GS6-45BZ variants - differences and compatibility?

[Taymar]

Hi all,

I need to pick up a reman transmission from BMW in the near future. I know the unit I want is a GS6-45BZ RWD unit. However, there's at least 5 different variants I'm aware of - but aside from what vehicles they were fitted to, I have no data to compare.

THD4 (earliest? e series n55 cars and the 1M coupe)
THY8 (used in F series cars, _35i models)
THAD (supersedes the other two, nonexchangeable retrospectively for the THY8. Also used in F series _35i models)
SHBT (used in the F80 M3, F82 M4)
SHBS (F87 M2, F80 M3, F82 M4)

I don't have any of these in front of me to take measurements. Eyeballing used units online and the BMW ETK, they look pretty much visually identical; the SHBS and SHBT in the ETK POSSIBLY have a deeper bellhousing, it's hard to tell because the render angle changed.

Anyway - to my question. Since I have to stump up the cash to buy one of these from BMW, I want to get the best version that'll work with my N54. I understand about the male/female pilot bearing situation swap. The guaranteed answer would be go for a THD4 but if one of the others is better/newer and would bolt right up, I want that.

Anyone know if spec sheets exist for these, if they are dimensionally identical, or even if they're all about equal in terms of durability and it's just been gradual evolution? I have nothing to go on?

 

[sonicnofadz]

Hi all,

I need to pick up a reman transmission from BMW in the near future. I know the unit I want is a GS6-45BZ RWD unit. However, there's at least 5 different variants I'm aware of - but aside from what vehicles they were fitted to, I have no data to compare.

THD4 (earliest? e series n55 cars and the 1M coupe)
THY8 (used in F series cars, _35i models)
THAD (supersedes the other two, nonexchangeable retrospectively for the THY8. Also used in F series _35i models)
SHBT (used in the F80 M3, F82 M4)
SHBS (F87 M2, F80 M3, F82 M4)

I don't have any of these in front of me to take measurements. Eyeballing used units online and the BMW ETK, they look pretty much visually identical; the SHBS and SHBT in the ETK POSSIBLY have a deeper bellhousing, it's hard to tell because the render angle changed.

Anyway - to my question. Since I have to stump up the cash to buy one of these from BMW, I want to get the best version that'll work with my N54. I understand about the male/female pilot bearing situation swap. The guaranteed answer would be go for a THD4 but if one of the others is better/newer and would bolt right up, I want that.

Anyone know if spec sheets exist for these, if they are dimensionally identical, or even if they're all about equal in terms of durability and it's just been gradual evolution? I have nothing to go on?

Generally speaking the gs6-45bz transmissions from the n55 are known for being weak and fragile. The version in the m2/3/4 is completely different animal apparently. I suspect it would also work with a 6 bolt n54, however it is LONGER than the n55 version due the bigger clutch/flywheel that is used with the s55. A lot of n55 guys ditch the gs6-45bz in favor of the 6mt from the n54 (gs6-53bz).

 

[S54ca]

Generally speaking the gs6-45bz transmissions from the n55 are known for being weak and fragile. The version in the m2/3/4 is completely different animal apparently. I suspect it would also work with a 6 bolt n54, however it is LONGER than the n55 version due the bigger clutch/flywheel that is used with the s55. A lot of n55 guys ditch the gs6-45bz in favor of the 6mt from the n54 (gs6-53bz).

Are you 100% sure that the S55 versions are longer?

Does anyone else know what the differences are between the multiple revisions / style codes over the years and how to differentiate them?

RealOEM lists different part numbers for F8x, F3x, and F2x - none of which appear to be interchangeable.

From what I can tell, the bell housing is very slightly different on the F80 versions at the top of the trans, which is identifiable via a harder jog in the casting and elimination of a thru hole above the starter.

 

[sonicnofadz]

Are you 100% sure that the S55 versions are longer?

Does anyone else know what the differences are between the multiple revisions / style codes over the years and how to differentiate them?

RealOEM lists different part numbers for F8x, F3x, and F2x - none of which appear to be interchangeable.

