Ideas? Sticking clutch pedal only when braking heavily

[Blackroot]

Originally Posted by Oldcarguy

Thanks BR. Hopefully it’s air bubbles that the fluid change will take care of, but one or more of the points you mention are definitely in the running.

The thing that gets me is that it only does it in conjunction with extreme braking.

According to the paperwork I received from the PO, the clutch only has ~4,000 miles on it. But, I do have a heavy clutch pedal even though the helper spring *appears* to be in good shape & working properly, the engagement point is good, no chattering, no leakage, no gear grinding etc. If a check of the helper spring and the fluid purge with my Motive doesn’t fix the issue I may kick it over to my indie. Too many other irons in the fire and no time to pull the transaxle and redo the clutch before first HPDE in April.

Frankly I am leaning toward a hinky throw out bearing or pressure plate but I don’t get why it only happens in conjunction with extreme braking. Front motor mount is relatively new (987), but maybe a transaxle mount?? Clutch is hydraulic and the transaxle/clutch assembly is a pretty solid unit so I just don’t see a possibility there.

Yup and as I said on the bottom here-
"Also, if you think about what you just said "when braking extremely hard with the clutch disengaged simultaneously (classic ‘panic stop’) the clutch pedal returns halfway and sticks", remember these are shared fluid systems, so the caliper might not be returning enough fluid to pull up the clutch.
Seems to point to air in the system"
If I was to bet, I would say air

[Oldcarguy]

Originally Posted by Blackroot

Yup and as I said on the bottom here-
"Also, if you think about what you just said "when braking extremely hard with the clutch disengaged simultaneously (classic ‘panic stop’) the clutch pedal returns halfway and sticks", remember these are shared fluid systems, so the caliper might not be returning enough fluid to pull up the clutch.
Seems to point to air in the system"
If I was to bet, I would say air

I’m on my iPad and I thought I read your whole post, but I missed your very pertinent point at the bottom. Those 4 pot calipers are holding a lot of fluid under extreme braking. Also, I have no records indicating that the fluid has been changed in the last few years so there may be who knows what in the system.

I’ll try to change the fluid and purge the brake and clutch systems (also ensuring to engage PSAM and ABS) next week. I’ll update as soon as I have the result.

[Blackroot]

Originally Posted by Oldcarguy

I’m on my iPad and I thought I read your whole post, but I missed your very pertinent point at the bottom. Those 4 pot calipers are holding a lot of fluid under extreme braking. Also, I have no records indicating that the fluid has been changed in the last few years so there may be who knows what in the system.

I’ll try to change the fluid and purge the brake and clutch systems next week. I’ll update as soon as I have the result.

I just used one of these with fantastic results. I did it dry @ 22PSI
https://www.amazon.com/Motive-Products-European-Bleeder-Pressure/dp/B0002KM5L0

Be quick on the bleeder or you will drain the brake fluid tank.
I'm a weekend warrior, like you

[Oldcarguy]

Originally Posted by Blackroot

I just used one of these with fantastic results. I did it dry @ 22PSI
https://www.amazon.com/Motive-Products-European-Bleeder-Pressure/dp/B0002KM5L0

Be quick on the bleeder or you will drain the brake fluid tank

My Motive just came in. I’ll have my shop assistant (wife) monitoring to ensure I don’t introduce new air into the system.

[Blackroot]

Originally Posted by Oldcarguy

My Motive just came in. I’ll have my shop assistant (wife) monitoring to ensure I don’t introduce new air into the system.

You can either use the bleeder screw on the slave cylinder or a brake caliper.
I would start with slave.
11mm socket, and be ready to get soaked unless you attached a hose to the bleeder valve to a tray.
Brake fluid actually doesn't taste bad, but don't swallow
Tight quarters.
Make sure the brake fluid tank is completely full
Also, start with clutch fully up, pump the bleeder tank to 22psi. get under car and open bleeder.
When air noise stops and a steady stream suddenly appears, tighten valve.
Get in car and try clutch pedal (fill the brake fluid tank first as it will have lowered)
Might be perfect right there.
If not, repeat

[Oldcarguy]

Originally Posted by Blackroot

You can either use the bleeder screw on the slave cylinder or a brake caliper.
I would start with slave.
11mm socket, and be ready to get soaked unless you attached a hose to the bleeder valve to a tray.
Brake fluid actually doesn't taste bad, but don't swallow

Duly noted

[Blackroot]

Originally Posted by Oldcarguy

Duly noted

I edited below, so here it was

Make sure the brake fluid tank is completely full
Also, start with clutch fully up, pump the bleeder tank to 22psi. get under car and open bleeder.
When air noise stops and a steady stream suddenly appears, tighten valve.
Get in car and try clutch pedal (fill the brake fluid tank first as it will have lowered)
Might be perfect right there.
If not, repeat

[Geof3]

Originally Posted by Oldcarguy

I’m on my iPad and I thought I read your whole post, but I missed your very pertinent point at the bottom. Those 4 pot calipers are holding a lot of fluid under extreme braking. Also, I have no records indicating that the fluid has been changed in the last few years so there may be who knows what in the system.

I’ll try to change the fluid and purge the brake and clutch systems (also ensuring to engage PSAM and ABS) next week. I’ll update as soon as I have the result.

HPDE events in my region require brake fluid replacement annually. Still seems like an odd symptom overall. Don’t forget to bleed your clutch slave as well...

[Oldcarguy]

Originally Posted by Geof3

HPDE events in my region require brake fluid replacement annually. Still seems like an odd symptom overall. Don’t forget to bleed your clutch slave as well...

Yes, our region also requires annual brake fluid replacement. I’ll definitely bleed the clutch. It is a strange symptom, first time I’ve run across something like this. It’ll be interesting to find the root cause.