Front Brakes Not Releasing

I have just finished some major reworking my 1980 KZ100 LTD, including power coating the front master cylinder, and both front brake calipers. Took it for a ride yesterday, didn’t get far from home when I noticed the bike wasn’t rolling like it should and when I pulled in the clutch the bike came to an abrupt stop. Didn’t take much checking to discover both front brake rotors were really hot. Turned around and got back home to check out. The rotors got pretty hot and I hope I didn’t destroy them. To get back home I rode slowly and at one point the brake light indicator in the instrument cluster came on. After getting home I opened one of the front bleeders, releasing some pressure. After applying the front brake, the again the brake wouldn’t release. Everything was too hot to look any further.

Looked at it this morning and it rolled fine, applied the brakes, released the handle, still rolled fine. Once it warms up enough I will take it for a ride and check it. Does anyone have ant thoughts on what may be happening? I don’t want to jump to any conclusions or say the power coated parts have anything to do with the problem, just describing the conduction.

My thought is the master cylinder once pressure is applied will not release pressure. Does anyone know if this master cylinder uses 1 or 2 holes between the reservoir it is the “trapezoid” type? I only remember seeing 1 hole.

Thank You
Jim Smith

The release hole in the master cylinder is blocked, either by a faulty brake lever not allowing the piston to retreat fully, a sticking piston or - very most likely - the bleed hole is blocked. This is very tiny and can be checked for clearance with a strand from a copper electrical wire.

Thanks faffi
This is pretty much what I am suspecting. Do you know if this is in front of or behind the primary hole, and how far apart? I made sure the primary hole was clear before assembly, but I did not see a second hole. when it was power coated they didn't mask off the reservoir and finding a hole that small will be hard, unless I know where to look.

I just went for a ride, went OK at first, but then started happening again.

Jim Smith

They are usually about 10 mm apart from memory and the bleed hole is really thin.

Thanks again, I will be pulling it off tonight or tomorrow sometime. I hope I can find it and clear it OK.

Jim Smith

Pulled off the Master Clyinder, finley was able to locate the small hole and clear it. Re-assembled and installed. Tonight I will bleed the brakes and test drive.

This is my first time haveing any power coating, learned a lot, in the future I will know to tell the shop doing the power coating where not to finish.

Jim Smith