hydraulic brake question

[kevbo22]

For some reason my rear hydraulic brake never stops braking. I have to open it up with a flat head. Then, once I step on the brakes again, it never opens back up.

What can cause this, and what recommendations do you have for me to fix this? Thanks.

 

[J_Walker]

too much brake fluid?

 

[Rickracer]

Sounds like it needs to be rebuilt, the piston(s) is/(are) hanging up, probably from corrosion inside.

 

[wagx2]

Sounds like it needs to be rebuilt, the piston(s) is/(are) hanging up, probably from corrosion inside.

 

[kevbo22]

Sounds like it needs to be rebuilt, the piston(s) is/(are) hanging up, probably from corrosion inside.

Ok, well Then I will look into how to rebuild it. I have no idea how it could have been corroded, its basically brand new. But thanks for letting me know. Off to search how to rebuild it.

 

[Brian Hadden]

Did you bleed them? Air in the small system on karts its enough to push but may not be enough for it to return to proper position,

 

[OzFab]

Disc runout also plays a part...

 

[kevbo22]

Ok I took apart the brake and it is what I would consider very clean and free of any corrosion.

I did not bleed the brakes, it came "done already". The two front brakes work great. Its the back break thats not working.

Disc runout??

 

[OzFab]

Disc runout??

No brake disc is perfectly straight, they all have a minute amount of side to side movement called runout; that small amount of movement pushes the pads away from the disc, allowing the disc to move freely...

 

[kevbo22]

No brake disc is perfectly straight, they all have a minute amount of side to side movement called runout; that small amount of movement pushes the pads away from the disc, allowing the disc to move freely...

Got it! Well when I hit the brakes, this closes all the way shut and never opens back up, even enough to get the brake disk in there unless I open it back up with a flat head screwdriver. After that, if I hit the brakes again.... same thing.

Have no idea what to do.

 

[Joe-405]

Do me a favor go hit the brakes and release the brake bleeder valve and tell me whether it releases that way or not. Do not use a screw driver. I can pin point your issue a lot faster that way.

 

[Rickracer]

How easily does the piston move when you go to reinstall it? Does it slide in easily? Maybe somebody used the wrong o-ring to seal it? Is it a round, or square cut o-ring? Generally, a square cut o-ring will go trapezoid shaped when the brake is applied, and then retract the piston just slightly, (going back to a square shape), when the brake pressure is removed. The pistons on my Explorer rear disc brakes were hanging up, pretty much like yours, not really any corrosion there either, but honing, polishing the pistons, and new caliper kits straightened it right out.

 

[wagx2]

Got it! Well when I hit the brakes, this closes all the way shut and never opens back up, even enough to get the brake disk in there unless I open it back up with a flat head screwdriver. After that, if I hit the brakes again.... same thing.

Have no idea what to do.

are you pushing the pedal to engage the breaks with caliper off the disc and saying they want open back up to get the disc in... they don't open and clamp automatically, with the pedal, pedal applies force on the piston which pushes the pad into disc, then let off the pedal, rotation of the disc pushes the pads away, cause pedal pressure is gone it allows disc to spin free. put it back together and mount everything up, and bleed then have someone sit in it, and hold break push it shouldn't move, release brake push again should be a little pressure needed at first to push but once rolling and it does roll it is working fine.

dido, post 16,17

 

[kevbo22]

Do me a favor go hit the brakes and release the brake bleeder valve and tell me whether it releases that way or not. Do not use a screw driver. I can pin point your issue a lot faster that way.

Ill try this out and let you know. Im gonna put everything back together.

How easily does the piston move when you go to reinstall it? Does it slide in easily? Maybe somebody used the wrong o-ring to seal it? Is it a round, or square cut o-ring? Generally, a square cut o-ring will go trapezoid shaped when the brake is applied, and then retract the piston just slightly, (going back to a square shape), when the brake pressure is removed. The pistons on my Explorer rear disc brakes were hanging up, pretty much like yours, not really any corrosion there either, but honing, polishing the pistons, and new caliper kits straightened it right out.

The piston does not slide very easy no. When everything is installed, the fluid moves the piston out and pushes the brake pads together but the piston never goes back in. Its so tight that even pring it open with a flat head is pretty tuff. I am pretty sure the o ring is round.

are you pushing the pedal to engage the breaks with caliper off the disc and saying they want open back up to get the disc in... they don't open and clamp automatically, with the pedal, pedal applies force on the piston which pushes the pad into disc, then let off the pedal, rotation of the disc pushes the pads away, cause pedal pressure is gone it allows disc to spin free. put it back together and mount everything up, and bleed then have someone sit in it, and hold break push it shouldn't move, release brake push again should be a little pressure needed at first to push but once rolling and it does roll it is working fine.

Yes the brake is off and not installed. I am going to try this. But I find it hard to believe that the disk would push the pads back out. It seems like the piston just sticks. Like I said even prying the pads apart with a flathead screwdriver is pretty tuff. But i'll let you know.

 

[wagx2]

I have another question, what made you start messing with the brakes, pads worn out? or kart wouldn't move locked up?? I'm thinking along the lines of your first brake job, when you compress the piston in caliper its to make room to get the new pads back in and back on to the rotor, so when you reinstall them bolt everything down and your done, the next time you push the pedal, your piston will adjust itself back into position against the rotor and sometimes have to push pedal two times. after that your pedal will get hard, means brakes are applied, when you release the pedal DO NOT expect the pad to move away but 10-20 thousands of a inch, they will not return to where they have the same gap they had when you reinstalled them. and doing this while caliper is off it will not open. and make sure park brake is not on, saw the end of park brake plunger in the caliper in the pic of you holding piston.

 

[OzFab]

The piston does not slide very easy no. When everything is installed, the fluid moves the piston out and pushes the brake pads together but the piston never goes back in.

It's not meant to; disc brake systems are designed to keep the pads in close contact with the disc so the pedal doesn't bottom out every time you press it...

Put everything back together & drive the kart; if you can move the kart after releasing the brake, everything is fine...

 

[ML-TOYS]

Yes the brake is off and not installed. I am going to try this. But I find it hard to believe that the disk would push the pads back out. It seems like the piston just sticks. Like I said even prying the pads apart with a flathead screwdriver is pretty tuff. But i'll let you know.

It's not meant to; disc brake systems are designed to keep the pads in close contact with the disc so the pedal doesn't bottom out every time you press it...

Put everything back together & drive the kart; if you can move the kart after releasing the brake, everything is fine...

Beat me to it, just like car brakes you cant just push the piston back in.

 

[doggerss]

no disc brake will retract the piston or bads the system is designed that way. every disc brake system has some amount of drag from this. you need to put it together and put it on you don't have a problem. the problem comes if when you press the pedal when riding and it locks up the reap axle and won't unlock then you have a problem. the pads will always seem to be tight to the rotor when installed thats normal.