[eatingpizzainthef87rules]

Not sure why you guys want all the shock running through your driveline when you pack gears on a 6MT - thats the job of the CDV. Great device, most manual drag cars and track cars run them.

Guess this is a good mod if you baby your car and putt around?

[XutvJet]

Originally Posted by eatingpizzainthef87rules

Not sure why you guys want all the shock running through your driveline when you pack gears on a 6MT - thats the job of the CDV. Great device, most manual drag cars and track cars run them.

Guess this is a good mod if you baby your car and putt around?

Agreed. Plus is well known that the ZF gs645bz 6MT, while very robust from a gear/input shaft/shift fork perspective, does have somewhat weak 1-2 and 2-3 syncros. The gs645bz was beefed up in 2014 for use in the M2/3/4, but it still can munch the syncros if driven hard, especially the 1-2 syncro which has immense torque load on it and more so if you've got power mods. I avoid ripping the 1-2 shift much at all for this very reason. There are no serviceable parts for the gs645bz either. Your options are:

1) Buy a new from BMW for $5000
2) Buy a remanufactured one from BMW for $3000
3) Find a used one

With all that said, the CDV does impact driving with these 6MTs. I've been driving manuals for three decades and I find the CDV very frustrating after 5.5 of ownership. It's my biggest issue with an otherwise amazing driving M235. The CDV makes smooth take offs and shifting the 1-2 and 2-3 somewhat difficult. You can feel the CDV's annoying operation by simply shifting and releasing and holding the clutch pedal just to wear it starts to catch While holding the clutch pedal in the same position, all the fluid finally pushes through CDV and the clutch engages while the pedal has not moved. It's odd and inconsistent flow of fluid is why the clutch pedal catch point can vary somewhat thus why it makes smooth driving difficult.

[F87source]

Originally Posted by XutvJet

Agreed. Plus is well known that the ZF gs645bz 6MT, while very robust from a gear/input shaft/shift fork perspective, does have somewhat weak 1-2 and 2-3 syncros. The gs645bz was beefed up in 2014 for use in the M2/3/4, but it still can munch the syncros if driven hard, especially the 1-2 syncro which has immense torque load on it and more so if you've got power mods. I avoid ripping the 1-2 shift much at all for this very reason. There are no serviceable parts for the gs645bz either. Your options are:

1) Buy a new from BMW for $5000
2) Buy a remanufactured one from BMW for $3000
3) Find a used one

With all that said, the CDV does impact driving with these 6MTs. I've been driving manuals for three decades and I find the CDV very frustrating after 5.5 of ownership. It's my biggest issue with an otherwise amazing driving M235. The CDV makes smooth take offs and shifting the 1-2 and 2-3 somewhat difficult. You can feel the CDV's annoying operation by simply shifting and releasing and holding the clutch pedal just to wear it starts to catch While holding the clutch pedal in the same position, all the fluid finally pushes through CDV and the clutch engages while the pedal has not moved. It's odd and inconsistent flow of fluid is why the clutch pedal catch point can vary somewhat thus why it makes smooth driving difficult.

+1

The worst part is no serviceable parts.

[AWC-F87]

Originally Posted by F87source

+1

The worst part is no serviceable parts.

There's no service parts for the M2 6mt trans?

[F87source]

Originally Posted by AWC-F87

There's no service parts for the M2 6mt trans?

Nope, no synchros, no gears, no input or out put shafts nothing. Just drain and fill plugs and the shifter carrier and maybe linkages but nothing in regards to the internals.


Maybe someone can contact zf and see if they'd be willing to sell some stuff.

[David.m]

A few days ago I removed the CDV and have to say I'm pleasantly surprised with the level of improvement (as most have described). The bleeding issues were the main reason I'd held off but after recently seeing a diy video on how to easily remove the CDV while leaving the slave cylinder in situ and being in lockdown I thought I would give it a go.

Once the car was on stands & splash panel off it was literally a 15min job to disconnect line from slave cylinder, remove the CDV & re-connect the line. The video is linked elsewhere on this forum but here it is again:

My first effort to bleed with a Motive Pressure Bleeder failed with a lot of air getting in the clutch line. I independently fill the reservoir (rather than waste expensive racing fluid going through the Motive that I also have to clean up afterwards) & didn't appreciate how small the clutch chamber is inside the brake reservoir!.

I then filled the reservoir to top of the fill neck, with pressure bleeder at 10-12psi released bleed nipple just enough to get fluid flowing then closed it when (I guessed) reservoir level was down to around the 'max' mark. Repeated that process 4 times and I had a perfect pedal. If only I had done this 1st time

This is without doubt the best mod for $ spent that I've done to this car.