Just joined? Please introduce yourself.
Page 1 of 3 123 LastLast
Results 1 to 10 of 29

Thread: Clutch pedal force

  1. #1
    Registered Member chevynut's Avatar
    Join Date
    Nov 2011

    Member #:115
    Location
    Fort Collins, CO
    Posts
    10,835

    Clutch pedal force

    As I mentioned in my build thread, my clutch pedal force is higher than I expected it to be. I may be spoiled by the ease of effort to depress the clutch in my Porsche, but i believe it has a dual disc clutch and pedal effort is really nice. I have read posts here from a couple of members complaining about pedal effort in their tri5 cars.

    I also went out and depressed the clutch pedal in my 56 parts car and it's a lot lighter than my Nomad. However, it has a 6-cylinder engine and the clutch is smaller at 9.5", and it's a stock setup. I can't find anything in the 56 Chevy specs about clutch effort/ force needed at the clutch fingers. BTW, Chevy did offer a heavy duty 11" clutch in both 6-cylinder and V8 cars.

    I'm using a Centerforce Dual Friction clutch setup, disc and pressure plate. It's an 11" diaphragm type clutch and they claim "light pedal effort". I'm now thinking that maybe I should have investigated dual disc clutches more at the time I got my setup.

    I designed my pedal and hydraulic clutch system to give about .6-.65" of throwout bearing movement including about 1/16" of gap between the TO bearing and clutch fingers. This is per Novak Conversions, where I got the info. They state that it takes about 0.550" of TO bearing travel to disengage the clutch. Then they add the .063" to get 0.613" total travel needed. They did tell me that their testing was with a new, not broken in clutch disc so it's likely conservative.

    McLeod says "Typically with OEM applications the throw-out bearing travel is.440”-.445”. I've read other sources with conflicting information.

    Have any of you actually measured your clutch pedal force, or fork travel, or have info on what it should be?
    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. #2
    Banned
    Join Date
    Nov 2015

    Member #:2775
    Posts
    1,426
    On my Camaro I used a Howe hydraulic throwout bearing which has a travel of .688 inches and it has been working perfect for 10 years. Every pivot point adds resistance to the pedal force and the hydraulic bearing eliminates 3 pivot points. It's never needed adjustment and the pedal pressure is smooth and light, easy to modulate with perfect travel. I even had to go to a 7/8' master cylinder to get less travel and it added little to the pedal force using a 7:1 pedal.

    Throw Out Bearings - Howe Racing Enterprises, Inc

  3. #3
    Registered Member chevynut's Avatar
    Join Date
    Nov 2011

    Member #:115
    Location
    Fort Collins, CO
    Posts
    10,835
    Quote Originally Posted by 55 Rescue Dog View Post
    On my Camaro I used a Howe hydraulic throwout bearing which has a travel of .688 inches and it has been working perfect for 10 years. Every pivot point adds resistance to the pedal force and the hydraulic bearing eliminates 3 pivot points. It's never needed adjustment and the pedal pressure is smooth and light, easy to modulate with perfect travel. I even had to go to a 7/8' master cylinder to get less travel and it added little to the pedal force using a 7:1 pedal.
    Thanks for the info. I thought about using a hydraulic TO bearing but decided against it after seeing so many of them leak in other projects. Maybe you got lucky. I didn't want to be pulling the transmission out again and again like one of my friends had to do. I also read a lot of horror stories online about leaking problems with them, even the Howe ones. The hydraulic TO bearing only reduces a master/slave setup by one pivot point, which is the fork/ball which does have a lot of force on it. Another friction location using a fork is the TO bearing sliding on the transmission yoke but I don't think that's significant since it's axial movement. It does all add up though.

    I used an external slave and a Lakewood 15500 clutch fork with a lakewood pivot ball. Yes that linkage adds a friction point from a hydraulic TO bearing, but it was a tradeoff to deal with any leaks. I can easily change the slave if it fails, and a simple fork/pivot is a proven design over decades of use. The rest of my linkage from the pedal to the master cylinder has heims and the bellcrank is on bushings. I'm not sure, but I don't believe at this time that friction in the clutch linkage is a big problem.

    Howe says the maximum travel for their 82876 GM TO bearing is .536" and their 82870 is .688" so you must have the latter. Typically a hydraulic TO bearing uses a 3/4" master cylinder for a 1 to 1 ratio.

