Manual Trans Swap - N54 Engine & N55 Transmission

[Lenk42602]

Hello All.

Decided to keep my car and perform a manual swap. Found an extremely low mileage N55 - (GS6-45BZ) trans.

There is a good bit of information on the interwebz about performing manual swaps and honestly it hasnt been too bad. However, the swaps documented revolved around the below configurations:

N54 Engine to N54 Manual
and
N55 Engine with N54 Manual

-----------but no N54 Engine to N55 Manual.-----------

Long story short - I've performed all the wiring, auto trans is out, flywheel clutch / pressure plate installed, but the transmission is not able to bolt up the the engine.

I have about .25" gap that i cannot close/mate bellhousing to the engine.

1) First attempt to fix this was to machine the end cap of the pilot bearing out - thinking it was bottoming out before fully engaging/seating into the flywheel.

That didnt work

2) second approach was to remove the input shaft shroud, thinking it might be hanging up on the spline collar on the clutch. was planning on machining that down if proved to be the issue. Upon trans re-install, still had this gap.

That didnt work

3) removed the trans again, and removed the throwout bearing/armature, reinstalled. thinking that perhaps the assembly had a taller profile than it should be.
That didnt work Still had this gap.


All of these efforts were intended to rule out where exactly this gap is being generated from, and I am left to think it is the flywheel. The flywheel/ Clutch I originally ordered and installed during this test fitting :

Flywheel
BMW Dual Mass Flywheel

Clutch
https://www.fcpeuro.com/products/bmw...uk-21207603248

As this didnt work, and i look for other solutions - these units are both intended for N55/N55 configurations. Now that i look around,

My new theory is that the gap i'm encountering is due to dimension variation (height) in the flywheel i have (N55/N55) versus the flywheel i need (N54/N55)required mating the N55 trans to the N54 engine

The ONLY factory oem N54 Engine/N55 Trans combo was the 1M. I'm planning on ordering this set up , but i sure would like some good intel before doing so.

does anyone have any experience here? lil help!!!

if i can confirm all of this i can document the whole process.

thanks in advance

len

[Lenk42602]

A little more research on realoem. com

I have the same 6 speed gear box cross referenced with a 1M
https://www.realoem.com/bmw/enUS/par...342&series=E82

N54 Short Engine is cross referenced between my engine and a 1M
https://www.realoem.com/bmw/enUS/par...828&series=E82

aaaaannnnnddd the crankshaft is the exact same.
https://www.realoem.com/bmw/enUS/par...881&series=E82


and that flywheel only fits the 1M
https://www.realoem.com/bmw/enUS/par...659&series=E82

the gamble here is that its not listed because no N54 135i was equipped with an n55 tranny...buuuutttt it should fit right???

[CalvinNismo]

As long as you have a 6-bolt crank you should be fine, otherwise you will have to go for a single mass, or some kind of weird modified dual mass. As far as I know, the N54 and N55 flywheels are the same height.

I have had the MFactory N54 single mass flywheel with an N55 pilot bearing pressed in fitted to my N55 and I am currently running the 1M dual mass with a 335is/550i clutch. Are you sure your clutch plate is the right way around?

The other thing to check is that your driveshaft is long enough as the GS6-45BZ is shorter than the GS6-53BZ. You will also need the GS6-45BZ shifter linkage as it is different. The GS6-45BZ is about 12kg lighter though.

[Lenk42602]

Hey there Calvin - i do have a 6 bolt crank.

I'm certain the clutch plate is oriented correctly.

So based on the the flywheels you've tried, they are compatible on both N54/N55 Engine Models (DCT). Interesting. I'm wondering now if there's no differnce in total stack with the clutch/FW/PP fference in the, but rather there is a different OFFSET between the n55&n54 flywheels

Does anyone have an old n54 flywheel to measure against? Better yet a fried 1M DMFW?

I got the tranny/driveshaft/shift linkage/etc all together so I'm good to go on the shorter trans implications

[CalvinNismo]

I have both a knackered N55 dual mass and the MFactory single mass lying about. I can take some measurements if you like? They are buried away though.

However, I was confident that the flywheels are interchangeable between the N54 and N55 for the same gearbox as the N54 DCT (non-is, European spec') and N55 DCT share the same part number. This is why I 'gambled' on the 1M flywheel fitting my N55.

Are you sure there's not a dowel or something stopping the gearbox mating to the engine properly?

I'm not trying to be patronising!

There's someone over on 'Boost Building Boulevard' that is running an F-Series 'box on their N54 also. This does sound unusual.

[Lenk42602]

Calvin - thanks for the replies, it is much appreciated. Regarding measurements, I'll revisit that after some additional test fitting exercises this week.

Since we've ruled out the pilot bushing, throw out bearing & armature, and trans input shaft cover, we are going to remove the pressure plate, test fit, then clutch disc, test fit, then fly wheel, test fit.

As far as dowel pins, etc. - still pretty confident. We've had the trans on/off the engine at least 5 times now and still run into the same issue - can't slide the trans housing up to the last 12 or so mm to mate to the engine properly.


