HELP, Locking rear diff stuck

[smileynialley]

I recently took my H2 to a garage to have the gasket between the transfer case and the gearbox changed as it was leaking.
I went to pick it up today and as i drove it away, noticed it was driving like a dog!
In drive, at rolling speed, if i put it on full lock (left or right) the car felt like it was seizing up and would only move if i throttled it a bit.
The rear wheels sound like they are slipping when i do this (turn corners) and i hear a skidding sound. the car seems to jolt a lot and to me this sounds like the rear diff is locked.
I've tried changing every setting on the console (4hi, 4lo, locking diff, etc) and nothing changes.
I've lef tthe hummer at the garage for them to sort it but do not have high hopes for them to have a clue what they are doing, seeing as they were supposed to fix a leak and ended up making things worse.
can anyone help or shed some light?
thanks
Niall

[PaHumBug]

I think the transmition needs to be in neutral in order to lock/unlock the diff.

[SummitUp]

...The rear wheels sound like they are slipping when i do this (turn corners) and i hear a skidding sound. the car seems to jolt a lot and to me this sounds like the rear diff is locked.
I have to agree that from your description it does sound like your rear diff is locked. The rear locker can't be engaged unless your in 4Lo, and when you shift back to 4Hi the locker should automatically disengage. Now if someone (like the Dudes who worked on your truck) were to engage the locker in 4Lo on pavement and make a sharp turn, it's possible (in theory) that the wheels turning at different speeds in a turn and being unable to slip on the pavement could bind up the locker to the point that the internal spring might not have the power to disengage the locker dogs (the locker is engaged by an electromagnet but it is disengaged by a spring when the electromagnet is de-energized). One way to find out would be to jack up one rear wheel to release any binding forces on the locker and see if that disengages the locker.

One other thing you might want to investigate is to see if some electrical malfunction is causing constant current to be sent to the locker, i.e. a damaged wire harness, sticking relay or switch. Easy to rule out, just check the wire going into the rear diff with a test light or multi meter. Or just disconnect that wire and see if the locker disengages.