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Clutch not disengaging (spec stage 3+)

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    Clutch not disengaging (spec stage 3+)

    Somewhat looking for input, but also somewhat just posting this so the information is available to others.

    Description of the problem:
    Harder than it should be to get into first gear from neutral at a stop, or into first while coasting down without rev matching (clutch pedal down). When pushing the shifter into first in the car will creep a little bit on a flat surface. Engagement is lower than with previous clutch (UUC 9 button "cerametallic") but not excessively low. Before the transmission came off for a second time the car was borderline undriveable. Very low clutch engagement, very difficult to get into first gear.

    What has been done:

    First go:
    • Flywheel resurfaced, second time since I have owned it, 0.013"/0.33mm step machined, machine shop removed roughly 0.015"/0.38mm.
    • New clutch and pressure plate (spec stage 3+)
    • New Sachs release bearing
    • New clip
    • New brass pivot (taller than OE plastic one by 3mm)
    • New pilot bearing (FAG brand)
    • Flushed clutch hydraulics (both cylinders and lines ~4 years max and 50-70k old) bled by pushing the slave cylinder repeatedly with the hose held at the highest point, a method prescribed by a mechanic familiar with E30s.
    • Removed aftermarket adjustable clutch stop and replaced it with a bolt that fits in its place and is much shorter
    • Clutch pedal eccentric adjusted so that the pedal is high


    Second go:
    • Clutch disc runout measured crudely at 0.34mm by measuring height from hub to disc at each "pad", out-of-round at 0.8mm by measuring diameter from spline flat to outside edge
    • Pressure plate inspected visually and with straight edge
    • New release fork, after cleaning the old one was found to be worn by about 1mm at the release bearing contact points and 1-2mm at the pivot/slave cylinder pushrod contact point. I did not notice any bends.
    • Bled clutch hydraulics by pushing the slave cylinder repeatedly with the hose held at the highest point


    Misc info:
    Flywheel 12-12.2mm (going by memory) from step surface to top of ring gear, using a flywheel of rusty but otherwise ok condition ring gear to back surface distance was measured at 18.4mm, yielding a total flywheel height of 30.4-30.6mm. This is below the minimum spec given in the Bentley manual:
    Originally posted by Bentley manual minimum flywheel thickness
    6-cylinder engine, 1985-1990, 32.0mm (1.260in)
    The rusty flywheel was a dowel pin donor, its height measures in at 31.27mm floor to lower step and it is of unknown history but presumably has been resurfaced multiple times judging by the measurement. Spec clutch representative was unable to provide an acceptable runout specification and only could offer troubleshooting help and to take the clutch back for inspection with a turnaround that is unacceptable given my car's DD status.



    My best guess at this point is that the Bentley spec of 32mm is correct and the clutch drag is the result of the flywheel being 1.4mm too short now. I'm going to extend the slave cylinder pushrod (on recommendation) by 6mm but do not expect that to make any difference, if my reasoning is correct if I was reaching the end of slave cylinder travel it would be pushing past the seals and leaking.
    Last edited by varg; 07-03-2019, 04:44 PM.
    @turbovarg
    '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
    [b u i l d]
    [Car of the month: April 2018]

    0c8b7c9527af628a346878feb14bf757

    #2
    hey i think i may have had a problem like yours.

    it would drive fine sometimes
    and then all of a sudden it wouldn't go into first and when it did
    there was some dragging so it would creep forward with the pedel down
    or turning it off and putting it in 1st would jump the car even if the pedal down.

    turned out to be my clutch master. hope that's whats going on here.
    i was thinking the same thing maybe extending the rod would work but no need.

    Comment


      #3
      I extended the pushrod by 6mm and as I expected it had no discernible effect. My clutch hydraulics are all new within the last 4 years/70,000mi tops. I previously tested slave cylinder pushrod throw before taking the transmission off a second time with the method in the Bentley manual and got a result of 22mm, which is over the minimum spec of 20mm. I will color the pushrod and test again, but I am fairly certain the hydraulics are not the issue. Luckily the problem did not get significantly worse during my 45min commute today and the car is driveable, just not perfect, and it's annoying to spend money on good parts instead of cheap junk and have a problem.
      @turbovarg
      '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
      [b u i l d]
      [Car of the month: April 2018]

      0c8b7c9527af628a346878feb14bf757

      Comment


        #4
        You got the correct throw out bearing carrier? I have previously had troubles using a gearbox designed for dual mass flywheel flywheel with a single mass flywheel. Not enough throw as something was different about the gbox from a dual mass flysheel car that made it so the throw out bearing wasn't pushed far enough and didn't disengage the clutch fully.
        Last edited by e30davie; 07-05-2019, 05:49 PM.

        Comment


          #5
          Yeah, it's the right one. The car previously had an aftermarket clutch which worked fine with the exact same setup, this clutch should be a bolt on affair with OE parts according to the manufacturer. At this point I'm guessing either the disc or pressure plate is in some way out of spec, it was quite frustrating that the manufacturer was unable to provide runout or out of round tolerance specifications when I provided the rep with my measurements. I expect better when directly calling the manufacturer.
          @turbovarg
          '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
          [b u i l d]
          [Car of the month: April 2018]

          0c8b7c9527af628a346878feb14bf757

          Comment


            #6
            figure it out?
            i still think it's the master because i was messing with the rod on the slave
            trying to figure it out but it was the master.

            Comment


              #7
              It's getting better with time, 410 miles on the clutch now and the drag is barely there. This points to the measured runout being the issue and not my relatively recent clutch hydraulics. The recommended break in period is 400-500mi, hopefully things continue on this path and I have no issues by 500mi.
              @turbovarg
              '91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
              [b u i l d]
              [Car of the month: April 2018]

              0c8b7c9527af628a346878feb14bf757

              Comment

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