520i diff same ratio as a 518i diff?

[slinky]

Hello all, Not sure if I'm posting this in the right place, if not sorry moderators!
I've got an e28 518i with a knackered diff which I'm replacing once I've found one. I've been offered a diff from an e28 520i auto and was wondering if anyone knew if this diff will be the same in my 518i.
Thanks in advance!

[Andyboy]

A 518i E28 has a 4.1 ratio diff. As for a 520i Auto, it depends on what year it is. Look on the rear diff cover and you'll see a steel tag under one of the rear 17mm bolts. Clean it up and that will tell you what the ratio is. Most were either a 4.27 ratio or a 3.91. A 4.27 would be a bit revvy, a 3.91 longer geared.
If you rarely use a motorway, the 4.27 will make it go better. I had 3 or 4 of these and they were a good old bus!

[slinky]

Cheers Andyboy, I'll have a look. I'll be wanting to use it for both motorway and town driving so I'm guessing I'll probably need a 4.1. I'm guessing the 3.91 would make it pretty slow on the uptake being that mine is a 518i?!

[Andyboy]

A 3.91 would probably be alright. It would blunt the acceleration a tad but not too much. What year is the 520i auto diff??

[slinky]

It's on a C plate, so 1984/85? It's only just down the road from me, I've not seen it yet but supposdly in reasonable nick.

[Andyboy]

Well if you can buy an E28 in half decent nick for peanuts it's worth buying then for bits. The last 525e I bought off Ebay for £65 broke to nearly £500 and I still had the engine I needed. To be fair though 525e stuff is more sought after than 518i/520i tackle.

I used to live very close to Oxford - given that I seemed to own every E28 within a 50 mile radius it was maybe mine at one point! What colour??

[Davenotouring]

I went from a 4.4 (? - Andyboy) on my 320i Touring Manual, to a 3.38 E36 Compact diff and it made it rev lower on the motorway but genuinely it didn't make much difference to the already lacking acceleration.

[Andyboy]

I went from a 4.1 on the Famous Gold Ring Turd to a 3.64. It would cruise at 100 mph with ease but it did blunt the massive torque slightly. Before, my 320i had sooo much power it would pull my pants down, with the 3.64 it wouldn't.

[slinky]

Andyboy, it's grey, possibly dolphin grey. Not sure but hopefully going to have a look tomorrow. If it's got the 3.91 diff I'll probably have it as well his front wings and petrol tank if it's not rusted to bug**ry like mine is!
thanks for your help! I'll keep you posted!