bleeding brakes

[abird4]

I have had a 2001 Sprint RS since the end of last year. Like it a lot, but have had a bit of a bit of a problem with the front brake getting spongy/long lever travel. First noticed this about 200 miles into ownership; brakes bled by mechanic, felt better; then noticed it again about 1200 miles later. In both cases I had moved the reservoir in order to adjust fork spring preload, in such a way that I may have put a bit of a kink in the hose, and driven around like that for a while.

Despite modest mechanical abilities, I decided to try to bleed the brakes myself. Bought and installed speed bleeders. Seemed to be going OK until I drained the reservoir too low and let air in the system. Then got floppy lever which did not push through the fluid when I added more.

I spoke to someone at the company who suggested loosening the fitting between the master cylinder and the line leading to the caliper, and pump the lever slowly. I did so, and eventually got fluid coming out of the speed bleeder (bubble free) although it seemed to be pumping a relatively small amount of fluid per stroke of the lever, compared to before. I then tightened that speed bleeder and went on to the next one.

I was unable to get any fluid coming out. I then tried the trick with loosening the master cylinder fitting again. Very little fluid seeped out around the fitting. It appears that there is still air in the system, but I don't know what my next step is. Not liking the fact that my motorcycle is unrideable at the moment! Have an email in to the company, but thought I would try here, too. Any advice would be much appreciated--thanks--Tony

[MrMoped]

abird,

Those speed bleeders are pretty good. Sound like you may have an air bubble in the line that connects the two calipers. They can be an absolute bastard to shift at times.
If this is the case, the simplest method is to undo the left hand caliper (with the single brake line), place a piece of timber between the brake pads (to stop the piston popping out) and raise that caliper so that the bleed screw is the highest point.

bleeding from here will dislodge the toughest air bubble.

Another trick to dislodge the stubborn bubble is, when you have brake pressure, to apply pressure to the brake lever and zip tie it to the handlebars to maintain pressure. Bubbles will travel back up the line and out the reservoir. You can leave it overnight like this if needs be.

good luck.

[RexxyPup]

there are several threads about this one. Two reasons appear to have emerged....

carp (anagram) on the caliper pistons
Master cylinder not man enough

I used to have your problem, but I now regularly clean the pistons off and push them back into the caliper and hey presto good brakes for another 3k miles.... it's jokingly called 'exercising your pistons' on this forum.

You can also get some special grease to lube the pistons with. A guy on the bay sells it

Rexx

[Rammstein]

Had the spongy feel of front brakes on my 06.
Bled the brakes , as i bled them i added new fluid as i went till i had totally replaced the old stuff.
Brakes are awesome now.

[jefftarlton]

I tie a loose knot in a 3-4ft long piece of clear hose that fits tightly over the bleed nipple. Hang the knot from the bars. It lets you see if air or fluid is escaping from the nipple. Bleed the right side, then the left.
Individual lines to each caliper make bleeding so much easier. I fill the reservoir and let gravity do the work usually.
Exercising the pistons made my stock brakes work fine, but after a thousand or so miles the sponginess came back.
Six piston tokicos and a larger m/c are the real solution.

[abird4]

I have been contemplating the master cylinder upgrade. Do you think that would take care of the issue on its own, or is the caliper upgrade also an important component of the solution? Tony

[clockwatcher]

I use this thing called a Mighty Vac. It's a little pricey, but it works well with very little mess.

Link

[abird4]

The mityvac totally came through! Thanks! Tony