Super Puzzling Clutch Hydraulics Issue - HELP!

[RushB]

I've got an insanely weird issue happening with the clutch hydraulics that is driving both myself and a few mechanic friends of mine crazy. I'm literally at the point when I will venmo someone $100 if they can help me nail the issue.

2018 GT350, 43000 Miles.

Context:

The issue started about 6 months ago after a spirited drive in the fall. During the drive, leaves had almost completely blocked all of the vents in the front, which meant my intake temps were much higher than usual for about an hour.

On the way home, I went for a redline shift from first into second and the car wouldn't let me into gear. The clutch pedal was also stuck on the ground, and I had to pump it a few times to get pressure again. I drove the car home gently with no issues and put it away for the winter. Bringing the car out for spring again has revealed it's now a consistent issue.

The Problem:

Driving the car around under 6K RPMS is completely normal. It never misbehaves.

Upshifting at redline always results in one or more of the following:
- Unable to get into the next gate, and clutch Pedal stuck on the floor and needs pumping(only one or two times) to feel normal again
- Successful shift, but clutch Pedal stuck on the floor and needs pumping(only one or two times) to feel normal again
- Successful shift, but clutch Pedal stuck halfway and needs pumping(only one or two times) to feel normal again

The hydraulic system itself is losing pressure when the issue occurs, as it always requires one or two pumps to feel normal again.

Troubleshooting:

Complete clutch bleed was always done following factory procedure (vacuum > pump pedal and repeat) after each step. Brake fluid is OEM Motorcraft and new.

- Replace Slave/throwout bearing w/OEM unit. This was CONFIRMED to be leaking a little bit as there was a bit of fluid in the bell housing.
- Replace Clutch master cylinder w/OEM unit.
- Inspect all clutch components while swapping the slave, which all look extremely healthy

After these repairs, the problem behavior is the EXACTLY same. There is NO brake fluid loss anywhere.

Thoughts and Next Steps?

- New braided metal cable? If the rubber cable is deteriorated it could be ballooning during high RPM shifts, but that shouldn't make the entire system lose hydraulic pressure.

- Still air trapped in the system? Behavior points to this, but we've bled it so many times.

- Overall, the key here is still that the system is losing hydraulic pressure when this happens and needs to be pumped one or two times to feel normal again. The diagnoses would need to align with this fact. For example, we're thinking it's not mechanical or clutch related, as that wouldn't cause the whole system to lose pressure.

Sponsored

 

[SHOdaddy68]

Interesting.

My fist thought is something within the clutch and/or pressure plate is getting stuck/in a bind at the higher RPM and won't release. Thus causing the TOB to remain extended and cause the pedal to stick on the floor.

2nd thought. Have you inspected the clutch fluid line where it connects to the brake master? There's a rubber seal inside the connector that can come loose and either leak or suck air. Easy fix if it's not properly connected.

A braided A/M fluid line will typically hold more pressure than the plastic factory line.

Good luck!

 

[RushB]

Interesting.

My fist thought is something within the clutch and/or pressure plate is getting stuck/in a bind at the higher RPM and won't release. Thus causing the TOB to remain extended and cause the pedal to stick on the floor.

2nd thought. Have you inspected the clutch fluid line where it connects to the brake master? There's a rubber seal inside the connector that can come loose and either leak or suck air. Easy fix if it's not properly connected.

A braided A/M fluid line will typically hold more pressure than the plastic factory line.

Good luck!

Yeah we've known about the clutch fluid line where it connects to the brake master and have ensured that it's on very snug.

If something within the clutch and/or pressure plate is getting stuck/in a bind, is there a way that that would cause the hydraulic system to lose pressure and needs a few pumps to normalize?

 

[Therealmattlex]

My fist thought is something within the clutch and/or pressure plate is getting stuck/in a bind at the higher RPM and won't release. Thus causing the TOB to remain extended and cause the pedal to stick on the floor.

I agree with binding in the clutch somewhere. I actually grenaded my clutch and friction material got wedged in everywhere. the clutch pedal wouldn't return but the clutch stayed engaged. I had to revmatch for the hour drive home.

 

[SHOdaddy68]

Yeah we've known about the clutch fluid line where it connects to the brake master and have ensured that it's on very snug.

If something within the clutch and/or pressure plate is getting stuck/in a bind, is there a way that that would cause the hydraulic system to lose pressure and needs a few pumps to normalize?

If the clutch gets in a bind and/or the PP wont release, there's no pressure to push the TOB back which could be the cause of your perceived symptoms of pressure loss. Meaning, the TOB is already fully extended. My money is on something in the clutch assembly. Makes sense in my mind anyway.

 

[Eyesac]

I had similar issues with my car and have replaced many things, it's slightly better now, pedal never sticks to the floor anymore, but it still "locks me out" of 3rd at high rpm from time to time. I'm convinced that some of these engines vibrate more than the next one and that the vibration at high RPM inhibits clutch plate movement until RPMs drop. Enough that I've considered replacing the damper some day. Idk, that sucks, good luck, if you fix this somehow let us know!

 

[Garfy]

I had similar issues with my car and have replaced many things, it's slightly better now, pedal never sticks to the floor anymore, but it still "locks me out" of 3rd at high rpm from time to time. I'm convinced that some of these engines vibrate more than the next one and that the vibration at high RPM inhibits clutch plate movement until RPMs drop. Enough that I've considered replacing the damper some day. Idk, that sucks, good luck, if you fix this somehow let us know!

It almost makes you wish you had an automatic instead, though it would be an option if they offered the 7-speed Tremec DCT the Shelby has.

 

[Weisjacob1$]

I am also having the same exact issue you have described. Cannot find an answer. Following this thread in case of a solution. 2015 GT has as described the same issue (with regards to engagement being at a slightly different rpm around 4000-4500 rpm)
Clutch pedal stays relatively normal under above rpm and in normal driving conditions, WOT or higher rpm is met with the aforementioned issues (difficult engagement/complete lack of pressure/ “lockout”), no fluid loss or leaks. I have done the braided line upgrade and it does not solve the issue. Gives you a stiffer pedal as desired but the results remain the same above previously mentioned rpm. Goodluck man hope someone comes up with a solution cause I’m about to have my clutch replaced and track it down at a performance shop. I’ve done everything else for my car myself so far which makes that decision very disappointing. At this point however, I’m willing to sacrifice the money to get my car back to a enjoyable condition.

Sponsored