View Full Version : How to fix a sticky disc brake

08-12-2009, 11:00 AM
I recently had the Joy of putting on a front end with sticky front brakes. Most old bikes or brakes are like that, or at least any I have found...

Now I'll be honest here, on my other front end, they were sticky too, but I pried the pads off the disc with a screwdriver, shot WD-40 on the disk and most importantly NEVER touched the front brake lever. Now all was good, but if somebody squeezed it or it got bumped, out came the screwdriver to pry it open again.

Well, I just couldn't see doing that again, so I asked the folks over at hondachopper.com. Red good and a few others taught me how to fix it, and it is actually REALLY EASY. I feel like a real dummy for not fixing the others sooner. This is really a doable fix! The brakes are real simple, basically 3 parts, the piston, the seal, and the body of the brake.

This got me on the road without sticky brakes, I thought It may help somebody.
The following is parts of the conversation:

Red: Take the calipers off and disassemble them and clean the daylights out of the grooves the o rings seat in , clean the o rings with just your thumbnail and reassemble with clean dot 5 brake fluid . Should be good to go .Red

Note: To get the pistons out, the safest way is to try to adapt a grease fitting to them and pumping them full of grease. This is messy and takes fittings. What I did is less safe I suppose but cleaner. Just took a piece of metal and put so the brake piston could not fly out. Then hooked an air hose to where the bleeder valve went. Give it a blast and it should come out. Trust me on this, use common sense and keep your fingers out of the way! The piston really shoots out hard! The best bet, like I said above, is to put some metal or wood spacer or something on there to keep the piston from shooting across the room.

I asked the easiest way to get the fluid out of the master cylinder.

Red: I generally use a shop rag and mop it out of the master , then clean the master spotless with a rag . Do all the brake work and hook it all up except the line at the master ,then fill the master with fluid .Then put my finger over the banjo bolt hole at the master and pump it till it has pressure . Then hook up the hose and check the way the master sits on the bars . If the brake lever is not above the banjo bolt line I loosen the clamp and slide the master along the bars till it is . Use a battery overflow tube on the caliper bleed screw and run it straight up the leg and tape it there . Then pump the master till you have fluid, once I have fluid in the hose I pump it and let the bubbles rise to the top , shut the bleeder nipple . Repeat on the other side for dual disc .

Because I do this lots I have a brake fluid bottle that has 2 holes punched in the top and a piece of mechanics wire thought the sides high up . The wire is so I can hang the bottle at the junction of the tube and lower leg . The holes in the lid are for the battery tube so you can use it as a catch bottle.

rakeNtrail: Boogieman, for what it's worth, I've seen where a tiny air bubble gets trapped in the banjo bolt at the MC. I usually place a box wrench on the bolt, wrap it with a shop rag, crack it open, squeeze the brake and tighten the bolt. Wipe up and top off. sometimes the brakes get much better.

Red: Check the o ring with your thumbnail ,should be coated in white shit . I think it is calcium off the road ,get all that off as well .

Rake , that's why you push the master forward till the lever is higher than the bolt , then the air bubbles travel into the master and bleed out .

Boogie a 6 piston differential bore state of the art caliper just has more parts .

I thought I may have a bit of air in the lines.

Red: Turn the bars so the master lever is the highest point and let it sit over night . Yes it does sound like you still have air .

This is a bit about actually bleeding the brakes.

I looked on YouTube and found http://www.youtube.com/watch?v=oA3HIVkup94 . I had helped bleed brakes on cars/trucks before but wasn't 100% sure on a motorcycle. It is pretty handy if anyone was like me and wondered if they were doing it right...

Basically, you hook a hose over the bleeder and put the end in a catch container (pop bottle... whatever)... have the master cylinder filled with fluid. Pump the brakes till they feel hard/harder. With the brake lever in all the way, crack open the bleeder valve with a wrench. Some fluid will flow out (and hopefully have air bubbles in it). With the lever still in all the way, close the bleeder valve. Pump the brakes till they feel hard, and repeat. Make sure you have fluid in the master and dont suck air in. Also, if you tap or hit the end of your bars bubbles will come out of the line into the master cylinder.

If ya like it, vote in the yellow box! If you have some more info or other methods, feel free to post them! The more techniques, the better!