I want to share my transfer case experience. I could not make a sharp turn with my H3 and it seemed that the car is stuck and not moving and I had to back up the car and go back and forth several times to park the car. The car was driving very sluggish and heavy and sometimes I heard a load metal on metal clunk noise when making a sharp turn. I had this problem on-off. Took my car to four different mechanic shops (including a GM dealer) and each of them found something broken and changed it but did not solve the problem. I ended up doing google search and reading the Hummer forums about other H3 owner's experience and found out about the TC plastic shift fork. Finally asked a transmission shop in Mission Viejo and ask them to open the transfer case (and agreed to pay $400 to open the TC). Turned out that the jaws of the plastic shift fork are worn out, and the TC is locked in 4hi/low. There was a lot of debris in the transfer case and the TC oil pump filter was torn which was replaced. The shift fork was replaced by a GM metal fork (I chose GM fork shift instead of Dormann since had better online reviews). The drive shaft was also changed. The improvement in driving is very noticeable. I can make sharp turns without problem and the car seems to drive faster and easier. I think I have been driving in 4hi/low lock for weeks because of the shift fork malfunction. Here are some photos.

 

That is a nasty looking T Case filter sock and Front Driveshaft CV.

Are you still on the OEM Transmission? If not, when was that rebuilt?

 

Hi Doc. Unfortunately I don't know. I bought the car from a used car dealer 3 months ago. He had no clue about the repair history of the car. The car was sitting in the dealership for 6-7 months or longer. I never met the previous owner. The Carfax report doesn't show any repairs over the past several years. I doubt if the previous owner took good care of the car. I have no major issues with the transmission however when accelerating often I feel a push or kick in the mid-rear part of the car as if the gears are not engaging/changing smoothly, and when changing the gear to reverse there a kick and grump feeling from the same area. I am planning on taking the car to a transmission shop for ATF and filter change, as well as power steering, and front/back differential fluid changes as I don't know when/if the fluids have ever been changed. The best price I found in OC for ATF and filter change is $330. As a cheap alternative, I thought about pumping the ATF from above using a manual pump and replace the fluid (without dropping the pan and changing the filter), however with the unknown history maybe it is better just to spend the money and get it done right by a professional.

 

If you google it, there are several very clear vids on how to change the H3 Trans Fluid and Filter. You only need a couple tools, drain pan, the correct trans filter/gasket kit, and 5 Qts Synthetic Dexron VI. Pretty easy stuff, but I get not everybody wants to do the job themselves. Diff lube changes are even easier.

You have a good plan. keep after it.