6-Speed Bell housing On SMG

[Atluisg]

I purchased a six-speed transmission and got scammed. Bought it off of some guy from offerup and didn’t inspect it great. It was dark, so it’s my own fault. Well, get home the next day and notice that the trans mount tab is broken and the part that holds the shifter is cracked. I’m now stuck with a trans that has a good bell housing, but can’t otherwise be used. I’ve searched on the threads here, but couldn’t find anything definitive. Some say it’s straight swap and no issues, while others say it could cause grinding issues due to some slight differences.

Can someone definitively tell me if I can just swap the manual bell housing onto an SMG trans without issue?

[Slideways]

I purchased a six-speed transmission and got scammed. Bought it off of some guy from offerup and didn’t inspect it great. It was dark, so it’s my own fault. Well, get home the next day and notice that the trans mount tab is broken and the part that holds the shifter is cracked. I’m now stuck with a trans that has a good bell housing, but can’t otherwise be used. I’ve searched on the threads here, but couldn’t find anything definitive. Some say it’s straight swap and no issues, while others say it could cause grinding issues due to some slight differences.

Can someone definitively tell me if I can just swap the manual bell housing onto an SMG trans without issue?

I have heard of a few people doing this without issue. You will also have to move the manual detent locking pins from the transmission side and cut threads for the gear recognition sensor.

https://www.mforum.net/forum/e90-m3-sedan-e92-m3-coupe-e93-m3-convertible-2008-2013/diy-ab/84-diy-comprehensive-smg-to-manual-conversion

[PetrolM3]

I have heard of a few people doing this without issue. You will also have to move the manual the detent locking pins from the transmission side and cut threads for the gear recognition sensor.

https://www.mforum.net/forum/e90-m3-sedan-e92-m3-coupe-e93-m3-convertible-2008-2013/diy-ab/84-diy-comprehensive-smg-to-manual-conversion

This.

I did this on my own M3 and everything went smooth... but, one thing to note is that you will likely end up with a slight 'whine' from the input shaft bearing, mostly at idle with clutch out. Something to do with the bearing (which resides on the bellhousing side) being perfectly matched to the input shaft (transmission side) at the factory to a very tight tolerance. Using a bellhousing from another unit throws this off just enough and puts some pressure on the bearing, causing a whine. Mine did this for almost a decade and many miles without getting worse or something breaking but it always bothered me to a degree and made me wish I had simply modified the original SMG housing. My car was mostly stock so if yours is modified with extra NVH then you might not care about this.

[bmwfnatic]

This.

I did this on my own M3 and everything went smooth... but, one thing to note is that you will likely end up with a slight 'whine' from the input shaft bearing, mostly at idle with clutch out. Something to do with the bearing (which resides on the bellhousing side) being perfectly matched to the input shaft (transmission side) at the factory to a very tight tolerance. Using a bellhousing from another unit throws this off just enough and puts some pressure on the bearing, causing a whine. Mine did this for almost a decade and many miles without getting worse or something breaking but it always bothered me to a degree and made me wish I had simply modified the original SMG housing. My car was mostly stock so if yours is modified with extra NVH then you might not care about this.

It’s a 2 part bearing that gets separated, with its inner race staying on the input shaft and the rest of the bearing remaining in the bellhousing. So yes in theory they should stay together.

[sapote]

It’s risky to swap another bellhousing as the input shaft bearing can be damaged from wrong clearance.

Find someone to weld the broken pieces back.

[Atluisg]

It’s risky to swap another bellhousing as the input shaft bearing can be damaged from wrong clearance.

Find someone to weld the broken pieces back.

Problem is there are no pieces. Trans mount tab was broken clear off.

[PetrolM3]

There are many forum members who have 6MT swaps with non-matching bellhousings, myself included, and to my knowledge, none of those transmissions have self-destructed. As long as you're not annoyed by the slight whine, you'll be fine..

[Slideways]

If being DIYed, I would swap the bellhousing; otherwise, what are you supposed to do with the perfectly good manual bellhousing? The other option is to use it as a doorstop lol

[PetrolM3]

If being DIYed, I would swap the bellhousing; otherwise, what are you supposed to do with the perfectly good manual bellhousing? The other option is to use it as a doorstop lol

you could sell it for very good money to someone who would happily use it for a 6MT conversion...

[Slideways]

you could sell it for very good money to someone who would happily use it for a 6MT conversion...

You might as well use it yourself, especially if you don't have a machine shop nearby that is very familiar with the bellhousing conversion. There are a quite a few bad conversions out there.

[sapote]

There are many forum members who have 6MT swaps with non-matching bellhousings, myself included, and to my knowledge, none of those transmissions have self-destructed. As long as you're not annoyed by the slight whine, you'll be fine..

Bearing whining is not normal. It's either not loaded properly, or the balls are crushed from not having enough clearance. Bearing will be damaged and they are NLA.

[simonnim]

Yeah, mines is converted, no whine.

[PetrolM3]

Bearing whining is not normal. It's either not loaded properly, or the balls are crushed from not having enough clearance. Bearing will be damaged and they are NLA.

I didn't say that it's normal but mine whined for 10 years without getting worse or imploding. Many forum members have sourced converted bellhousings for their SMG delete and sent their own unit back as a core. I haven't seen a single report of an input shaft bearing failure yet...

[sapote]

I didn't say that it's normal but mine whined for 10 years without getting worse or imploding. Many forum members have sourced converted bellhousings for their SMG delete and sent their own unit back as a core. I haven't seen a single report of an input shaft bearing failure yet...

People changed wheel bearings when it has abnormal noise, not when the wheel fell off.

[PetrolM3]

kaiv

Hope you don't mind me looping you in but I thought your input here would be valuable considering how many SMG to MT conversions you've done including bellhousing conversions, etc. Have you heard from any customers with whining bellhousings regarding the issue getting worse or having to replace the bearing?