The definitive transmission compatibility guide, with pictures

[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.

[Andy.B]

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

[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?

[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]

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]

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]

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

I believe you have put it together and had it work, however, there are also accounts of people using a single mass flywheel with a transmission from a dual mass car, and having it not work:

(abridged quote from this thread)

... I am 100% positive that my 88 super eta transmission was the deep bellhousing. My proof? well... i measured it and it came out to 6 7/8 where as my 325i is 6 1/2. i had my friend measure and take a second look also because i couldn't believe it. also, i had to wait a damn week for the euro 323i throw out bearing (longer length to make up the gap) to get in so i could put it together and drive it. the clutch would not engage with the rest of my I parts.

....

So I KNOW my transmission's bell-housing is a late eta that was equipped with a dual mass flywheel, and the bell-housing has a 6-7/8" depth.

I have a single mass i flywheel, clutch, and pressure plate stack to install.

Every quantified measurement indicates that there IS a difference between the two transmissions depths.

While I see people saying they had luck matching that combination of parts, I also see people saying it didn't work out, and they needed the thicker throw out bearing.

I don't want to do this job twice. I'm doing it on my back in my driveway.

Lets say that both combinations of parts will work, but the i flywheel/clutch stack IS a little shorter than the dual mass eta flywheel/clutch stack, then using the 323 throw-out bearing will keep the slave cylinder plunger in its 'normal' operation range, while the i throw-out bearing will require it to extend further. The only thing I can think is that some people get lucky, and the i stack works, but the *better* way (at least in terms of maintaining correct geometry of parts) is to use the 323 throw-out bearing, right? I mean, from all accounts, even if the i throw-out bearing CAN work, the 323 throw-out bearing WILL work.

If that is the case, I am willing to spend a few extra dollars to save some hassle.

I just want to understand why there is so much contradiction on this subject before I start putting this all back together.

[Andy.B]

Bump: I will send $5 via paypal to anyone who can post pictures of the bell-housing depth measurement on an i transmission so we can accurately document this.

[AwakenNoMore]

I'm running into the same issue. I'm probably going to just buy the two different throwout bearings unless this thread brings some results.

[Andy.B]

Someone out there MUST have an i transmission sitting around that they can measure.
Do I need to offer more than $5?
How about a donation in your name to the 'People Fund'!
I'll write your name inside the bellhousing to be preserved forever!
I'll get your likeness tattooed on my butt (I won't).
I'll gift you 'Goat Simulator' on steam!
If we ever meet in person, I'll buy you an ice cream cone! (unless you are lactose intolerant, in which case, I'll buy you frozen yogurt, or some other desert of your choice)

[Andy.B]

If you post a picture of the measurement of an I transmission, I will change my r3v signature to anything you want* for 3 months, and will make sure to post regularly in lots of topics so it gets lots of mileage. It can be an ad, joke, picture, insult, junk, your junk (wink wink), political ad, misquoted quote, etc.














*as long as it is legal and not prejudiced. In poor taste is acceptable, and expected.

[FLG]

I have a tranny sitting in my garage. I'll check pn and measurements tonight. Idk what it's from off hand. Came from an e but looks to be swapped at one point... Well see.

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[Andy.B]

Bumplestinltskins.

[Andy.B]

I have a tranny sitting in my garage. I'll check pn and measurements tonight. Idk what it's from off hand. Came from an e but looks to be swapped at one point... Well see.

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eta trans part number is 260.0.1270.90
i transmission part number is 260.0.1346.90

I'd love to see proof that there are different depth's among eta transmissions, and that the i is different from the late eta's.

[FLG]

I'm of no help it's an Eta trans... But I can give you some other interesting info.. Kinda.

I believe this trans was a replacement from bmw...

Orange warning label says that it needs to be filled with oil

Hmm I'll go measure anyways

Soooo, measurement it seems from inside of where slave cylinder is to bell housing is 6 1/2 but my digital calipers seems to be dead and i couldnt find my straight edge so i had to make due with what i had. I have the motor this trans was on, and its a dual mass flywhee.

TOB that was in it was same as an I TOB, i had a spare laying around.






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