Also - you are mentioning DCT flywheels - looking at the images they seem to be different in design from a standard 6MT (Not a DCT) am i missing something?

Thanks again

Len

[bbnks2]

People put n54 boxes on N55 engines... nothing special is required outside of the difference in wiring harness, driveshaft length, and shifter assembly.

The n54 has the input shaft IN the flywheel. To put an n55 transmission on an N54 engine you would need to bang the input shaft OUT of your N54 flywheel and press an N55 pilot bearing into your N54 flywheel. That's the only difference I can think of that would affect mating the N55 transmission to an N54 engine. Otherwise, everything else is interchangeable (except the shifter assembly and driveshaft).

I have an n54 box waiting to go into my N55. Got it dirt cheap so ill sacrifice the 25lbs.

[Lenk42602]

Thank bbanks.

I have an n54 engine (originally auto) and mating an N55 manual transmission. My assumptions were the same as yours considering the logic, and what i've seen/read on the interwebz.

However, curiously enough there aren't any confirmed, documented installs of N55 Transmissions to N54 Engines that i can find.

unless i am missing some basic oversight, maybe there is a difference in offset between flywheels on an N54 engine vs N55.

I.E. the flywheel for N54 engines would have to be for n54, not the n55
I have.

We'll see once we get through the process of elimination exercise this week.

I'll report back.

Thanks for the help! gotta be a solution here.

[CalvinNismo]

Originally Posted by Lenk42602

Also - you are mentioning DCT flywheels - looking at the images they seem to be different in design from a standard 6MT (Not a DCT) am i missing something?

The point I was trying to make about the DCT was that the transmission part number is the same between N54 and N55. The flywheel part number is the same between DCT N54 (not 335is/Z4 35is) and E-Series DCT N55. So therefore the end of the crank in relation to the gearbox mating face is the same between the N54 and N55. So parts are interchangeable! Sorry that wasn't clear!

[Lenk42602]

CalvinNismo

I understand your logic. However the difference here is that BMWs DCT Transmission remained the same design (part#) across all N54 and N55 Model years. If the transmission is the same, the dimensions and design did not change. It would make sense that as a result, the flywheels could be used across both Generations.

The well known design differences between the N54 6MT and the N55 6MT include the pilot bearing locations, overall length, and weight. But what about the differences in input shaft length? Input shaft offset realtive to transmission face? Etc, etc, etc. Are there any?

I've access to the factory BMW TISU website but there is no dimensional info to this degree available.


more to come

[Jeff9962]

Originally Posted by Lenk42602

CalvinNismo

I understand your logic. However the difference here is that BMWs DCT Transmission remained the same design (part#) across all N54 and N55 Model years. If the transmission is the same, the dimensions and design did not change. It would make sense that as a result, the flywheels could be used across both Generations.

The well known design differences between the N54 6MT and the N55 6MT include the pilot bearing locations, overall length, and weight. But what about the differences in input shaft length? Input shaft offset realtive to transmission face? Etc, etc, etc. Are there any?

I've access to the factory BMW TISU website but there is no dimensional info to this degree available.


more to come

Have you tried to bolt the transmission up to the engine without a flywheel in place? This would be just to make sure there isn't some kind of weird dowel pin issue going on. If it sits down flush then bolt up the flywheel without the clutch and pressure plate in place and see if it seats flush. This way you can identify or eliminate things that are causing the problem. Just my thought process.

[Lenk42602]

Jeff - thats exactly the plan.


I'll report back once i get to it.

[Lenk42602]

SO results....

Continuing through the plate/disc/flywheel exercise, we determined the following:

The trans housing mated up to the engine with no gap using the existing N55 flywheel, clutch disc, and pressure plate.


--- What changed? The clutch disc was not aligned properly on the first attempt. This kept the input shaft from fully engaging all the way to the pilot bearing. Far enough into the spline to engage, but not all the way.


@CalvinNismo - your suspicion that there was a basic assembly error was correct! Thanks for being patient with me!

I'm just glad i don't need to throw more $$$ at it with a new flywheel.

Fresh Pressure plate screws are on the way and we will continue.

Planning to take some photos.

To CONFIRM - The flywheel/ Clutch I originally ordered and installed during this test fitting :

Flywheel
BMW Dual Mass Flywheel

Clutch
https://www.fcpeuro.com/products/bmw...uk-21207603248


IS COMPATIBLE WHEN MATING AN N55 6MT TRANSMISSION TO AN N54 ENGINE

Should have her buttoned up by end of next week!

[sliebhard]

Thanks for the thorough follow up. This is especially helpful as I'm prepping for this over the summer. Knowing I can grab either trans is great.

[Lenk42602]

you bet - i'll get to some pictures and stuff once the fastners come in. Its nice to find a thread on a forum that has both a beginning and an end.

[Jeff9962]

Originally Posted by Lenk42602

Its nice to find a thread on a forum that has both a beginning and an end.

