rear brake problem

[79-GS550-L]

Hi everyone,

I'm having some trouble with my rear brake partially locking. It doesn't lock up *completely*, immobilizing the bike, but it doesn't quite release all the way, and so it drags. Makes it really difficult to not stall out at traffic lights! I thought I was just a crummy rider until I discovered the brake problem If I put it on the center stand, I can turn the wheel with my foot but I can't get it to spin. If I pry the caliper away with a screwdriver then I can spin the wheel. When I press and release the brake, again I can turn it but can't spin it.

This happened a while back, and I sprayed a whole lot of PB blaster all over the caliper, prying, and braking, over and over. It didn't do too much. Then I used something (I don't remember whether it was WD-40 or PB blaster) and sprayed it around where the brake pedal linkage enters the master cylinder, and also lubed the brake pedal pivot itself, then everything was perfect. A ride or two later, it's causing problems again.

How can I figure out whether it's the cylinder or the caliper that needs help? Does this sound like a rebuild is needed, or just some more lubing?

[koolaid_kid]

Sounds like the pistons are sticking in the calipers. These are easy to rebuild, and certainly a safety factor in your case.
They carry the parts on-line, such as at Bike Bandit. You would need the piston seals and the dust seals. Also lube the brake pad pins, which the calipers slide on.

[baco99]

what's the best thing to lube the pins with? lithium grease? or copper grease?

[Ironriot]

I ain't no expert in bikes but lithium grease is the best grease for everything that needs greasing IMO

[TheCafeKid]

It could very well be your caliper pistons, but it could also be your master cylinder. I just had this very same problem and it was my master cylinder, tho i broke the calipers down and cleaned the pistons anyway. It's cake to rebuild the master, as long as you have circlip/snap-ring pliers. But just check your pistons first. They'll require the least amount of effort. If you pull the cups out of the pistons, inspect them closely for rust or surface abrasions. Use steel wool to clean em up. If that doesnt fix your prob, move to the master cylinder. Like i said i had the EXACT same problem on my 750, and since it seemed to get better when you sprayed the linkage with PB, id bet its the cylinder. Sometimes, even with that rubber gusset over the plunger, it still gets rusty. Pull it all apart, take a wire wheel to the plunger arm and the cylinder seal (the metal cap on the bottom of the cylinder) flush the cylinder out really good, inspect the inside of the cylinder, removing any rust you may see with steel wool (you might have to shove it up there and clean it out with a screwdriver or dowl, just be careful not to score the sides of the cylinder) flush it again, install your rebuild kit, put it back together, prime the cylinder, making sure you get as much air out of it as you can, and install it. Bleed your brakes and you should be good togo. You can order a rebuild kit from any motorcycle parts supplier. But make sure you have those pliers!! Otherwise you'll do what i did and snap that circlip that holds the bottom seal in and then you might be fuxored. I got lucky and found a replacement at autozone in a assorted pack of them. But it was a bloody b!tch..lol.

Any questions, just ask!!
TCK

[79-GS550-L]

Ok I'll start with the caliper and then move on to the master cylinder if needed. Now, if I were to upgrade to stainless lines I guess now would be the time to do it... but there are only two very short sections of flexible brake line going to the rear brake, it's mostly rigid metal tubing. Will I see any benefit from stainless lines? Or is that something more worthwhile for just the front?

Anything I need for the caliper other than the 4 total seals (bikebandit shows two "piston seals" and two "piston boots")? Do I need new pistons? Any washers to replace?

I have no idea how to bleed these brakes or prime them... I guess I'll have to do a bit of research. Are there any threads/articles/how-to's about brakes?

