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Sierra 7" diff Help Required
Zetecron - 24/11/15 at 07:09 PM

Hi guys,your help would be appreciated on this! Is it possible to change any CWP from any 7" open diff into any Xr4x4/ Cossie 4wd 3.62 Viscous LSD? Read most places say yes, but also read some say no!! Some of the crown wheels look thinner than others, is this an issue?? Don't want to buy to much parts if there no good to me.


mark chandler - 24/11/15 at 08:32 PM

Yes, I run a 4x4 LSD with a 3.14 CWP

You keep all the 4x4 housing, carriers etc and swap in the new CWP.

When you start pulling them apart leave the big diff carrier adjusters soaking in penetrating oil for a week, I also needed to warm the outside before the castellated nuts started to move. Do not get to hot as there is a rubber O ring or knock the castellated lumps with a hammer as they will snap off!

You Used be able to buy the tool on eBay to undo, you will also need a very deep socket for the pinion, I forget the size get a cheap one, cut in half and weld 2" of scaffold tube between the two halves to make this.

People will tell you to measure back lash, it must be done by an expert etc, I just wound up by hand pinion until it started to drag slightly as bearing preload. For the crown wheel set the preload out of mesh then marched it across until it just started to bind when spinning and back out 20 degrees.

You will need new seals, you can recover the collaspable washer by gently tapping it out over a rod.

[Edited on 24/11/15 by mark chandler]


Neville Jones - 25/11/15 at 10:26 AM

Be careful when buying the diff housings, as some 4x4's came with 7 1/2" diffs. The 7" innards won't fit, or vice versa.

I've had a couple of early 2.8 xr4x4's definitely with 7 1/2" diffs, and a later 2.9. I've got a Cosworth viscous diff here, and it's a 7 1/2" as well.

All of the 7 1/2's have been 3.65's, including the Cosworth.

Be aware.

Cheers,
Nev.