1990 M20 Swap to 1985 325e

[Lirker]

Hello all.

1990 M20 automatic, swapping whole head and block into 1985 325e.
I want to use the manual transmission on the 85 325e.

My questions are;

The wiring harness on the 325e has 2 sensors leading to the early eta transmission for crank position sensors. The 325i harness doesn't have these. What do I do about that?

Also, is there anything else I need to look out for the swap as far as transmission goes like fitment or compatibility?
Btw I already have the adapter from round to square plug.

[reelizmpro]

You should run everything from the 325i including Motronic 1.1/1.3 which doesn't need those sensors on the transmission. Just removed them. You'll need to swap the flywheel also.

[Lirker]

You should run everything from the 325i including Motronic 1.1/1.3 which doesn't need those sensors on the transmission. Just removed them. You'll need to swap the flywheel also.

So the dual mass flywheel that's on the 85 transmission won't work?

[reelizmpro]

It will, I meant swap the automatic flywheel to the manual trans one.

[Lirker]

It will, I meant swap the automatic flywheel to the manual trans one.

thanks i sent you a PM

[TobyB]

automatic flywheel

aka torque converter?

Yes, you can keep the 85 style clutch and flywheel.

You may have trouble with wiring- is your 85 a square body- to- engine harness connector?

If it's round, check pin 20- early cars used that for ground, late cars used it for airbag
(or something) power, and when the 2 meet, smoke gets out. did that...

If it's square, look for the writeup on how to splice the 2 together...

t

[Lirker]

aka torque converter?

Yes, you can keep the 85 style clutch and flywheel.

You may have trouble with wiring- is your 85 a square body- to- engine harness connector?

If it's round, check pin 20- early cars used that for ground, late cars used it for airbag
(or something) power, and when the 2 meet, smoke gets out. did that...

If it's square, look for the writeup on how to splice the 2 together...

t

Thanks for the reply. I actually have an adapter ready to go thats spliced. it's square on the 85. so I have that settled already. Do I still need to worry about pin 20?

What about the throwout bearing, do i need a different version? or is everything okay

[TobyB]

If you use all 85 parts, they will work fine. The deeper bellhousing is offset by the thicker flywheel.

You do need a pilot bearing in the crankshaft, but you knew that.

If the adapter is made for a late engine harness you should be fine.
If I recall, the problem is when a green body harness wire mates to a red engine harness wire...

t

[Lirker]

If you use all 85 parts, they will work fine. The deeper bellhousing is offset by the thicker flywheel.

You do need a pilot bearing in the crankshaft, but you knew that.

If the adapter is made for a late engine harness you should be fine.
If I recall, the problem is when a green body harness wire mates to a red engine harness wire...

t

Such great help. Thanks a lot fam.