diff locks explained

[stoop44rio]

hi, i'm going to look at a 90q next week and want some info on the diff locks please- how they work,how to check they're working,possible problems to look out for,etc. thanks for replies - its a type 85/c reg if its makes a differance.

[Booty]

The diff locks are pneumatic or air controlled if you like. They are fed by a small diameter pipe from the engine bay, around the side of the battery box ( yours will be in the engine bay on the passenger side ) through the bulkhead and into the back of the switches on the centre console. You have two locking positions.

1, Position 1 - first click - This locks the centre diff on the back of the gearbox, you should get a little green LED light up. This setting is used for driving in slippy conditions like snow, icy roads or wet roads etc. You can drive perfectly safe on tarmac with it in position one.

2, Position 2 - second click - This 'totally' locks the system all together, centre and rear diffs together. So in other words, as you go round a reasonably tight corner, all four driven wheels are locked together and will not 'yield'. This setting is for when you are up to your neck in mud, sand e.t.c. It will dig it's way under ground on this setting!

The centre console control distributes two further air pipes to the centre and rear diffs. These end up attached to plastic actuators that have an arm attached which dissappear inside the diffs. These can seize and the acctuators can brake and seize too. To test they all work you need to sit very quietly, and I'm not joking here, with the engine running and turn the rotary knob on the dash to position one. You should hear a faint hissing sound as the air runs and operates the centre lock. The green LED should light up too. Turn it back to the off position and the noise should be heard again, and the light should go off. Try this again for the rear diff. Now, sometimes they wont come off if they are a bit 'sticky' and you may need to drive a few yards to unlock them but you'll get the idea wether they work or not from the above. To test that they do work put the car onto some gravel and lock them all totally, then try and turn the car 'semi - sharply', the car will just dig and the inside wheels will try and 'bounce' as they are fully locked.
A few people do say ' well why do you need diff locks, I,ve never used them' ' who cares if they work or not'?! Well to me they are a fundamental part of the quattro system and should work, if you drive on snow the difference that having the centre lock in is amazing, real rally driving stuff!
Don't let it put you off though if they are not working as they can be fixed / un-freed.

Hope this helps.

Rich.

[stoop44rio]

cheers booty,i don't think i could've got a better explaination! thanks!!

[msh]

Originally Posted by Booty

2, Position 2 - second click - This 'totally' locks the system all together, centre and rear diffs together. So in other words, as you go round a reasonably tight corner, all four driven wheels are locked together and will not 'yield'. This setting is for when you are up to your neck in mud, sand e.t.c. It will dig it's way under ground on this setting!

How front wheels can be locked together if front differential isn't lockable?

[Booty]

Originally Posted by msh

How front wheels can be locked together if front differential isn't lockable?

Buy a quattro and you'll find out.

[MikeNZ]

Another explanation can be found here:

http://www.kvquattro.com/techdocs/diffLocks.html

[20vcqdriver]

Occasionally depending on the positions of the locking rings in the gearbox and diff, selecting the diff lock will not immediately bring on the green lamp, however moving forward or back slightly on lock should engage them and bring on the lamp.