Screaming rear axle.

[Bonehead]

Hi chaps. First of all, the initial symptoms:

Transmission was v. whiny on a trailing throttle when I bought it. Vendor claimed it only needed the axle servicing, which he also claimed to have done.

Sho' nuff, noise abated. For around a month. Then the whine came back with a vengeance.

Finally, after about 2 weeks, pulling out from a junction on a hill, a loud BANG and then.... nothing.

When letting the clutch out, the vehicle would not move, but... well... imagine the metallic grinding noise of worn out pads and discs, but mated with all the holy hounds of Hell and LOUD!!!!!

I am trying to figure out where the break is. If I try to move the vehicle as normal, it makes the awful noise but will move on the flat.

If I put the handbrake on, the vehicle will move without much noise, but the rear propshaft does not turn. It jiggles back and forth.

If I lock the centre diff, the vehicle moves in a straight line OK. It also turns without any noise save the occasional "clunk" as (IMHO) the rear diff jumps the sheared teeth.

My theory is that the rear diff has sheared all its teeth. With the centre diff unlocked, the engine torque is mostly directed at the rear axle, as there is less resistance. The diff grinds as the propshaft tries to turn faster than the halfshafts. Howver, with the diff locked, both propshafts are turning at the same speed as the halfshafts, hence the relative absence of noise.

I plan to remove the rear propshaft tomorrow, and try to move the vehicle with the diff unlocked and then locked. This is to try and eliminate the transfer box as the site of the break. If I am correct in my theory, with no diff lock, the rear propshaft flange will simply spin and the vehicle will not move, whereas with the diff locked, the vehicle will move as normal, and the rear axle will be silent save when I turn a corner.

My questions are as follows:

i) Can anyone find fault with my diagnosis?

ii) Any OH MY GOD DON'T DO THAT tips on replacing a differential? I have a Haynes, but it doesn't cover diff replacement.

Many thanks in anticipation,

Mark.

p.s. vehicle is a '94 300 TDi Manual, with 88,000 mls on it.