Clutch won't disengage

Discussion in '6.9L IH & 7.3L IDI Diesels' started by jim x 3, May 11, 2018.

  1. jim x 3

    jim x 3 1988 F-350 DRW

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    For some time, my clutch pedal would not immediately return to "pedal-up" position, mainly when shifting out of gear when coming to a stop. Pedal would come to about 75% off the floor and then pop to 100% off the floor after a few seconds.

    I figured the problem was mechanical in the pedal linkage under the dash, but everything looked OK, including the master and slave cylinders and fluid level in the master reservoir. Today the pedal failed to come all the way up while shifting between gears. The problem gradually grew worse while driving until the pedal would not come up at all. At this point I found my clutch would not disengage. I managed to drive the rest of the way home without a clutch, forsaking 5th gear.

    Truck is at 270,000 miles. History prior to 235,000 miles is unknown. There have been no prior clutch related problems or repairs since 235K.

    I have not had a chance to further diagnose the problem. Has anyone else suffered these same symptoms?

    Thanks for the help.
     
  2. DrCharles

    DrCharles Full Access Member

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    My first thought is that you have a leak in your clutch hydraulics somewhere. But if the level in the reservoir isn't going down, it has to be something mechanical loosening. Is it still full?
     
  3. Macrobb

    Macrobb Full Access Member

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    The problem is the spring in the pedal box pushing down on the pedal too much if it doesn't return all the way - at that point, it will slowly bleed down as the hydraulics "auto adjust". Fix the mechanical side of it such that it returns all the way.
    Check firewall flex, bushing wear on pedal box to MC, and if needed, do the 'heim joint mod' and lengthen the MC cylinder rod as required.

    I just ran into this on an '84 we were converting from a c6 to ZF, and we ended up being able to pull the short lever(the one with the pin that the MC rod attaches to) and found that it was splined. Reinstalled it one spline 'down' and the problem was fixed.
     
  4. jim x 3

    jim x 3 1988 F-350 DRW

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    Hydraulic Problem.

    Firewall was previously reinforced.

    This morning I found some minor fluid leakage on the slave cylinder. Master cylinder reservoir was dry - there is a rubber funnel-shaped dingus in the mouth of the reservoir that stays full of fluid. This deceived me in thinking reservoir was full. Feeling dumb.

    So I may have had a low and lowering fluid level for a long time. Or I may have a good leak at the slave.

    I imagine I will have to bleed the hydraulic system now. I haven't found a bleed screw on the slave.

    Thanks for your help on this.
     
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  5. Mulochico

    Mulochico Supporting Member Supporting Member

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    I had something similar, it ended up being the housing that the pivot rod for the clutch peddle went thru. It had elongated and had some binding when it moved in the housing. Got one from LMC that has worked well for over 5 years w/o noticeable wear.
     
  6. Macrobb

    Macrobb Full Access Member

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    Bleed screw on the slave is a small allen screw on "top" of the slave cylinder , right at the back end of it(opposite where the rod comes out).
    You pretty much push down the pedal(so the pedal box spring is pushing it down), go under there and loosen it a little so fluid/air comes out, re-tighten, then pull the pedal back up and repeat.
    You always want the screw closed when pulling the pedal back up. Once you get only fluid out of the bleeder, you will still have no "pedal feel" - it'll go straight to the floor with no resistance.
    At this point, you just pump it a bunch(I like to hold for a half-second at the bottom and top of each stroke) until you get a normal pedal feel. It'll start out with no resistance and gradually get more and more as you "pump" it up.
     
  7. jim x 3

    jim x 3 1988 F-350 DRW

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    Filled the reservoir with DOT 3 brake fluid. The pedal pumped up without bleeding. I'm surprised there is no nipple on the bleed port.

    Firewall is OK and there are no leaks at the master. Clutch pedal springs both up and down. I will (soon) need to do the heim joint mod. The plastic bushing is a half moon on the non-pressure side and the only thing holding the banjo on the stud is the big flat on the pressure side of the stud.

    So symptoms are gone and its time for a test drive. At about 7 miles the lazy pedal and constant clutch engagement returned. Checking below, there is a good leak on the slave cylinder. It seems to be coming from the end with the line attachment. Master reservoir is now empty again.

    So it looks like a slave cylinder rebuild is needed. Maybe I'll do the master and heim joint at the same time.
     
  8. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Boy that's almost an understatement. It always seemed to take hours of pumping when I did it. I know it didn't, but it sure did take a loooong time.
     
  9. jim x 3

    jim x 3 1988 F-350 DRW

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    Did the slave replacement only.

    Replaced just the slave cylinder. Slave clip comes off the transmission bracket with a large screwdriver as lever. Roll pin holding line in place comes out with a 3/32" pin punch. Bleed screw is a 5/32" allen hex - no nipple. New slave was Chinese aluminum, old was USA plastic. I was unable to find a rebuild kit - I guess that's not done by mechanics anymore.

    No leaks yet. I'll still need to do the heim joint mod at some point.

    Regards,
     
  10. chris142

    chris142 Full Access Member

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    Replace both hydraulic parts together. If you dont you may have the other one fail soon. Mine did.
     

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