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The Official 7.25" Clutch Thread

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  • The Official 7.25" Clutch Thread

    I thought I'd start another thread to put more definitive info on what it takes to fit a 7.25" clutch in an S-Chassis as I get it. I'll post up part numbers and info in this thread as I definitely confirm things.

    There's lots of good info in this earlier thread:

    http://www.nissanroadracing.com/showthread.php?t=3724


    I've also attached an Excel file to this post, where you can calculate what the approximate pedal pressure will be for different release pressures.
    Attached Files
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


    DefSport Koni Sleeve and Spring Perch Buy!!!
    http://www.nissanroadracing.com/showthread.php?t=5902

  • #2
    So my measurements were probably +/- 1/16" on the components, and the linkage ratios do change somewhat as the pivot point moves during travel. That plus the non-linearity of the PP spring accounts for the changing pedal pressure through its stroke. But the numbers should be roughly in the ballpark, and it gives a good idea of where you will be and what MC/SC area changes will do for the pedal pressure.

    For my case, I have a grey spring cover, so I'm looking at about 42 lbs on the pedal with stock stuff. It seems like that would be classified as a "stiff" pedal, but could probably be driveable. I'd estimate my previous ACT HD PP pedal force was in the 30-35 lb range before. It was stiff enough that it was fairly difficult to press by hand.

    Also interesting is that a slave cylinder in the 13/16" to 7/8" range would drop the pedal pressure down quite a bit (~35.5 lbs and ~31 lbs respectively).

    I need to look up the travel requirements, but the stock ratios give a pretty low ratio, 1" at the pedal moves the TOB 0.067". A hair over 1/16". The free height above the PP fingers has to be at least 0.200", so that's a minimum of 3" of pedal travel with stock stuff. I imagine for full disengagement it won't need much more travel than that, and the maximum bearing travel is 0.280". Is that after the TOB contacts the fingers, or MAX OVERALL travel? That seems like a lot if it's contacting the fingers, maybe that's max including the 0.200" of free height, so they really don't expect the TOB to travel more than 0.080" into the PP fingers when everything is brand new? That means the stock setup is actually pretty well suited for clutch travel vs. actuating the clutch if 0.280" max is all you can stroke it.

    There's still a little room to change the hydrualic ratio via a larger slave cylinder to tweak pedal effort and change the abruptness of the engagement slightly.
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


    DefSport Koni Sleeve and Spring Perch Buy!!!
    http://www.nissanroadracing.com/showthread.php?t=5902

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    • #3
      Just found the nismo slave is listed as 20.5mm opposed to 19.05mm for stock.

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      • #4
        The .24" travel max listed by tilton was specified as after the bearing has contacted the fingers, the free play before the bearing contacts fingers is listed as .160"-.240"

        so total travel of .400" - .480"

        Comment


        • #5
          Seems like a lot of travel on this tiny clutch. That's about 7-1/8" of stock S13 pedal travel for the 0.480" max TOB movement.

          I'm guessing the clutch disengages almost immediately after the PP pulled up, and the max travel is really a "never go beyond this limit" value. Seems like you would only want a little bit of travel beyond disengagement when new.
          '18 Chevrolet Volt - Electric fun hatch for DD duty!


          DefSport Koni Sleeve and Spring Perch Buy!!!
          http://www.nissanroadracing.com/showthread.php?t=5902

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          • #6
            Originally posted by Def View Post
            Seems like a lot of travel on this tiny clutch. That's about 7-1/8" of stock S13 pedal travel for the 0.480" max TOB movement.

            I'm guessing the clutch disengages almost immediately after the PP pulled up, and the max travel is really a "never go beyond this limit" value. Seems like you would only want a little bit of travel beyond disengagement when new.
            Thats exactly what it is, and the little bit beyond disengagement is listed, I copy/pasted it into the other thread, it says to jack the car up, adjust it till it releases, then another .25" of pedal travel.

            Comment


            • #7
              Good stuff, Def.

              In the other thread you guys had briefly mentioned different contact diameter throw out bearings so I did some quick calcs using rough dimensions pulled from the Tilton Drawing 4075 (http://www.tiltonracing.com/pdfs/82.pdf). Without know what they-would-call ratio pressure plate shown in the drawing you get a mech ratio of 2.14 using the 44mm nominal contact diameter shown. If you drop this to a 40mm contact diameter bearing you decrease the release pressure by ~7%. This is ignoring spring rates and release distance, however.

              Maybe something you want to book keep in your spreadsheet?
              S12 || N13 || S13 || B16

              Comment


              • #8
                If it's strictly a track car and doesn't make a ton of torque the QM 5.5" works great also!



                NASA Time Trials TT3


                BTW I work for Garrett

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                • #9
                  I figure the 7.25" will stand up to occasional street driving much better than a 5.5".


                  Btw, what's the release load of your clutch and what are you doing for a tob?
                  '18 Chevrolet Volt - Electric fun hatch for DD duty!


                  DefSport Koni Sleeve and Spring Perch Buy!!!
                  http://www.nissanroadracing.com/showthread.php?t=5902

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                  • #10
                    Originally posted by Def View Post
                    I figure the 7.25" will stand up to occasional street driving much better than a 5.5".


                    Btw, what's the release load of your clutch and what are you doing for a tob?
                    Oh yeah........the 5.5" is not a street clutch!

                    I prefer to winch the car on the trailer now and especially if the ramps/trailer are wet. When the clutch is cold you can slip it a little but when it's at operating temp......forget it; churp the tires or stall it.

                    Not sure about the release load......but it's not bad. I'm using a QM TOB for a 240Z with a longer Nissan TOB carrier. I can dig up the part number of the carrier if you want. There is also one that is shorter than stock.
                    NASA Time Trials TT3


                    BTW I work for Garrett

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                    • #11
                      Is the Fidanza flywheel the only option? I'm assuming it is aluminum with a replaceable steel friction service like their other flyweels?

                      I've found instances of people getting custom 7.25" discs made by Clutchnet and others with Marcel springs and sprung hubs. Might be a decent option for making this whole deal a little more street/slipping friendly? However it also adds another set of variables, and setting up the pedal and slave when you have to contend with Marcel springs compressing seems a little more annoying too.
                      Examples:
                      http://www.spruellmotorsport.com/clu...ic-p-2282.html
                      Last edited by turtl631; 04-23-2012, 11:49 AM.
                      ~1992 240SX, SR20/Koni track day car
                      ~2016 M3, daily driver

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                      • #12
                        That would be great... I'll probably be going that same direction soon, whether it's with the stock tranny or a dog box..
                        Originally posted by SoSideways
                        I don't care what color they are as long as they are LONG AND HARD.
                        '04 G35 Sedan 6MT- The DD
                        '96 240SX- The Track Toy

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                        • #13
                          Originally posted by Matt93SE View Post
                          That would be great... I'll probably be going that same direction soon, whether it's with the stock tranny or a dog box..
                          Yea it's pretty nice from that standpoint because you can just swap disks to go to any gearbox.
                          '18 Chevrolet Volt - Electric fun hatch for DD duty!


                          DefSport Koni Sleeve and Spring Perch Buy!!!
                          http://www.nissanroadracing.com/showthread.php?t=5902

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