From what I can tell, the bell housing is very slightly different on the F80 versions at the top of the trans, which is identifiable via a harder jog in the casting and elimination of a thru hole above the starter.

Yes. I have an f80 m3 6mt trans sitting in my shop, it is longer than the f30/e90 n55 trans, because of the elongated bellhousing. The bellhousing is the same bolt pattern, it is just LONGER because of the beefy clutch/flywheel setup for the s55. Go on ebay or realOEM and look at the factory flywheel/clutch setup for the n55, and compare it against the s55, huge difference. FYI the m2 also uses the same trans, even though it uses the n55. I'd love to compare transmission dimensions directly against the f30/e90 n55 6mt trans, that would make it much easier to see which driveshaft and shifter combinations might work with various chassis...

**EDIT**

Now that I have thought over this more, I think I am making assumptions. The "stack height" of the s55 clutch+flywheel seems much longer than the n55's, although I've not directly measured them. I have NOT directly measured the length of the n55 trans and compared it against the s55 version, so it is possible they are the same length, I am assuming it IS longer due to the bell housing, however I could be wrong! If anyone on here has access to a regular n55 gs6-45bz, take some longitudinal measurements and post here. I can do the same for the s55 version....

 

[S54ca]

Yes. I have an f80 m3 6mt trans sitting in my shop, it is longer than the f30/e90 n55 trans, because of the bellhousing. The bellhousing is the same bolt pattern, it is just LONGER because of the beefy clutch/flywheel setup for the s55. FYI the m2 also uses the same trans, even though it uses the n55. I'd love to compare it directly against the f30/e90 n55 6mt trans to get some dimensions to compare it against, that would make it much easier to see which driveshaft and shifter combinations might work with various chassis..

The shifter / driveshaft was going to be my next question.

I grabbed a F80 version from someone who had it in an e82 after their original trans failed. It has an n54 shift linkage attached and came with a shortened driveshaft, which coincides with it being longer.

I have a e9x n55 variant in my car; I’ll get under there soon to measure and compare.

Would still like to see / hear technical differences between the variants if anyone knows.

 

[sonicnofadz]

The shifter / driveshaft was going to be my next question.

I grabbed a F80 version from someone who had it in an e82 after their original trans failed. It has an n54 shift linkage attached and came with a shortened driveshaft, which coincides with it being longer.

I have a e9x n55 variant in my car; I’ll get under there soon to measure and compare.

Would still like to see / hear technical differences between the variants if anyone knows.

I edited my response from above. I am not 100% sure the s55 version is indeed longer, although it certainly seems that way. If you can take some measurements of the e9x n55 variant (maybe some pics as well) please post back here with your findings!

 

[S54ca]

Confirmed that the front case / bellhousing of the F80 version is about 1” longer (16” vs 15”).

I’m not able to measure the input shaft depth, as the N55 version is still installed in my car. I suspect, but am not sure, that this would be common across both versions though.

So, in sum, they are NOT a direct swap, and on a E8/9x you will need at least a N54 shift linkage and a shortened front section of driveshaft to swap it in.

With that said…. Anyone looking for a F80 trans swap kit??

 

[sonicnofadz]

Confirmed that the front case / bellhousing of the F80 version is about 1” longer (16” vs 15”).

I’m not able to measure the input shaft depth, as the N55 version is still installed in my car. I suspect, but am not sure, that this would be common across both versions though.

So, in sum, they are NOT a direct swap, and on a E8/9x you will need at least a N54 shift linkage and a shortened front section of driveshaft to swap it in.

With that said…. Anyone looking for a F80 trans swap kit??

Dude, thank you for taking the time to collect that data. This is what I suspected, but you have proven it. For my swap into an e90 (8 bolt n54), i am going to attempt to use all factory parts, but if I have to fab a shifter so be it. There are quite a few different length factory drive shafts to choose from, hoping one of those works out. I will report back when I can start on my swap

 

[martymil]

Just to help and correct your information the 1m coupe never came out with DCT.