GS 850 Font brake master cylinder --help

[Anonymous]

Hi, I have a 1985 GS850 G over here in the u.k. I have have just recently un-seized my front brake calipers and fitted them with new pistons and seals.

But now that i have come to bleed the brakes i cannot seem to be able to get the brake fluid to pump out of the master cylinder into the brakelines.

I have thoroughly checked the master cylinder and it appears to have plenty of pressure at the lever but it just refuses to leave the cylinder.

Has anyone else come across this problem, if so i would greatly appreciate any help, many thanks.

P.S ( My deepest thoughts to anyone who suffered on the 11th sept 2001).

[Anonymous]

Just a related tip

It sound like you have a clog somewhere. Could be at the caliper, a junction, or the master cylinder. The reason I am posting this reply is to let you know that if you rebuild the master cylinder you need to keep two things in mind. One is making sure the fluid is clear to be pumped out to the calipers. The other is that it has to return. The small hole at the bottom of your resivoir is the return valve. Neglect to make sure it is clear and your brakes will not open after you let go of the lever.

[Anonymous]

Either that, or you still have lots of air in the system.
Had the same problem with my GS850, after replacing the break lines. Had to pump for at least two hours, before most of the air was gone. Then there was lots of pressure on the lever, but no breaks. Turned out there was still some air left.
A mechanic told me that the air accumulates in the horizontal zones of the breaking system, so it can't go anywhere, unless you keep pumping and pumping and pumping.... :x

Good luck Tim!

[Don Lobacz]

The problem is due to the air that is present at the exit point of the master cylinder. After you release the lever, this air is sucked back into the compression compartment. Since air produces only a fraction of the force that the compressed fluid is supposed to, and the net result is that a tiny amount of fluid dribbles out of the master cylinder and down the brake line. The air in the line easily rises up to the exit point and the cycle repeats. A good power bleeder will usually be able to pull the air down before it can sneak back up, but not always (hydralic clutches are the worst example of this). Filling the caliper and line from the bottom up will push the bubbles up, but this can be messy. The method I use can be a little messy until you've done it several times so COVER OR REMOVE EVERY PAINTED / COATED SURFACE!! I fill the exit point of the master cylinder with brake fluid using a medium sized syringe and then attach the brake line, washers and nut, being careful to route the line UP so that the fluid has to go up over a hump before continuing down to the caliper. Mount the master cylinder on the handlebar (making sure that the back of the master cylinder is slightly up, turning the handlebars to accomplish this), 3/4-tighten the banjo bolt with a wrench, half fill the resevoir with fluid, and lightly 'tickle' the lever to get air bubbles coming up the hole into the resevoir (are you wearing your safety goggles?). After a minute or so of this, you should be getting pressure at the lever. Once you get pressure, you can work quickly and bleed the brakes normally (pressure / release at caliper / keep resevoir from emptying). After you get full pressure, carefully loosen the banjo bolt just enough to let you redirect the line downward, and then tighten the bolt like it's supposed to be. Make sure that the resevoir is at the proper level, everything is tight and that your brake light wires are attached. Spray down any dribbles with brake cleaner and wipe everything clean with a rag. Hope this works for you.

[Anonymous]

Get a brake fluid pump.

Here in the U.S. you can buy a brake fluid pump that pumps fluid from the bleeder. They cost $25.00 here. They look kind of like a gun with a resivoir.