I'm glad it worked out to be something that was a zero cost issue and good job on closing out the thread for future search reference.

[Lenk42602]

thought i'd follow up here:
Transmission is in.
Reflashed the DME VO and all is good on that front.

Last issue has to do with the driveshaft - particularly the front half.

So just to review here, I have an N54 Engine, an N55 Trans, and an auto (small pumpkin) diff.

as part as the N55 package I obtained from the donor car, I received the driveshaft, but no manual diff.

Didnt think much about this until we started buttoning up the back end of the car but ended up discovering that the N55 driveshaft, when bolted to the rear diff (auto) positions the rear driveshaft behind the mounting location where the CSB mounts.



I'm assuming this is due to the dimensional differences between the larger manual diff and the auto currently installed.

Second image shows both front and rear n55 driveshafts attached to the guibo up front/diff in back:


No sweat - my back up plan was to just reuse the entire auto driveshaft that orginally came on the car. Watching Vehicular DIY's videos and realoem indicated the differences between the manual driveshaft and auto driveshaft in terms of length (on the e90 he did the swap on) was only 2mm difference.

What i did not take into account, however, was this was based on using an N54(GS6-53DZ ) manual, not the n55(GS6-45BZ). This is important because the (GS6-45BZ ) is dimensionally shorter than the (GS6-53DZ).

The difference can be seen in the amount of exposed spline when re-using the 135i Auto driveshaft:



So thats where I am. Going back and forth right now on how I should solve this. Options:

1. Just buy a manual diff and cv axles (finding a right and left pair of GKNs is impossible now, not ponying up for the bmw shafts. all I can find right now are some ebay shafts https://www.ebay.com/itm/16539183746...53.m1438.l2649

Plenty of diffs are out there but I'm a little uneasy about slapping the above axles on my car...



2. Front half of drive axle -
- Lengthen it at a driveshaft shop?
- Use the front half from another bmw model?

I've been doing some reading here - on the 128 LSD Q/A thread there are differing statements regarding the spline compatibility between manual 128i drive shafts and automatic 135i driveshafts. If these splines are the same, there are a multitude of lengths that these entire axles come in.


I am going to start acquiring measure ments on the front halfs and start seeing if I can just pick the best fit once info is compiled.

My current auto drive shaft is on the car, so i cant get a dimension until it comes back off. Realize I can view the full length on realoem.com - what i am looking for is just the front half. The logic here is that any small diff auto car should share the same dimension from the nose of the front dif to the CSB mounting point. What really matters here is the baseline measurement of the 135i auto, plus the dimension of the gap of exposed splines in teh last picture. the holy grail would be finding a front half that shared the same spline pattern/size that also is an end to end length that meets the dimension I am aiming for.

If anyone can help out, I would appreciate dimensions for the following front halfs of each drive shaft. Measuring from the flange facing the guibo to the end face of the female spline on the CSB side:

135i Auto Front Half: ?
128i Manual Front Half?
E90 auto front half?


Len

[CalvinNismo]

I'll have an N55 driveshaft, diff' (with Wavetrac) and axles available in the not too distant future, but I'm not exactly local!

[Lenk42602]

Thanks Calvin!


Shipping would be a deal breaker, but appreciated none the less.


Thought about option two over the weekend. Seems silly to try and bodge something with the existing driveshaft, so I'm all in with the diff/axle swap.

Still hunting for a diff and axles stateside here.

[Lenk42602]

Thought I would follow up here:

First wanted to grab that gap dimension in the above picture before pulling and replacing with the manual setup. Would be useful for anyone looking to run the n55(GS6-45BZ) trans with an other wise automatic drivetrain. One could simply take the front half of the drive shaft to a shop and request it be lengthened.

The front half of an auto driveshaft would require lengthening by 35mm.

So, that out of the way i picked up a great used diff/axle unit from a user here on the forum - @kisenwether thanks my man!


Next I dropped the exhaust, auto drive shaft, auto diff/axles and began the swap.

Got the manual diff in, driveshaft installed, passenger side cv axle. Ran into a tiny issue with the driver cv axle - threads were boogered up a bit so i had to get a die - rethreaded yesterday and all is good.



should have chased the threads on the passenger axle as well - they feel real nice.


I'll be ending up with a large amount of automatic parts for sale, as well as a few exhaust bits - pretty nice Borla stanless axle back muffler, & possibly the oem muffler.


Needed to order some new axle nuts, so i'll be back at it this weekend.

[Lenk42602]

Update:

Car is all swapped! Final effort was completed last week -

Used ProTools app to change vehicle order and update all modules. Entire process took all of two minutes.

Below is an image of the steps:


If doing this - a note on step #5 ......

resetting Engine adaptations is done in protools. when you execute this step, the throttle adaptation is reset. It will throw 2CFB and 2D09 codes.

In addition, the idle will be bouncing around - which was a bit unnerving... It is also necessary to perform a "manual throttle relearn" .
Ign on, not running, accelerator pedal down for 30 seconds.
Then fire it up, clear all dtc codes (throttle related above)

Car is all good!