What's my Diff?

[DavidC]

Hi,

I bought a diff a couple of weeks ago, the one that was advertised on Findit.co.uk, advertised as a "Sierra XR4 rear slippy diff (viscous type)" as far as I can remember.

It's got the following letters/numbers on the tag:

91 GG GA 391

4A 1M11 00 47

Can anyone make any sense of that?

The top mount measures 7.5" end to end, and there are various other sets of letters and numbers on the other parts of the casing.

It seems quite large, with the back plate of the case being kinda square in shape, 8.5" wide, 9" tall. And it's def a Type B with the flages for bolt on driveshafts.

Is any diff expert willing to hazard a guess as to exactly what I've bought?

Cheers

David C

[Bananaman]

Sounds like a Cossie diff if its 7.5"

[Nick M]

Seconded.

[DavidC]

And do you have any idea what the letters and numbers on that tag refer to, or what ratio this diff would be?

Cheers

DC

[stu999]

David, have you got a Westfield build manual?

Most, if not all the diff part no's. are listed in there, and cross reference to the ratio too.

[DavidC]

Ah, no manual yet. I'll pick one up at Autosport Intl

[Mike H]

In my experience of diffs that still have their tags, the last 3 numbers of the first line usually give you the ratio. So yours could be a 3.91:1. Test it by counting the turns of the input shaft required to get one turn on the output flanges.

You can find the LSD test mentioned loads of times on here, but to save you searching (sorry Blatman) if you turn one of the output flanges then the other output flange should turn the same way. ie.turn one as if the car were travelling forward and the other side should do the same.

HTH

Mike

[DavidC]

Well the LSD test doesn't give a promising result on this diff, But I had read somewhere that the LSD effects don't work on these ones until they're sujected to load.

Is that actually the case?

Should the input flange rotate at all if I rotate on of the output flanges by hand?

DC

[tonym]

To check viscous lsd stop the prop shaft turning, put a socket with a torque wrench on the hub nut (with car jacked up if on the car) & turn hub in direction of normal rotation half a turn taking approx 1 sec.  It should take a torque of 52 +or- 22 ft lbs. bulls*** about both shafts turning in the same direction - that only works with plate type lsd.

[DavidC]

Ah well, I haven't got the car yet (Just diff, uprights, and gearbox), that's what I'm going to Autosport for.

I'll just wait it's fitted to something.

[Mike H]

To check viscous lsd stop the prop shaft turning, put a socket with a torque wrench on the hub nut (with car jacked up if on the car) & turn hub in direction of normal rotation half a turn taking approx 1 sec.  It should take a torque of 52 +or- 22 ft lbs. bulls*** about both shafts turning in the same direction - that only works with plate type lsd.

Does that prove it's viscous?

or

Does it just prove that if you know it's viscous already then it's in decent condition?

I don't see why turning one output flange on a vsicous lsd does not prove it's an lsd of some sort. If you can explain otherwise then fair enough.

Mike  

[stu999]

To check viscous lsd stop the prop shaft turning, put a socket with a torque wrench on the hub nut (with car jacked up if on the car) & turn hub in direction of normal rotation half a turn taking approx 1 sec.  It should take a torque of 52 +or- 22 ft lbs. bulls*** about both shafts turning in the same direction - that only works with plate type lsd.

So allowing the propshaft to turn ( or not even having one connected i.e. diff on the garage floor) andIf a flange was turned, with the prop 'free' the 'LSD effect' in the description described above will cause both flanges to turn the same direction, whereas a free diff doesnt have the drag to overcome the  pinion pre-load, and the flanges turn in opposite directions. Just as a plate diff would AFAIK...

[windy]

Plate diff: Both shafts turn the same way

ATB diff: both shafts turn the same way

Viscous diff: both shafts turn the same way

Viscous diff x 2 (knackered): both shafts turn the same way but can be made to turn opposite ways with only a little effort.

I have all these in my posession. The only certain way of telling what you've got is to take the back cover off (5 min job) and look inside.

Windy

P.S. ATB diff is the best for the Westy.

[conco]

Hi!

sneakin read from sweden!

Wanna ask Windy how i can see in the diff that its a LSD?

Thanks in adv....

and merry C-Mas to all you Westies

Conco