Diff lock in the snow :)

[ralleyquattro]

NEVER EVER engage the diff lock unless the car and rear wheels are completely stopped. Otherwise, you will damage the teeth in the lock, leading to rear diff damage. $$$

I think you mean not to engage when possibility for speed differential between two sides is high.
Otherwise it is pretty safe to engage at any road speed BTDT many many many times over the last 20 years of Canadian winters with both center and rear locking diffs (typ 85).
Unless you are turning sharply the slight speed differential between flanges is actually beneficial for engaging when the teeth are not aligned and disengaging when there is slight tention in the system and vacuum actuator is not strong enough to do its job.
On my B4 I cut the blue/white wire that provides the speed signal so I can lock (and disable ABS) on the fly as well... it also helps on the ice.

http://www.youtube.com/watch?v=pO_-QF8_M-I

My $0.02

[sam80quattro]

im with ralleyquattro on this 1, white/blue wire is snipped (first thing i do to any quattro i own) and my diff lock button gets switched as often as the indicators lol only seems to lock when you decelarate anyway, also my green light doesn't work, but the diff is definitely locked, 2nd drifts and donuts in the dry proves this haha

[Tonybolony]

Diff Lock Switch

Anyone had any experience of faulty switch causing intermittent ABS Warning Light? Is it possible for corrosion in the switch to bring the light on intermittently? This fault is slowly frying my brain

[UrS4boy]

I think you mean not to engage when possibility for speed differential between two sides is high...

Martin: My comment was meant for the folks who are stuck in the mud or snow with the diff lock NOT engaged, one wheel spinning and THEN they remember the diff lock and hit the switch, i.e. high speed difference between the two sides = BAM, grind, grind, tinkle. My comment also relates to the intended use of the diff lock, including its release at 15 mph (or whatever) via the white/blue speed wire, not using the diff lock for "normal" driving and/or drifting.