Ideas? Sticking clutch pedal only when braking heavily
I know a sticking (on return) clutch pedal can be a symptom for slave going bad, air in lines, clutch bearing, etc. but I’ve got a slightly different manifestation.
Under normal and spirited (heel and toe) driving I have no clutch pedal issues. Smooth engagement, proper pedal travel, etc. Clutch has ~4,000 miles on it since rebuild by PO’s independent shop. However, when braking extremely hard with the clutch disengaged simultaneously (classic ‘panic stop’) the clutch pedal returns halfway and sticks. If I depress it again, it returns normally. I discovered this because I occasionally engage the abs on purpose to exercise it. But sometimes the pedal will also stick under very heavy braking without getting into the abs. Brake and clutch pedals are firm. I’m going to purge the brake/clutch fluid (with Motul 600) and see where I’m at. If nothing changes regarding the sticking pedal, looks like I may be headed for a clutch slave cylinder replacement next. I need this fixed before I put the car on the track for HPDE events. Any thoughts? |
Why don't you try to cleaning (and lube) the shaft where the pedal hangs from and the return spring as well?
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DOT 4+ is DOT4 + The volume isn't going to change in the master or slave with new fluid. Might want to see if the slave cylinder hard line (12mm flare wrench used only) is tight. The slave bleeder is 11mm. Could be many things... 1. pressure plate springs are weak or failing. 2. slave cylinder is not quite right with air bubbles. 3. Bad throw out bearing or in pieces 4. Master cylinder return spring (mentioned) 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 |
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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. |
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"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 |
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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. |
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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 :) |
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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 |
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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 |
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Nothing against Pelican as they are tremendously valuable, and I source them for almost everything I do. Up always worked for me. |
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Any update ? |
Unless I am mistaken ( I certainly could be) you must bleed the clutch with the pedal down
see: http://986forum.com/forums/boxster-general-discussions/73188-clutch-bleeding-power-bleeder.html |
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Both times failed miserably and I lost 16$ worth of brake fluid. I found success with pedal up. I have driven the car 400 miles since all the work and it shifts like it just came out of the factory. Butter. Again, pedal up worked for me, and doesn't mean the best way. Just to be clear, I have a 2004 S special, and I had a new slave cylinder that I installed on the gear box before it went back in. Also, be sure to drain and re-fill your gearbox while you have it out. 75W Mobile 1 BTW, there is nothing more rewarding than driving your car after all that hard work. Faster/better or not, it was worth every minute of work. In fact, next time I can do it in half the time from this experience. |
Ideas? Sticking clutch pedal only when braking heavily
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Ran smack into the Holidays and they stopped my 986 work like running into a wall. Got back to it today, lifted the car and discovered I have a torn left CV transaxle boot. Must have just happened. Replaced the front plastic “air guides” that keep the radiator heat from the front brakes and called it a day with a refreshing adult beverage. I’ll update as soon as I have her back on the ground, but it will be a while (.5 quart sump extension, oil pump extension, sump baffle, underbody plastic repair, CV boot replacement, brake fluid purge and bleed). https://uploads.tapatalk-cdn.com/201...64a3ed4466.jpg https://uploads.tapatalk-cdn.com/201...8d45e97ae8.jpg Sent from my iPad using Tapatalk |
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