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Thread: Clutch pedal force

  1. #11
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    I am using the Wilwood reverse mount clutch/brake pedals with the reservoirs and compact Howe master cylinders under the dash which suck for adding fluid. I went to a bigger master to reduce pedal travel. With the 3/4 cylinder and the pushrod adjusted to engage the clutch just slightly off the floor my clutch pedal was a lot higher than the brake pedal with a light effort and long travel. I could push it down by hand. Going to the larger master I was able to lower the pedal travel and the clutch/brake pedals are even and it still has light effort, but I didn't use a heavy-duty clutch either. The throwout bearing travel is controled by pedal travel adjustments.
    I misinterpreted your "reduce travel" comment because the TO bearing travels FAR more than you need it to travel per the experts. I assumed you were reducing TO bearing travel, not pedal travel.

    Looking at Wilwood's site the maximum pedal ratio they list for their reverse mount pedal assemblies is 6.25:1. I thought I saw pics of your Camaro with the master cylinders on the firewall. They do offer 7:1 ratio in that configuration, but not with the reverse mount.

    So your overall ratio is actually only 4.59:1 with the 7/8" master cylinder and the 6.25:1 pedal ratio. That should make your pedal force with an assumed 400 pound clutch 87 pounds, which is way more than mine. And you max out the TO bearing's .688" stroke at only 3.1" of pedal stroke. Even with the 1:1 master/slave ratio your clutch force with that 400 pound clutch and 6.25:1 pedal would be 64 pounds. At 7:1 it would be 57 pounds which is still higher than mine is.

    Either you have a really weak clutch or a very strong left leg if you think 87 pounds is light. And pushing 64 pounds by hand isn't easy. That's nearly twice the pedal force as I theoretically have with the same clutch. Do you have any way to measure it? I really don't know what the clutch pressure plate force is but I've read 400 pounds is in the right range.

    My overal ratio is increased by 2X due to the 2:1 clutch fork even though my pedal ratio is only 3.92:1. So I have a 7.84:1 effective pedal ratio with equal sized master and slave.

    Here's an interesting read on the subject of pedal force....

    https://www.gt40s.com/threads/clutch...-i-want.32131/
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  2. #12
    Registered Member chevynut's Avatar
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    Quote Originally Posted by Rick_L View Post
    For my T56, I have an 02 Camaro t/o bearing, along with a Tick Perf. speed bleeder and a Tick Perf. clutch master which uses a slightly bigger bore Tilton cylinder than GM used. Slightly increased force but also a bit more t/o travel vs. pedal travel than the Camaro m/c.
    Any idea what your pedal force is with that setup? I'm trying to figure out if mine is typical or if I need to tweak it some. It seems that my TO bearing travel is in the right range at .637" per Novak, but it's more than Mcleod says you need. I guess I won't know til I drive it, but it's easier to change now than later.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  3. #13
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    I didn't know what it calculates out to, but the clutch pedal force feels nearly the same as all the other hydraulic bearing cars I've owned over the years, and my setup works even better than a most of those did. Yes, the reverse mount was a 6.25 ratio. I forgot after buying it like 20 years ago. My 55-brake pedal is 7:1. I originally set up the clutch with the recommended cylinder and it needed to be tweaked for a bigger one to not have such a long pedal travel was all I needed to do. The only friction point is the pedal pivot and just fluid power from there making it very smooth.
    Last edited by 55 Rescue Dog; 03-23-2023 at 03:25 PM.

  4. #14
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    I adjusted my clutch disengagement/take-up point by having someone turn a rear tire and adjusting the pushrod on the master cylinder. It was pretty simple and haven't touched it since.

  5. #15
    Registered Member chevynut's Avatar
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    I sent Centerforce an e-mail yesterday asking 1. how much does the throwout bearing have to move to disengage the clutch. 2. What is the force on the throwout bearing as the clutch is being disengaged. 3. What is the clutch finger ratio (pressure plate versus TO bearing movement) and 4. What is the clutch clamping force for my model. All questions relate to part number DF148552.

    I got a reply from a tech saying it took 3/8" of throwout bearing motion to disengage the clutch. That's all he answered. So I asked again about the force at the TO bearing and he said it takes 400-450 pounds to release it. He never did answer the other two questions, but they're not critical for my work. Getting technical info from these guys is like pulling teeth.

    So I only need 0.375" of TO bearing travel plus say .063" of free play which is 0.438" total, which is consistent with what Mcleod says you need. None of these companies are very clear about what their dimensions actually mean. I told centerforce that I assumed their 3/8" was after the TO bearing contacted the fingers, and he didn't acknowledge anything.

    According to these numbers, I'm over-driving my clutch per my calculations. I'm going to put a dial indicator on the clutch fork and see what I'm really getting there, and make adjustments based on that and how the clutch actually feels when I drive the car. I estimated I was at somewhere around 50 pounds at the pedal when I first depressed it (based on my gym workouts, LOL) and my calculations using the quoted 400-450 pounds at the fingers give me 46-52 pounds at the pedal.

    If I can drop the TO bearing stroke by using a smaller master cylinder, the pedal force will move lower accordingly. That assumes I have room to drop it and still maintain adequate TO bearing stroke.

