Clutch Pedal Fade

Rawkkrawler · #1 (**permalink**) 11-04-2011, 05:58 PM

Not sure what to do next....

I'm using a floor mounted Wilwood 1" bore master with a hard line to a push type slave (not sure of the brand). I do have the Wilwood 2lb residual valve in line as well.

When driving, the clutch seems to need two to three pumps to get a good pedal. If I lift off the pedal (sort of a snap motion) the pedal loses 50% of it's feel. If I do it twice it's almost gone.

I then have to pump it two to three times to get it back. If I rest my foot lightly on the pedal, it seems to be better for some reason. Almost seems like it needs a little preload, but that doesn't make sense.

No fluid is leaking out at all and the MC was bench bled.

Any thoughts?

blykins · #2 (**permalink**) 11-04-2011, 06:16 PM

My bet is that there is still air in the line.

Is the master cylinder new?

mreid · #3 (**permalink**) 11-04-2011, 08:21 PM

Why the residual pressure valve? It is only really needed if your mc reservoir is below the slave. Is it?

elmariachi · #4 (**permalink**) 11-04-2011, 08:24 PM

Quote:

Originally Posted by blykins

My bet is that there is still air in the line.

x2. Bench-bleeding or not, there is air in the line or MC. Find someone with a bleeding system that can pull all the air out and you'll be in business.

Rawkkrawler · #5 (**permalink**) 11-04-2011, 08:38 PM

MC is brand new.

Simple unit with a built in large resevoir.

Floor mounted. Slave is about 8" above MC.

Brakes had a similar issue. I was using a hand operated vacuum pump at each bleeder then moved to a air operated vacuum bleeder with no luck. The old fashioned two person forced out the remaing air and the brake now feels good.

I tried the same method to the clutch but didn't get the results as the brakes.

RICK LAKE · #6 (**permalink**) 11-05-2011, 04:24 AM

Rawkkrawler Lets get a little info first,
Does your clutch pedaL problem happen all the time? Car hot or cold?
Does your Hydro slave cylinder have a bleeder valve?
I have not seen any cars running a check valve in the line for a bleed back system. I would want the fork and bearing to come clear of the pressure plate in the bell housing. If the system has a high mounted reserve tank there should be no problem with where the master and slave are mounted. If the air is blend out and correct adjustments are done.Try this way to bleed
1/2 Fill the little tank and cap it get car of floor jacks, you will need 2 people to do this. Push in the slave cylinder piston all the way in. This check valve maynot allow this way to work, Have your top person, SLOWLY press the pedal in to expand the slave again until it hits the fork. You want to do this a couple of times, after 4-5 time, do this and have someone watch for air bubbles in the fluid when the slave is pushed in. If there are small bubbles you still have air in the system and will need to keep doing it this way until they stop or add vacuum to the resv tank and repeat this method. Once this is done now we will bleed the system again from the bottom if you have a bleeder on the slave cylinder, Just like bleeding brakes, Pump,Hold, Bleed, and release a couple of times. Use a small clear hose to catch the fluid in a bottle that has some fluid into we don't want any air being sucked back into the system. Do this 4-5 times. If you see air, keep bleeding. DON'T pump the pedal fast. Slow steady speed.
After you have the bubbles gone with the system we need to check fluid temp after a drive. If the pedal is hard at the start of a drive and turns to a sponge after 20 minutes sound like a heating problem or bad seals in either the master or slave cylinder. If the line is right by a header or the block, we need to get some shielding material to stop the heat from heating the fluid. They sell raps, tubes or heat reflector tape at Jegs or Summit. The Homedepot sell this stuff in rolls for heating/ac systems. It's siulver on one side and 3M stickem on the other. Cut to size and rap twice. You may also have to run a DOT 4 fluid instead of a Dot 3. It will take a higher heat. If this doesn't work either rebuild the master and slave or replace both and repeat above. Good Luck Rick L. Ps took me 3 hours to get mine working and not having a spongy pedal. I have evrything shields or rapped to help with heat soak problem.

mreid · #7 (**permalink**) 11-05-2011, 12:42 PM

The built in reservoir with the slave higher means you need a check valve. The blue 2 lb. sounds about right, but that means that there is always some pressure on your t/o bearing. There are different camps on this, but personally I don't see this as a problem. I don't like wraps for insulating lines as it tends to keep the heat in rather than out. A shield with an air gap behind it is much more effective. I also think you still have air in the line. Make sure the slave bleeder is pointing straight up and that you can cycle the clutch pedal through the entire range of the master cylinder.

RICK LAKE · #8 (**permalink**) 11-06-2011, 03:19 AM

mreid It doesn't matter what system is designed as but why would you want the thrown out bearing riding on the forks or diapham of the pressure plate?? Even some hydros require clearance of the bearing to pressure plate. I have the old system and a heavy spring to pull back the fork.
As far as raps, if they are solid ones you do have a small heat build up. I should have said tube insolators or sleeves with clips. If you drive on the street and control the abuse, you are right about not needing this extra protection. Different story if you go track racing. I have seen guys have accidents from loosing brake pedals for over heated fluid. Some of this applies to the different between running DOT 3 and DOT 4. I have added 3 small cooling fans to remove and help control the heat under the hood. The ERA car has only about 2-3" between #8 header tube and the line for the clutch. After 20 minutes of track time the clutch pedal is soft. Car cools off and pedal is fine. A clutchless trans also helps in this issue of being able to finish a 20 minute run. It all depends on what pedal system you have in the car too and location. Rick L.

tcrist · #9 (**permalink**) 11-06-2011, 10:48 AM

Rick,

My clutch is set up like that. It rides on the PP all of the time. According to the Ford mechanics, it has been that way for a long time. Ford has designed the throwout bearing to ride on the PP with 8 LBS of preassure at rest.

I don't like it but that is the way they designed it. I have been working on a way to redesign my clutch pedal for more throw so I do not have to do this. BTW, I am using the cable pull clutch setup.

Rawkkrawler · #10 (**permalink**) 11-06-2011, 01:44 PM

Thanks for the comments.

The 2lb blue residual valve is in line and does not seem to be allowing too much pressure on the throw out bearing or fork.

To narrow it down a little, heat has played no part in the issue. If I sit in the driveway without moving I can simulate the clutch fade. All I have to do is tap the clutch pedal, It doesn't need to be depressed at all. With the tip of my foot just tap it allowing the spring to bounce it back I lose the pressure. If I do this 3 times I have no pedal. If I pump it fully to the floor 3-4 times, the pressure comes back.

At rest, the pedal does not lose pressure.

Today I lengthened the pushrod to the MC to add some tension, now the pedal holds pressure. This seems wrong to me. It is the equivilant to me resting my foot lightly on the pedal. It des not appear to be moving the clutch fork at all, but still seems like the wrong way to fix the problem.