both front and rear brakes gone?

[a_man0311]

So im working on fixing the brakes on my gs now that it's running (it's an 850GL.) Anyhoo:

When I bleed the back brakes, I can get nice pressure, however after a few brake operations they become soft again. Could this be a problem with the rear brake piston seal leaking air into the system? Or does it sound like lines? I'd expect lines to leak fluid, and everything is clean, so my only thought is that air is entering the system from somewhere. This is born out by the fact that if I re-bleed after losing pressure I get a lot of air out again, only to repeat the "i think im done but after a few pumps of the brake it's soft again" problem. I have the dual piston rear brake caliper.

The front caliper is baskically locked in the "pushed in" position. It looks like there is a LOT of sediment in the master cyl. Admittedly I haven't looked hard, but is there a basic tuneup FAQ for this that I can work with? Or should I scrap it and find another cyl/rebuild the one I have?

I've heard the suggestions on new lines which I will do. Any other advice? Thanks in advance for any info!

[Nessism]

Time for full system tear down; remove the caliper pistons, split the rear caliper, remove the master cylinder pistons (front and rear), and if the bike has the original brake lines throw them in the trash.

After everything is torn down scub the parts with soap and water and inspect the master cylinder bores for pitting, as well as the caliper pistons, and replace the parts as necessary. I recommend replacing the caliper piston seals at minimum and the master cylinder plunger as well if you want to be safe (particularly that rear which seems to be done for).

For brake lines most people go for stainless/Teflon. You can make your own set from Earl's parts for about $100 if you are handy with tools.

No short cuts on brakes since your life may depend on them.

[Turtleface]

Time for full system tear down; remove the caliper pistons, split the rear caliper, remove the master cylinder pistons (front and rear), and if the bike has the original brake lines throw them in the trash.

After everything is torn down scub the parts with soap and water and inspect the master cylinder bores for pitting, as well as the caliper pistons, and replace the parts as necessary. I recommend replacing the caliper piston seals at minimum and the master cylinder plunger as well if you want to be safe (particularly that rear which seems to be done for).

For brake lines most people go for stainless/Teflon. You can make your own set from Earl's parts for about $100 if you are handy with tools.

No short cuts on brakes since your life may depend on them.

Just did this myself, it's well worth the effort for the peace of mind. Not terribly expensive, if you consider the cost of a trip to the ER. Don't go cheap and try the K&L rebuild kits, OEM is the ONLY way to do it right.

[a_man0311]

thanks!

I was thinking this is where I needed to go - glad to have it confirmed.

[Turtleface]

You noted that you have the dual piston rear caliper. If it's anything like mine, you'll have an o-ring that's sandwiched between the two caliper halves. It's hard to pick out in the parts fiches, make sure you pick it up. I didn't catch it and had to wait a few days for the part to arrive.