Successful F8x M3/4 6MT retrofit

[e80two]

Pretty sure this is the first swap for this platform. I started experiencing the 2nd gear synchro failure with my N55E powered e82. When it started popping out of gear on 1st gear roll outs, that was it. The thought of making a left turn and popping out of gear resulting in getting t-boned on the passenger's side was enough to park the car until I replaced the trans. I know the N54 guys are making 700hp+ on their 6MTs, but that trans is discontinued, and that would be going backwards. Also thought about another N55E 6MT, but didn't want the same issues again down the line. Doing some research, I found an article from BMW which talked about how the F8x M3 6MT trans is built more robustly (https://bmwrepairguide.com/virtual-l...te-Vehicle.pdf) pg 34

4.2.1. Manual gearbox
In the F80/F82 a manual gearbox is installed as standard equipment. It is an enhanced version of the familiar K-transmission, which is known from the production vehicles of BMW AG. The transmission was adapted to the higher power requirements of the M3/M4 Coupe.

and another post referencing the F80 6MTs stock clutch handling FBOs easily.

I did some poking around and found this thread on e90post

https://www.e90post.com/forums/showthread.php?t=2085272

and it seemed pretty straightforward so I did it by myself in the garage. Since I have another vehicle, I wasn't in a rush, and was doing the work on Sundays. I do have a Quickjack and a transmission jack, both of which made the job quite a bit easier.



I've been a shade tree mechanic for a minute, having experience swapping Honda engines, including converting my truck from auto to manual, replacing the engine in it a few times, etc, so while I personally don't think this was a difficult job, YMMV based on your experience.

I had a DKIM clutch in there, and I honestly think it would have worked, but the STOCK S55 clutch lb-ft rating is pretty much the same, so I went ahead and used the used s55 clutch that came with the transmission purchase. I also had to use a cutoff wheel to cut off 1/2" of the transmission output shaft to get it to clear the guibo.






After I got everything buttoned up, I realized the reverse lights weren't working, so I cut the 2 wire harness, brought the harness into the cabin, and wired in a normally open magnetic switch, and used a neo magnet attached to the shifter to activate it. When the shifter is in the reverse position, it's close enough to complete the circuit inside the switch, activating the lights.

Parts list:
-F80 M3 transmission, clutch (+ bolts), flywheel (+bolts)
-135i DCT rear trans mount, p/n 22326778060. The stock F80 mount doesn't work, neither does the stock e82 6MT mount, but the 135i DCT mount allows it to bolt directly in. I spent a few days studying mounts and ordered a couple different ones before I found this one fit.
-5 bell housing bolts, p/n 23001222893 (these are M12x75, which will replace the 5 M12x90 bolts currently in use, reason being is that bellhousing "lip" that the bolts pass through is shorter than the E82 bellhousing lip, so you'll either need these, or you'll have to shim the stock bolts so they snug up to the bellhousing)
-N54 shifter arm, p/n 25117524720. You'll have to trim out the underside of it as per the e90post linked above
-on the old tranny, the slave cylinder is held into place by two nuts. On the new transmission, you'll need 2 bolts (p/n 07119907207) to hold it in place, as the bell housing is threaded.


Special tools needed/recommend:
-This gear puller https://www.amazon.com/dp/B0CKPLHKW3 and this nut wrench https://www.amazon.com/dp/B0BG1K2TS3 (along with 2 M12 -1.75x45mm cap screws) to pull off the transmission flange.


-An E-torx bit and socket set: https://www.amazon.com/dp/B08ZJ56Z9W
-A 36mm 12 point, deep socket
-about 4ft of extensions to remove the starter bolt which has to come off to pull the trans (you may be able to get it from the engine bay, but for me, it was easier to do it from under the car)
-a 1/2" - 13 drill and tap set, specifically Milwaukee p/n 49-57-5560. $15.99 @ Home Depot. (necessary to tap the new transmission for the reverse light switch)
-a breaker bar
-a torque wrench

Everything else was just regular hand tools.

These videos will pretty much walk you through the uninstallation/reinstallation:

[moose09876]

I had also looked into the N54 trans swap for quite a bit. Which linkage had to be shortened? I know the shifter on the N54 swap had to be sourced from the donor. Looking forward to the ablum since I'm still not convinced my transmission doesn't have some issue.

[e80two]

Originally Posted by moose09876

I had also looked into the N54 trans swap for quite a bit. Which linkage had to be shortened? I know the shifter on the N54 swap had to be sourced from the donor. Looking forward to the ablum since I'm still not convinced my transmission doesn't have some issue.

I had to shorten the trans shift lever carrier. I picked up one from a N54 135i, one from a F80, and I have the one from my car. In the e90post post, the OP used the N54 trans shift lever carrier and modified it to resemble the N55 trans shift lever carrier. My thought was that I could probably use the one from my car, but it was too long for the new trans. So I took about an inch out of it, and then compared it to the N54 piece....and it was pretty much the same length. So it's either you get the N54 piece and mod it like the OP from that thread, or get the N55 piece and take a section out. Regardless, it looks like the N54 selector rod (p/n 25117524722) has to used, so I ordered a N54 DSSR instead, which'll be here on Saturday.

[e80two]

The DSSR that was supposed to be shipped 1 day and arrive on 7/25 was instead shipped UPS ground and will arrive 7/31. Holding pattern while waiting for it to arrive.

[e80two]

Updated the first post w/some pics.

[moose09876]

Originally Posted by e80two

I had a DKIM clutch in there, and I honestly think it would have worked, but the STOCK S55 clutch lb-ft rating is pretty much the same, so I went ahead and used the used s55 clutch that came with the transmission purchase. I also had to use a cutoff wheel to cut off 1/2" of the transmission output shaft to get it to clear the guibo.

Parts list:
-F80 M3 transmission, clutch (+ bolts), flywheel (+bolts)

Does anyone have info on the difference with the S55 clutch? I have an F10 clutch with a DMFW and a clutchmasters setup with aluminum SMFW. Would definitely like to re-use one of those.

Edit: Kind of answered my own question. The M2/3/4's have a longer bell housing and a thicker flywheel. Requires to use a clutch with the correct spacing. If I had my own lift and I wasn't borrowing time on a friend's, I'd investigate a workaround.