Rear brakes locking up

[B.Jones#8]

I put a rebuild kit in the master cylinder and ever since i did that i can do about 4 laps and the rear brakes will lock up.Ill have to loosen the bleed valve to get it to move, the rotor and caliper are extremely hot.Does anyone know whats causing this to happen?

[alberto]

This happened to my sons 400ex last year. What had happened is that the brake pedal would stick and the brakes would drag. What I did to fix it was remove the brake pedal and found tons of rust and mud inside the hole where the pedal attaches to the frame. I removed the rust and grime and sanded the hole and pedal to bare metal. Panted and applied a liberal amount of water proof grease. Tested and all is OK with the brakes.

[B.Jones#8]

Alright thanks ill try anything....Would a bent rotor cause it, possibly creating to much heat and causing the pressure to build and lock them up

[Honda4life05]

a bent rotor could def cause it to drag an eventually lock up. i was stupid running withouuh a skidplate an bent my rotor on my 300ex. you can put your quad on a jack an spin the wheels to see if it's bent

[trailrider894]

not to go off topic. but how do you know if you need a new one even if it isn't bent?

[Scro]

If your rotor is bent, your brakes would either lock up completely (because the bend won't allow the rotor to pass through the caliper) or you will lose pressure at the brake pedal (because the bend in the rotor is pushing the piston back into the caliper).

The only reason I would change a rotor (if it isn't bent), would be because of grooving caused by excessively worn brake pads. There should be a flat surface when you run your finger across the rotor.

[Homerx]

Originally posted by trailrider894
not to go off topic. but how do you know if you need a new one even if it isn't bent?

Measure it with a caliper. There is a minimum thickness stamped on it. I think it 3mm for rear rotor.