    Another thing I did a little research on is whether or not the TO bearing should be in constant contact with the clutch or not, which affects how much stroke you need. Some guys say it's designed to rotate continuously and should last as long as the clutch. They say that by only rotating when the clutch is disengaging, it has to make contact with the fingers and get it spinning, which wears the clutch and the TO bearing face. The other camp says that the finger wear isn't an issue and they are adamant that that the throwout bearing should not spin all the time. Some say you need as much as 1/8" -0.3" of clearance!! Not sure which is better, but I've always assumed there should be a small gap between the TO bearing and the clutch fingers unless the clutch was depressed. RAM Clutches says their hydraulic throwout bearing always rides on the clutch fingers. Someone else said that new modern TO bearings, like modern wheel bearings, are made better and are packed with better grease and are made to spin constantly.

    Here's an interesting thread on the issue....

    http://www.clubcobra.com/forums/tran...s-contact.html
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #16
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    I didn't know what it calculates out to, but the clutch pedal force feels nearly the same as all the other hydraulic bearing cars I've owned over the years, and my setup works even better than a most of those did. Yes, the reverse mount was a 6.25 ratio. I forgot after buying it like 20 years ago. My 55-brake pedal is 7:1. I originally set up the clutch with the recommended cylinder and it needed to be tweaked for a bigger one to not have such a long pedal travel was all I needed to do. The only friction point is the pedal pivot and just fluid power from there making it very smooth.
    Do you know what clutch you have? if you have a 6.25" pedal ratio, a 7/8" master cylinder and a 3/4" slave cylinder the calculations say that you have a pedal force of 87-98 pounds with a 400-450 pound force at the TO bearing. That seems really high. Also with just 4" of pedal travel you'd drive the TO bearing forward .87" which is far more than the specified maximum travel. You must have a large air gap between the TO bearing and the clutch fingers.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #17
    Registered Member chevynut's Avatar
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    Bottom line in all my research on the subject is that clutcha pedal force in the 40-50 pound range is typical. I may try to figure out how to measure it just to see where I am. The math says 46-52.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  8. #18
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    Quote Originally Posted by chevynut View Post
    Do you know what clutch you have? if you have a 6.25" pedal ratio, a 7/8" master cylinder and a 3/4" slave cylinder the calculations say that you have a pedal force of 87-98 pounds with a 400-450 pound force at the TO bearing. That seems really high. Also with just 4" of pedal travel you'd drive the TO bearing forward .87" which is far more than the specified maximum travel. You must have a large air gap between the TO bearing and the clutch fingers.
    I don't have a slave cylinder since it is a hydraulic TO bearing. There is no free play. There is no pressure on it since it just gets pushed back out of the way like a brake caliper piston, so it isn't really spinning if at all, and has no load on it. I have no idea what the actual stroke on the bearing is and really don't care since it works perfect with travel room to spare as the clutch wears. All I would need to do at some point to keep the engage/disengage point the same is turn the master pushrod in as the clutch wears. Instead of spending a bunch of time trying to overcalculate everything, just hook everything up, adjust it and see how it works and make a change is needed after testing it. No math needed to measure pedal force, since I can just feel it and it is easy to push. I've driven a few cars with stiff clutch pedals and know what that feels like without any calculations. The clutch I'm using is a stock 10.5-inch diaphragm with the fingers bent on the ends, which is designed for a hydraulic release bearing. Also using a lightweight L-88 flywheel that I think is around 18 lbs.
    Last edited by 55 Rescue Dog; 03-25-2023 at 06:30 AM.

  9. #19
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    I don't have a slave cylinder since it is a hydraulic TO bearing. There is no free play. There is no pressure on it since it just gets pushed back out of the way like a brake caliper piston, so it isn't really spinning if at all, and has no load on it. I have no idea what the actual stroke on the bearing is and really don't care since it works perfect with travel room to spare as the clutch wears. All I would need to do at some point to keep the engage/disengage point the same is turn the master pushrod in as the clutch wears. Instead of spending a bunch of time trying to overcalculate everything, just hook everything up, adjust it and see how it works and make a change is needed after testing it. No math needed to measure pedal force, since I can just feel it and it is easy to push. I've driven a few cars with stiff clutch pedals and know what that feels like without any calculations. The clutch I'm using is a stock 10.5-inch diaphragm with the fingers bent on the ends, which is designed for a hydraulic release bearing. Also using a lightweight L-88 flywheel that I think is around 18 lbs.
    A hydraulic throwout bearing IS a slave cylinder. Many of the hydraulic throwout bearings are held by pressure against the clutch fingers and they turn constantly. Maybe yours doesn't. They're supposed to work assuming the master and slave are the same size (3/4") since 1" of travel at the master gives 1" of travel at the slave, as I understand it. If there's no play, where is that .877" of travel going that you pedal stroke of only 4" causes? Maybe you should have done some calculations first and you wouldn't have ended up with too much travel at the pedal. Now you end up with limited pedal travel and your must have some gaps somewhere because your throwout bearing only travels .688" max. Do some simple math and prove it to yourself. If you like it, that's fine. I prefer to design my systems to work using simple calculations. But those calculations are dependent on good information.

    I did assemble my clutch and tried it, and this thread was asking about what the pedal force should be. You gave me a bunch of numbers from your car that I thought might help, some of which were not right. As usual, you never even answered my original question, you just threw a bunch of stuff out there about your car which wasn't even right. Sources say an OEM 10.5" clutch takes about 400 pounds to actuate. Do your own calculation as to what your pedal force would be with your setup. I appreciate your "trying" to help but as usual your last comments are typical of how these discussions end.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  10. #20
    Registered Member chevynut's Avatar
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    Maybe I'm misinterpreting the size of the hydraulic throwout bearing slave's equivalent bore. I had assumed it was equivalent to a 3/4" master cylinder based on the stuff I read online.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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