[TorkeySixx]

A little over a month ago I completed swapping the GS6-53bz (N54 6mt) into my 2013 F30 N55 rwd. I only know of one other person who completed this swap, but it was on an xDrive so I'd like to share with everyone what I learned.

A few key differences in the 53bz:
-heavier by 40-50lbs
-shifter throw is longer by ~1in (rough guesstimate)
-1/2" longer OAL; factory driveshaft works
-more durable synchros

I chose to do the swap after breaking my factory GS6-45BZ. The 2nd gear synchro is a known weak point on these transmissions, especially with powershifting like I was doing. I knew this going into my powershifting shenanigans, even on my 550i clutch+smfw+cdv delete/e90 slave. It can't be *that* bad, can it? It is. 2nd gear started grinding in no time.

A replacement 45bz was around $3k used which sucks so I searched for alternatives. I found some threads on the 1 series forums where they did this same swap. These gave inspiration to one of the xDrive guys (Ryanfknt) who wound up being successful, so I decided to give it a shot. I found a transmission from an '09 135i with 90k on it for $1.1k shipped.

Here's the thread for the xDrive. https://f30.bimmerpost.com/forums/sh....php?t=1855290

I tried to take pictures when I could, but I was more concerned with getting everything to work so I ended up not getting a whole lot. That being said, the whole swap is essentially a parts swap minus modifying the shifter rod and the shifter bracket. This involves welding, which a friend did for me.

Understand that this is the combination of parts I chose to use. You may elect to use a different combination which may or may not work, but you will have to modify them differently.

The only N54 parts you actually need are the transmission and the flywheel. Everything else you can reuse.

If you have an Mfactory 6 bolt flywheel like I do, you will leave that shaft pressed in the center because the pilot bearing will now sit in the input shaft. I lost & had to reorder mine, it was ~$70 shipped. I don't know if other flywheels do it like this, but the mfactory does.

I used the F30 N55 shifter bracket. You will need to cut a few notches out of that shifter bracket in order to clear the knuckle that your shifter rod will go into. The following picture shows how much room we're dealing with.



Bonus picture, here's how close that knuckle gets to the guibo.



Anyway, I cut a total of three notches out of the bracket. It looked like this.



What's critical here is to make sure that knuckle can clear the bracket no matter what gear it's in and where it pivots on the transmission. The bracket doesn't move much by design so that last part is more for good measure than anything.

The shifter rod, also from the F30 N55, needs a bunch of mat'l ground away to clear the mounting tab for the shifter bracket on the transmission. You'll end up grinding through the cross pin that goes into the knuckle so you might want to give that a tack weld or two just to be safe.

You will just need to shorten the shifter bracket and shifter rod by 1.250" because the mounting point on the transmission sits that much farther back. The user from the thread I linked earlier, Ryanfknt, stated that he made a jig for both of these items. It's not a bad idea as there are some geometry relationships which must be maintained, but it isn't *super* critical. I eyeballed it, it worked just fine. An experienced toolmaker could come up with something fairly easily.

When shortening your bracket, remove the material from inbetween the horizonal transmission mounting point and the fulcrum point to the shifter. When welding it back together, be careful to maintain perpendicularity between the horizontal axis of the bracket's trans side mounting point and the vertical axis of the shifter. If you're off, it'll affect how straight the shifter sits.

As for the rod, those cross pins must be perpendicular. The trans side knuckle that it mates to is designed with some side to side pivoting so you do have a little bit of room for error.

Here's what it looks like with both of those in car, without the guibo.



This is exactly as complicated as it gets. You'll notice that there is no spot for the gear position sensor to sit. Zip tie it up and let it hang somewhere, you'll just lose auto start/ stop which honestly is an upgrade. You will also need to lengthen the wires to the reverse sensor.

You may have notice that the 53bz is about half an inch longer from bellhousing to tailshaft. That's because it is, which you have enough slack in the factory 2pc driveshaft yoke to make up for it. The trick is to unbolt your center support bearing to get enough room to slip the guibo on and then the driveshaft.

I did this swap to save some money, and it turned out successful. I've run the new transmission through the same powershifting that killed the last and from what I can tell the 53bz is tougher at least under the power of a fbo n55. Can't speak for big power. It's a much bulkier and heavier transmission, there has to be a good 40-50lbs difference. Considering the price of a used 45bz, I feel safe calling this a cheap upgrade. I think I got about everything, I'll try to update this post as necessary.

Thank you for reading, I hope this will help you.

[thejeremyman9]

Nice writeup! I guess if you lose gear position you also can't boost/power by gear? Not sure how much the 6MT people use that

[TorkeySixx]

Originally Posted by thejeremyman9

Nice writeup! I guess if you lose gear position you also can't boost/power by gear? Not sure how much the 6MT people use that

Thanks! The car won't know what gear the transmission is in without it so I'm sure you'd lose boost/ power by gear but I don't use it so I don't know for sure how it would behave.

[ezhik]

Thanks for writing this up!

You mentioned a SMFW and then that you used an N54 flywheel.

I'm in a similar situation; tired 2nd gear synchro, and want to swap the N55 transmission for something beefier.

The part I don't quite follow is the flywheel compatibility. I have the SMFW/Clutch combo:

SPEC STEEL FLYWHEEL SB55S-2
SPEC Clutch SB553F-2 | Stage 3+


Will that work for this swap?

[TorkeySixx]

Originally Posted by ezhik

Thanks for writing this up!

You mentioned a SMFW and then that you used an N54 flywheel.

I'm in a similar situation; tired 2nd gear synchro, and want to swap the N55 transmission for something beefier.

The part I don't quite follow is the flywheel compatibility. I have the SMFW/Clutch combo:

SPEC STEEL FLYWHEEL SB55S-2
SPEC Clutch SB553F-2 | Stage 3+


Will that work for this swap?

Apologies for the late response, but to clarify:

I could reuse my Mfactory N55 flywheel because the only difference between that and Mfactory's 6 bolt N54 flywheel is a shaft that presses in the center for the N54 cars. That shaft is needed because the orientation of the pilot bearing it goes into flips; it now sits in the transmission input shaft instead of the flywheel.

That clutch should work. The flywheel may just need a shaft pressed in like mine did. I don't know how Spec makes that flywheel, it makes sense to me that they would do it like that but I would call and ask them to make sure that's the case.