New clunk

[Enter Hummer]

In the last few weeks i've developed a new clunk. It happens when I put it from reverse to drive or drive to reverse. Shifting from R to N, no clunk. D to N, no clunk. R or D into P, no clunk. Only from R to D and likewise. That could be a U-joint which I have not checked yet BUT there is also a clunk in the front somewhere when braking, which I wouldn't see why a U-joint would cause that.

If I come to a stop very slowly, no clunk. Only when I get on it a little harder and the front dips just a little. It is only a faint little clunk that you can only hear with the windows down.

I took the hummer out and did a little rock crawling today and when the front articulated, no clunk. I can hear and feel the gear clunk, but only hear the brake clunk.

Any idea what could be causing this? Are these clunks related? I haven't had any time to look under recently but the last time I did everything looked good. I didn't notice anything out of the ordinary.

 

[cgalpha08]

The clunk when shifting from 'D' to 'R' or 'R' to 'D' could be a U joint, but it may also be just typical GM driveline slop, all 3 of my past GM's have made a noticeable clunk when shifting from 'D' to 'R' or 'R' to 'D', including the silverado i bought with 200 miles on the ODO.

The clunk when you are driving, could possibly be the front differential crossmember bushing has gone bad, allowing the diff to hit the crossmember when loads change.

Here is a youtube vid that i made of the differential bushing movement on mine.
https://www.youtube.com/watch?v=jY2z2_EB_ws

 

[Enter Hummer]

Thanks for the speedy response! Those bushings, are they easy to replace or a total PITA?

 

[cgalpha08]

Kinda, you have to cut/press/burn out the old bushing and then press in the new ones. I had 4speed's help and we cut/punched out the old bushing but then pushed in the new ones with a press. There are two options that i know of, scorpwerks, they are a sponsor here, they have a core program where you send them your crossmember and they send you one with a new bushing in it (they may have diy available now, not sure). Other option is outfitter design, if you google them you should find them. I went with outfitter designs, but many people have gone with both and have been happy.

If you replace the crossmember bushing you may as well replace the outboard bushings as well.

 

[Enter Hummer]

Thanks will do!

 

[Enter Hummer]

Ok, so I got the new OutfitterDesigns crossmember bushing in today (took me 4 hours with no press just a hammer) and the differential no longer moves! HOWEVER, when shifting from D to R to test the new bushing (my brother was under watching the bushing) the driveline had a pretty nice clunk from at the Transfer case. Im going to look at the U joints next week. The truck has over 185k miles so none of this is really a suprise.

My new question is, if it is not the driveline, that means its the T case right? Is there any kind of normal maintenance or common failure for the T case? Anything I should look for while the driveline is off?

 

[cgalpha08]

What year is your h3? I wouldn't be surprised if your t case just needed a rebuild and there was some slack in the chain. If your rebuilding a common upgrade is to install the metal shift fork instead of the plastic one that some of the early model ones had.

Sent from my SM-T820 using Tapatalk

 

[Enter Hummer]

Its an '07. Ill check that out and be back next week to see what im doin. Thanks!

 

[Enter Hummer]

Ok I pulled the driveline off and it all looked good so it was definitely not the driveline. The Transfer Case had a some play when turning it by hand so Im pretty sure thats whats causing the problem. It drives much better with the new bushings so Ill leave it at that 'til the problem becomes more obvious/worse.

Like you said, it could just be GM slop in general or the T case chain.

 

[4speedfunk]

Check the CV joint on the rear end of the front driveshaft. There is a small steel cup about 3" in diameter (where it bolts to the t-case). Inside this cup is a rubber boot, and six steel balls. This boot often gets ripped and all the grease flings out. The CV goes dry and it can make all kinds of noise (including the clunk you speak of). You can usually take a flashlight and shine it up in there to see the rubber boot. If its ripped...the CV is junk.

 

[Enter Hummer]

When I pulled the driveline I didn't see any sign of grease or excessive wear so Im pretty sure its the Transfer case. When I pull the Transfer case I will have to pull the driveline so I will double check that. Also, the clunk when braking still happens. I replaced the crossmember bushing and verified that the differential does not move. When grabbing the driveline I can twist it about 1/16" to 1/8" and hear it hit the teeth in the diff. It seems as if when Im braking, the tension comes off the driveline and rolls back a tiny little bit into the the differential. Is that the GM slop or worn out gears?

 

[rascole]

How many miles are on it? When I had my TC rebuilt when the plastic fork went out the slack almost disappeared but after 20k miles and a lot of off road trips, the slack is back. If you haven't had the TC rebuilt, I would definitely do it now, upgrade to the metal fork and you'll be good for a while.

 

[Enter Hummer]

Its got 185k miles. The T case will definitely be rebuilt when I can get to it.

 

[Enter Hummer]

Update:

Well I got good news and bad news, I have eliminated the hard clunk when shifting with a brand new Transfer case. Bad news is I still have the clunk while stopping. I took the truck into GM and twice they told me the front driveline would need replaced soon. The boot is old but not torn.

So today I took the front driveline out and 2wd it for a while, clunk remains. This leads me to believe its the rear driveline, something with the differentials, or the transmission crossmember (thanks rascole). Will check crossmember tomorrow since thats the easiest, then the driveline. I have no clue what I am doing with differentials so that will wait.

More on this later.