Sticky Brakes

[CatatonicBug]

Both wheels seem to have a problem with the brakes continuing to grab after I let off the brakes. Thinking it was the spooge holes that needed to be cleared, I started with the front hand brake. I removed both calipers from the wheel and took them both apart (separately), cleaning as I went. I reassembled the one front caliper, and began the process of bleeding the brake. It bled properly, but when I got done, the front wheel does not spin freely like I think it should. So, I opened the bleeder valve to releive the pressure, and nothing happened. The brakes still have a lot of friction and won't allow any free-spinning at all. Is there something in the caliper that might be preventing it from letting go of the rotor?

[boyat68]

CatatonicBug:

By chance did you loose the pad spring when you reassembled? Perhaps the piston seal was not installed in its groove properly or was stretched and folded over to wedge in the barrel when the brakes were applied. This would prevent the piston from returning.

[Axel]

Linked brakes

Unless I'm mistaken an 81 MNS has linked brakes so you'll have to clean the spooge hole in the rear master for the rear disc and the left front disc. I didnt see anything about cleaning the front master either . Thats where the spooge hole is that causes the troubles - in the masters . If I am wrong- someone straighten me up !

[CatatonicBug]

I made sure I didn't loose any parts. We are only dealing with the Right front brake at this point, as I have removed the left front caliper altogether while I try to figure the right one out. The poston seemed to have gone back in the caliper just fine. The thing that I am unclear on is, what sucks the piston back away from the rotor when you let off the hand brake lever? I figured that by opening the bleeder valve, I would be taking the spooge holes out of the equation by aleiviating all pressure in the system. Is there a spring that should push the piston back away from the rotor and keep it from grabbing so hard?

When I took it apart, I had 8 parts:
1. Main caliper body
2. Secondary caliper body/rotor guide piece (not sure of technical name)
3. piston
4. large shiny metal sheet that went between the main and secondary caliper pieces
5. tiny shiny metal sheet that rests against the brake pad and the secondary caliper piece
6. shaft that holds the brake pads in - held in with a cotterpin
7. shaft that holds the secondary Caliper piece to the primary - held in with a cotterpin
8. formed metal plate that rests under the brake pads - didn't seem to serve any logical purpose in my mind.

There was no springy anything to push the piston away from the rotor. should there be? The left brake caliper had all the same parts, so I figured it was not missing anything.

[bikerphil]

There is no spring that pushes the piston away from the rotor. Did you clean out behind the piston seal? This o-ring type seal comes out using a small pick. Gunk underneath this seal in the caliper housing will bind things up for sure. Also, using anything else than clean brake fluid to clean the rubber parts will result in swelling that will cause binding. Make sure there is absolutely no cr@p behind the seal or anywhere else in the caliper.

[CatatonicBug]

I will take it back apart and remove the piston again and clean under the seals. I didn't remove the seals last time, I just cleaned the whole thing while it was still attached to the piston. Of course I only used brake fluid to clean with. Should I lubricate any part of the caliper when I put it back together? it was hard to tell if any of the parts had lube on them, or if they were just dirty.

Maybe I need a lesson in brake theory...

How does the piston let go of the rotor if there is nothing forcing the piston away from it? Does the action of letting go of the hand lever "suck" the brake fluid out of the caliper and thereby pull it away?

[egsols]

I believe the piston returns because the braking system is a closed system, that is, no air, just brake fluid. Fluid cannot be compressed so it must have somewhere to go. When you squeeze the lever you are forcing the fluid through the lines, as it can't compress it forces the piston onto the rotor, when the lever returns, so does the fluid and the piston returns into the caliper. If the spooge hole is not allowing the fluid to return properly you can encounter a sticking piston.

[CatatonicBug]

Ok. I have taken both master cylinders apart and cleaned them. Seals all looked good and did not seem to be in need of replacement. I did run into one small issue though...

The bleeder valve on the rear caliper does not have a hole in it to let anything out! I thought maybe it was just dirty or clogged, so I took it out and blew in it with compressed air, and even torched it to try to burn out any junk. There is no hole at all in the thing.. I assume that is NOT normal?? Should I worry about it, or should I just loosen the threads and let the bleeding happen around the threads of the plug?

Also, what do you guys use to add brake fluid to the rear master cylinder while bleeding it? The little opening is in such a weird angle that it's almost impossible to pour into it. I tried using a modified drinking straw with one end spread apart (like an Icee straw) so I could pour into the wide end and run it into the opening. Is there a better way?

[Axel]

ya

I also use a small funnel with a tube on it so I can refill the rear master when bleeding . This is preferrable to removing the 3 screws and taking off the top cap . They decided to make it easy on us with the hex head cap filler - not!

[redbone]

same probs

cata, the bottom line is that the xs1100 brake system sucks. that being said...i've had this prob off and on with my 1980 mns. sometimes the piston will go "cocked' in the caliper when you use the brake and will not release. this is usually identified by gouge markes in the caliper and on the end of the piston. here's what i did that worked. take the piston out of the left caliper and put in the rite caliper and vice verse. now i know this sound idiotic but after 27 years there are miniscule imperfections in the piston and the caliper. moving this imperfection sometimes fixes it. it worked for me. like someone else said also make sure the seal is not rolling or folding when putting the piston back in [lube it well]. hope this helps.

[CatatonicBug]

I think I actually got lucky on this issue. I removed and thoroughly cleaned both Master Cylinders and I can now roll freely down my driveway. The fluid in the rear was all black, so I imagine it had not been changed in a very long time.

[XSPastor]

Also, what do you guys use to add brake fluid to the rear master cylinder while bleeding it?

I use a turkey baster. It holds quite a bit of fluid and gets in there without spilling it. I'd replace that bleeder valve.

8. formed metal plate that rests under the brake pads - didn't seem to serve any logical purpose in my mind.

Are you talking about the brake shims? If you are, they help the brakes to not squeal. Use anti squeal grease too. That will ensure quiet braking.

And for everyone; in the interest of clear communication...
Loose = not tight
Lose = I can't find it.