HI Bagga , yes with my own hands once mechanic took it apart I felt the bore and piston and there was no pitting or corrosion on either , all very smooth

 

The bike being discussed is a 1990 model, with tapered timken roller wheel bearings...

OP: what type brake fluid is being used, any chance DOT 4 and Dot 5 could have been mixed at some point (this bike should use DOT5) ?

Have you replaced the guide bushings and pins?

 

If a rebuild gives a hint of problem, you should replace caliper and master. No real way to measure for wear it other problems.

 

Bleeding brakes , especially ones that are completely empty of fluid can be a little tough . There's a good chance that you might still have air in the lines . Once you've changed the brake line , I would bleed them , don't be afraid to pump lots of fluid through , let it sit and pump more through it .

Anyone know if the hose from the reservoir to the master is supposed to be soft like squeezable ?

If I'm not mistaken , once the bleeding is complete , you should not be able to " pinch " the line . Pretty much should be hard as a rock .

 

Use something to hold the brake pedal depressed all night, sounds like you have air stuck in there somewhere and this will usually help push it out. It works great for front brakes as the bike sits, sometimes with rear brakes you might need to lift one end of the bike to make sure the air can run up toward the front or back to the rear.

 

Doesn't the piston close off the reservoir when it is fully depressed creating a sealed hydraulic system to actuate the caliper pistons? It seems that you would want to leave the lever extended or half-way depressed to allow the air in the lines to migrate up to the reservoir...

 

I am not seeing how air in the line can cause the brakes to stick on...

If the hydraulic system is clean and full of fresh fluid, the problem must be mechanical.

The grooves for the seals in the caliper must be absolutely clean, no residual brake fluid or corrosion, the seals must seat fully into the groove.

The pins must move freely in the bushings, worn out or corroded pins/bushings will cause the caliper to bind.

Make sure the caliper is running in the correct position over the disk, not pressing on one side or the other.

However, RIPSAW has a valid point: the caliper is 30 years old, it doesn`t owe you anything at this point...

New caliper assemblies are still available from the dealer. A little over 200 bucks.

 

It's very possible that the hang up is the master. Wear and improper alignment of the piston to vent intake of the reservoir will lock up the caliper. Also, if the system is new or rebuilt, the master should always be bled into itself. Then connected to banjo fitting. All bleeding needs to be done with cap off. The system is sealed relying on the bellow seal to pull down in normal operation. That is not enough for bleeding operation. Also over tighten of the master cap will squash the vent slot in the top side of the bellow . Not having air on top of bellow will keep it from coming back up. This and heat from rotor run-out can self apply brake.

 

The only time I have had a brake caliper drag was from debris in the hydraulic system. A small piece of debris was lodged in the fluid return port in the master cylinder, and preventing fluid from returning to the master cylinder.

 

the intake port has a very small hole and a hole about 1/8". I stuck my finger in the bore and plugged the larger hole and poured fluid into the intake port....the fluid wouldn't flow thru the very small hole. I kept my finger over the 1/8 hole and blew air into the intake port. it blew what ever was in there out. I kept the bigger hole plugged with my finger and poured fluid into the intake port and then the fluid flowed thru the very small hole. you might want to recheck it.