Clutch Noise Diagnosis -- Video Clip

[ATB88]

Had a thread a couple months ago about what I thought was an issue where sometimes on clutching at high revs, revs would go up instead of falling and also loud clutch noise. The revs going up part was strange and actually stopped happening, so, it seems like an isolated issue and I'll deal with it if it happens again. In any case, the loud clutch noise remains as an issue so I'm making this thread to focus on it without the confusion about the other rising rpm issue being associated with it.

Summary of the issue: when driving more aggressively (higher RPM), when I put the clutch pedal in, when it reaches the bottom of its travel, I'll get a loud noise from the clutch as the revs fall, and I feel some mechanical feedback from the clutch pedal. This generally doesn't happen when driving more gently around town, only when I've been driving on the freeway fro a while at higher RPM. But once I get it to start happening at higher RPM it'll start happening at lower RPM until I let everything cool down.

Here's a video demonstrating the issue: https://youtube.com/shorts/i_InYHY6T7o?feature=share

Anyone have any thoughts about what it could be? Bad throwout bearing? Clutch stop maybe got pushed down too far over time? I'm guessing that whatever it is I'm dropping the transmission, but it would be good to figure out what it is beforehand if possible.

Thanks guys!

[sapote]

Park it on a slope -- driveway or road -- head down and engage 1st gear (if head up then engage reverse), engine off, no brake. Slowly press down the clutch pedal until car start rolling, note down the pedal position compared to you normal pressed down position. The stopper should be about 3/4 to 1" lower.

[ATB88]

Follow up: 2 years later, this is still an intermittent issue. Still only develops after driving the car hard. If I don't drive the car hard doesn't happen, even if I drive for a long time. But once it gets into this state it stays this way until it cools down.

At this point, once it gets into this state, I can reproduce the noise at idle in neutral. Here's a video: https://www.youtube.com/watch?v=DRov...b_channel=QI88

Is this a smoking gun that it's the TOB? Or is there still a chance that the clutch stop is some how smashed down too far? If I shift at shallower clutch pedal position, no issues at all. It just happens when the clutch pedal hits bottom of travel (or very close to). Sapote, I like your idea for measuring the clutch stop position, but it's logistically pretty hard to do this safely accurately, especially alone.

Additional context: I 6MT swapped this car 7 years and 50k miles ago, so every part from the clutch pedal and clutch stop all the way down to the clutch, PP, TOB, and pilot bearing are quite new. It would be a real bummer if somehow I fucked up the install this bad :/ Could be a red herring, but back when I installed the clutch in 2018, I made a rookie mistake and bolted up the PP and released the self-adjusting mechanism before realizing that I forgot to install the pilot bearing. So i had to pull the PP off, install the pilot bearing, and then try to "reset" the self-adjusting mechanism and reinstall the PP, which was a giant pain. I may not have reset the SAC mechanism correctly, but it's not obvious to me how that could manifest in this behaviour just popping up at this mileage?

[sapote]

Is this a smoking gun that it's the TOB? Or is there still a chance that the clutch stop is some how smashed down too far? If I shift at shallower clutch pedal position, no issues at all. It just happens when the clutch pedal hits bottom of travel (or very close to). Sapote, I like your idea for measuring the clutch stop position, but it's logistically pretty hard to do this safely accurately, especially alone.

In this video (not the first post) the noise for sure is not the bad TOB. It sounds more like the TOB is hitting some radial metal bars of the PP as the TOB moved too far into the PP.

What I suggested is very easy to do, and safe. Park it on a slope surface in 1st, then press pedal down along a ruler slowly, and pull the hand brake as soon as it rolls, then mark where the pedal is while car stopped by hand brake.

Try this: tape a 1/2 to 3/4" piece of wood on top of the stopper to stop the pedal higher. Drive test if the noise gone.

[ATB88]

In this video (not the first post) the noise for sure is not the bad TOB. It sounds more like the TOB is hitting some radial metal bars of the PP as the TOB moved too far into the PP.

What I suggested is very easy to do, and safe. Park it on a slope surface in 1st, then press pedal down along a ruler slowly, and pull the hand brake as soon as it rolls, then mark where the pedal is while car stopped by hand brake.

Try this: tape a 1/2 to 3/4" piece of wood on top of the stopper to stop the pedal higher. Drive test if the noise gone.

Thanks for the suggestions! So, I agree that it feels/sounds like noise of TOB going too far onto PP in some sense, and it was unclear to me whether or not this point that used to be okay is "too far" because the TOB has degraded, or if I'm acutally pushing the TOB farther than it's ever intended to go and that's causing the noise on the PP. I feel pretty confident that the noises in the first and second videos are being caused by the same problem, just happening at very high vs low RPMs.

