Centre Diff lock

[beermonster]

I know that the early WR used a pair of levers in the car to engage / disengage the diff locks..... Then they went to a vauum driven system with 2 actuators on the rear diff, and the centre diff controlled by a long bowden cable. Is it possible to change this setup to the later version with the centre diff actuator mounted on the gearbox?

[Jim Haseltine]

Possibly, but I can see the only good reason being that most (if not all) of the parts are still available. The centre lock method changes from a long spring loaded cable mounted at the rear of the box to a long rod mounted on the bellhousing.

Unless you've got the parts to hand I'd guess that it would be pricey.

Bet it's not that straight forwards either.

[puglife]

The diff locking mechanism is simple, its literally a pushrod with an arm that slides a selector across the two splined ends of the diff shafts.

I took some photos of the mechanisms which i'll send you tonight when i get a free moment james. Also got my Digital Camera fixed so can do some high res 2400x1800 pictures.

[quattrokid]

if I disconnected these shafts, then will this prevent the diffs from locking and unlocking at their own will.

I have also disconnected the vacuum hose which goes along the firewall into the dash diff module

[puglife]

the differential shafts are driven rich you cant disconnect them but you could remove the centre locking arm and cog. Let me get some photos and explain... or see my Type 85 Quattro gearbox dismantling photos in image section.

[JimH]

How about you disconnect the vacuum supply pipe to the diff lock control, and connect a pressure gauge to the open pipe end. See if you ever see positive pressure down that line.

If you do, locate and replace the one-way valve behind the dash, or (easier if you can't locate the valve), add another one-way valve in the vacuum supply line.

There should be vacuum on that line at all times (there's even a reservoir to hold vacuum if the engine is not generating any) to hold the diff locks in the "off" position.

This really should be an easy thing to fix, so it'd be a shame to botch it IMO.

[quattrokid]

hi Jim,

i have disconnected the hose going to the dash console under the bonnet by the W.O.T solonoid.. is there another valve further "down the line" going to the console?

where is the resevoir then? is it the green dome thing in the boot lining?

t.i.a

[JimH]

Originally Posted by quattrokid

hi Jim,

i have disconnected the hose going to the dash console under the bonnet by the W.O.T solonoid.. is there another valve further "down the line" going to the console?

Yes, behind the dashboard.

where is the resevoir then? is it the green dome thing in the boot lining?

t.i.a

Yes.

Simply disconnecting all vacuum feeds to the diff locks will not necessarily make them stay in the off position - they will be free to "float" on & off.

There should be vacuum applied to the "unlock" side of each diff lock actuator all the time to hold the diff lock in the off position.
I suspect you have a leaking one-way valve behind the dash which is allowing positive pressure down the line, through the control knob to the "unlock" side of the actuators. As the system is designed to work with vacuum, not positive pressure, it will then do the opposite of what it is supposed to do - positive pressure to the "off" side of the actuators will actually make the diff locks come on.

I think, assuming the actuators are not broken / leaking you will fix this by replacing the one-way valve hidden behind the dash, or just add another one in the supply line to the diff lock knob.

See:-
http://homepage.ntlworld.com/jh.666/diff_lock_diag.jpg

[quattrokid]

thanks Jim

[Phil Payne]

> where is the resevoir then? is it the green dome thing in the boot lining?

Instant test - get the engine running, wait a couple of minutes, then pull the hose off the reservoir. If your vacuum supply is good, it will hiss like crazy as it refills with air.