Took the gs850 out for a ride.

[Scudder]

Finally go the rear brake to work so I took my newest project, 1980 gs850L out for a couple miles last night. All is well so far. I am having some difficulty getting my front brakes going. I bought a new master cylinder and I am doing what I've done in the past (pump the lever several times, holding it and the loosening the bleeders and supposedly letting the bubbles, etc. out.

I've done this routine plenty of times, but never had it take this long. I did have all the brake flluid drained from the calipers and the line, so I expect it will take a bit longer to get the brake fluid from the master cylinder, through the lines to the calipers. I guess I'll just be patient and continue with the process. Anyone know an easier way?

Scudder

 

[UncleMike]

Finally go the rear brake to work so I took my newest project, 1980 gs850L out for a couple miles last night. All is well so far. I am having some difficulty getting my front brakes going. I bought a new master cylinder and I am doing what I've done in the past (pump the lever several times, holding it and the loosening the bleeders and supposedly letting the bubbles, etc. out.

I've done this routine plenty of times, but never had it take this long. I did have all the brake flluid drained from the calipers and the line, so I expect it will take a bit longer to get the brake fluid from the master cylinder, through the lines to the calipers. I guess I'll just be patient and continue with the process. Anyone know an easier way?

Scudder

Take master cylinder and caliper apart and clean everything.

 

[Normk]

There are many posts on this subject on various bike groups. A problem with bike brake bleeding is the small volume master cylinder combined with the vertical distance and line volume. It can be difficult to move air downward effectively with the small volume pumping action available from the master cylinder.

I use a vacuum bleeder with either a Mityvac hand pump or continuous volume powered pump which makes things easier. In many cases it is easier to position the bars so that the master cylinder is at the highest point and lever end angled upward. Pump the brake lever with rapid short strokes and bubbles should be ejected from the compensating port into the reservoir. It can take some time to clear the air in this manner but it can be very effective. If bubbles are not ejected from the comp. port, the port is likely blocked and requires cleaning. Take care that you do not create a burr on the inside of the bore or it will destroy the piston seal.

I think the fact that you hadn't mentioned bubbles is why Uncle Mike mentioned disassembly and cleaning as we seem to have jumped to the same conclusion.

I have sometimes found it to be effective to push a caliper piston back a small amount (with caliper in place, wedge a brake pad) in order to push air back out of the compensating port. Take care not to push too far or too rapidly or you may spray fluid over everywhere. Pumping the lever a few strokes will push the caliper piston back out, wait a bit for the air to reach the top again, tap the lines, fittings and brake components to dislodge adhering air bubbles and then push the caliper piston back again.

I have done this for field repairs where no brake bleeder was available with good success.

A few more details might be helpful.