rear diff option for 1988 520i e34

Hi all,
I have 1988 520i e34 manual, and current rear diff ratio is 4.45 (as shown on the tag).

I am considering to change to lower ratio. Anyone has done this, and which ratio have changed to? Any side effect on engine?

Can i do bolts-on swap a diff from 1989 525i Auto? I think it's either 4.1 or 3.63?

But, there are too many rear diff from 525i 24V version, which is different to my 520i 12V version. It's a 3.91 LSD. If i want to use this, it seems i have to change the whole rear subframe? Is this worth to do? Do i need to change prop shaft too?

BTW, after changing this, i am considering to swapped engine with bigger CCs.

it all depends on what kind of subframe and diff that car uses, i saw a picture of a early e34 520 once and it looked a lot like a e28s rear suspension, and if it is that opens up a few doors, like e30s and e28s which interchange between one another by swapping the rear cover and popping out and swapping the drive flanges (easyly knocked out with a block of wood) the e30/e28 diffs mount to the subframe with 4 bolts on the top of the diff plus one on the rear cover and have a 4 bolt flange for the driveshaft. i can't say for sure as all e34s imported to the us had the later suspension

WInfred,
Thanks for your reply. I went again the to junkyard. So happen to found one that close enough with 3.65 (this is good).

Yes, it has 4 bolts on top, 1 on rear cover. But the rear cover is mounted to diff body with 8 bolts. I believe e30 has 6 bolts?

The previous i had, the bolts are on the right side and one on top plus 2 diff mounting bolts at the rear cover.

I'll give it a try and see if it will fit my e34.

rahman

theres large and small case e30 diffs, the 4 cylinder cars have a small case here and the 6s have the big case and can also have a posi traction unit in them, the e28 uses the big case here

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Originally Posted by nsbone_1988_520i

WInfred,
Thanks for your reply. I went again the to junkyard. So happen to found one that close enough with 3.65 (this is good).

Yes, it has 4 bolts on top, 1 on rear cover. But the rear cover is mounted to diff body with 8 bolts. I believe e30 has 6 bolts?

The previous i had, the bolts are on the right side and one on top plus 2 diff mounting bolts at the rear cover.

I'll give it a try and see if it will fit my e34.

rahman

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did you swap a manual tranny into your car? is that why you have 4.45's and a 5-spd? :D

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Originally Posted by bimmerd00d

did you swap a manual tranny into your car? is that why you have 4.45's and a 5-spd? :D

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Yes, a 4.45 and 5 spd. It's a standard config for 520i 12V here in Malaysia. THe 3.91 from later M50 engine would be too much work for conversion.

I just gotten a right diff (i hope)with 3.64 ratio. Now, i am hoping the 3.64 can be fitted bolts on. And, what pros/cons will i get from the new ratio.

Is yours a M20B25 engine? What's the diff ratio? Is there any diff part no to identify the diff?

rahman

I wonder if your 5th gear is a 1:1 like the one on my 1993 525i US spec with a 3.23LSD. If it is an overdrive 5th gear, you might run into a problem with the engine not being powerful enough to move the car with a lower ratio.

Quote:

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Originally Posted by bimmerd00d

I wonder if your 5th gear is a 1:1 like the one on my 1993 525i US spec with a 3.23LSD. If it is an overdrive 5th gear, you might run into a problem with the engine not being powerful enough to move the car with a lower ratio.

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OK, i believe you have an M5x B25 engine, which rear differential would be different to earlier ones.

My gear is std gearbox with OD. and i realize, it will kill the ability to move the car. A M20B25 conversion is also on the way...

ahh I see. There's a chart of which diffs came in which E34's on Bruno's site. www.bmwe34.net

Quote:

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Originally Posted by bimmerd00d

I wonder if your 5th gear is a 1:1 like the one on my 1993 525i US spec with a 3.23LSD. If it is an overdrive 5th gear, you might run into a problem with the engine not being powerful enough to move the car with a lower ratio.

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