Different Differentials ??

[A518catcher 0]

Can the Diff Gurus tell me what on earth is going on with my Diff.

I purchased a 1989 nz new 520i, lovely car but i straight away noticed noise from the rear.

ive pulled out the Diff and sure enough its noisy, maybe a pinion shaft bearing.

heres the catch.

The tag says 4/45.

This is not a Diff that comes standard and some ones thrown it in.

The other point is that my speedo is way out. 130km/h at 2700 revs but only feels like 100km/h .

this diff only came out in a 318At i think,

From looking on the net the 4/45 is a bit rare and might be worth something.

either way i just want a quiet diff and a correct speedo for the wife.

[E30-323ti 66]

Presuming you have a M20 E34 not a M50 Then:

According to the BMW ETK it will have a 4.45 Medium Case (Type 188) diff.

It is quite a rear ratio for Medium (type 188) diff, but unfortunately the E34 case won't fit into anything else except maybe E32's.

You can get a lower ratio diff from most 325 E30's & E36's and E28 5 er's.

But you will have to take the two (yours & the new lower ratio diff) to a Diff shop and the internals swapped over.

[Carl 3]

If you're sure your speedo is out of whack then either your wheel size is significantly smaller than the stock size or you have a faulty pickup.

If you're in the market for a new diff then I have a ratio & rpm vs speed graph spreadsheet you can use to determine what you ratio you want.

[A518catcher 0]

thanks for the info about the ratio graph, and i think your right, the pick up is stuffed.

but i think ill just go for the standard ratio for that model/year or get this one fixed.

all a learning curve