what diff

[peter2482]

as per the title really, been looking around but not really sure which one i need, size wise and ratio etc
thanks

[HandyAndy]

i take it you are not going to have a donor car?

if it helps, my diff came from my donor which was a 1.8cvh sierra estate & its ratio is 3.92 with push in halfshafts .

andy

[peter2482]

I was thinking against a donor simply because i dont have the space to keep one whilst i strip it, although i realise this will proberly work out dearer in the long run,

[peter2482]

is there any way to tell what ratio a diff by lookin at it? or how do u find out
thanks

[AshG]

if your planning on a car engine and a non race setup any sierra diff will do the job to be honest. if you look in the haynes manual for the sierra it says what diffs come with what engines.

[peter2482]

ok thanks is it possible to change the ratio of a diff,

[snapper]

Diffs are generally cheap, the Limited Slip ones are more, usually £150.
The most common are the Sierra 7" ones with 3.6 and 3.9, you can also get 3.38 and 3.14 but very rare.
Cosworth diffs and some Granada ones are 3.6 and 3.9.
All 4x4 cars are LSD but not Granadas with Traction control.

2 ways of telling what ratio you have, the VIN plate will have a code in box 10 maked Axle.
A metal tag on the diff will have letters and numbers 2 or 3 As = LSD the number will have something like 400362 for a 3.6 and 400392 for a 3.9 diff.
You can mark the input flange and the output flange and measure howmany turns you get. i.e one turn of the output = 3.9 input if it is a 3.9 diff.
The only time it is worth changing the ratio is if you have a LSD and want to change the ratio from a non LSD diff, you then have to change both Crown wheel and Pinion as they are matched, all new bearings should be fitted and the end float needs to be set by someone who knows how to do it.

[peter2482]

thanks snapper, just another quick question, do i need a 7" or a 7.5" diff, or does it not matter.

[snapper]

It really does not matter unless you are going for very High BHP.
The 7" is smaller and lighter and there are more of them.
I would go for a 7" one with bolt on (Lobro) shafts, then you can swap them with ease. I have also not seen many LSD pushfit diffs.