    Also going from a 3/4" master cylinder to a 7/8" one INCREASES the travel of the TO bearing. So it makes no sense to increase the MC size to get a shorter TO bearing stroke.

    You probably have around 6" or so of usable pedal travel, and that means you have .86" of pushrod travel at the master cylinder with a 7 to 1 pedal. The TO bearing should move that same amount with a 3/4" MC. To decrease the stroke at the TO bearing you'd have to go to a smaller bore MC.

    It really doesn't matter how you get there, mechanically or hydraulically, as it's the amount of work done that matters. So if you need to push say X pounds Y" at the clutch fingers you need to do X*Y in-lb of work.

    I calculated my TO bearing throw based on actual measurements and it's theoretically .637" now with 5.5" of usable pedal stroke. With an assumed 400 pounds needed at the pressure plate, my pedal force is theoretically 46 lb ignoring any friction. I haven't figured out a way to measure it yet but some kind of spring scale might work.
    Last edited by chevynut; 03-22-2023 at 12:03 PM.
    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

  4. #4
    Registered Member chevynut's Avatar
    Join Date
    Nov 2011

    Member #:115
    Location
    Fort Collins, CO
    Posts
    10,835
    By the way if you read the 2 reviews on that 82870 Howe TO bearing, they're both complaining about leaks.

    https://howeracing.com/collections/throw-out-bearings/products/82870-hydraulic-throw-out-bearing-stock-clutch


    The other issue I was concerned about was trying to adjust the clutch if needed, and using shims wasn't attractive to me. Once it's installed, you get what you get. I do understand they're somewhat self-adjusting once they're set up as the clutch wears. I see pros and cons.
    Last edited by chevynut; 03-22-2023 at 12:06 PM.
    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

  5. #5
    Registered Member
    Join Date
    Apr 2012

    Member #:571
    Posts
    4,671
    I don't think the hydraulic t/o bearings used in OEM GM applications have a big complaint list regarding leaks. Pretty much anything with a T56 has one, as well as S10s etc. I don't know what full size pickups with manual transmissions use, but they're also rather rare. The T56 t/o bearings are shimmed for initial setup, similar to the aftermarket t/o bearings. I don't regard that as a big deal.

  6. #6
    Registered Member chevynut's Avatar
    Join Date
    Nov 2011

    Member #:115
    Location
    Fort Collins, CO
    Posts
    10,835
    I'm going to assume you actually went to a smaller .625" bore master cylinder to reduce the TO bearing travel. Also, I think you have Tilton pedals and they only have a 5.0 or 6.2 ratio available as far as I can tell.

    So if you have 6.2:1 pedal ratio and a .625" MC bore you would have an overall ratio of 8.95 which is about the same as mine at 8.64. So our pedal forces with the same clutch would be almost the same, with only a 3.5% difference. With an assumed 400 pounds at the pressure plate, you would theoretically have 44.7 pounds at the pedal, and I would have 46.3, both assuming no friction.
    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. #7
    Registered Member chevynut's Avatar
    Join Date
    Nov 2011

    Member #:115
    Location
    Fort Collins, CO
    Posts
    10,835
    Quote Originally Posted by Rick_L View Post
    I don't think the hydraulic t/o bearings used in OEM GM applications have a big complaint list regarding leaks.
    Bruce went through 3 OEM GM throwout bearings on his LS engine before he got one that didn't leak. He's the one who finally changed my mind on using one. I know there's millions in use but there are lots of complaints online about leaking throwout bearings, some OEM. I opted to avoid the issue altogether and the master/slave setup was used successfully for many years on GM and many other cars. What did you use?
    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. #8
    Banned
    Join Date
    Nov 2015

    Member #:2775
    Posts
    1,426
    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.

  9. #9
    Banned
    Join Date
    Nov 2015

    Member #:2775
    Posts
    1,426
    A good way to ruin a hydraulic release bearing is to let it overtravel, which is most likely to cause a leak banging on the snap-ring stop from not having a lower pedal stop that a lot of people don't consider important, but it is.

  10. #10
    Registered Member
    Join Date
    Apr 2012

    Member #:571
    Posts
    4,671
    What did you use?
    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.

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •