How to keep the rear disc brake on my 88' katana motorcycle from locking up?

Question

1988 suzuki katana 600cc: rear calipers occasionally lock up pretty good, more frequently in colder weather. Ive blead them out and put new brake fluid in. sprayed brake cleaner on the calipers. spread the calipers apart manually. but it always seems to lock back up after used. if i ride the bike for around 10min it usually lays off. but id like to fix the problem...any suggestions???

Answer 1

This is vary dangerous stop riding your motorcycle please! You need to replace the calipers! Get new pads,disc,brake line,and rear brake pedal master cylinder while your at it. Brakes are a critical part of your motorcycle. Do what I said to insure proper function. Don't take chances!

Answer 2

Disc Brake calipers use a square cross-section "O-ring" as their piston seal.

Piston Travel during brake application is VERY small.

That square-section ring doesn't Slide in the bore,,
It actually STICKS.

As the piston MOVES,,,that Square is distorted into like a parallelogram to accomodate the Piston Travel.

Then when Line Pressure is RELEASED,,,the elastomer's "memory" returns back to square shape.

That Tiny bit of distortion & memory is what Retracts the Piston.

Which is how Disc Brakes RELEASE without using any Return Springs,,,,and also how they are "self-Adjusting"....

At certain degrees of Pad Wear,,,Piston Travel Overcomes the
Seal's Friction and only THEN does piston actually Slide thru seal.
Then once in New Position,,the seal friction/Grip RESUMES,,,and seal goes Back into NO Slide-Thru>Distortion mode.

In Your case,,an '88,,,,that's a LOT of YEARS to be flexing a glorified rubber band.

Sounds most likely the Bore Seal is just exhausted.
that seal is actually "the return spring" which retracts piston & releases the brake.

I'd take it apart,,clean piston & bore GENTLY and Carefully,,and put a new bore seal in it.

Inspect both the Piston and the bore for any unusual wear.

Good Luck!

................................
Here's a Picture of the effect,,of what actually Releases disc brakes.

The Distortion is exagerated,,but easier to see the action.
(Obviously,,and Old,Hard,COLD,Stiff rubber will regain some compliance and elasticity once brakes heat-up well......
Which might help explain why sticky when cold and better when warmed up a bit.
A STICKY caliper when cold,,is actually due to a SLIPPERY Seal.
When it warms up,,SEAL gets Sticky and Brake tends to retract/release more correctly)

http://www.dippy.org/svcman/image/05h04.jpg

Answer 3

The most common problem (95%) of hydraulic brake sticking is crud build up under the seal. It causes the seal to squeeze against the piston, not allowing the piston to return. The caliper will have to be rebuilt.

Answer 4

It may be the master cylinder thats causing your problem, it may not be releasing pressure or maybe its in some kinda bind. Has the bike been dropped on the right side before? Inspect the brake lever and linkage really good.

Answer 5

take them off