C2 new LUK clutch but odd pedal feel - NCRS Discussion Boards

C2 new LUK clutch but odd pedal feel

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  • Timothy B.
    Very Frequent User
    • January 1, 2004
    • 438

    C2 new LUK clutch but odd pedal feel

    I finally managed to get my new LUK Rep Set clutch set installed and the trans back in. No easy task on my 67!! When I had the assemblies back together and tried out the clutch, I was surprised and disappointed at the feel of the clutch pedal. I am hoping this forum might offer some advice before I continue to reassemble things such as shifter, exhaust, etc. The car has not be started or driven with the new clutch setup yet.

    The clutch I replaced was a GM unit from the mid 80's - all GM parts. The clutch feel was good, with even force required to depress throughout the travel. Per discussion on this forum, I went with the LUK replacement set. I also replaced my correct 1 3/8" ball stud with a new 1 1/2" unit in an attempt to allow for more clutch adjustment. My adjustment had always been at the very end of the push rod from the clutch pedal. The new ball did indeed give more adjustment travel just as expected.

    The new set feels very different. The force seems higher to depress, and is not even throughout pedal travel. Feels almost like an over centering mechanism, with less force in the middle of the travel area. My concern is that the force seems high in the area of the travel where I would expect engagement to occur, which would make modulating the engagement very difficult. My basic concern is should I expect the feel of the clutch to change once the car has been run and has a few miles on the new setup, or should I change back to the GM parts now(which weren't worn out, replace primarily because I figured I should while I had the trans out for other reasons). Does anyone have any comments on the clutch pedal feel and evenness of force for the LUK setup as compared to the GM parts? Also, is there any reason to think that the change in ball stud alone would cause the change in pedal feel I am describing??
  • Mike McKown

    #2
    Re: C2 new LUK clutch but odd pedal feel

    I'll go with your last sentence. The longer stud could effectively reduce your leverage at the top of the pedal stroke and increase leverage as the clutch pedal goes down. Just speculating of course.

    It would be interesting to see what happened if you put your old stud back in and checked it out.

    Comment

    • Timothy B.
      Very Frequent User
      • January 1, 2004
      • 438

      #3
      Re: C2 new LUK clutch but odd pedal feel

      Hum. Put the old stud back in. That is ALLOT easier said than done... I cringe at the thought of it! The difference in length of the two studs is only 1/8", so I have a hard time imagining that is the culprit for the difference. I will wait for some more input from the forum before I dive into that.

      Comment

      • Jim T.
        Expired
        • March 1, 1993
        • 5351

        #4
        Re: C2 new LUK clutch but odd pedal feel

        Is the throwout bearing properly installed in the fork and the old and new throwout bearings the same length?

        Comment

        • Timothy B.
          Very Frequent User
          • January 1, 2004
          • 438

          #5
          Lesson learned!! The ball stud is the difference

          I figured out how check the ball stud theory without having to disassemble everything. I just slid the trans out slighting to gain access to the Allen slot on the back of the ball stud, and loosened it enough to simulate the shorter stud. I slid the trans back in place and tried the clutch and low and behold there was a big difference! Actuation force was much more even and didn't have the over center feel. Clearly, GM used the shorter ball stud for a real reason. I figured out how to replace the longer stud (pn 3729000) with my original 1 3/8" stud (pn 3887159) in place and proceeded to mount everything back up. All other clutch parts are correct GM parts for the car, which is a 67 SB.

          There is a significant difference in clutch actuation feel with the (correct for the car) 1 3/8" clutch fork ball stud. Apparently, the minor difference in geometry in the linkage caused by the stud length has a big effect on clutch feel, with the shorter stud being much more even and smooth. The only reason I was changing ball studs in the first place was to gain adjustment range in the linkage, per an earlier thread (linked below) the consensus was that switching to the longer stud might correct the adjustment issue and have no other consequence. Well I tried that, and there IS a negative consequence as outlined above. I am sure glad I stopped to investigate this before I reassembled everything! By the way, the LUK clutch is still stiffer than the one I replaced, but I shall see how that feels once I have the car running and driving again.




          Comment

          • Mike McKown

            #6
            Re: Lesson learned!! The ball stud is the differen

            Glad to hear you checked it out, Timmie boy. I don't feel too stupid now. I personally wondered why everyone was concerned about the lack of adjustment when the fact of the matter was, if the clutch wore, it would eat up threads on the adjustment rod. Not the other way 'round.

            Comment

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