Why does my clutch chatter?

[nachob]

I have owned four BMW manuals since 2004 and eventually all of them develop this issue. I had this going on from driving nicely. Then one day I took my 325i autocrossing and the chatter stopped for a long time after that. Then I drove super mellow and it would come back.

Here is the best guess I have as to what causes it. I do not know for sure but this seems to make the most sense. These cars use a self adjusting clutch pressure plate that comes spring loaded from the factory. You install the clutch and pressure plate, then release a pin that releases a ratcheting (ramped) spring mechanism.

As you drive, the clutch begins to get thinner and you are not getting full pressure plate contact like you did when it was new. This can lead to slippage and hot spots on the clutch surfaces. The self adjusting mechanism ratchets so eventually the disk and flywheel will wear enough that the adjusting system will adjust to the next level and you get full pressure plate/disk contact and the clutch works better until it happens again.

That is why sometimes the problem goes away then comes back again. It would also explain why after my autocross, it worked well again for some time. This self adjustment is stepped not linear so there are long periods where you are not having full pressure between disk and pressure plate. This can cause slippage and hot spots that might go away once it adjusts and you get full pressure. However, if you drive hard during a point where you have less than full pressure, this can cause damage that will not go away.

The CDV does not cause this issue but I can make it more noticeable because it slows the clutch engagement ever so slightly but not having it also causes jolts to the drivetrain and in the clutch is a wear item. Your driveline is not. With cars making 300-400 lb/ft of torque at 1500 rpm, this is a big jolt to the system. So the engineers at BMW did not sit around and say, hey lets just throw this CDV valve for fun into the clutch. These guys know more than you or I. In low power cars like the E46 that were low torque, it was not as big a deal but these cars are pushing the limits of manual gearbox construction. Some manufacturers of muscle cars are even foregoing sought after manuals because they cannot source a manual transmission rated for contemporary torque/hp. Even automatics like the DCT are beginning to hit limits here too.

Here is a video that explains the self adjusting clutch:

Unfortunately, this is a BMW common issue. I had my E46 325i clutch replaced under warranty for this issue and it came back again slightly at 12K miles. I just got used to it and would drive it harder for a bit until the clutch adjusted on its own.

I hope my guessplanation helps!

[mackeroni]

Originally Posted by Dackelone

You might also check your quibo or rubber flex disc between the output shaft of the trans and the driveshaft. Maybe its starting to crack ?

Good idea. I did have the guibo replaced as part of the June 2017 Recall Campaign 17V-067 for the CV joint.

Thanks Dack, but over the two years since I made the original post, my clutch shuddering has settled down quite a bit. Maybe it was the guibo. Anyway, at 65,000 miles, the clutch generally engages smoothly. I don't know the real reason why, but I am grateful.

Peace... Mack

[HawkeyeGeoff]

Originally Posted by nachob

I have owned four BMW manuals since 2004 and eventually all of them develop this issue. I had this going on from driving nicely. Then one day I took my 325i autocrossing and the chatter stopped for a long time after that. Then I drove super mellow and it would come back.

Here is the best guess I have as to what causes it. I do not know for sure but this seems to make the most sense. These cars use a self adjusting clutch pressure plate that comes spring loaded from the factory. You install the clutch and pressure plate, then release a pin that releases a ratcheting (ramped) spring mechanism.

As you drive, the clutch begins to get thinner and you are not getting full pressure plate contact like you did when it was new. This can lead to slippage and hot spots on the clutch surfaces. The self adjusting mechanism ratchets so eventually the disk and flywheel will wear enough that the adjusting system will adjust to the next level and you get full pressure plate/disk contact and the clutch works better until it happens again.

That is why sometimes the problem goes away then comes back again. It would also explain why after my autocross, it worked well again for some time. This self adjustment is stepped not linear so there are long periods where you are not having full pressure between disk and pressure plate. This can cause slippage and hot spots that might go away once it adjusts and you get full pressure. However, if you drive hard during a point where you have less than full pressure, this can cause damage that will not go away.

The CDV does not cause this issue but I can make it more noticeable because it slows the clutch engagement ever so slightly but not having it also causes jolts to the drivetrain and in the clutch is a wear item. Your driveline is not. With cars making 300-400 lb/ft of torque at 1500 rpm, this is a big jolt to the system. So the engineers at BMW did not sit around and say, hey lets just throw this CDV valve for fun into the clutch. These guys know more than you or I. In low power cars like the E46 that were low torque, it was not as big a deal but these cars are pushing the limits of manual gearbox construction. Some manufacturers of muscle cars are even foregoing sought after manuals because they cannot source a manual transmission rated for contemporary torque/hp. Even automatics like the DCT are beginning to hit limits here too.

Here is a video that explains the self adjusting clutch:

Unfortunately, this is a BMW common issue. I had my E46 325i clutch replaced under warranty for this issue and it came back again slightly at 12K miles. I just got used to it and would drive it harder for a bit until the clutch adjusted on its own.

I hope my guessplanation helps!

Yeah can confirm if you have a shitty self adjuster, this could happen. On modern clutches this should never happen as once it adjusts one way, it should not adjust back the other way. Adjustment is also only supposed to happen upon first clutch press when driving a car (aka when you turn the car on). LUK and Sachs clutches in general are really good in this aspect.

[Thunderguts]

My clutch shudder was getting really bad. When cold it was manageable, but when hot, it would shudder so badly it made smooth launches nearly impossible. The other day I slipped the clutch enough to heat it up and it has improved dramatically. Slipping the clutch at high RPM essentially glazes the clutch slightly so that it has uniform friction. I'm guessing clutch shudder has less to do with adjustment and more to do with deposits on the flywheel. Just like my BMW brake pads constantly leave deposits on the rotors which cause brake shimmy, I think the clutch is doing something similar. I cannot wait until I replace the stock brake pads with some Hawk HPS pads. I'm thinking about going with an aftermarket clutch for the same reason.