GS6-45BZ variants - differences and compatibility?

Taymar

New Member
May 18, 2022
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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

New Member
Nov 25, 2022
9
3
0
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).
 
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S54ca

Private
Apr 4, 2020
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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

New Member
Nov 25, 2022
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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....
 
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S54ca

Private
Apr 4, 2020
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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.
 
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sonicnofadz

New Member
Nov 25, 2022
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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

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Apr 4, 2020
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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??
 
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sonicnofadz

New Member
Nov 25, 2022
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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
 

manubidegain

New Member
Aug 14, 2023
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Ride
M135i f20 2013 (N55)
Hey, @Taymar, im in the exact same situation, can you give me some advice here ? Which one you pick up finally ?
 

xquatch

New Member
Feb 25, 2024
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I have a 2011 335i rwd 6mt with bad synchros, so picked up a used (newer) unit from another N55, but now that I have both sitting out of the car side by side, the new one has a longer bellhousing (~3cm) .

What was the outcome of installing the longer variant into your e90? What mods were needed?

More in my follow up posts.
 

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xquatch

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Feb 25, 2024
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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.
Can anyone confirm if the stock e90 335i N55 flywheel and clutch will work within the extended bellhousing? I have two GS6 45BZ units. One original OEM unit out of my 2011 335i N55, and a second donor unit I picked up from a local yard. The output shafts on both terminate approx 1 inch from the bellhousing mounting edge. The shaft in the unit with the longer bellhousing is longer respectively. What's not clear is if my original e90 slave will be 1 inch too short.
 

xquatch

New Member
Feb 25, 2024
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More about my situation: I have a 2011 335i 6MT with the 2nd gear synchro issue. I picked up a used 6MT locally from a source that said it would fit, but now that I have both units out of the car side-by-side, the replacement (donor) unit has a couple of differences, including longer bellhousing and slightly longer gimble yoke.

Here are some data points:
  • Bellhousing is about 1 inch longer than my stock GS6-45BZ
  • Trailing gimble yoke is about .25 inches longer/thicker
  • Bellhousing bolt pattern is the same, with one extra unused hole near the starter on my stock unit
  • The QRL codes on my original OEM unit are S027613833 10893011071A on the gearbox and RS06GSP1089301079 3SS028813845RSEOT on the paper tag on the bellhousing
  • The QRL codes on the donor unit are 1089 301 146 S720419627 S on the gearbox and 06 P1089301161 3S7160320068 on the paper tag on the bellhousing
  • My original OEM casings are stamped 1089 401 084 on the bellhousing, and 1089 401 051 on the main gear housing
  • The donor unit casings are stamped 1089 401 161 on the bellhousing, and 1089 401 145 on the main gear housing
  • There are a few other subtle differences on the outside of the case
  • The input shaft inside the bellhousing of the donor unit is the same, but longer equal to the extended bellhousing and terminates the same distance from the mounting edge as my stock unit
Observations
  • My original e90 335i shift linkage will be off (short) by about 1 inch
  • Driveline will be too long by about 1 inch, or need to source a shorter one
  • Not clear if the stock slave cylinder will work or if I need to source a different one to accommodate the longer reach within the bellhousing, or if there is a different pivot arm required.
  • Donor unit was sourced near Vancouver, BC. My car is in Seattle area.
I do not know how to determine which variant of 45BZ as the paper label on the unit is washed out. Does anyone know how to cross reference the above casing numbers to better identify the the doner transmission?

Some related images posted here
 

xquatch

New Member
Feb 25, 2024
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Quick update - some units recently hit ebay that list the same QR code (model #) of my donor unit (1089 301 161) and list them as coming out of the F80 F8* M3 M* cars, so this appears to be one of the SH** variants. Anyone have access to ZF aftermarket to cross-reference the QR codes?