Just got myself a project, an '89 Jeep Comanche.

Both front brakes were seized up, so I put in new brake hoses, calipers, & pads. The passenger side brakes work mint now, but on the drivers side, the caliper piston does not retract when I release the brake lever.

I can manually retract the caliper piston using a flathead with minimal effort.

What else could be causing the piston to 'stick'?

  • Do you mean it does not release pressure from the brakes? The two things that come to mind are 1) master cylinder not allowing the fluid to return, or 2) defective caliper. I would lean more toward #1 since the piston returns manually when you push it. – CharlieRB Jun 15 '17 at 19:39
  • @CharlieRB, You are correct, pressure is not relieved. This problem only effects the drivers front brake, the other three work normally. Could this still be a master cylinder problem? – Calvin Jun 15 '17 at 20:04
  • Depends on the configuration. How many lines come out of the master cylinder? Does this have anti-lock brakes? Do you know what caused the brakes to seize in the first place? Are you testing this with the engine running? – CharlieRB Jun 15 '17 at 20:20
  • @CharlieRB, not sure about the line count, ill take a look in a bit and get back to you. No anti lock brakes. Not sure why they were seized. I was testing without the engine running. Another tid-bit that may or may not be useful... This truck has rear drum brakes and (obviously) front disc brakes. Take a look here for more detail on the lines: repairguide.autozone.com/znetrgs/repair_guide_content/en_us/… – Calvin Jun 15 '17 at 20:29
  • It sounds like you got a bad caliper. – Pᴀᴜʟsᴛᴇʀ2 Jun 15 '17 at 21:01

tl dr: It sounds like you have a bad caliper.

The way calipers work is the seal doubles as the retracting device. When the piston (which is basically a cylinder inside the caliper body) is pushed out by the hydraulic force of the brake fluid as you press on the pedal, the piston moves out of the housing and sort of takes the seal with it. The seal gets sideways a little bit in the housing. The piston will continue to slide out of the housing until it meets resistance, which is usually the pad against the rotor face. When the brake pedal is released, the hydraulic force is reduced and the deformed seal will now return to its regular shape. When doing this, it pulls the piston back with it. If when the piston is pushing out against the seal, it isn't meeting any resistance from the seal, the seal will not become deformed as it's supposed to and then won't retract the caliper piston. This would also be why it's very easy to push the piston back into the caliper body with a screwdriver. I usually use a screwdriver to collapse the piston with the caliper still on the vehicle (depending on the style of caliper, of course). It usually takes a lot of force to get it to go back past the seal. If you aren't getting much resistance, this would be another clue which may validate my theory.

My suggestion? Take the caliper back and tell them it doesn't work. Either get a new one or a refund.

  • 2
    Bought a new caliper, worked like a charm. Thanks. – Calvin Jul 1 '17 at 18:37

I normally push them down ( GM and Nissan) with a large "C" clamp. Although my 1985 Nissan could be "threaded" back with a flat screwdriver.

  • 2
    This does not answer the question. Please read it again and I think you will see what I mean. – CharlieRB Jun 15 '17 at 19:39

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