Rear End Noise

chris_kucia · June 8, 2004

New to the board, but I trolled awhile and checked the archives.

Have a 2k Sierra Extended cab with 4wd and the Z71. Just bought it used with just under 100k.

I have an odd sound coming from the rear end. It occurs every time I accelerate from a stop, and sometimes occurs multiple times.

Originally thought it was the parking brake sticking, but I removed the shoes (they were worn to the metal and I'm waiting for replacements) and changed the rear pads (also verified the calipers were working properly) and the noise persists.

After reading the board, I dropped the driveshaft last night. Universals are OK and the yoke slides freely into the trans.

While I was under the truck, I laid down under the differential, put my feet on the bumper and shook the truck back and forth. When the driveline slack is taken up and the rear end engages, there is an audible noise just like when I move the truck from a stop.

It isn't a clunk, its more of a low-pitched whine, like you would expect to hear if the brakes were hanging. I'm nearly 100% sure the noise is coming out of the differential. I also checked all the spring linkages and I verified the calipers weren't hanging.

I just put new shocks in the rear, and I can't duplicate the noise by bouncing the truck in any direction, other than forward/back to get the driveline to tigthen up.

I have the locking differential, I believe with the 411 gear option.

My best guess now is that the clutches in the locking differential are worn and are slipping, but before I take the thing all apart, I was hoping to see if anyone else had similar experience, or has any other ideas I could check.

The clutches aren't all that expensive (about $100 total), but taking apart the rear end to replace them is going to be a good weekend job I expect. I'd like to rule out anything else before attempting that. I have to get in there anyhow to replace the parking brake shoes (axles need to be pushed out to get them on), but pulling the axles is a lot less involved than pulling out the differential internals.

Thanks in advance,

Chris

chris_kucia · June 8, 2004

One other thing that just occured to me...

I suppose that if I disconnected the driveshaft from the differential, jacked one of the rear wheels off the ground while keeping the other on the pavement, and then rotated the free wheel back and forth, I should be able to get the same noise to occur if the differential is the source of the problem.

Something to try tonight I guess.

snoman · June 8, 2004

If this is a 1/2 ton with a 10 bolt rearend and a gov lock, they are not noted for their hardiness. The clunk you hear might be the carrier worn from abuse. I would not waste money on rebuilding it. I would replace it with a Eaton LSD (non gov loc) or a true track gear LSD. Both of these are a lot better than the gov lock.

chris_kucia · June 8, 2004

Its a half ton. I believe its the 10-bolt with the 8.6" ring gear, although I forgot to measure it when I had it apart last.

It may have been abused by its previous owner(s) although it seems in good condition overall.

I don't plan on hauling too much with it. I live in a pretty snowy area, so I primarily bought it for the 4wd and the heft (compared to my old S-10), with the occassional trip to Home Depot for plywood and drywall.

Any way I can tell if the carrier is worn? When I pulled the pin to get the axles out, it looked to be in decent shape and the unit itself doesn't appear sloppy.

Although, to be honest, I have more experience with FWD cars than 4wd/Rwd trucks. Rear differentials are kind of a new thing for me.

Can I change out to a different one easily? Is it just a swap of the internals, or do I need to replace the entire assembly? I think I can replace the clutches without worrying about backlash and the more complicated aspects of working on a differential.

snoman · June 8, 2004

You seem to know your way around with a wrench which is good. It is hard to see the wear unless you field strip it. As far as changing the differentail it is not the tough. Basically you have to do two things. At the start before you pull the pig you want to use a dail inicator to measure the backlash between pinion and ring gear. (should be about .005" to about .010") Write this down! WHen you install the new carrier after moving ring gear to it, you need to determine the preload in the carrier bearings. You keep adding shims to both sides until there is no play/clearance between carrier bearing races and housing while keeping backlash as previously recorded value. Once you have reached zero play with correct backlash, add .004" to each side of housing and torque down caps replace cover and you are done! Note this is for a 10 bolt and changing the differental/carrier assembly but reusing same gears. Did I lose of scare you?

chris_kucia · June 9, 2004

Your description seems pretty straightforward. If this was a second vehicle, I'd probably be a little more willing to attempt it. Not ruling it out yet, but I'll need to put some pennies aside for this...

I checked my service manual last night.

Apparently you have to stretch the differential case with a tool to get the innards out? What's up with that?

bigBP · June 9, 2004

To pull out the carrier you'll have to remove the c-clips that hold the axles in place, then pull the axles out 3 or 4 inches. As far as "streching" the case to get the carrier out, it's can sometimes be a pain in the a@# trying to pry a 20lb hunk of metal out of the case. You should be fine with a crowbar and some muscles to yank the carrier out, just don't go rambo style and damage something.

chris_kucia · June 17, 2004

Been living with the noise a little while longer.

My Dad's a mechanic from way back, and he and I spent some time investigating.

We're pretty sure the noise is coming from either the rear end or driveshaft. He agrees that the differential internals could be the culprit, but it could also be the front differential yoke or the rear universal.

A couple days ago, I dropped the driveshaft, verified again that the front yoke is OK, and removed the rear universal and regreased it. One of the joint axis is a little on the tight side. The differential yoke is in good condition. I'm wondering if perhaps the tight joint is binding under torque and generating the noise.

I jacked one wheel off the ground and put a broomstick through the differential yoke to hold it from turning as best I could, and I couldn't duplicate the noise by rotating the wheel back and forth, although I also couldn't put nearly as much force through it as I could have by rocking the vehicle back and forth with the driveshaft attached.

I figure a new universal won't cost all that much, and will eliminate that as a source for the noise, so I'm going to try that first before poking around the differential any more.

quackmaster · June 17, 2004

I had a roar that almost sounded like a tire whine. Turned out to be the pinion bearing in the rear differential. This was at 70k miles. The bearing had nicks and flakes off of it, thus causing the roar in the housing.