Pistons not reacting evenly in my front 2-Pot Calipers
07-08-12, 07:12 AM
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Pistons not reacting evenly in my front 2-Pot Calipers
Hey folks. Hoping someone has some expertise and can offer some advice. I recently changed out the front brake pads and rotors on my '99 GS400, which uses 2-pot Calipers. When I did it I used a c-clamp to push the pistons back in after installing the thicker pads but I still had some trouble getting my left caliper to fit over the new pads. Turned out that one of the two caliper pins was not pushed all the way into the caliper bracket (the other pin was). I used a breaker bar to eventually turn/loosen the pin and then I was able to hammer it in all the way into the bracket and the caliper fit. However, I had another issue...
While holding the caliper out of its bracket, but still connected to the brake line, when a friend pushed the brake pedal, the two pistons did not both react the same. One moved a much greater distance than the other. Hit the brakes a second time, and the same thing happened. Applied the brakes a third time and by now the piston that had not been moving much completely stopped while the other continued to move. Thinking that this was a malfunction / stuck piston, I purchased a refurbished caliper, installed it and bled the brakes. After doing this, I had the same problem with the new caliper. I did an experiment using the c-clamp and half of an old brake pad to keep the piston that was moving the most from moving and had a friend apply the brakes and then I finally saw the other piston start moving fully. I hoped that this would loosed the 2nd piston so it would have full range of motion, but when we applied the brakes without the c-clamp the two pistons came out unevenly again.
Then, I tried the whole experiment again on my front right caliper with exactly the same results. Basically, only one of the two pistons in each of my front 2-pot calipers has full movement, the 2nd piston in each only moves a little and after it has moved a short distance doesn't move further. This is true of my old front left caliper, my refurbished front-left caliper, and my front right caliper (have not messed with the rears). This leads me to question whether or not there is really a problem or whether this is the intended operation of these calipers. If there is a problem, then I'm wondering if it's actually a caliper problem or if there is something else with my brake system that would cause this problem universally.
Appreciate your expertise.
While holding the caliper out of its bracket, but still connected to the brake line, when a friend pushed the brake pedal, the two pistons did not both react the same. One moved a much greater distance than the other. Hit the brakes a second time, and the same thing happened. Applied the brakes a third time and by now the piston that had not been moving much completely stopped while the other continued to move. Thinking that this was a malfunction / stuck piston, I purchased a refurbished caliper, installed it and bled the brakes. After doing this, I had the same problem with the new caliper. I did an experiment using the c-clamp and half of an old brake pad to keep the piston that was moving the most from moving and had a friend apply the brakes and then I finally saw the other piston start moving fully. I hoped that this would loosed the 2nd piston so it would have full range of motion, but when we applied the brakes without the c-clamp the two pistons came out unevenly again.
Then, I tried the whole experiment again on my front right caliper with exactly the same results. Basically, only one of the two pistons in each of my front 2-pot calipers has full movement, the 2nd piston in each only moves a little and after it has moved a short distance doesn't move further. This is true of my old front left caliper, my refurbished front-left caliper, and my front right caliper (have not messed with the rears). This leads me to question whether or not there is really a problem or whether this is the intended operation of these calipers. If there is a problem, then I'm wondering if it's actually a caliper problem or if there is something else with my brake system that would cause this problem universally.
Appreciate your expertise.
Last edited by jawboxxx69; 07-08-12 at 08:52 AM.
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