320i diff upgrade

[Andy_magic]

I've got a 320i with rear disks/ABS but want to change the diff as it's 4.11:1 and it revs its guts out at motorway speeds. The diff is also a small case and is just waiting to turn itself inside out.

First question is what RPM will the car be with either a 3.64 or 3.91 when cruising at 80mph, its currently 3900.

Second question is what's involved in swapping a small case diff for a large one, I WAS under the impression it was plug and pray until a local 'specialist' told me the driveshafts need changing as well as the diff. Personally I got the feeling I was being fed a crock of cack.

Cheers

[320Touring]

AFAIK

to change to a big case diff all you need to do is shorten the propshaft....

as for ratio-depends what you want

3.91 gives great accel

3.64 is a bit more relaxed

or you could use the one off the eta for sub 2k cruising at 80mph

[Andy_magic]

Don't tell me that, I have just binned an ETA diff after taking the engine & box out of it...

Having said that an ETA diff would be overkill I think.

[320Touring]

Don't tell me that, I have just binned an ETA diff after taking the engine & box out of it...

Having said that an ETA diff would be overkill I think.

dammit squire!i'd have had it off ya!

2.97 or 3.05 i think for em-all good

[Andy_magic]

I'll find out tomorrow if it's actually gone from the guy who scrapped it, I wouldn't hold my breath though.

[Templ8e30]

The e30 driveshafts are all the same length and bolt pattern so you don't need to change them.

The propshaft has a nut just behind the centre bearing, loosen this nut and push the propshaft forward on its splined section. This shortens the prop to accept the large case diff.

Simple (ish) swap, be aware that the large case is significantly heavier than the small case and can be awkward to hold in position whilst lining up mounting holes.

The mounting holes are also in the same position although the clearances are very tight so sometimes it feels like it won't fit, persevere and it'll go in.

I had a 3.64 on my 320i and it felt a bit too tall, I'd go for a 3.73 or a 3.91.

The 3.91 will give around 3700 rpm @80mph

The 3.64 will give around 3500 rpm @80mph

Cheers,

Iain T

[Brianmoooore]

or you could use the one off the eta for sub 2k cruising at 80mph

You'll need a calendar to measure your 0-60 time though, and I doubt if it would reach 80.

[Brianmoooore]

Don't tell me that, I have just binned an ETA diff after taking the engine & box out of it...

Eta diff is what you need for M50 conversions, as the matching gearboxes have 1:1 5th gears.

[Andy_magic]

Cheers for the Info Temple, just what I was looking for.

I don't think I'll be putting an ETA diff in my car just yet, but will find out if it's gone for 320Touring.

I have a nice calendar somewhere, failing that I have a moon phase chart but I hear they aren't accurate due to global warming making the oceans bigger and thus putting more drag on the moon as it moves.....

Not all 320i's are as gutless as the people would have you believe.

[320Touring]

or you could use the one off the eta for sub 2k cruising at 80mph

You'll need a calendar to measure your 0-60 time though, and I doubt if it would reach 80.

it'd reach 80 ok

as for the accel-given my driving style, accel at WOT is not of prime importance to me, I have no trouble with taking a bit longer to get to cruising speed, esp if its offset by better fuel consumption

[BrAdZ]

just fitted a 3.64 lsd to my 20, love it, fuel is better (well i can hold it at about 50-45mpg doing 75ish)

I dint really notcie a loss of accel, the only thing i noticed is it doesnt spin up in 2nd when given a foot full

No complaints here........and its soo much smoother drifting too