Is My Transmission Toast? Unidentifiable Vibration Coming Through Shifter

[sina]

Hi All,

Since my 6MT conversion, there has been an annoying vibration coming through the shifter, particularly pronounced when in 3rd and 4th gear. It is worse under load and makes the shifter vibrate both visibly and audibly. At first, I thought it might be the guibo, but after replacing that, the problem remained.

So, I finally just decided to take it to a shop. They put it on a lift, drove the car in 4th gear, and saw nothing external to the transmission that could be causing the vibration, meaning the only possibility is coming from inside the transmission.

That caught me a bit off guard, as it doesn't really seem like something that I could have screwed up during the conversion, just because there really isn't that much that could have gone wrong. The mechanic's only idea was that the PO was doing a bit too much flatfoot shifting while it was still an SMG, and at this point to drive it till it dies and then replace it.

I just wanted to gather some opinions and see if anybody has experienced anything similar. If there are any SMG conversion gurus around here, I'd love to hear your opinion about what might be going wrong. Any thoughts?

I will try to attach a video of what it looks like in the cabin when I get a chance. Thanks.

[sapote]

So, I finally just decided to take it to a shop. They put it on a lift, drove the car in 4th gear, and saw nothing external to the transmission that could be causing the vibration, meaning the only possibility is coming from inside the transmission.

No external vibration and no vibration on the shifter, or it vibrating as when driving on the road? This might not be simulating the same as actual driving.
Set up a camera or smart phone and shoot some footages of the tranny tail where the shifter entered while driving with the shifter having vibration. This will prove if it is internal or external induced vibration.

The mechanic's only idea was that the PO was doing a bit too much flatfoot shifting while it was still an SMG

Even this caused the bad synchros but I don't see a way for the damaged synchro to cause vibration to the shift rods via the shift forks. And, you didn't say anything about grinding with bad synchro, so don't take the mechanic too serious.

Question: do you feel the shifter vibrate on the fore/aft direction only, or with left/right also? There is nothing internal that can rotate the shifter left/right, but when the tranny rear end vibrates then the shifter can do left/right vibration.

[BMWE46M3]

It's also possible that the driveshaft itself needs to be balanced.

[duracellttu]

Has the center support bearing been replaced and preloaded properly?

[admranger]

Has the center support bearing been replaced and preloaded properly?

This is what I'm thinking too. Maybe a u-joint going bad or the rear joint on the driveshaft going bad.

[Cubieman]

Is the vibration made better or worse when shifting gears?

[duracellttu]

This is what I'm thinking too. Maybe a u-joint going bad or the rear joint on the driveshaft going bad.

Agreed. It’s in the driveshaft somewhere if I had to guess. Work your way down the line…CSB, U-joint, CV joint. Easy enough to check yourself too. Just drop the exhaust and heat shield then start tugging on the driveshaft to look for play.

[Icecream]

Just gonna mention lets not start rumors that SMG ruins transmissions lol. It puts clutch in, matches revs/cuts throttle and engages gear, flat foot or not.

[bigjae46]

I had a vibration above 100mph…was the driveshaft CV. Can’t really blame the gear since it could be between a certain speed and at a particular load. You can replace the CV without balancing the shaft. A used driveshaft could certainly be out of balance as well.

I can get DS rebuilds for $535. But I’d pull the driveshaft and inspect the CV.


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[sina]

Question: do you feel the shifter vibrate on the fore/aft direction only, or with left/right also? There is nothing internal that can rotate the shifter left/right, but when the tranny rear end vibrates then the shifter can do left/right vibration.

Good question, fore/aft is definitely the most noticeable, but I will take a closer look next time - and hopefully grab a video too.

The CSB is original, and it's likely that I did not preload it properly. Thanks for the suggestions, I will definitely look into that next. Would be easy to diagnose as well by seeing if the vibration still exists with the driveshaft disconnected.

Is the vibration made better or worse when shifting gears?

It is at its worst when it is in gear. 4th being the worst, then 3rd, then by some distance second. If you are in fourth and apply load you don't even have to look at it to know it's vibrating because of the sound it makes.

Just gonna mention lets not start rumors that SMG ruins transmissions lol. It puts clutch in, matches revs/cuts throttle and engages gear, flat foot or not.

This would have surprised me because for everything people flame about SMGs, the one thing that seems to be agreed upon is that whenever they are taken apart that they are in better condition than manual boxes of the same mileage.

Thanks for all the opinions, sounds like a great next step and definitely feels more logical than something in the transmission having broken during the conversion, or during its time as an SMG.

[enjoy_m3]

In addition to checking the center support bearing. You need to take it to someone who's good at diagnosing. If the car doesn't make noise on the lift, then it's causing noise when there's weight on the drivetrain. Inspect everything carefully, maybe 2 or 3 times. It could be as simple as shifter bushings, or shifter carrier not set in properly, or even a heat shield getting in the way. The shifter is hitting something under load so inspect and see what it hits. Is it hitting the bolts on the guibo or something else maybe?

[Seppa]

Hi All,

Since my 6MT conversion, there has been an annoying vibration coming through the shifter, particularly pronounced when in 3rd and 4th gear. It is worse under load and makes the shifter vibrate both visibly and audibly. At first, I thought it might be the guibo, but after replacing that, the problem remained.

So, I finally just decided to take it to a shop. They put it on a lift, drove the car in 4th gear, and saw nothing external to the transmission that could be causing the vibration, meaning the only possibility is coming from inside the transmission.

That caught me a bit off guard, as it doesn't really seem like something that I could have screwed up during the conversion, just because there really isn't that much that could have gone wrong. The mechanic's only idea was that the PO was doing a bit too much flatfoot shifting while it was still an SMG, and at this point to drive it till it dies and then replace it.

I just wanted to gather some opinions and see if anybody has experienced anything similar. If there are any SMG conversion gurus around here, I'd love to hear your opinion about what might be going wrong. Any thoughts?

I will try to attach a video of what it looks like in the cabin when I get a chance. Thanks.

Hey,

did you resolve the issue? I have the exact same problem. Mine is an SmG converted with a CAE shifter.

[tlow98]

Who did you guys buy your bell housings from?

[sina]

Hey,

did you resolve the issue? I have the exact same problem. Mine is an SmG converted with a CAE shifter.

Unfortunately not. My current living situation doesn't really allow for under car DIY-ing, and the couple of shops I've had take a look weren't able to figure it out either.

Who did you guys buy your bell housings from?

I bought mine from Kevin.

[sapote]

I suggest to machine your own BH and not replace it with another one, to avoid input bearing damage.