Brake Bindage

[GS250]

How can i check and determine if my brakes are binding? I checked my service manual and it says to check for bindage. what exactly am i looking for?

[TooManyToys]

With the wheel off the ground, does it turn freely? If not, then maybe the brakes are binding. Need to also check this hot.

As brakes age there can be a number of issues. The pistons not retracting back into the caliper bores due to oxidation or brake fluid decomposition. Brake hoses can form an internal tear and act like a one way valve. Master cylinder issues ....... adjustment. The list goes on.

[GS250]

with the wheel off the ground it will turn but it won't spin on its own. i've already rebuilt the mastercylinder and the brake pads and line are in good condition. i'm thinking the caliper might need some work. thats the only thing i havent rebuilt since i ran out of cash. how can i fix or clean it up without spending more money, i have plenty of brake fluid.

[TooManyToys]

You can never know a brake hose is good by looking at it. Just a comment.

I always replace the seals and boots in a caliper when I take them apart, but I read here that others have not. Piston retraction is dependent on the elasticity of the square cut O-Ring, which ages over time. And old bikes usually can use new rubber.

It's usually easy to take apart a caliper, unless the piston is corroded in place. Then you need to use the hydraulic force from the master it get it out. With a bike, I prefer to pop the piston while the caliper is still hydraulically connected (a little more tricky with twin calipers), and once the piston is out tie the brake lever on (or foot pedal down) so the fluid won't completely drain out. Then you can remove the hose banjo bolt from the caliper, freeing it for bench work. There will be two copper washers, one on each side of the hose that you will need to reuse if you don't have new ones. But even before I do this I check if the bleeder screw can be removed from the body. Sometimes they are corroded in so tight that they break off, and then I just get a replacement caliper.

With the piston out, remove the boot and the O-Ring from the bore. If the piston is pitted, it's time for a new one as that surface is one of the hydraulic sealing surfaces. I never reuse a piston with any pits. The caliper bore can usually be cleaned up with Scotchbrite pad or fine sandpaper after cleaning it of brake fluid by using alcohol. Never use any petroleum-based products around brake parts.

What you need to pay attention to are the grooves for the boot and O-Ring. Any corrosion in these areas push the rubber parts harder into the piston, which makes retraction harder. You need the retraction for running clearance between the pads and rotor when you’re not applying the brakes. I use a pick tool to remove any corrosion in these grooves, and I also have some abrasive cord (from an industrial supply house like McMaster) to get in there a little better. Again, I don't want to abrade this area too much and loose sealing ability. Once I'm comfortable with clean surfaces, I wash everything with alcohol. If you’re contemplating painting the caliper, now is a good time.

To assist in getting everything back together, I use brake assembly fluid, which is glycerin based. I do not use brake fluid as it is hydroscopic (readily absorbs water) which can lead to faster corrosion around the boot area. You used to be able to get small gel packs of assembly fluid from auto parts stores like NAPA. You do not want to use any petroleum-based grease or oil for this.

Brake fluid is glycol based and the rubber used with this chemical is not compatible with any oil. Petroleum will make the rubber swell and degrade. It may take a while, but it's going to happen. So don't just pull something that's handy off the shelf to use as an aid in getting the caliper back together.

First I wipe assembly fluid on all the caliper internal surfaces, which assists in preventing any air bubbles from attaching to the walls, then the O-Ring as well. The O-Ring is easy to fit into the tangential groove cut into the caliper body. The groove is usually larger then the O-Ring which is part of the design. Next I fit the boot into it's groove and use finger pressure to make sure its fully seated into it's bore.

The next part can be the frustrating part, getting the piston into the boot and down past the O-Ring. Remember with the O-Ring this is a compressive state. I wipe the piston with assembly lube like I did with the caliper body. I have already taken an aluminum soda can and cut it so I have a center section about 1 to 1 1/2 inches high. I then cut it on this band's side so the two edges can overlap and be adjustable for the piston size. De-burr any nasty edges. I fit this into the boot first (not past the O-Ring), then push the piston into the center of the band so the piston can slide past the caliper boot's opening. Then push the piston into the bore so it goes past the O-Ring. You can use a socket or extension to keep away from the sharp edge of the band. If it takes more then hand pressure, then the O-Ring may not be into the groove all the way. You need to start over and recheck the O-Ring and it's groove. You can avoid issues with the aluminum band if once you get the piston past the boot by pulling the band up and off, leaving the boot on the piston before pushing past the O-Ring. You'll see what I mean when you’re doing this.

The soft copper washers are needed to seal the hose block to the banjo bolt and caliper body. If you don’t have new ones, they should be softened first. When the copper is compressed it gets work hardened, and sometimes when reusing old washers to get a proper seal you have to toque the bolts down pretty hard. Rather then risk the bolt or caliper body threads, all you have to do is heat the copper washers to red hot and let them cool naturally. This will anneal the metal and allow it to seal beast. I usually do this by putting them on a piece of wire and heating them with a propane torch, but you can get creative with a gas stove, barbeque, or other heat source.

Motorcycle calipers rarely have a lot of corrosion issues, save the bleeder screw. It’s usually brake fluid coagulation that forms a goop in the caliper body. If the little rubber caps are left off the bleeder screw water can get down there and advance the galvanic corrosion between the steel bleeder and aluminum caliper body.

[Nessism]

In my experience with rebuilding half a dozen GS bikes so far, you have about a 50% chance of having corrosion pitting on the caliper pistons. Pop out the pistons with compressed air and clean everything out. If the seals look good you can reuse them if money is tight. For the caliper sliding pins you need to get some caliper grease, not regular grease.

[TooManyToys]

Pitting on the pistons is not what I meant by corrosion issues.