2008 Hummer H3 Alpha here with 304k. Original trans was replaced around 187k. Last night on highway, bad vibration under load that would go away when letting up on gas. Did it a couple of times, pulled over each time. Checked underneath to make sure no major leaks or anything like driveshaft failure. Drove fine rest of way home. I decided perhaps stupidly to see if it would hit passing gear a few blocks from house. Kaput. Every gear to include park acted like neutral. Checked trans fluid. Looked fairly clean and full. It’s definitely leaking now probably from the lines. Decided to try out the other drive modes and put it in 4HI and drove it the few blocks home and parked it. Drove fine. Thoughts?

 

Transfer Cases don't slip, they have a chain so it there is a T Case problem it is likely never going to be intermittent. Transmissions slip, overheat, cook the fluid, and die... or the valve body has a stroke and they don't work.

Transmission issue is my guess.

When was the last time you changed the T Case fluid and check the level?

 

All fluids were done maybe 25k ago and 3-4 years ago. Additionally, when in 4hi the drive shaft from T case to front axle just spins and all gears act like neutral. When I switch 4hi lock or 4 lo the truck will drive in all gears and no more spin. Front diff is where leak is coming from I think now.

 

blew a CV or the front diff.

 

Blew a CV shaft, front diff part or prop shaft.

 

Yep. That is the short answer.

The clue, you have to lock the T Case to get it to move, just like when you remove the front drive shaft.

 

So the H3 is at the shop and my mechanic is having a hard time sourcing a front diff. Any suggestions of where to obtain one?

 

Local Pick n Pull, Ebay, Craig's list. New Carriers, rings and pinons are available from GM parts sources, and online.

If it needs a front diff, I would have your local ring and pinion shop do a rebuild with new innards. If your mechanic wants to just do a swap which is probably cheaper and a spin of the mystery wheel as to what you end up with, then you need a front diff from another Alpha.