Motorcycle Repair: rear brakes seizing, master brake cylinder, brake caliper

Question
Hi Wayne, my name is josh and i have bought my son a 2010 korian kx import 125 motor bike, he got a puncture in the rear tyre, i took it off to be repaired and put it back on, everything went back on the right way and now the brakes are rubbing and sticking after about 10 minutes riding ,i have noticed that the caliper is wobbling a little when the wheel spins, the brake disic is not warpped and i sprayed the pad locating pins with lubricant in case the pads where not sliding back in place properly. I have tried everything i can think of still with no luck

Answer
Hi Josh,

Sometimes, if it has a hydraulic brake
the fluid will have small bubbles
in it which are hard to get out.

I would try pumping some new brake
fluid through it if you don't find
any mechanical misalignments.

Get a jar and add some fluid to it
and connect a small hose to the
bleed screw on the brake caliper.
Submerge the end of the hose in the
fluid.

Open the bleed screw a bit and
pump some fluid out. Keep the
master brake reservoir full
so it doesn't suck air in the top end
where the fluid is stored.
Tighten the bleeder gently again.

Check if the pads are free on the caliper
pins and if the pads are releasing after
applying the brake.

If they stick try prying the pad
with the piston on it back a small amount.
Try brake again and if the piston/pad keeps
sticking then the caliper will have to
be cleaned out and checked for seal
or mechanical problems.

The "KX" bikes have had some brake problems
in the past. Check the parts for misalignments
and do not overtighten the rear wheel.

Make sure your wheel is aligned straight
by checking if the chain is running true.

Check the pads for bad surface alignment.
Some new pads are just ground incorrectly.

Recheck your assembly and if bleeding,
cleaning and reassembly doesn't
help it might be a blocked air bleed
hole inside the master brake cylinder
where the fluid is stored.

Since the bike is not old it must be either
air in the system, bad alignment or assembly somewhere
or just some faulty new parts.

Sometimes even a new bike can be assembled
incorrectly so check a parts manual if possible
to make sure it was right originally.

Wayne S

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