Brake Pistons won’t retract!!
Thread Starter
3rd Gear
Joined: Apr 2024
Posts: 3
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Brake Pistons won’t retract!!
Bought New Brake calipers in all 4 corners. Wilwoods in rear, strange in front. All are 4 pistons. I deleted abs system and deleted brake booster. I have strange master cylinder 1.125 bore, which is recommended for 4 pistons in all 4 corner. I bleed the brakes a million times and bench bleed the master cylinder.
my issue is my brake pads on all 4 corners will not retract from the rotor! So the pads are sitting on the rotors even when I release my brake pedal. Every single piece to my brake system is Brand New.
What can be my issue on the pistons not retracting?
my issue is my brake pads on all 4 corners will not retract from the rotor! So the pads are sitting on the rotors even when I release my brake pedal. Every single piece to my brake system is Brand New.
What can be my issue on the pistons not retracting?
Race Director
Joined: Dec 2013
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Check the pedal adjustment for push rod,since if master plungers are not allow to come back to get past return bleeder channel, then pressure from master is not allowed to be relieved.
Think this, with the clear resivor channels to plungers, and the push rod needs to allow the plungers to come back past the reserve flow channels to allow correct pressure release/fluid refill.
As for standard caliper, rotor kick back when they are spinning and you come off the pedal is what will cause the pads to push the the pistons back in,
While on true race calibers, will be springs inside the pistons to push the pistons outward with light pressure back towards the pads, for when you are coming out of a corner and have major rotor pressure from flex in wheel hub bearings that cause the rotors to over kick the pistons in wards instead.
Think this, with the clear resivor channels to plungers, and the push rod needs to allow the plungers to come back past the reserve flow channels to allow correct pressure release/fluid refill.
As for standard caliper, rotor kick back when they are spinning and you come off the pedal is what will cause the pads to push the the pistons back in,
While on true race calibers, will be springs inside the pistons to push the pistons outward with light pressure back towards the pads, for when you are coming out of a corner and have major rotor pressure from flex in wheel hub bearings that cause the rotors to over kick the pistons in wards instead.
Thread Starter
3rd Gear
Joined: Apr 2024
Posts: 3
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Are you saying my pushrod for the master cylinder to brake pedal Should be shorten?
is it possible I also have to much fluid in the reservoir which isn’t all pressure to be released. It’s fill to the top with a small space between the cap.
is it possible I also have to much fluid in the reservoir which isn’t all pressure to be released. It’s fill to the top with a small space between the cap.
Race Director
Joined: Dec 2013
Posts: 12,502
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Yes, if plunger assembly is not able to come all the way back with pedal at top rest, so compensation ports are not blocked.
No, fluid level in is not going to cause the problem,
As stated, if you just open up the bleeder and it solves the problem, then problem is back up at master with rod adjusted too long, plungers can not get back behind the reservoir compensation ports in the master to allow the fluid pressure to be relived.
Simply, shorten the adjustment rod until you have a good 1/4" of slop back at the pedal at top of stroke rest point, then slowly adjust the rod linkage out until you end up with about 1/16" inch at top of stoke in the end. This allows the master plunger assembly to come all the way back to it normal back rest position in the master, so pressure built up in the master, can be dumped back through the compensation ports, and back into the reserve tank fluid.
If breaking the bleeders do not solve the problem to relive the pressure in the lines, then suspect that pistons do have spring in them, to push the pistons back in during rotor flex kick out. Such works great for road course work, but not for street use, since it will cause the pads to wear a lot faster when your not dealing with rotor flex kick out over and over again down the technical sections.
Race Director
Joined: Dec 2013
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And remember, is not you coming off the pedal that is going to cause the pistons to be pushed back into the calipors, but the rotor spinning that will vibrate on the pads, for them to push the piston slighlty back in (short of spring loaded pistons that the springs will push the pistons back-out).
So not on the brake pedal, should be able to spin the rotors, and until spinning rotor vibrates the pistons back in slightly, will still have a slight grab of pads to rotor.
If no amount of force can spin the rotors with you off the pedal, then problem is back at master adjustment rod, with plungers not able to retract past the compensation valves, to dump the pressure in the lines.
So not on the brake pedal, should be able to spin the rotors, and until spinning rotor vibrates the pistons back in slightly, will still have a slight grab of pads to rotor.
If no amount of force can spin the rotors with you off the pedal, then problem is back at master adjustment rod, with plungers not able to retract past the compensation valves, to dump the pressure in the lines.
