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Front Left Caliper not releasing completely

Discussion in 'Modified Alpine' started by donchiotos, Jul 31, 2022.

  1. donchiotos

    donchiotos Gold Level Sponsor

    I am having an issue with my left front caliper not releasing completely when driven a few miles. I have rebuilt the caliper with stainless steel pistons and new seals from Sunbeam Specialties. When I first reattach the caliper, then spin the tire by hand, the wheel has a little grab, but nothing abnormal. After driving the car a mile, and jacking up the front, and turning the tire by hand, there is quite a bit of grab. It's like the piston isn't being pulled back enough. I thought that was the purpose of the rubber O ring that is in the caliper. Tried looking for a replacement caliper- Needless to say none found. Does anyone have any ideas, comments, or know where I can get a rebuilt caliper? Thanks, Don C
  2. MikeH

    MikeH Platinum Level Sponsor

    Try opening the bleeder and see if the caliper releases. How old are the flexible lines? They could balloon inside and not release the pressure.
  3. Pete S.

    Pete S. Bronze Level Sponsor

    That's really odd. There is no valving or anything else that prevent the pistons from releasing. Does the piston release if you open the bleeder? Does it slowly release over time?
  4. alpine_64

    alpine_64 Donation Time

    Sticking caliper is normally a sign of the rubber line failing internally and collapsing closed and acting as a non retun valve.
  5. donchiotos

    donchiotos Gold Level Sponsor

    Thanks for the ideas. I haven't tried opening the bleed screw yet when the wheel has tension on it. I do know that after the car cools down the tire is easier to turn and back to it's normal tension.
  6. alpine_64

    alpine_64 Donation Time

    Another quick thought. Is the wheel getting hot.. Could also be a wheel bearing.. Any grinding sounds?
  7. pruyter

    pruyter Donation Time

    Sticking brake pads could be a culprit too. Filing off some mm of the side of the pads may help.
  8. donchiotos

    donchiotos Gold Level Sponsor

    Yesterday I ordered a new brake line from Sumbeam Sperialities. I'll put it on this weekend and try driving it again. I'll let you know the outcome. Yes over time the pad releases and wheel turns normally.
  9. alpine_64

    alpine_64 Donation Time

    Honestly.. Its worth replacing them all at once both front and the rear one.

    You have to bleed the brakes anyway and this way they are all the same age... No.. "Which one did i do last ?"
  10. GlennB

    GlennB Silver Level Sponsor

    I've always promoted the idea of shaving 1 mm off the sides of pads as it caused me a problem some years ago. Then, to confirm my experiences my latest set of pads (I change them every race) would not even slide into the calipers at all. So I actually had to take nearly 2 mm off this latest set. The symptoms of sticking pads were a pull to one side and for me not necessarily even to the same side each time.
  11. donchiotos

    donchiotos Gold Level Sponsor

    Well, I'm an idiot. Should have done this in first place. I'm pretty sure the issue with the sticking front brake was due to me connecting the front brake to the smaller reservoir and the back brake to the larger reservoir. I found this by pumping the brake several times then checking the drag on the wheel. After pressing on the brake pedal several time, I tried to turn the wheel, and it had resistance, to much. I then opened the bleed screw and then tightened it . Now normal resistance. I followed this procedure for all connections, all the way to the master cylinder. Resistance wet away in all cases. So that left the master cylinder. Looked this issue up on Google, and low and behold the larger reservoir is for the front, not rear as I piped it. I will put the wheel and tire and put it back on the ground and go for a test run to make sure this sloved the the problem. Thanks for all the help from everyone!
  12. donchiotos

    donchiotos Gold Level Sponsor

    Just came in from retesting and the issue is back. The problem is when pushing on the brake a few times, then trying to to turn wheel. The wheel has tension due to pads not releasing completely. When I turn the fitting out of the front master cylinder slightly. The tension goes away, and the normal tension is felt. Seems I have an issue of some sort with the master cylinder not releasing pressure? Any comments, or ideas or verification this is the issue?
  13. Filister

    Filister Donation Time

    Assuming this is a series Alpine, as you have a dual master cylinder I assume the brake system is modified. Has it ever worked in this configuration or is this a start-up? Brake systems have valves in them that hold a residual pressure in the system. Usually approx 2 psi for disc and 10 psi for drums. Sometimes they are built into the master, sometimes in the proportional valve and sometimes as add on valves. Could you have got these mixed up? The 10 psi for drums would cause a drag on discs. Is the master cylinder the only change?
    Other ideas:
    A brake line too close to an exhaust pipe.
    A pinched hard line.
    A twisted caliper seal.
    A malfunctioning brake booster if you have one

    The curious part is that the way the stock brakes are plumbed on a non boosted alpine both brakes should have the same pressure. I think boosted also but I'm not sure. If that is how you are plumbed it would indicate a problem with the caliper.
  14. Toyanvil

    Toyanvil Gold Level Sponsor

    My guess is the push rod is not adjusted right, to tight and not releasing the fluid back into the reservoir and holding pressure on the system. The left front caliper is the closest to the master cylinder and would be the first to fail. With the car at rest, does the push rod have a little play? It would help to know what dual master cylinder have?
    Barry and Bill Blue like this.

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