Trying to get an 85 735 5-speed onto an 80 M30 engine

[aerokurt]

Hi all,
This is all going into a 59 Bristol with a higher ratio diff, so I needed to find a 5-speed
that bolts up.
Now back on the project with an 85 trans from a 735. It bolts up fine.
Don't know yet if it's a good fit.
Seems that the clutch slave and the pressure plate are different.
All the other parts are the same.
Anyone have an idea of which way to go from here?
More challenges!
Cheers,
Kurt in Phoenix for a while

[Lock]

I would say find an e28 553i or e23 735i single mass flywheel for your M30, then you can use all e28 clutch, clutch slave and all that gear.

Others on here might know for sure, but I don't think the e12 clutch fits on an e28, better to use a flywheel that goes with the gearbox. That will make all the parts for running gear consistent.

[aerokurt]

I do have the original flywheel, disc and pressure plate for the 80 E12 M30 engine.
Not the slave though.
I do have the slave that came with the 735 trans.
Do not have a throw out bearing yet.
Still have to get any throw out bearing, then do a mock up with everything installed, then measure the distance from the slave mounting surface
to the throw-out fork.
I wonder if the only difference between them is the length of the pushrod?
it seems that the 85 735 used a dual mass flywheel, and I think they are fatter than the other by an inch or two.
So I might find out that I have to use/make a longer push rod.

[Mike W.]

Flywheels 101.

Up to E32/E34, all M30 flywheels are single mass, 240MM clutch size. I don't care what realoem says. Motronic requires that little tab on it to generate an electrical pulse when it goes by the crank sensor, but that is the only functional difference.

Weights are a big deal however. 5/6/733 and E28 M5 use a 14 pound flywheel. Revs up quick, real quick, you notice the difference. E12s used a 17 pound, considered a performance upgrade over the E28 535 flywheel, which weighs in at 22 pounds. Upgrade as long as you're not running stock Motronic 1.0/1.0a engine management which needs that tab.

Clutches. This gets a little complicated as it's tranny specific.

G262 or G265/6 (and probably G265/5, but I'm not positive) I think any M30 clutch will fit.
G260/5 This one I'm a little weak on, I think a 535 E28 clutch will fit, but I'm not positive. An E28 M5 clutch will not fit.
G260/6 Any M30 clutch should fit.

Complications. Mixing and matching. You don't want to use a E28 535 friction disc with an E12/533 pressure plate. The hub is bigger and will hit at pedal to the floor clutch disengagement. Not real bad, but I ran it for a while and installed a spacer so I couldn't depress the pedal all the way. The lighter E12/E28 533 clutch will hold a 3.5, I ran it that way for 130K with no issues and believe me, I wasn't babying it. Not thrashing it, but not babying it at all.

Slave cylinder. I have seen odd listings for E23s at times, but just go with E28 stuff. It's common enough they should have the right part numbers.

Clutch master. In the OP's case, use either original to the car, hydraulics don't care, or E12 as it bolts to the firewall. E28s use an odd one that bolts sideways to the pedal bracket.

Special note to OP, 85 735s/E23s, used the same tranny and bellhousing as an '80 E12, except the bellhousing had provisions for the motronic sensors which run the FI. Mechanically they're 100% interchangeable.