[papnschmilees]

I've got a weird issue I'd like to bounce off some of your heads.
I've been having a weird intermittent issue with losing my clutch engagement point after getting on it for a bit.

I can't seem to put my finger on what's happening.
I'm not seeing any leaks anywhere.
It's works flawlessly under normal driving conditions.
No difference after flushing the brake fluid.
It doesn't bleed down if I stand on the clutch for a long period of time.
It doesn't do it if I shift quickly.
It only does it after WOT runs, so it may be RPM related somehow.

I might just swap out the master cylinder and see if anything changes.

I've done the CDV delete at 15k miles. I'm at 40k now.

2017 SRT 392

Symptoms are that the clutch doesn't disengage until closer to floor than normal. A few pumps of the pedal and it's back to normal.

I've noticed it most when dropping down and running through 2nd and 3rd. Sometimes to the point I miss 3rd gear because it won't engage.

Open to hear some thoughts or ideas for me to try or look into

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[Himmelkat]

To be clear, the clutch is experiencing a disjoint between pedal motion and ENGAGING?

Does you mean that the clutch is not transmitting power from engine to trans, or it refuses to let go of transferring power so you can shift to 3rd?

3rd gear synchros would be a prime additional suspect, too.

Also, the Barton shifter eliminates THAT known wobbly link between you and the transmission.

A) clutch does not disengage until close to the floor until pumped a couple times.
B) clutch will not connect engine and trans in 3rd gear, at times.

It sounds like air in the lines or clutch cylinder(s) but you said it did not change after flushing. I assume you did not use Mushmaster 5000 silicone fluid, as that stuff is like stepping on a trampoline. They say fluids are not compressible. Very much wrongness. That stuff compresses like a poorly-inflated ball.

Things to know:
A) is the slave cylinder/TOB moving in direct proportion to the pedal at all times? (This is by observation, directly, not via observing the car's behavior.)
B) is the clutch responding normally when the slave cylinder/TOB is moving? Again, direct observation. Can you see the diaphragm spring move?
C) Are all parts bolted in place properly and have all pieces in good order? (No missing or present-in-wrong-place-or-position clutch pucks or anything else, no worn-out friction material, no foreign objects in the works, no oil or leakage on surfaces in the clutch

Another thing that sounds like the problem is the multi-pump to "get the pedal up;" that is a symptom of a bad master cylinder, which I have experienced with brakes when using a "rebuilt" master cylinder that wore out in mere weeks. It was so bad I had to pump the pedal multiple times to get braking coming up to an intersection.

 

[Slidd]

I've got a weird issue I'd like to bounce off some of your heads.
I've been having a weird intermittent issue with losing my clutch engagement point after getting on it for a bit.

I can't seem to put my finger on what's happening.
I'm not seeing any leaks anywhere.
It's works flawlessly under normal driving conditions.
No difference after flushing the brake fluid.
It doesn't bleed down if I stand on the clutch for a long period of time.
It doesn't do it if I shift quickly.
It only does it after WOT runs, so it may be RPM related somehow.

I might just swap out the master cylinder and see if anything changes.

I've done the CDV delete at 15k miles. I'm at 40k now.

2017 SRT 392

Symptoms are that the clutch doesn't disengage until closer to floor than normal. A few pumps of the pedal and it's back to normal.

I've noticed it most when dropping down and running through 2nd and 3rd. Sometimes to the point I miss 3rd gear because it won't engage.

Open to hear some thoughts or ideas for me to try or look into

Sent from my Pixel 5 using Tapatalk

You can get clutch issues like that when the clutch is on it's way out and starting to slip under a load, the excess heat from the slip will heat the fluid in the slave cylinder and cause these problems.

Lots of issues a few years back with GM clutches on the diesel pickups after adding a tune or towing heavy, the clutch pedal would go dead or get stiff until it cooled down a little.

At 40K, you might just need a clutch.


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[papnschmilees]

Appreciate the reply's.
To clarify a few points.
@Himmelkat The worst time when I say the engagement point moved means. sitting still idling in gear. Releasing the clutch pedal the car starts at maybe half pedal and is fully engaged by 3/4 from the floor. Worst I've seen so far from the floor it started engaging at barely half an inch from the floor. I believe the self correcting nature of the pumping might be related to this being a self bleeding system. although it doesn't feel like it has air. when I flushed the brake and clutch system I used Amsoil fluid. I drive this car daily and the problem comes up and remedies itself very abruptly. All equipment is OEM, no leaks that I can find. Bell housing is dry and free of any kind of debris when looking through the inspection port. I do have a Barton shifter on the car. Zero issues with syncros when the pedal is normal.

