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Old 01-13-2009, 02:48 AM   eBay Motors  #1 (permalink)
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Rear end clunk?

My truck has done this for as long as I can remember, but recently it seems to be getting worse.

Basically whenever I brake to a stop (stoplight, whatever) when I step on the gas I get a VERY noticeable clunk from the back end. It's something you can hear and feel, and even passengers have noticed it so it's not very subtle. The odd thing is that it's only from a stop, and occasionally you will feel it under moderate braking when coming to a stop. On and off the gas it doesn't do it, only accelerating from a stop, and only once.

I pulled the rear wheels off to check everything over. Thought maybe the U-bolts could be loose and allowing the axle to shift. All bolts are tight, and there is no sign of any movement in the mounts. Bushings appear in good shape, brakes are tight and have good pads, ebrake is adjusted properly, there's no lateral slop in the driveshaft or pinion, and the amount of rotational free play in the rear end seems pretty normal.

I took a friend, who designs lift kits for a major company out for a ride, and without me mentioning it he noticed the clunk right away and said that he has a chevy in the shop that does the same thing and also has no idea what it is. At this point all I can think of is the differential itself. Did these trucks come with any kind of limited slip or locker? I've never seen this behavior from an open diff, but I could imagine a worn out LSD or locker could do something odd like this.

It's an 03 CC shortbed 4x4 if that helps. Thanks.

Dallas
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Old 01-13-2009, 02:59 AM   eBay Motors  #2 (permalink)
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Post your vin in the vin check section. It will let you know if you have the g80 locking rear gear. Also use the searh feature and you will see there has been 5-6 threads posted on this in the last few weeks.
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Old 01-13-2009, 03:20 AM   eBay Motors  #3 (permalink)
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VIN check forum says you need 25 posts, and I'm not there yet. I'm sure I could post a bunch of BS to get there, but that's just rude. I'll do some searching, just not sure what words to use. I imagine typing in "rear end" will get me a million results.
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Old 01-13-2009, 04:34 AM   eBay Motors  #4 (permalink)
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Lightbulb Ok,I have a few ideas on this...Tell me if u understand my typin...lol

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Originally Posted by StinkBug View Post
VIN check forum says you need 25 posts, and I'm not there yet. I'm sure I could post a bunch of BS to get there, but that's just rude. I'll do some searching, just not sure what words to use. I imagine typing in "rear end" will get me a million results.
Few ideas..The company I used to work for used ONLY Suburbans and YukonXL's they bought around 40 of these a year....few things i remember forsho.....

1.For some reason the rear brakes do not feel like they are evenly proportioned to the front,and when slowing the binding there is noticeable..seems this is a GM thing?
2.U-joints/hanger bearing,also called carrier bearing..
3. The rear diffs always seem to get some slack quickly,[dunno why],so I know the clunk,but i don't have it on my rig,BUT my work truck does it!!
4.This may be a stretch,but are the specs[for the rear end]all within acceptable limits?[i know,that has to be checked]Be sure there is gear oil in the differential..
5. Maybe the driveshaft turning under engine power then slowing down brings the noise,like when the Allison has pressure on it,then you press brake or let off throttle and it slows itself[hard to x-plain dis]and that may be the clunk if anything is outta spec range in the rear end...[what i mean is that the diff may not be shimmed correctly at the ring/pinion...
6. Check and see which locker you have in there.. someone may have added the wrong lube?
It almost sounds as though the locker is not disengaging,does the rear feel ''binded''when you go round a corner??If it's the locker,that'll clunk like u described..It might[i dont know forsho]be engaging when you slow down?The locker kinda works on momentum/centrifigal force to engege...thankfully there is a easy way to test the locker,spin the tires on wet grass or something like that,when one wheel spins faster than the other by a few hundred rpm it kicks the locker in,then as you take off the force is releived from the discs and it disengages..
If I can think of anything else I will post it up for you....Shoot me a pm...sorry for long ol post,just trying to help out....

Kevin
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Old 01-13-2009, 04:59 AM   eBay Motors  #5 (permalink)
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Your clunk is common on older trucks, it has to do with old grease becoming solidified on the driveshaft spline. Solution, pull it, clean it, grease it, install it. Had it on my '02, never occurred on my '05. I've never done this maintenance myself, but it's commonly known at the Dealer.

Since you're going to pull it, you may entertain the thought of having a drive-line shop pull it. With it out there, they can spin and check the balance, inspect the carrier bearing, and all of the U-joints for wear and potential problems down the road.

The Carrier Bearing seems to wear out the quickest, and it has to be pressed on/off with the right equipment. Hmmm, not sure if the 4wd has the carrier bearing though. With the age of the truck, it would be a good chance for preventative maintenance before you're left stranded from a dangling driveshaft.
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Old 01-13-2009, 05:02 AM   eBay Motors  #6 (permalink)
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Talking wow,my fingers hurt from all that typin.....hahaha..

Quote:
Originally Posted by Hook'em_Horns! View Post
Your clunk is common on older trucks, it has to do with old grease becoming solidified on the driveshaft spline. Solution, pull it, clean it, grease it, install it. Had it on my '02, never occurred on my '05. I've never done this maintenance myself, but it's commonly known at the Dealer.
I wanna be like Hookem'Horns when I grow up...LOL.J/K hookem...nice diagram on wiring bud!!!
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2006 GMC 4x4 CC/SB/sle1/LBZ**312,000 miles!!** PPE HOT+2 225 TUNE beeeyotch:-)AutoMeter egt/boost Suncoast 5 trans w/1056TC!,billet in/out shafts/MagHytec pan!!,M/A built T-Case,4 in.str8piped,5%tint all around......
2007 Chevrolet 4x4 cc\sb,lbz.......SOLD to blunova
Also, I speed and don't come to complete stops at stop signs.


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Click below/pictures of my junk!!
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