front brake problem

[orlands]

hello everybody
i have a gs1000S and i've been experiencing some problems with my front brake...
after i break, the brake stays stucked !!!
i found out that if i open the little purge valve (excuse my english..), a few drops of liquid come out and then it's fine again until i brake again a few times....
thanks for your help and suggestions.....the weather is so GSable right now in Paris....

[Redman]

Probably really needs the front calipers to be completely dissasembled. Remove the pistons, and clean up the cyclinder bore, clean up the seal and possibly replace the seals. That is what I have been told I have needed to do on occassion of such as you described. But I really didnt want to take the piston out of the caliper (nor am I equipped to do so).

Or maybe can have some improvement by first bleeding out some of the old fluid from the calipers. Do this for two reasons 1)to remove old maybe thickened - contaminated fluid, and 2) to lower the level in the resivour. Pump out the old thick gray-brown looking stuff, till you see good new looking fluid.
THen also push back the brake pads (and piston) by what ever method you can. Either with a clamp, or my favortite method: using wooden wedges intended for shimming door frames, but by what ever method you can arrange. As pushing back the pads, you can expect fluid to go back to resivor and maybe overflow if not carefull. Then pump the pads back into position with the brake lever action (may need to add fluid to resivour). Sometimes just exercizing the pistons in this manner a couple times can provide some good improvement. This is what I have done, with good results.

I think this situation of the brake 'hanging up' and not fully releasing, happens from the fluid not being changed in too long of a time (years), and then thick sludge and other contaminates get stuck in the piston seal.

.

[orlands]

thanks a lot redman for your quick info...
old fluid seems to be the problem...
going to replace it..
going to check the pistons ..hope it s not too complicated/risky to take them apart....
i have too double check but i had the feeling that there was not fluid coming out of the resevoir when i pressed one of the pistons with a clamp...
i hope there's not a problem with the master cylinder that i got used on ebay....
am going to check for some info on cleaning the pistons...
thanks again

[Nessism]

Rebuilding the caliper is a fairly easy task. The trick is getting the piston out - compressed air works well. The brake fluid solidifies after a while and you will need to clean all the chunks out. New seals of course, and if the piston has pitts in the metal on the sealing surface, replace that as well.

Good luck.

[gremlin]

let me put my .02 cents in. after time on every thing you drive. you can check with every owners manule. you will need to change brake fluid after a certan milage.

what happens over time a very fine dust will work its way into the system. this will build up in side the caliper. you get the gunk in the right spot and your caliper will start hanging, with heat your fluid will expand. cousing the friction to stop the bike. this will even give you poor gas mileage. you may not even notice it in your car or truck. you bike is lighter and it will stop easyer.

if your front is doing it, i bet your rear is in the same condition.

acording to the owners manual your to replace the brake hoses every 2 years. then use dot 3 or 4 brake fluid. i would say if you replaced hoses every two years you would be draining and refilling the system.

[brand new bike zealot]

I had exactly the same problem on my 78 550. Didn't check the year on your ride, but it could well be the same thing, my brakes would work allright, but the lever would get progressively harder untill they were basically on all the time. Sucked. The bike had been sitting for over ten years, so I cleaned out the caliper completely (easy job) but it still didn't help. I took apart and cleaned the master cylinder, but to no avail. What it turned out to be was I missed a tiny bleed hole on the master cylinder piston so the pressure wasn't releasing properly. This hole is tiny, I shoved a twist tie through it and blew it out with compressed air. Now the brakes work perfectly.

I'd suggest cleaning and flushing everything anyway, it's not difficult, I did it with basically no mechanic experience, just keep track of how it all came apart... Pay special attention to the master cylinder piston and you should be fine!

[orlands]

ok..
so i starded with the easyest...
changed the liquid...
started the bike...did a little (very little) ride...and same problem....

it certenly is ,like Gremlin said, the heat that expands the liquid,i guess...beacuse it gets worst the more i ride (without touching the front brake)...
brand new bike zealot: the bleed hole is it one of the 2 inside of the thank ?

my story is : MC leaking >bike seat for the winter..> no pressure at all > got used MC on ebay...
after i changed the fluid yesterday, i still didn't have a very strong pressure...i can press until MC goes all the way...maybe its normal...
Am just afraid to take apart the caliper and piston to realize the problem is coming from the MC i just got...

[Nessism]

You may have gotten air into the system when you changed the fluid. Careful bleeding of the system is necessary to get all the air out.

That said, the system needs to be taken apart and cleaned. Changing the fluid is not the recommended soulution since the old fluid has already solidified in the system as evidence by the sticking piston.

[KEITH KRAUSE]

Lots of good advice above. Odds of what's wrong with one or both of your calipers depends on the past history. Have they sat a long time with the same fluid, etc?
Most common "stuck caliper" problem on your model is swelled/old piston seals. Also, make sure the second tiny return hole under the reservoir is clear. You have to remove the reservoir to reach it. Brake lever return action will be poor if this hole is blocked.

[orlands]

hello everybody....
so i took everything apart (caliper and pistons) and cleaned....
the litle return hole (wich is inside the reservoir, right?) is clean...
and after a litle run, everything seems to work fine...
if it gets stuck again, i ll go for a MC detailed cleaning...

[orlands]

so ...
after a longer ride...its still working...knock on wood....
i just still think that the lever is not very strong...but the bike seems to brake pretty well..-- i know this is usualy due to air in the system..but did the purge and everything seems ok...
any sugestions ?

thank you everybody..all your suggestions helped me a lot to understand brake systems and to fix my problem (old stycky fluid..i guess..)...

my bike would have been sitting in a basement or sold for parts if this site
wasn't existing...
thanks to everybody
thanks to the GS resources

[Steve]

Having "been there, done that" more than once , I will agree that the main culprit here was the little drain/bleed hole in the bottom of the master cylinder. It allows the expanding fluid from the wheel cylinders to come back into the reservoir without building pressure. This hole sits right next to the piston seal, so the first thing that happens when you move the lever is the hole gets covered and can no longer bleed pressure. This give full braking pressure to the disks.


.