The definitive transmission compatibility guide, with pictures

[mkcman17]

I've done these swaps many times, usually using a single mass flywheel and an eta trans (easier to find). It will work.

[Andy.B]

Ok, measured a different way:

Removed the slave cylinder to measure outside surface of bellhousing:


I put two marks on the dowel. Notice that the actual mounting surface of the slave cylinder is raised away from the surrounding area a little bit:


And here is the mark level with the slave cylinder standoff mounting surface:
It looks like 6-7/8" to me!

[mkcman17]

The transmissions are the same, just run a t/o bearing that matches the clutch setup (single mass) and a manual driveshaft that matches the bolt pattern on the rear flange. Done.

[Andy.B]

Here are some pics:

The vin: indicates car was manufactured 7/87


PN:


Date stamp says 85/86. I don't know what that means:


Large output shaft flange:


Large flange driveshaft:


Small flange driveshaft (for comparison):

Everything indicates it should be the late/deep eta bellhousing.

My confusion comes from the actual measurements. I keep seeing the same numbers thrown around, but I'm not sure where people are measuring from...


This picture is a little misleading because of the angle. The actual reading is 6-9/16" inch, while the numbers everyone posts are 6-1/2" for single mass flywheels and 6-7/8" for dual mass flywheel. Is that number from the slave cylinder side of the housing or the inside?

[Andy.B]

The transmission also has the larger output flange. Good thing I had one of each driveshaft to choose from.

[Andy.B]

I have seen all sorts of threads saying all sorts of different things on the subject. Some people say 'only x transmission with y flywheel' while others say 'as long as you match flywheel clutch and pressure plate, it doesn't matter'.

None of this is new news, and I don't claim to have figured anything out. I got sick of all of the contradicting information and secondhand claims on the subject, so I thought it would be helpful to have pictures and part numbers of everything together in one thread.

Late 325's with the eta engine were equipped with dual mass flywheels that are thicker than the single mass flywheels on 325 i cars. To compensate for the extra thickness, late eta cars had a deeper bellhousing.

Late eta transmission with large output flange:

PN:


Removed the slave cylinder to measure outside surface of bellhousing:


And here is the mark level with the slave cylinder standoff mounting surface:


ETA's equipped with a dual mass flywheel had a bellhousing depth of 6 3/4"
(6 7/8" to slave cylinder mounting boss)

i transmission on the other hand, have a different part number and a different bellhousing depth:




Meanwhile, i transmissions have a bellhousing depth of only 6 1/2"

Which means that there is a half an inch difference between the two bellhousing depths.

While some report having had luck using a standard i throw out bearing when matching an eta transmission to an i single mass flyweel, it is better to use a thicker euro 323i throw out bearing that makes up the difference in the extra 1/4" bellhousing depth:

PN: 21511204525

323i throw out bearing on the left, standard 325 throw out bearing on the right.