engine and drivetrain E21 Open Diff Swap Worthwile While Doing 5-Speed Swap?

[Jace]

I bought the drivetrain from an '82 318i, diff and driveshafts included, and wonder if its really worth doing when i swap in the 5speed. I'll probably want an LSD down the track but not for a while.

 

will a custom 5-speed tailshaft work with both diffs or are the forward lengths or input flanges different between a 12/'75 2002 and a E21 318i?

[M3M3]

depends on what ratio the diff is and how you drive the car.

[Jace]

Australia got a mixed bag of foreign spec'd cars but i believe the E21 diff is a 3.90 (11 & 43 stamped on the side, with a 10 as well?)

 

I'll check what my 2002 is.

[Mike Self]

Your 2002 should have a 3.64 diff; the 11/43 diff you got is in fact a 3.90.  Installing a 3.90 will give you approximately the same revs for a given speed in 5th as your 4 speed would have in 4th.  So you'll have better acceleration at the cost of higher revs on the highway.  

 

If you plan on much highway driving, I'd stick with the 3.64 diff (I did with my 5 speed conversion).  At ca 70 mph, your revs will drop from 4000 (4 speed) to 3200 (5 speed) with the 3.64.  But if you'd rather have the acceleration and don't do much highway driving, go for the 3.90.  Hang onto the 3.90 anyway; someone else will want it.  Or look for a 3.64 limited slip from a 2 liter, 4 speed E21.

 

mike

[ray_]

Your 2002 should have a 3.64 diff; the 11/43 diff you got is in fact a 3.90.  Installing a 3.90 will give you approximately the same revs for a given speed in 5th as your 4 speed would have in 4th.  So you'll have better acceleration at the cost of higher revs on the highway.  

 

If you plan on much highway driving, I'd stick with the 3.64 diff (I did with my 5 speed conversion).  At ca 70 mph, your revs will drop from 4000 (4 speed) to 3200 (5 speed) with the 3.64.  But if you'd rather have the acceleration and don't do much highway driving, go for the 3.90.  Hang onto the 3.90 anyway; someone else will want it.  Or look for a 3.64 limited slip from a 2 liter, 4 speed E21.

 

mike

 

 

Or, go with a 4.10.

 

[Beaner7102]

Jace, +1 with what Mike said, but if your current diff is ok, why change it until you find an LSD. 

Hang onto the E21 diff though, its alwas handy to have a spare.

 I havent seen you car around,  where in Victoria are you? Are you on Doug's register?

Beaner7102

[Jace]

quality post Mike.

 

i can't find a stamping on the 2002 diff because it's covered in rubberized underbody paint, but being so slow off the line and going off what the generic manuals say then you'd be right.

 

We didn't get 320iS's so finding an E21 LSD locally is not likely to happen.

Jace, +1 with what Mike said, but if your current diff is ok, why change it until you find an LSD. 

Hang onto the E21 diff though, its alwas handy to have a spare.

 I havent seen you car around,  where in Victoria are you? Are you on Doug's register?

Beaner7102

 

i'm from Geelong, are you not in the Facebook group?

[jimk]

Don't change it out and if you don't like the old one, then install it.

[Mike Self]

3.64 LDSs aren't easy to come by even in the US of A...took me several years to find one, and it ended up coming from Switzerland (thanks, Gregory!).  IIRC they came on the E21 323is cars--the early 6 cyl M20 version of the E21 that was never imported to the US.

 

mike

[2002haus]

The information below is to clarify what is known to be available.

 

3.45 ratio LSD's are difficult to find in this country.  They were usually the ones installed on the European version 323i w/either the close ratio or overdrive transmissions.

 

The 3.64 LSD was used in the 77-79 320iS.

Edited March 14, 2014 by 2002haus

[TobyB]

 

 

Installing a 3.90 will give you approximately the same revs for a given speed in 5th as your 4 speed would have in 4th

Nope. For once, I gotta disagree.  The G240/245 has a .81:1 overdrive.

So:

A 3.64 *.81 = 2.94 final drive ratio in 5th.

A 3.91 gives you a 3.16- much lower than the stock 3.64 

A 4.10 gives you a 3.32

A 4.27 makes it 3.45

And a  4.56 makes it a 3.67.

 

So you can actually run a 4.10 with a 5- speed and still have a lower final drive than stock.

 

t

[Jace]

i'll be using a 245.0.054.0.00 but while i haven't found conclusive gear ratios for it specifically, all the manuals i have all give a 1:1 5th gear.

[TobyB]

It very well could have been a close- ratio box- there was one for the E21.

 

Trivial to tell which it is- put it in 5th, and turn the input one rev.  You can do it with the engine attached.

If the output turns one rev, you're in- close ratio box, very nice to have.

In this case, keep your 3.64.

If the output turns about half a bolt LESS than a rev, you have a standard E21 5- speed

and oughta run the 3.91 diff.

 

Either way, yes, the pinion dimension is the same for the 2002 and the E21 so that will work.

With the E21, you'll want to put a 2002 CV onto one end of each CV, and use the 320 halfshafts,

as the E21 diff is narrower than the 2002 diff, but the output shafts make up that difference, and

also adapt the 10mm bolt flanges of the E21 to the 8 mm bolt flanges of the 2002.

 

hth

 

t