For the people who know differentials..please help

[danutt 4]

ive asked around , spoken to many stupid people who know nothing and spoken to some that seem to know something but no one actually seems to know anything haha

i have an e28 1985 with a 3.91 ratio diff and 4 speed auto box.....i have to use alot of the pedal just to stay going the same speed on a hill let alone accelerate up it so ive decided to change it closest to a 4.45 as i can

yes people say rediculous things like itl buzz the cockpit but my mate has an e30 running a 4.45 diff on a 6 cylinder and its goes really well and doesnt rev high on the motorway cruising

my car gets 75 in first

120 in second

and who knows in third

heard you can swap the internals???(it has 6 bolts on output flange so its medium case?...should be able to swap internals from a medium case e30 diff as long as its 6 cylinder??)

can use e30 drive shafts?

i cant really tell if its a mdeium case or large case diff as far as i can tell it measures a little longer and a little wider than the e30 diff with 6 bolts on the flanges

i have already found a 4.27 from an e30 looks like a medium case with 6 bolts either side on the output flange

so yea if there are some people here that know how to proceed it would be greatly appreciated!!

[CamB 48]

If they are both medium case diffs, you should be able to swap the rear covers and the drive shaft flanges (they just pop out) from your e28 diff to the e30 diff ... and you're done. You might need to change the plug for the speed sensor.

Which city are you in - could be keen on the 3.91 at the right price.

[morerevsm3 7]

if they both have 8 bolts holding rear cover on, they are medium case, and just follow instuctions above^

[danutt 4]

just had a look again now at the rear covers and the e30 diff has 6 bolts holding the rear cover on and mine has 8 bolts

what case is the e30 diff?thought it would be medium case diff coming out of a e30 2l straight 6??

yea id let the 3.91 go for cheap if i can get a 4.27 or 4.45 on the e28

[BM WORLD 1283]

most 320ia have small case .

some 320i manuals and SA models have medium case .

all 325i have medium case but much lower ratio numbers like 3.64 and 3.73 etc

it will be harder to find 4.11 and 4.45 in a medium case

[danutt 4]

most 320ia have small case .

some 320i manuals and SA models have medium case .

all 325i have medium case but much lower ratio numbers like 3.64 and 3.73 etc

it will be harder to find 4.11 and 4.45 in a medium case

well i can get my hands on a 4.27 and 4.45 small case diff

possible to swap these internals??

anybody know for sure??

anybody done this before?

thanx

[danutt 4]

just found out can only swap medium to medium case so not keen to even get into trying my hand at swapping the internals

so i got a price for a 4.45 thatl go straight in but what i want to know is if anyone here has a 4.45 medium case diff and for how much??

thanx

[*Glenn* 854]

just found out can only swap medium to medium case so not keen to even get into trying my hand at swapping the internals

so i got a price for a 4.45 thatl go straight in but what i want to know is if anyone here has a 4.45 medium case diff and for how much??

thanx

With the 3.91:1 diff in the car the engine will be doing 3,200rpm @ 100kph in top gear with the tyre size your running.

With a 4.45:1 diff it will be reving to 3,673rpm @ 100kph

Is that what you want ??

Are you sure your performance issues are not engine or gearbox related ? Remember also your car is quite heavy and only a 2 litre

Edited June 24, 2009 by *Glenn*

[BM WORLD 1283]

just convert it to a manual . i have all the parts (from a e28 525e) except the gearbox it self , but they come up pretty often.

or do a 2.5 or 2.7 engine swap while you are at it

[danutt 4]

With the 3.91:1 diff in the car the engine will be doing 3,200rpm @ 100kph in top gear with the tyre size your running.

With a 4.45:1 diff it will be reving to 3,673rpm @ 100kph

Is that what you want ??

Are you sure your performance issues are not engine or gearbox related ? Remember also your car is quite heavy and only a 2 litre

dont think it will rev that high at 100kph my brother has a 320i with a 4.45:1 and its doing just under 3500 at 110kph thats more than fine with me

yes the car is heavier but a higher ratio will make a drive up a hill less effort and thats what im after

have managed to locate a 4.45 now just to get the cash together and il let you all know how it goes after:)

cheers for all the help