have play but the play seems limited to in-out vs up and down or side to side. I couldn't locate my socket that fits the pinion nut during lunch today.

My thoughts on courses of action:

1. Check and see if the pinion nut is loose. If loose, attempt to tighten it properly. Refill and see if the issue is resolved. (Not having high hopes)

2. Disassemble the rear diff, replace the pinion bearings, crush "sleeve" and associated other parts on the pinion.

3. Rebuild the whole thing.

This is the first time I have ever attempted this repair so thoughts please on anything I am missing.

 

[evilunclegrimace]

Ok, so u-joints appear and feel ok. Tight but not overly so. Nice and smooth movement.

Pinion.....well let's just say it ain't good. It does have play but the play seems limited to in-out vs up and down or side to side. I couldn't locate my socket that fits the pinion nut during lunch today.

My thoughts on courses of action:

1. Check and see if the pinion nut is loose. If loose, attempt to tighten it properly. Refill and see if the issue is resolved. (Not having high hopes)

2. Disassemble the rear diff, replace the pinion bearings, crush "sleeve" and associated other parts on the pinion.

3. Rebuild the whole thing.

This is the first time I have ever attempted this repair so thoughts please on anything I am missing.

If you are going to replace the pinion bearings I would recommend using a pinion spacer set over a crush collar. USA Standard Gear part number USA55009 on rock auto. $9.12. A spacer set allows you to replace a leaking pinion seal with out having to reset your pinion bearing preload.

 

[Erik the Awful]

If you have play, tightening the pinion nut is not the fix. This is the problem with crush sleeves - with wear they crush further. Your only option is to tear it down and replace the crush sleeve, and as the crush sleeve is the deepest part of the rearend, you'd be a fool not to just rebuild the whole thing.

Absolutely ditch the crush sleeve and get a shim kit. Don't look for a "crush sleeve eliminator", look for a "pinion solid shim kit". It'll cost half as much for the same parts. The downside of the shim kit is that you'll put it together and take it back apart about a dozen times before you get the pinion depth right.

Also, buy a spare larger bearing for your pinion. Emory out the inside of the bearing so that you can slip it on and off the pinion to get your pinion depth right before you press the un-modified bearing on for good.

 

[Stepbyrd]

Well, pinion nut was as loose as a goose. Once I got everything cleaned off the rear yoke, I saw that there was only one thread showing. I couldn't turn it by hand but once I put a socket and ratchet on it, it turned easily. I tightened it up and removed the play that was showing. At least I feel I can move it around the property until I get the proper parts in.

Thanks everyone for the comments so far. Anyone has any other advice, please continue to share.