Anyone want to swap diffs?
 

I've got myself a 3.92 Sierra diff off eBay with driveshafts hubs and book uprights, but with the BMW gearbox I've got, the ratios will only give me a top speed of 111 in 5th, and first will probably be un usable.

Anyone in the fareham area with a longer ratio fancy a swap? Don't know if it's 7" or 7.5" yet as I don't know where to find the code.

What size push in shafts are they ? Ive got a 3.62 7" diff that takes the larger of the 2 sizes of splined shafts if you fancy a drive round to the other side of the M25.

What BMW gearbox?
What redline?
Most 4th gears are 1.1 and I get 120mph with 14" wheels and a 3.9 diff

Mine has bolt-on shafts, does that mean that it might not be the ratio it was sold as? I think it's a 7.5" diff, but I don't quite understand all the different codes on Sierra diffs.

My gearbox is from a 328i e36, I calculated the speeds on an online calculator based on 15" wheels and a 7k rpm limit. I could have got it wrong though.

I was originally going with a bmw lsd modified to a 2.91 ratio I picked up, but it was too big.

beardydave, Sierra diffs are a complete zoo. Ratios, LSD or not, push in or bolt on, there were almost all permutations produced at one point or another. Admittedly, some are rare. You can tell 7" from 7.5" by the shape of the housing cast. Here's a page that will, hopefully, shed some light on them. http://www.super7thheaven.co.uk/Sier...r_Differential

I've been and checked my diff, and it's definitely 7.5" with 100mm lobro shafts.

I'm also certain it's open (or if it was LSD it's not any more! ;) ). There's no tag plate, and i bought it off ebay, but on the back it's got 3.92 written on in yellow paint pen, and the ratio of turns of the input shaft are approximately that so i've got no reason to doubt it.