@Slidd I can follow that logic. I bought the car with 12k miles on it so I have no idea how it was treated during that time. It doesnt feel like its slipping at all, I can easily get my p4s's to chirp 3rd and 4th gear. No dust in the bell housing or any smells. I dyno'd at 470rwhp/465rwtq so I am over original output. Do you know if the hellcats have a different clutch than the 392's?

I've ordered a new master cylinder and will report back after I get it swapped out. My next step is to drop the trans and change out the slave.

 

[Himmelkat]

Fascinating and educational. I await the results.

 

[Slidd]

Do you know if the hellcats have a different clutch than the 392's?

Yes they do. Both are dual disc but Hellcat is 258mm compared to 392 240mm and would be a nice upgrade. And it's a direct bolt in.



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[papnschmilees]

Yes they do. Both are dual disc but Hellcat is 258mm compared to 392 240mm and would be a nice upgrade. And it's a direct bolt in.

well then. I wonder what the 240 mm one is rated for. I guess Ill just go full monty and order a hellcat clutch and a new slave cyl.
I will check but do you know if the slave is different for the 258mm?

 

[HeadHowie]

Most likely a heat issue with the fluid. My c5 used to do this after a couple hard WOT drag strip runs. It would correct itself after it cooled down. Pedal engagement height would be all over the place and the pedal would get stuck to the floor if I really got it hot.

 

[Slidd]

I will check but do you know if the slave is different for the 258mm?

I don't know but probably can check the part number on the diagram at Steve White Parts.




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[papnschmilees]

I appreciate all the replies guys. Ill try flushing it out again when I swap the master cylinder and in the meantime ill start ordering what I need to get over to the hellcat clutch and a new slave as well.
Ill keep you guys posted

 

[Himmelkat]

Most likely a heat issue with the fluid. My c5 used to do this after a couple hard WOT drag strip runs. It would correct itself after it cooled down. Pedal engagement height would be all over the place and the pedal would get stuck to the floor if I really got it hot.

While I hesitate to recommend silicone brake fluid, it has ONE redeeming quality other than its complete lack of hygroscopic nature: it boils, under any conditions we face, at 700 degrees Fahrenheit. It IS one method for determining if heat is an issue. If you put in the relatively-spongy fluid and it stays at the same level of sponginess regardless of conditions, then temperature is most likely your issue.

 

[papnschmilees]

Yeah, you can't mix the two types though. I don't think I would want to tackle that.
I may give Redlines RL-600 DOT 4 a shot when I change out the master cylinder

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[Himmelkat]

Why could you not mix the two types? They are not mutually exclusive. If one could have the juice only in the calipers isolated from everything else somehow, the extra temp capacity and lack of hygroscopic action might make them viable, but how to transfer very high pressure from the high-zoot DOT 5 or whatever stuff to the DOT 7 fluid is the issue.

 

[papnschmilees]

Everything I've read about silicone based DOT 5 say you can't mix it with any glycol based types like 3,4, or 5.1. the clutch system in our cars isn't isolated. It pulls from the bottom of the brake reservoir

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[Xylander]

You can upgrade the clutch if you like, but at that mileage, the original clutch is probably just worn out. The Hellcat clutch is heavier, so be ready for that.

 

[Himmelkat]

Everything I've read about silicone based DOT 5 say you can't mix it with any glycol based types like 3,4, or 5.1. the clutch system in our cars isn't isolated. It pulls from the bottom of the brake reservoir

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Maybe, but for the purposes of the test, one could just disconnect the small hose between the two. I don't think temperature is his problem, though. I think it's a bad clutch master cylinder.

 

[papnschmilees]

I've changed the slave out and the results were the same. I haven't gotten around to doing the master yet.

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[Modirt]

Sorry to bring this older post back but y’all seem very knowledgeable with the M6.

I want to flush the brake fluid and wondering if a shop does this do they also flush fluid from clutch system? I know they use the fluid from same reservoir but do they have to do anything with bleeding the clutch after? Just push on clutch few hundred times? Tremec seems to think I may have air causing clutch to not engage/disengage properly. Figured I would replace fluid as car sat for long time and may help with my grinding/clashing issue. Thanks.