GS850 front brakes sticking

[reign180]

Hi guys,

I've just finished rebuilding the front callipers on my GS850.
When I first bought the bike the callipers were sticking so badly that I couldn't roll the bike at all. After removing the callipers, the pads were literally just chunks and dust.

So now after fitting new seals, giving everything a really good clean, it's still sticking. Not as bad as before but if I go for a ride I never need to use my brakes... She just stops automatically

Any ideas?

[Lunchbox88]

Did you remove the pistons from the calipers and inspect their conditions? I have a feeling they may be worn and for the lack of a better word "scraping" the caliper cylinder walls.

Link to Basscliffs caliper rebuilding guide :

http://members.dslextreme.com/users/storagecliff1/images/brake_caliper_overhaul.pdf

[hillsy]

Either the calipers are still sticking (did you scrape out the corrosion in the grooves underneath the seals?) or the MC is not flowing back when you let go of the lever (more than likely this).

Crack the banjo bolt at the MC and see if the calipers let go. If so, then the return hole is blocked and you need to clean out the MC. Probably best to fully dismantle it and flush it thoroughly.

If the calipers still stick after you crack the banjo bolt, then that's were the problem is and you need to re-build them. (again).

[cowboyup3371]

Make sure you take a small gauge wire strand from say an 18gauge wire and poke through the return hole to clear it.

[reign180]

Stupid question #1: Where is the return hole on the MC?

[Big T]

Take the MC cap off

Then, very gently squeeze the brake lever and let it go

There should be a small spurt in the fluid from the "returning" fluid

You'll have to look down in there. There's a small hole

Did you put fresh fluid in the system?

Did you rebuild the MC?

If your caliper seals are crap, what condition do you think the MC seals are in?

[Steve]

What year and model is your 850?

I ask because they had different master cylinders.

If you have the rectangular master cylinder, there is a plastic tab that is part of the reservoir that covers that hole so you can't see it.
You have to either turn the reservoir or remove it to see the hole that you need to clear.

.

[reign180]

It's a n '81.
It has the rectangular type MC. The seal for it seems to be in good condition, no warping or crustyness. I put all fresh fluid into the system and bled it to death.

I'll try cracking the banjo bolt tomorrow morning and see if the callipers let up.

[cowboyup3371]

Reign,
Instead of just cracking the MC you REALLY need to go clean it thoroughly. If not, you won't get rid of the problem at all.

[bwringer]

Reign,
Instead of just cracking the MC you REALLY need to go clean it thoroughly. If not, you won't get rid of the problem at all.

Yes, this. The answer has already been given -- there is dirt/mung/nasty stuff in your master cylinder.

You have to disassemble the master cylinder and physically clean out the little green men and toe jam in there. More bleeding won't do any good.

[reign180]

Thanks guys.

I'll attack the MC tomorrow if this torrential rain lets up.

Appreciate the advice


Simon