Bleeding a Chevy hydraulic clutch system.

Discussion in 'Shop Talk' started by Darren, May 20, 2012.

  1. Darren

    Darren Still an :censored:

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    A week ago I parked the truck, 1987, in a shopping center parking lot and got a ride to a meeting with a friend. Never had a problem with the clutch before. That evening the pedal went straight to the floor with no clutch.

    Fluid level was OK.

    1. Replaced both master cylinder and slave.

    2. Truck front end is jacked up.

    3. Bleeder is on the slave.

    4. So far I've run a quart and a half through the system trying to bleed the air.

    5. The outside of everything is dry which should mean no leaks.

    6. I've used a vacuum pump on the slave cylinder which seems to be drawing air in around the bleeder threads. By bleeding in the conventional way I can get to the point no air is coming out.

    7. Still no clutch pedal.

    Any ideas?
     
  2. Old Vet

    Old Vet In Remembrance

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    Check the clutch to see if there are no broke parts. You can do this by using a screwdriver where the slave cylinder hooks on. If you push it and the clutch is not released you have a broken part.
     

  3. Darren

    Darren Still an :censored:

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    If the clutch had an internal problem such that the slave cylinder couldn't activate it, wouldn't that cause a hard pedal? There's very little resistance when you press on the pedal. In closed hydraulic system filled with fluid and without compressible air, Wouldn't the slave try to move? If the slave couldn't move, the pedal couldn't move unless there's air in the system.

    I can still drive the truck. So the clutch is engaged. I'd prefer not to drive it without using the clutch.
     
    Last edited: May 21, 2012
  4. HermitJohn

    HermitJohn Well-Known Member

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    Whatever the brand/make of vehicle, those internal clutch slaves are just a real fun time..... NOT! Only thing that compares to them is the pre-bled all plastic external system Ford used prior to the internal slave setup. Ford dealer only sold replacement as a prebled master, line, and slave all together for a mere $400. You could buy individual part copies from parts store much cheaper, but bleeding the thing was a nightmare. Thats why Ford dealer only sold it as a pre-bled assembly. Also what passed for a bleeder screw would eventually strip the plastic threads in the slave housing... sooner than later.

    I ever get stuck with internal slave, I will spend time to re-engineer it to external and use Wilwood universal aftermarket slave and master. Sorry to those that believe in factory engineering no matter how stupid, but I have loads of time and not going to suffer stupidity of OEM engineers trying to save 5cents of extra labor on the assembly line, even if it takes some custom parts. I have Wilwood setup on my '84 Ranger and it takes all of 5 minutes to bleed it BY MYSELF. Can replace everything in half hour. Parts are all metal and dont cost anymore than the stupid plastic stuff if you shop around.
     
  5. Darren

    Darren Still an :censored:

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    At least this setup on the 87 is either aluminum or cast iron and it is an external arrangement.
     
  6. pancho

    pancho Well-Known Member

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    I had the same problem.
    I found that if you park in the sun you won't have a clutch.
    If you park in the shade the clutch will work fine.
    Just have to look for parking places in the shade.
     
  7. Darren

    Darren Still an :censored:

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    That makes no sense, Pancho.
     
  8. HermitJohn

    HermitJohn Well-Known Member

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    According to RockAuto.com, you are right, GM didnt go to internal slave until 1996. I hadnt realized it was that late for them. Pretty sure they did internal earlier on some of their rear drive cars. Nope, just looked at '95 Camero with 350. Has external.

    But even back into 80s they do look like non-adjustable linkages, at least from what I can tell from pics shown. Dont have manual to actually know for sure.

    Then problem is just not bled well enough. With non-adjustable linkage, you have to have them bled within a knats eyebrow of perfect. With older adjustable linkage, you could fudge a bit as long as there was 'enough' travel.
     
  9. Darren

    Darren Still an :censored:

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    That's where I'm having a problem. I'd like to fill the system from the bottom up, but the check valve in the master below the connection to the reservoir complicates that. I'm wondering if I set up a can with brake fluid attached to a hose connected to the bleeder on the slave I can adjust the can level to flow the fluid backwards (up) without closing the check valve.

    I noticed that GM designed the master so it slopes up to the connection to the reservoir. At least air in the master cylinder should exit to the reservoir.

    I was thinking about buying a Ford 3/4 ton later this year. When did they go to an internal slave?
     
  10. pancho

    pancho Well-Known Member

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    It works.

    A build up of heat under the hood causes the clutch problem.
    I gave my car, that had the same problem, to a friend. She took it too several mechanics. They had all kinds of reasons but it still happened. She finally took my advice and parked in the shade.
    When I had it, sometimes I would start it in gear. When I drove a short distance the heat would be removed from under the hood and the clutch would work.
    It worked great in the winter.
     
  11. wy_white_wolf

    wy_white_wolf Just howling at the moon

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    Pancho - One ends up with a similiar problem with brakes when you have water in the fluid that boils when it gets hot. Did anyone try completely flushing out the system?

    WWW
     
  12. pancho

    pancho Well-Known Member

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    Yes, even replaced the system.
     
  13. Darren

    Darren Still an :censored:

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    Pancho, what year and model?
     
  14. Darren

    Darren Still an :censored:

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    The truck sort of fixed itself. I worked on it over a 2 week period. Thursday I took the slave cylinder off and let in hang by the hose leading to the master. The idea was that air in the cylinder would float up to the end with the bleeder. The bleeder was closed. Friday when I reinstalled the slave to start bleeding the system again, I had to compress the actuating rod so I could get the assembly in place and positioned against the clutch fork. As soon as I compressed the cylinder I heard the air bubbling up the hose into the reservoir.

    All of the bleeding I went through did not remove the air in the hose. I had taken a small plastic bottle, drilled a hole in the bottom and shoved 3/8" tygon tubing into it. I was going to reverse bleed the system by letting brake fluid flow into the slave cylinder bleeder and float the air up to the master and then to the reservoir. I didn't have to do that.

    I'm not sure why these are so difficult to bleed. I've never had the problem with brake systems and the hydraulic clutches on larger trucks.
     
    Last edited: May 26, 2012
  15. HermitJohn

    HermitJohn Well-Known Member

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    All hydraulic clutch linkages I've ever run across (except Wilwood system I mentioned) have been more difficult to bleed than any brake system. But modern stuff seems especially hard to bleed. Part of problem is newer linkages have no adjustment, they are designed so system has to be bled perfectly, not just good enough. I ever have to deal with hydraulic clutch linkage on some new to me vehicle and its going to get converted to Wilwood even if it takes some serious effort to re-engineer it. I've NEVER seen anything else that easy to bleed.