E30 M40B18 Man diff

[SAP1]

Hi my diff on my e30 is making a churning/whining sound I have changed the oil. Any idea on why the noise is still there?
Thanks

[Grrrmachine]

Sure it's the diff and not something else at the rear, like the handbrake shoes?

[SAP1]

Hmmm could it be the fuel pump?

[Grrrmachine]

Depends; does it happen when the car is stationary?

[SAP1]

No it's doesn't

[Grrrmachine]

Then it's probably not the fuel pump

[SAP1]

How do you stop the diff from churning/whining?

[Grrrmachine]

Rebuild it or replace it.

[Brianmoooore]

Changing the oil in a noisy diff. is a last ditch, clutching at straws, action in the vague hope that it may effect a cure. Chances are that it won't, but it's cheap and easy, so worth a try.

[JF008]

I will be changing my diff this week as part of an engine conversion, I have a 318 as well must be the same type? let me know if you want to replace it we will sort a price out. As for your problem I don't have a clue

[SAP1]

Thanks for the input guys! Probably replace the differential then for a Z3 unit what is a good ratio to use
Cheers

[Grrrmachine]

http://www.e30zone.net/e30zonewiki/inde ... fferential

[SAP1]

Thanks for the reply

[Brianmoooore]

Thanks for the input guys! Probably replace the differential then for a Z3 unit what is a good ratio to use
Cheers

That would need to be used with a direct 5th gear gearbox, such as E34, E36, Z3, etc, rather than an overdrive 5th like on an E30 box.

[SAP1]

Sorry mate don't understand what you mean

[Brianmoooore]

E30 gearboxes are developed from a four speed design, by adding on a section containing an overdrive 5th gear. When you are in fourth gear (the original 'top' gear) the input and output shafts are turning at the same speed - the two shafts are locked together, and the gearbox proper is doing nothing. When fifth gear is engaged the output shaft turns faster than the input.
The E34, E36, etc. boxes were designed as 5 speed boxes from the start, and the input and output shafts are locked together when fifth gear is engaged. The same thing has now happened to these, with a bit added on to make the six speed boxes.
If you use a diff. ratio intended for a Z3 with an E30 box, you will effectively have no first gear, and fourth gear will be the same ratio as the fifth gear you have now.
If the engine conversion you have in mind is a M50/M52, then if you fit it complete with gearbox, the Z3 ratio will be usable.

[SAP1]

Ohh sh1te I planned on keeping the engine and gearbox the same. So there is no way I can upgrade my diff due to the gearbox.

[Grrrmachine]

It depends what you mean by "upgrade". What do you want; better cruising ratio, faster acceleration, better fuel economy or Limited Slip?

If you're thinking "it's from a Z3 so it must be better" then sort your brain out - you've already got a BMW

[SAP1]

I feel that the ratio on my diff is too high and I want one with better fuel economy and a good cruising ratio. Which one will be compatible with my gearbox?

[Grrrmachine]

You've probably got a 4.27 on there at the moment. Try finding a 4.10 or even a 3.91, although be prepared for your acceleration to feel blunted because of it.

[SAP1]

Yeah don't mind the acceleration difference as long as I get better fuel economy lol
Thanks for the information ;)

[Brianmoooore]

To give you an idea of what the difference is in practice, an E30 with a 4.27 diff in fifth gear will be at the same engine revs. as an E30 in fourth gear with a 3.46 diff.
Go too far, and both acceleration AND fuel consumption will suffer.
If fuel costs are an issue, have you thought about LPG? All my cars have run on this for the last 13 years.

[SAP1]

I want a lower ratio diff because when doing 80-90mph (In a controlled environment ) the car revs it's nuts off. Well at 80 the car does 3500rpm I want a diff that does at least 2900-3250rpm at this speed. And LPG naah not my style