E30 diff knock wanting to change need help!

[ThreeDLee]

I have a e30 320i auto 1984 and the diff is making drone sounds and knocking when putting your foot down and when it changes down gears, its defiantly coming from the back end...

What diff do i get? what ratio?

Thanks, lee.

[ThreeDLee]

325i OPEN DIFF 3.64 RATIO MEDIUM CASE?

[ThreeDLee]

Can anyone help ? :/

[Widge]

Hi Lee,
Are you absolutely sure that it's the diff that's the problem?
Droning whining noise could be the rear axle/wheel bearings, and the knocking could be the rear subframe bushes.
Difficult to tell without hearing it.

[Brianmoooore]

If it is the diff., I'd want something a bit numerically higher in a 320 auto than a 3.64.
4.1 small case would be about right, or a 3.91 at the lowest.

[ThreeDLee]

When you do kick down it clunks it happens with in the auto lag, like something is slack, what would you say I should do? Any other tests I can do?

[Widge]

I'd agree with Brian on the ratios if it is the diff. You should have plenty of choices too as you aren't looking for an LSD.

Best thing is to try and get the car up in the air and check out the back end. See if there is a lot of play in the sub frame mounts. Also remember the 3rd subframe mount is on the back of the diff. Have a good look at that because if it's in the way out it will make a clunk from the diff area n hard acceleration or kick down.

Diffs do go eventually, but the rubber parts are more prone to perishing. Having said that if you find that all the mounts need doing it would be an opportune time to change diff when you have the subframe off.
Good luck.

[ThreeDLee]

I will check the above before getting a diff! Will a different ratio to what's on it give false readings on the speedo?

[Widge]

Nope, no issues with speedo readings because the speedo sensor is in the diff itself.

[ThreeDLee]

This any good?

BMW e30 320i 4:45 diff

[ThreeDLee]

Thanks for your help people

[Widge]

I'm not a ratio expert, but that seems to be going in the right direction.
Bit numerically higher than the 4.1 Brian suggested, but I don't think it would od much harm.

[ThreeDLee]

If I go with a small case diff will I have to change anything else? Drive shafts or other bits?

[Widge]

No idea mate. Somone else will have to answer that one.

[aimlessrock]

I would also use this opportunity to overhaul the back end, given you will likely need to drop the rear beam to remove the diff (they are fecking heavy).

[Brianmoooore]

If I go with a small case diff will I have to change anything else? Drive shafts or other bits?

I would expect your car to already have a small case diff., but they are directly interchangeable anyway.
Small case diff has spacers built into its output flanges to make up the width, and the rear half of the propshaft has a splined section which is adjustable for length.

[Widge]

Yep I'd second that. Paint diff, paint rear beam, new subframe bushes and wishbone bushes, new flexi and rigid brake pipes - new rear wheel bearings if you can be bothered. Good opportunity to get up under the back of the car with a bit of stonechip too.

[hazd31]

I have a good 4.2 and 4.4 ratio diffs if your local. £40 each collected. All tested and good

[ThreeDLee]

Cool, I might well e interested in one of thos diffs! An you inbox me you number please?

Thanks for your help again guys!

[hazd31]

Cool, I might well e interested in one of thos diffs! An you inbox me you number please?

Thanks for your help again guys!

Pm sent