Brand new member, I was hoping I could get a little guidance on my little problem. I have a 2009 5.3L H3 (95k miles) that has this single clunk sound when starting from a stop which can be felt in the floor. The strange thing is it doesn't do it immediately - but about a second later after the car starts moving. The harder you hit the gas the louder the clunk. The sound seems to be from the area between the transfer case and the front diff. Also occasionally it will be a series of smaller clunks and goes away when the car gets up to speed. There are no other noises or vibrations when cruising highway speed. I started searching around underneath, prying and grabbing - everything seems really solid except the front output shaft from the transfer case wiggles side to side a bit. I attached a video, is this normal?

 

Welcome to HF. Moved this to the correct forum.... H3 questions go in the H3 section.

Miles on the vehicle would be important.

Depending upon that miles information.... when was the last time the front U Joint was replaced? Have you ever replaced the CV Joint at the front of the T Case?

 

Thanks for the greeting, this place is a treasure of knowledge. The rig has 95k miles and the front U Joint and CV are the original ones that came with the car - so they have never been replaced. The boot on the CV is not torn but has small cracks and the U joint seems solid (grab with hand and shake). I have a new front drive shaft on order but wanted to address the issue of that movement in the transfer case output shaft, it isn't leaking at the seal but that seems like a lot of play.

 

Most T Cases will go a lot longer than 95K before needing TLC. That doesn't mean all will, but they usually do.

I would install the new front shaft and see what happens. If it still has a clunk then look at the T case. However, while under there.... when was the last time the T Case fluid was changed?

Once the front drive shaft is out of the way.... might as well change the Trans fluid and filter if it hasn't already been done. Be careful when ordering a Trans service kit (gasket & filter) the H3s use a special only H3 version due to the shape of the Trans pan providing clearance for the front shaft.

Good luck. Give us an update.

 

I changed the fluid changed about 20k miles ago, fluid only. That filter is probably way over due for changing. but I will update as soon as I get that new shaft.

Thanks man!

 

We hear of the same complaint often. The front diff bushings are most likely shot and causing the clunk.

 

I should have mentioned that I swapped the front diff crossmember with the beefy scorpworks upgrade a few years ago. Also the other two bushings (the ones on those plates on the left and right of the diff) appear intact and not cracked or crushed. The swaybar bushings look good too. No clunks when bounding down a dirt road, just one big clunk a second after hitting the gas. Super weird that it happens about a second after the car starts moving, you would think that it would be immediately when force is applied to the drive train.

Crossing my fingers it is only the driveshaft

 

Ive also had the clunk issue when the pinion bearing was junk and lost preload. Happened on several of the front diffs we had and one rear but they had north of 150k miles which is to be expected.

One other clunk we chased down on my personal H3 was due to a stretched transfercase chain which is a cheap easy fix if you can do the work yourself.

 

Update: swapped the front driveshaft and no go, still clunks when taking off from a stop, although a small win was the old shafts cv had some rotational play in it. I have a desert trip planned in a couple weeks and one of the guys going is 4x4 guru and should get to the bottom.

 

Will also mention the stretched chain issue and pinion bearing issues. I have a feeling this is boiling down to pulling the transfer case. Will post the results of the next attempt.