I'll try your suggestion when I get back from my trip next week.

Until then, though: it's obvious from how this feels and what I can visually see in testing that if I raised the clutch stop a little bit (1/4 inch or maybe even less) the noise would for sure go away. But absent of understanding exactly what the problem was, this may not be a good solution.

My concern about accepting that as a solution is that what if raising the clutch stop would cause shifting that "sounds good" but causes me not to release the clutch completely while shifting, which would long term damage the transmission/syncrhos?

As always thanks for your thoughts and ideas

[sapote]

My concern about accepting that as a solution is that what if raising the clutch stop would cause shifting that "sounds good" but causes me not to release the clutch completely while shifting, which would long term damage the transmission/syncrhos?

My suggestion of parking on a slope is for you to find out the position of the pushed down pedal where the clutch is disengaged completely, then add 1/2" distance before hitting the floor stopper, for safety margin.

Why this happens to yours? All PP need the correct distance movement of the fingers in order to release the clutch, and if the fingers not moved far enough then it doesn't release the clutch, and if moved too far then the PP diaphragm is over extended and damaged. The PP auto adjust might have been setup wrong as you did and so the fingers are now a little bit more forward than normal, this leads to the pedal stroke pushing the fingers too far forward into the PP as you pushing the pedal to stopper. To fix the issue, you have to find the position of total release, add 1/2" and set the pedal stop.

[ATB88]

My suggestion of parking on a slope is for you to find out the position of the pushed down pedal where the clutch is disengaged completely, then add 1/2" distance before hitting the floor stopper, for safety margin.

Why this happens to yours? All PP need the correct distance movement of the fingers in order to release the clutch, and if the fingers not moved far enough then it doesn't release the clutch, and if moved too far then the PP diaphragm is over extended and damaged. The PP auto adjust might have been setup wrong as you did and so the fingers are now a little bit more forward than normal, this leads to the pedal stroke pushing the fingers too far forward into the PP as you pushing the pedal to stopper. To fix the issue, you have to find the position of total release, add 1/2" and set the pedal stop.

I see. This more or less makes sense, I think I need to think about the self-adjusting mechanism more to understand fully. IF I knew my PP and SAC mechanism had been set up correctly, then I would be really worried about the reason why the "normal" bottom of the clutch travel is now pushing the PP too far. But if we blame my possible error in trying to reset the SAC mechanism then this is a pretty reasonable theory.

Anyway: my concern that I was expressing above is that I had read in the past that only the full intended bottom of the clutch travel (where it hits the stop) is where the clutch is fully released and only there is it fully safe to shift. I'd seen threads (a long time ago I think on the old forums) where people were considering a slightly raised clutch stop to be a beneficial "mod", and others chimed in to explain why that was a bad idea. Anyway, if 1/2" past where the clutch will let my car roll down the hill is definitely a "fully released" PP then that's great!

But, devil's advocate: there is one thing about the above explanation and solution that I'm not sure fits with my symptoms: this issue *only* occurs after I've been driving the car hard at high RPMs, after which it will go into this state where I get this noise at the bottom of the clutch pedal travel. It will remain in this state until I cool the car down for a while then go back to normal. If I just drive the car normally (which is most of the time), there is zero issue, and taking the clutch to the bottom of its travel feels perfect -- no noise, no vibration felt through the clutch pedal, doesn't matter if I shift at high or low RPM, there is no issue with full clutch extension. So then: what is it about driving hard for a bit that causes this "state" to appear and then disappear after cooldown?

Thanks again for the brainstorming!!

[sapote]

Anyway: my concern that I was expressing above is that I had read in the past that only the full intended bottom of the clutch travel (where it hits the stop) is where the clutch is fully released and only there is it fully safe to shift

Don't worry, as you will find out that my suggested rolling down slope proves that the interested pedal position is fully disengage the clutch -- car rolling in 1st gear so the clutch must be disengaged, right?

[ATB88]

Don't worry, as you will find out that my suggested rolling down slope proves that the interested pedal position is fully disengage the clutch -- car rolling in 1st gear so the clutch must be disengaged, right?

Hmm yeah, fair enough!

Raising the clutch stop should prevent the issue as it's currently presenting. Still very curious about that this only comes on after hard driving though -- you'd think that if the problem really was that that the PP fingers are being pushed too far, then that should be the case at all times, when the car first starts and during normal driving, not just after. Anyway, we may not know until I eventually drop the transmission.