I have a 1998 Rm 250 and the back brakes will work fine then they get stuck on. Please tell me how to fix it.?

Question

Once the brakes cool down they become free moving. Can anybody Tell me what wrong with my back brakes?

Answer 1

Sounds like a bad Master Cylinder to me,,it may not be releasing line pressure.

That's a very common mode of failure ,,,,effectively making the hydraulic line a Closed System.

When fluid gets Hot and expands,,,there's no place for that pressure to go .

The Point of Least Resistance yields First.

Caliper Pistons are made to be sensitive and responsive to pressure,,,

they are the point of least resistance in closed-circuit mode.

The heat-expanded fluid causes them to press against the rotor,,,apply the brakes.

When Fluid Cools,,,brakes release.

What we call Calipers are SLAVE CYLINDERS.

No Brain,,,they just do what they are told.

They have no self-energizing capability.

A Sticking IRON Caliper Piston usually works Better in a HOT Swollen Aluminum Caliper Bore than it does in a Cold One.

And if it STICKS when it's HOT,,,,guess What happens when the Aluminum Cools and Shrinks down onto the iron piston?

Next Time your brakes lock up,,,theres a Very Simple Test you can do.

Open the Bleeder Valve on the caliper and see if doing so releases the brake.

Really,,at your bike's age,,it would be wise to do a full hydraulic system rebuild.

Not that hard or expensive,,,,,and you'll be done with it for another 10 years.

Answer 2

Your brake caliper seals are swelling under the heat of braking. It is most likely caused from moisture in the brake fluid. Drain and flush the fluid and rebuild the caliper. that should fix the problem.

Answer 3

you will probly have to rebuild the caliper but first you should replase all the fluid in the lines

Answer 4

Biker for Life hit the nail on the head...

you need to go thru and re-build the caliper and flush all the old fluid and replace with fresh.

alot of the time the fuild will either get moisture OR if not replaced regularly can get what is referred to as burnt meaning it has gotten overly hot numerous times.  typically, the brakes will squal or squeek loudly when the fluid is contaminated.

could also be the caliper piston is worn or the disc itself is warped from excessive heat too ... but more than likely, merely a caliper rebuild & fluid flush will correct the issue.

edit:  DOH!!!  right thought, wrong word... Master cylinder rebuild not caliper ... I was picturing in my head the right thing just didn't type it out correctly after reading the earlier response... master cylinder rebuild... DOH!!!