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Grinding shifting gears

Discussion in 'Mondial' started by yelcab, Apr 28, 2020.

  1. yelcab

    yelcab F1 Veteran
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    Nov 29, 2001
    9,829
    San Carlos, CA
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    Mitchell Le
    Mondial 3.2
    New slave cylinder, re-using the Ferrari fork
    New clutch plate, new pressure plate, new throw-out bearing, new pilot bearing
    Now it grinds going into gears while engine is running, as it the clutch is not disengaging the gearbox from the flywheel.
    Already bled the clutch circuit twice. Pedal feels very firm.

    Any ideas as to what to try next ?
     
  2. yelcab

    yelcab F1 Veteran
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    Nov 29, 2001
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    Additional information.
    I found some specs on the clutch in the WSM.

    B. Length of slave cylinder rod at rest: spec to be 102.5mm
    A. Maximum stroke travel with new clutch: 20.5mm
    C: Stroke travel when clutch is worn out: 13.3mm

    What I have now:
    B: length of rod at rest: 99 mm (pretty close)
    A. Maximum stroke travel 18mm (less than spec, but way more than minimum when clutch plate is worn out)

    I think at these numbers the clutch should disengage the flywheel and the gears should shift without grinding. Don't you?
     
  3. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,853
    Can you push the car while in gear with the clutch pedal depressed ? (motor turned off)
     
  4. yelcab

    yelcab F1 Veteran
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    More updates.

    After the last bleed, and futzing about, the gearbox will shift into all forward gears with engine on and clutch pedal depressed all the way down. Reverse still grinds but … even my 328 will grind sometimes into reverse so …

    I think the clutch plate measured in a 9.3mm (unloaded) needs to wear in a little bit so that the pressure plate does not have to travel so much to disengage.
     
  5. Wade

    Wade Three Time F1 World Champ
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    Mar 31, 2006
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    EastMemphis likes this.
  6. yelcab

    yelcab F1 Veteran
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    Nov 29, 2001
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    Wade,

    The old one came out looking like the deep dish on the left of your picture. I cannot remember if the new one is the same or not. The replacement unit is a non-Ferrari slave cylinder and it can very well be the problem of not having enough travel, 18mm vs 22.5mm spec. The shortened travel may be Ok for an old clutch but not enough for a brand new thick clutch plate and reverse gear.

    Effing bummer.
     
  7. Wade

    Wade Three Time F1 World Champ
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    Mar 31, 2006
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    Mitchell, check out the thread that I linked to, lots of great comments and ideas if you haven't seen it. Don't forget to expand the quoted comments...

    Also, it appeared that my slave cylinder was the wrong one and that someone shortened the length of the rod to fit.

    [​IMG]

    Tijn had an elegant fix that allows a wider range of slave cylinders.

    Image Unavailable, Please Login
     
  8. yelcab

    yelcab F1 Veteran
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    Nov 29, 2001
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    Having a longer rod, how does that change the total travel length of the slave cylinder? Isn't the amount of travel dependent on the piston of the slave cylinder?
     
  9. yelcab

    yelcab F1 Veteran
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    Wade

    I have been thinking through this whole scenario as well as reading through the thread you provided.

    The source of the problem is the non-OEM slave cylinder which is of a different design and therefore does not provide enough travel to fully release the brand new clutch plate. My measurement of the travel is 18mm vs a specification of 20.5 mm for a difference of 2.5mm, slightly more than 10% of the travel spec. The difference in design may have been the slightly larger bore of the non Ferrari slave which explains the shorter travel for the same volume of fluid being displaced.

    The elegant solution is to buy a Ferrari spec slave cylinder at 5x the price. The non elegant solution is to wait for the new clutch plate to wear down some so that the pressure plate does not have to travel as much in order to release its grip on the clutch plate against the fly wheel. This also explains why the new non Ferrari slave cylinder I put into this car 2 weeks ago did not result in reverse gear grinding because the old clutch plate was in there. It was so worn out, any slight push on the clutch pedal would release it from the flywheel. It also explains why a longer push rod at the slave cylinder did not work for you.
     
  10. FerrariJB

    FerrariJB Karting

    Jun 8, 2019
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    FerrariJB

    Make sure all air is out. From my own experience I know that bleeding is not easy. I managed to get the last mm of stroke by pushing the slave up and then bleeding again. A little air came out regularly, and another mm stroke. The maximum stroke is very important.
     
  11. yelcab

    yelcab F1 Veteran
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    I bled using the motive pressure bleeder. The pedal is very firm. But, I will certainly do another bleed since it is pretty easy.
     
  12. Wade

    Wade Three Time F1 World Champ
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    It was unfortunate for me that I was unable to determine the baseline (at the time) since neither the slave or the rod were of OE specs. Ultimately I just gave up by buying OE (and didn't measure their specs).

    But yeah, Ricambi has an OEM slave for $365.26. As you know, time is money. ;)

    https://www.ricambiamerica.com/107867-clutch-slave-cylinder.html
     
  13. yelcab

    yelcab F1 Veteran
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    #13 yelcab, Apr 29, 2020
    Last edited: Apr 29, 2020
    Ain't that the truth. I will bleed it one more time before recommending "buying OEM or living with it"
     
  14. yelcab

    yelcab F1 Veteran
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    Nov 29, 2001
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    Let me close this thread off. I ended up "adjusting" the rod about 2.5mm longer to see if it would meet specs under actual use. It did absolutely nothing at all. The non-OEM slave cylinder is slightly different from the factory one and will only move so much against the master cylinder. I was still 2mm too short for a full stroke. So the distance moved is entirely dependent on the master and slave cylinders.

    While messing about with this, the new slave threw up all of its innards because it does not have a snap ring like the old one. So, after cleaning up the mess and reassembling the slave cylinder, bled the whole circuit again, and now the car will ginger just engage all gears with the clutch pedal down all the way to the floor.

    I do expect it to get better as the new clutch plate and pressure plate wear in a bit. Lesson learned, if you want original, buy original.
     

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