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Brake Caliper Rebuilding?

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  • Brake Caliper Rebuilding?

    One of the pistons on the rightt front wheel of my Chevy 2500 seized up on the way home last night. It was hotter than fire by the time I got home (didn't know it until I got there). I pulled the caliper off after it cooled down and removed the offending piston. The bore looked perfect, and the piston looked pretty good too, with only minor crud on it. I just took a fine Scotch-Brite pad and cleaned up the piston an reinstalled it in the bore, same seals and dust boot (cannot get a rebuild kit for these calipers). The piston slid in and collapsed very nicely.

    Question is: without a 'new' seal, do you think what I did is likely to work out? Everything was clean, but I don't want to reinstall it and bleed the system if it's likely to crap out or leak.


  • #2
    Hi Mark,
    I've done the same in the past and got away with it...

    Was the crud just a build-up of dust etc. or was the piston marked and pitted? If there's any pitting it *will* leak (and eventually the seal *will* fail) and you may need to keep topping off the fluid. Here in the UK that would fail the MOT (our annual inspection)

    I'm surprised there's no rebuild kit available - it might be worth calling at a brake shop to see whether there's another vehicle that shares the same size piston and seal, just to be Safe?

    Dave H.
    Rules are for the obedience of fools, and the guidance of wise men.

    Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools


    • #3
      It is the resilience of the piston's seal which retracts the piston a few thou after the brake fluid pressure is released.
      After being subjected to the heat of braking for years the seal becomes hard and looses it's ability to completely or adequately retract the caliper's piston.

      I've encountered this situation numerous times and have found new seals in an undamaged clean bore is the only permanent fix.
      Home, down in the valley behind the Red Angus
      Bad Decisions Make Good Stories​


      • #4

        I had a similar problem with a caliper overheating on my OLD VW many years ago and I took it apart and cleaned the internals and one day the light came on-- the brake hose to the caliper had swelled shut internally and did allow the high pressure fluid to go to the piston and it did not allow the piston to retract. The process cost me a brake rotor and new hoses. Check the hose!!


        • #5
          The piston only moves in the seal to take up pad wear.

          The seal groove doesn't have a square bottom, instead it's at an angle of about 10 degrees. When the brakes are applied the piston moves forward and the seal 'rolls' in the groove. When the brakes are released the seal pulls the piston back. In the 80's in an attemp to meet CAFE requirements some calipers had a 20 degree angle in the groove and a much larger pullback to reduce brake drag. They then had to have a dual piston 'quick take-up' mater-cylinder. If the pressure valve stuck you suddenly got a very 'long' pedal. If you have a buildup of sludge or corrosion behind the seal then it can't 'roll' and will cause the brake to bind.

          I had to rescue a Kawsaki Z400 front brake. There was so much corrosion at the bottom of the groove that the seal was actually distorted. New seals simply weren't available and the bike was worth very little in cash terms. Left for a week or so in brake fluid it recovered pretty well and was re-fitted to the now clean groove. It worked without problems for a couple of years before the bike was given away and was apparently still working fine recently.
          Paul Compton


          • #6
            My thinking is extreme heat on a rubber seal is not good and your looking at a brake failure when you need them the most.

            Replace the caliper.

            OTOH, you can always stop fast against the vehicle in front of you.
            It's only ink and paper


            • #7
              Are you sure it was the piston? I saw a lot of rusty/nasty brakes living in NY and 99.9% of the time the troubles with a caliper locking up are caused by the pins the caliper floats on sticking in the bores. Most dont regrease them when they do brakes, and they dry out eventually.
              "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."


              • #8
                I'll just assume you are going to do the other side as well.

                And check those pins as mentioned. And the hoses.
                Last edited by topct; 06-01-2011, 06:10 PM.


                • #9
                  That's funny. When I worked in a parts store (about 5 years ago) we had caliper rebuild kits on the shelf for Chevy 2500's and 3500's...The problem was; none of the shops wanted to rebuild them. They ALWAYS tried to sell the customer a new or remanufactured caliper...most of the time it was 2 calipers (matched set (??) Also, few, if any, of the guys in the shops actually knew how to rebuild a caliper, anyway.

                  When I worked in the fleet shop, we used to see an occasional Chevy 2500 come in with a hung caliper. Certain year models had the distance between the caliper frames and the slides machined to fit too loose, and were subject to cocking...Kinda like when the gibs are set too loose on a machine tool.
                  GM even issued a bulletin regarding the badly machined caliper frames and described how to determine if you had one that was too loose.
                  Not good news for some C-2500 owners, because the caliper frame is part of the spindle on some.
                  No good deed goes unpunished.


                  • #10
                    Yeah I'm going to do both fronts, but not rears. The piston was not pitted in the least and the bore looked brand new. I didn't know that the seal was an angled job, but it is beefy. The pins float perfectly since I did a brake job about six months ago. I always clean the heck out of everything I touch.

                    I called around today and can get new calipers for about fifty bucks each. Not worth the effort or doubt... will buy new... along with hoses. They feel a bit squashy.

                    Oh well, it's only money.


                    • #11
                      Disk Brakes

                      I would go for the new too. If you can't go when you want to, you're just stranded for a while. If you can't stop when you want to, it can be life threatening for you or someone else.


                      • #12
                        Originally posted by garagemark
                        I didn't know that the seal was an angled job, but it is beefy.
                        The seal isn't angled, it will be the usual square or rectangular job as it is on all automotive calipers. It's the seal groove that has an angle at it's base.

                        Aircraft were one of the first applications for disc brakes and used O-ring seals because brake drag was not considered to be an issue. Early race car calipers also used O ring seals and it was one of the things that delayed their universal adoption.
                        Paul Compton