Transmission "thunk" and the CDV in the 1M

[HALOTHANE]

Due to the apparent number of owners reporting a transmission "clunk" during clutch-in while coasting at very low speed in 1st gear, I wanted to get some feedback from our fellow 1M drivers. Please comment whether you have experienced this issue and if the CDV modification has provided a remedy.

According to the 1M manual, transmission clunks are a "normal" characteristic in these cars. The same phenomenon was present in my 2012 MT 135i.

[Franklin Joseph]

post modified cdv, the clunk has mostly gone. I got it a couple times when i was short shifting from 1st to 2nd.

[MusclezMarinara]

i blame CDV

[HALOTHANE]

Originally Posted by Franklin Joseph

post modified cdv, the clunk has mostly gone. I got it a couple times when i was short shifting from 1st to 2nd.

Did you require additional transmission fluid to flush the system during the CDV modification job? If so, this could be a challenge, given the US shortage of MTF-LT5.

[Franklin Joseph]

cdv uses brake fluid...not transmission fluid. yes you will require brake fluid to bleed the system.

[Dackelone]

I think IF you are hearing a "clunk" when downshifting something is not right. Maybe your clutch isn't fully disengaging. Maybe you are rushing the syncros? I never hear those types of noise on my 135i. IF the shifter lever doesn't want to do what your trying/moving teh shift arm to do... somethings not right.

[HALOTHANE]

Originally Posted by Dackelone

I think IF you are hearing a "clunk" when downshifting something is not right. Maybe your clutch isn't fully disengaging. Maybe you are rushing the syncros? I never hear those types of noise on my 135i. IF the shifter lever doesn't want to do what your trying/moving teh shift arm to do... somethings not right.

The clunking is only heard/felt during clutch-in while in 1st gear, and only if coasting slowly in 1st gear. It is not related to actually shifting between the gears. It almost feels as if the transmission suddenly releases loading when the clutch pedal is depressed. With the AC on, the symptom can be magnified.

[Dackelone]

^^Most transmision problems first start out with noises or the shiftlever not slotting into gear properly into the gear/gate. Later in the trans life this will also be apparent with a grinding noise or banging when doing the same action.

Perhaps you guys with this issue should check your trans fluid level? That would be my first plan of action. When you uncrew the trans fill plug some trans oil should spill out/or be level with the fill hole.


Dackel

[HALOTHANE]

Originally Posted by Dackelone

^^Most transmision problems first start out with noises or the shiftlever not slotting into gear properly into the gear/gate. Later in the trans life this will also be apparent with a grinding noise or banging when doing the same action.

Perhaps you guys with this issue should check your trans fluid level? That would be my first plan of action. When you uncrew the trans fill plug some trans oil should spill out/or be level with the fill hole.


Dackel

Thanks. The filler cap dipstick indicates FULL. However, the reservoir is not filled completely to the rim opening. The fluid level is 1.5-2 inches below the screw cap opening. Is the empty space in the reservoir to accommodate thermal fluid expansion?

[Antomero]

I thought M cars have no cdv....

[Franklin Joseph]

Originally Posted by 1MVO

Thanks. The filler cap dipstick indicates FULL. However, the reservoir is not filled completely to the rim opening. The fluid level is 1.5-2 inches below the screw cap opening. Is the empty space in the reservoir to accommodate thermal fluid expansion?

I think u just checked the power steering reservoir. The tranny fluid is contained within the tranny itself.

[HALOTHANE]

Thanks, Frank. My mistake. Learning from you guys, so I appreciate your patience. Interestingly, I mentioned this issue to the BMW SA at my dealership, and he explained that the occassional thud experienced when clutching-in during 1st gear is due to the dual mass flywheel and is considered normal. Any thoughts? Could the CDV delete help?

[Ky1M]

Originally Posted by 1MVO

Thanks, Frank. My mistake. Learning from you guys, so I appreciate your patience. Interestingly, I mentioned this issue to the BMW SA at my dealership, and he explained that the occassional thud experienced when clutching-in during 1st gear is due to the dual mass flywheel and is considered normal. Any thoughts? Could the CDV delete help?

Man I hate to hear these problems, I can only hope that all this stuff is taking care of when I finally get my freaking car. Deposit Oct 2010 , allocation Oct 2011.

[Franklin Joseph]

Originally Posted by 1MVO

Thanks, Frank. My mistake. Learning from you guys, so I appreciate your patience. Interestingly, I mentioned this issue to the BMW SA at my dealership, and he explained that the occassional thud experienced when clutching-in during 1st gear is due to the dual mass flywheel and is considered normal. Any thoughts? Could the CDV delete help?

The thud in my car is due to my (bad) driving style. As i'm depressing the clutch down, i'm already moving the gear out of 1st, that's when the thud happens. Post cdv mod and that same thud is gone.

Maybe you can try slowing down your shifts and see if it goes away, but it still doesnt hurt to do the CDV mod. Thanks to the folks here, i'm a CDV mod believer!

[AA5IB]

Originally Posted by Franklin Joseph

The thud in my car is due to my (bad) driving style. As i'm depressing the clutch down, i'm already moving the gear out of 1st, that's when the thud happens. Post cdv mod and that same thud is gone.

It's not your bad driving style. The CDV delays the clutch disengaging so you are shifting out of first the transmission is still under load because the clutch isn't fully disengaged. The CDV is not the finest example of BMW's Engineering excellence.