[TheCafeKid]

Well there are no real washer to replace, and if your seals look good, ie no damage or tears or cracking/rotting, you'll be able to reuse them. I did, and it works just fine. what you'll want to do is carefully pull the piston seals off (now keep in mind i am talking from my 750 experience, i dunno how many pistons or seals you'll have in your calipers, i have twin piston.) and use a pair of vice grips to pull the cups out. Try to use even pressure as you do so, so you dont bind the cup or bend it/put teeth marks in it. they'll be a little hard at first but once you get them moving they'll pull right out. Inspect the outsides of the cup for tarnish/rust/debris etc. and remove it with steel wool. You'll want to do your best not to score the cup's sides. once you've cleaned them well (you can even dip them if you wish) make sure the holes (i dunno what they'd be called) where the cups came from are clean, as well as all the fluid ports in the caliper itself. Use some carb cleaner/brake cleaner and compressed air (like air duster, cos it has that convenient little tube on it, fits well in all the holes) then once youre satisfied that its clean, pop your cups back in, put your seals back on and put her back together (make sure the rubber gromit that sits between the caliper halves where fluid feed from one side to the other is seated well. and bolt them back together TIGHT or you'll suck air, and all of your bleeding will be for naught).

Again, im not sure how your rear break setup is, but my rear has two bleeder valves. One for the front side and one for the back. I started with the front side because i figure if you have an air bubble there, its not going to feed fluid to the back anyway. If you can purchase a self bleeder kit i highly suggest it, otherwise its gonna get messy and it may take two people. Basicly, with a self bleeder, you hook a clear rubber hose to the bleeder valve that is connected to a little bottle it help to keep air from being sucked back in thru the bleeder valve as well as contains the mess. I would also purchase a bottle of brake fluid, cos it may take that much depending on how much air is in the line. To bleed, front valve or back, the basic concept is to open the valve while putting slight pressure on the brake pedal, and then before you hit bottom with the pedal, close the valve to avoid sucking air. Its sometimes a long process, but in the end, your brakes will be a hell of alot more functional. You need to repeat this process untill you see no air bubbles in the fluid coming from the valve. Repeat the same steps for the rear valve.

To prime your master should you need to, and this is the way i did it, im sure there is a more pro way, but i dont have the tools, nor the experience with these cylinders, so this way worked quite well for me, but its a bit messy. have the master removed from the frame. Youll need the banjo bolt from the top of the cylinder too, or one that is the same size and thread. Under the resivour there is a bolt. Take that out and the banjo bolt out. Pour fluid into the hole under the resivour, as this will help to push air out of the cylinder. once it fills up pretty good, replace the bolt. Then pour just a bit thru the hole where the banjo bolt was. Now put your finger over that hole tightly, and slowly push the plunger in by hand, and as you release the plunger, tight your finger over the hole as hard as possible to try to prevent air from sucking back in. You'll notice as you push in the plunger air bubbles escaping around your finger. Keep repeating untill the bubbles are very few. You prolly wont be able to get all of them with this method but bleeding will help get rid of the rest. Once you are satisfied, take it to the frame, and put the hose and banjo fitting back on, try to be quick so you dont have the risk of air getting into the system. If you have to rebuild the cylinder, youll want to prime it before you attempt to bleed your system.


Like i said, im sure there are better ways, but this worked for me quite nicely for me. I had it cleaned and rebuilt in about an hour ( would have been faster with snap ring pliers heh) and back on the bike and bled and riding inside of a half hour. Good luck!!

TCK

[TheCafeKid]

oh and as for stainless lines, you may get some benefit out of them, i havnt changed mine over. They are pretty safe where they are at, and i would consider stainless more for the front since its going to take all of the flying at you stuff. I would however get hose casing for the line leading to the caliper since its a bit exposed.

TCK

[baco99]

from what i understand, stainless lines in the rear won't help too much. i added stainless lines to my GS500E before i sold it and they made a HUGE difference in braking. the only downside was they made front end dive worse without progressive springs in the shocks. once i added progressive springs, the bike handled very well.

i think the only reason to go SS in the back is to complete the look. And you'll need 2 pieces. i was just on bikebandit.com and they sell Biker's Choice brake lines in a variety of sizes. Measure up what you need, then get a few screw-in fittings, and you're on your way. Custom look and better performance without the customization.

[79-GS550-L]

Ok I ordered the seals for the caliper. Let's hope this fixes it!

[baco99]

Ok I ordered the seals for the caliper. Let's hope this fixes it!

so...? how'd it go. new seals all around for me and it seems to be working great.