[Lameboy]

Hi, I drive an F32 428i 6MT and when I shift it really quick the car just holds revs high but doesn't really accelerate. When I have it in gear and floor it the car pulls strong though, and if I just shift a tiny bit slower it pulls just fine. It's only when I shift very quickly, I think the clutch slips. Maybe I'm already on the gas before I am completely off the clutch? I'm not sure. I'm wondering if there's any BMW technology or system that may be causing this because other than when I shift quick, it shows absolutely no signs of a slipping clutch. Thanks in advance to anyone who might have some ideas!

[f30nick]

Originally Posted by AZN_F32

Hi, I drive an F32 428i 6MT and when I shift it really quick the car just holds revs high but doesn't really accelerate. When I have it in gear and floor it the car pulls strong though, and if I just shift a tiny bit slower it pulls just fine. It's only when I shift very quickly, I think the clutch slips. Maybe I'm already on the gas before I am completely off the clutch? I'm not sure. I'm wondering if there's any BMW technology or system that may be causing this because other than when I shift quick, it shows absolutely no signs of a slipping clutch. Thanks in advance to anyone who might have some ideas!

Could be your clutch slipping. I recently just replaced the clutch in my car. Easy test, drop your car into 2-3k rpms in a higher gear. Foot to the floor, if the RPMs rise without increasing speed, your clutch is slipping. Let me know how it goes

[B58 parts]

Could be DSC interfering. Try DSC off mode (hold traction button in).

Could be the bastard CDV. Search here for CDV. Take it out of your slave cylinder, you won't regret it.

Go up a hill put it in 4th and mat it around 2k RPM. If the revs fly up your clutch is out. If it stutters you have a misfire or a bad 02 sensor.

[COKen]

If you try to engage the clutch when the engine is at excessive RPMs, BMWs will usually just spin on the clutch and not engage until the engine and clutch RPMs get closer to the same speed. Since you say you are trying to "shift very quickly", you may just be giving it gas before the clutch can start to engage.

[MacklinUSOB]

Originally Posted by YuminNuman

Could be DSC interfering. Try DSC off mode (hold traction button in).

Could be the bastard CDV. Search here for CDV. Take it out of your slave cylinder, you won't regret it.

Go up a hill put it in 4th and mat it around 2k RPM. If the revs fly up your clutch is out. If it stutters you have a misfire or a bad 02 sensor.

This is top of my mod list, I just can't decide whether or not I can accomplish it with jackstands. I miss my CDV-less manuals.

[Lameboy]

Originally Posted by f30nick

Could be your clutch slipping. I recently just replaced the clutch in my car. Easy test, drop your car into 2-3k rpms in a higher gear. Foot to the floor, if the RPMs rise without increasing speed, your clutch is slipping. Let me know how it goes

Car pulls just fine, no jumps in rpm, just accelerates normally.

[Lameboy]

Originally Posted by COKen

If you try to engage the clutch when the engine is at excessive RPMs, BMWs will usually just spin on the clutch and not engage until the engine and clutch RPMs get closer to the same speed. Since you say you are trying to "shift very quickly", you may just be giving it gas before the clutch can start to engage.

Really? Is there a name for this or more info on it? This is exactly what I thought was happening but I wasn’t sure if it was possible.

[Wgosma]

Originally Posted by YuminNuman

Could be DSC interfering. Try DSC off mode (hold traction button in).

Could be the bastard CDV. Search here for CDV. Take it out of your slave cylinder, you won't regret it.

Go up a hill put it in 4th and mat it around 2k RPM. If the revs fly up your clutch is out. If it stutters you have a misfire or a bad 02 sensor.

Clutch could be slipping but......I bet it's the lock valve (CDV) effect he's experiencing; it's designed to slow the clutch engagement speed ever so little so as prevent shock to the driveline/u-joints. On older cars w/manual transmission these valves were screwed into the slave cylinder (and easily removed) - I think on these newer cars the valve is internal to the slave cylinder assembly and can't be removed.

Good luck/Bill

[B58 parts]

It is internal to the slave, but it _can be removed and a lot of us have already done it. There's a big thread here, google f30 CDV.

[COKen]

Originally Posted by AZN_F32

Really? Is there a name for this or more info on it? This is exactly what I thought was happening but I wasn’t sure if it was possible.

Yes, this is a thing. When releasing the clutch you should have the engine RPMs near to the clutch RPMs. If you have the engine RPMs quite a bit above the clutch RPMs, then the clutch will slip until they can get back to the same RPMs. Other issues could make this happen (as mentioned above), but the least costly is to first be sure you are not causing it by getting back on the gas sooner than you should be.

[Wgosma]

Originally Posted by YuminNuman

It is internal to the slave, but it _can be removed and a lot of us have already done it. There's a big thread here, google f30 CDV.

Removing the CDV was pretty much "Mod #1" for car owners back in the days of E46, E39...

[Wires]

Originally Posted by COKen

Yes, this is a thing. When releasing the clutch you should have the engine RPMs near to the clutch RPMs. If you have the engine RPMs quite a bit above the clutch RPMs, then the clutch will slip until they can get back to the same RPMs. Other issues could make this happen (as mentioned above), but the least costly is to first be sure you are not causing it by getting back on the gas sooner than you should be.

If that was true, you'd destroy a clutch in a short period of time. It might close the throttle to drop revs, but slipping the clutch will destroy the flywheel over time.

Syncros in the transmission take care of getting the engine and transmission speeds matched.

[COKen]

Originally Posted by Wires

If that was true, you'd destroy a clutch in a short period of time. It might close the throttle to drop revs, but slipping the clutch will destroy the flywheel over time.

Syncros in the transmission take care of getting the engine and transmission speeds matched.

I agree this will wear out the clutch fast if you do that all the time.

Also, the "syncros" don't have anything to do with the clutch or engine speed, they synchronize the gears when you are trying to put your car into a specific gear with the clutch depressed. Here is a more technical description - "A synchronizer, or "synchro," lets the collar and gear synchronize their speeds while they're already in contact but before the dog teeth engage.".

Speed matching the engine and transmission is the driver's responsibility.

[Wires]

Originally Posted by COKen

I agree this will wear out the clutch fast if you do that all the time.

Also, the "syncros" don't have anything to do with the clutch or engine speed, they synchronize the gears when you are trying to put your car into a specific gear with the clutch depressed. Here is a more technical description - "A synchronizer, or "synchro," lets the collar and gear synchronize their speeds while they're already in contact but before the dog teeth engage.".

Speed matching the engine and transmission is the driver's responsibility.

Fully a driver controlled function. But what you said above: "BMWs will usually just spin on the clutch and not engage until the engine and clutch RPMs get closer to the same speed.", you may just be giving it gas before the clutch can start to engage." claims otherwise, which simply is not true.

[COKen]

Originally Posted by Wires

Fully a driver controlled function. But what you said above: "BMWs will usually just spin on the clutch and not engage until the engine and clutch RPMs get closer to the same speed.", you may just be giving it gas before the clutch can start to engage." claims otherwise, which simply is not true.

I didn't intend to imply that this was exclusively a BMW problem, but that if someone tries to engage their clutch with the engine at much higher RPMs than the transmission the results is the clutch will not engage, but would just spin. BMWs seem to have more of an issue with this than other cars (in my experience and also with others I have talked with about this), but it will happen with most (all?) manual transmission cars. It is not the car's problem, but the way the driver is controlling the car. As a Teen Street Survival Instructor I see this happening all of the time.