clutch disc hardness

Discussion in 'PSI Superchargers Tech Questions' started by mark6052, Feb 2, 2013.

  1. mark6052

    mark6052 Member

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    I'm buying new clutch disc for my program. a 6.50 et blown alcohol car. I use a 10" pedal clutch. I have found some disc that have a rockwell rating of r-57 all the way to a r-69. Without giving away some secrets what is the "normal " spread of hardness to use. or how soft .
     
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  2. hemi altered 378

    hemi altered 378 Blown Altered

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    low to mid 60's works great for me
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    62 to 65 will work great for your application
     
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  4. WIZBANG

    WIZBANG Member

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    What scale do you use ?
     
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  5. Mike Canter

    Mike Canter Top Dragster
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    The clutch industry standard is the Rockwell "S" scale, 100 kg load, .500" ball. Call any clutch disc company and they will all use and talk the same standard.
     
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    Last edited: Feb 3, 2013
  6. mark6052

    mark6052 Member

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    thanks for the info. for some reason the last couple disc my friend got they were marked with an R 57. They were much softer than he had ran before and caused a lot more slippage until we changed the static pressure. :eek: Learning as I go.
     
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  7. Mike Canter

    Mike Canter Top Dragster
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    You need to make sure you specify a hardness range when you buy discs.
     
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  8. mark6052

    mark6052 Member

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    I guess that's part of my question. how big a spread? 10 points I assume is to much. 3-5 would be max? So far I haven't had tire shake for my driver. so far :D but I'll get him.:rolleyes:
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    You have to give the clutch supplier a little spread. Sometimes they can give you them with all the same number. 62 to 65 is a good spread.
     
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  10. JustinatAce

    JustinatAce Member

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    Hardness measurements on the best machines are only good for +/- 2 when we get to the Rockwell "s" scale.. The calibration block even says it's hardness was +/-1 when it was certified.

    Hardness is a good tool for wear, but primarily just another tool for consistency. Typically takes a 7-10 point spread to really notice a difference depending where you start from. If you change hardness 4-5 points somewhere in the 60's and notice a huge difference, your discs are either not as advertised or you have something else going on. If you go from high 70's to low 60's you will notice a difference. From mid 60's to mid 50's you'd see a difference. Low-Mid 60's just seem to offer the best balance of wear, aggression and predictable behavior for almost every application unless you're wearing too much clutch, then you'd go harder. Different mfg's have different behaviors at different hardness too, so just remember, the right spread is the one you can get to haul ass.
     
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  11. Frontenginedragsters

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    Clutch hardness

    Justin:
    Can you give some material specs on floaters?
    Thanks: Matt
     
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  12. JustinatAce

    JustinatAce Member

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    Different companies use different materials for floaters, but typically they are some form of low/mild carbon steel in a normalized state(not heat treated or annealed). Biggest reason being you don't want them to get too brittle. SFI material specs are pretty specific on minimum tensile strength, but probably more importantly percentage elongation to withstand the forces without breaking/cracking.

    Also a good reason to cool your clutch and clutch pack with nothing but air(fans are fine). Sometimes if you hit parts with brake clean while still pretty hot, you can actually quench the part a little. Air cooling lets the parts normalize, if you cool them down too quickly you can actually have a heat treating effect on the parts which can change that percentage elongation. Anybody who has hit the flywheel or hat and donut a little too quick with brake clean between rounds and has heard that "ting" noise, that's a good sign it's still too warm.
     
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