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Thread: Why do we need a slave and master clutch cylinders?

  1. #1
    Senior Member Totally 80s's Avatar
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    Why do we need a slave and master clutch cylinders?

    This is probably a really dumb question as I am no mechanic but I was working on my 66 VW Bus clutch line today and it begged the question. Why does a simple lever work on a VW Bus/Bug but not on a Delorean? Why couldn't the clutch on these cars be designed to simply move a cable to open and close the clutch pin?

    The Delorean clutch mech is so clumsy and complicated (and stiff). Would one of you mechanical experts school me on why a simple cable wouldn't work on these cars but it does on a VW Bus?
    -Alex
    We work jobs we hate, to buy shit we don't need, to impress people we don't even like.

  2. #2
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    the difference is 20 year plus of mechanical engineering between your bus and the D. Hydraulic systems wear less over time, and have good "feel".

    hydraulic activated clutches are still in use today (when you can find a manual) while cable kinds are long gone.

    why do you think its clumsy and complicated? its not...

    the only bad thing was the use of the original plastic line easily remedied by use of a stainless one. Stiffer than the bus? well thats your perspective, mine is not. The more powerfull the engine, the more clamping force is required on the clutch thus usually a stiffer feel, but not always.

  3. #3
    Senior Member Totally 80s's Avatar
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    My bus cable lasted 50 years and 80,000 miles my slave cylinder died at 25,000 miles not sure I am in agreement with the D wearing less over time.

    By clumsy & complicated I was talking about the placement. It's a nightmare changing a slave cylinder. I wish the slave was easier to change and work on.

    Your vintage VW bus clutch is stiffer than your Delorean? Mine is light as a feather. What year/model do you have?

    I guess my question is would a cable driven clutch line work on a Delorean? Is the 130 HP too much for a cable system? Or was the car too luxurious to put an old fashioned cable system in? The cable set up is so incredibly simple it just made me wonder.

    You are right about the "feel" The Bus has very little "feedback" where the Delorean you know right where that clutch grab is.


    Quote Originally Posted by mark w View Post
    the difference is 20 year plus of mechanical engineering between your bus and the D. Hydraulic systems wear less over time, and have good "feel".

    hydraulic activated clutches are still in use today (when you can find a manual) while cable kinds are long gone.

    why do you think its clumsy and complicated? its not...

    the only bad thing was the use of the original plastic line easily remedied by use of a stainless one. Stiffer than the bus? well thats your perspective, mine is not. The more powerfull the engine, the more clamping force is required on the clutch thus usually a stiffer feel, but not always.
    Last edited by Totally 80s; 01-22-2019 at 01:34 AM.
    -Alex
    We work jobs we hate, to buy shit we don't need, to impress people we don't even like.

  4. #4
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    Quote Originally Posted by Totally 80s View Post
    My bus cable lasted 50 years and 80,000 miles my slave cylinder died at 25,000 miles not sure I am in agreement with the D wearing less over time.

    By clumsy & complicated I was talking about the placement. It's a nightmare changing a slave cylinder. I wish the slave was easier to change and work on.

    Your vintage VW bus clutch is stiffer than your Delorean? Mine is light as a feather. What year/model do you have?

    I guess my question is would a cable driven clutch line work on a Delorean? Is the 130 HP too much for a cable system? Or was the car too luxurious to put an old fashioned cable system in? The cable set up is so incredibly simple it just made me wonder.

    You are right about the "feel" The Bus has very little "feedback" where the Delorean you know right where that clutch grab is.
    Mustangs still ran cable clutches up into the 00’s. Plenty more hp and much stronger clutches. Can’t say I’d want a cable that long in a Delorean. Likely be fairly awkward
    Last edited by Gfrank; 01-22-2019 at 01:55 AM.

  5. #5
    Senior Member Rich's Avatar
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    Three additional points about these two types of clutch actuation.

    1. Engineering: Routing the actuation system from the footwell are to the clutch - wherever it happens to be - is generally simpler with hydraulics.
    2. Maintenance: Clutch cylinders fail mainly because owners don't manage to flush/fill the system every 2-4 years. Properly cared for they last decades.
    3. Adjustment: Mechanical systems need to be adjusted so as to maintain the correct amount of free play at the top of the pedal travel. Hydraulic clutches don't need adjustment.

    And, yes, the location of the slave cylinder in the D isn't great. Bleeding the clutch is something I'm happy to pay my local shop to do. Regularly. Half an hour of labor. No biggie.
    March '81, 5-speed, black interior

  6. #6
    Senior Member Totally 80s's Avatar
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    Quote Originally Posted by Rich View Post
    Three additional points about these two types of clutch actuation.

    1. Engineering: Routing the actuation system from the footwell are to the clutch - wherever it happens to be - is generally simpler with hydraulics.
    2. Maintenance: Clutch cylinders fail mainly because owners don't manage to flush/fill the system every 2-4 years. Properly cared for they last decades.
    3. Adjustment: Mechanical systems need to be adjusted so as to maintain the correct amount of free play at the top of the pedal travel. Hydraulic clutches don't need adjustment.

    And, yes, the location of the slave cylinder in the D isn't great. Bleeding the clutch is something I'm happy to pay my local shop to do. Regularly. Half an hour of labor. No biggie.
    Number 3 is a huge disadvantage especially if you are trying to sell a luxury vehicle. In a VW it's just assumed you gotta adjust a bunch of stuff from time to time. So it was engineered to be as easy as possible to do so. It would probably be just as bad trying to adjust a clutch lever cable in a Delorean as it is replacing the darn slave.
    -Alex
    We work jobs we hate, to buy shit we don't need, to impress people we don't even like.

  7. #7
    Administrator Ron's Avatar
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    +1 Rich
    simpler = less moving parts to wear out too.

    =====

    Could be way off here, but it sounds to me like you (Alex) simply don't like the feel. Which brings up another point- You can probably get an aftermarket hydraulic MC/Slave set up with different bores/strokes/etc. to get closer to the feel you want...I'd say easier than re-doing it with a cable system, especially considering where a D's slave is located.

  8. #8
    Senior Member DMC-81's Avatar
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    Clutch Stiffness

    I can attest to the fact that the stiffness is related to deterioration and/or wear. I completely reconditioned my clutch system (from the rubber pedal pad to the clutch disc and everything in between with OEM parts (except I opted for the the improved SS clutch line), and I can report a silky smooth and predictably progressive clutch action afterwards.

    Setting the hydraulics aside, I would say that these areas contribute to clutch stiffness and/or squeaking noise:

    - a dry pin in the pedal
    - a dry/ rusted pin assembly in the clutch fork
    - a dry/ rusted pivot ball
    - a dry /rusted input tube to release bearing interface.

    ...and I suppose rusted tines/fingers on the pressure plate.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  9. #9
    Administrator Ron's Avatar
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    +1

    ...plates certainly (for other reasons too, e.g, aftermarket, performance,"rebult").

  10. #10
    Delorean Guru
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    The PRV/Renualt was designed to use a hydraulic system. Since it was already designed it probably was the easier way to go rather than design a cable system from scratch. Two big advantages of the hydraulic system, you can build in exactly what mechanical advantage you want, and it automatically adjusts. When installing any drivetrain compromises must be made concerning accessibility and maintenance. You don't have to get to the slave cylinder often and if you are diligent with flushing the fluid every other year the system can last a long time. Besides, how many owners, when they buy a new car, even care about this stuff? Could it have been designed better, of course. Considering the car was the first iteration in production, many things would have improved if things continued.
    David Teitelbaum

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