Brake Caliper Rebuild?

[Da-Bubble]

Hello,

I'm trying to rebuild the brakes on my 79 special with little success. I found the tech tips about cleaning the master cylinder but nothing for the calipers. I have rebuild kits for each one but cannot get the pistons out. The bike is completely disassembled right now so no fluid in the brakes. How can I get the pistons out?

Thanks!

[wingnut]

Blow it out

Do a search on the web site and a whole bunch of methods will come up. The most common method is to use compressed air. Keep your digits out of the way or you may find this method painful. Failing that method some have plugged the inlet line port and used a greasegun thru the bleeder port to push the piston out. A little messy but it will work.

[raqumup]

the best way is with compressed air. you remove the bleeder screw, put a rag between the caliper and the piston (as if the rag were the brake pad) keep your hands clear and give a small blst of air in the bleeder screw hole and the piston will shoot out. be very carful if your hand or fingers are where the brake pads go it will break your hand. this is the only way i know to get any piston out of a caliper. i was tought this by my auto shop teacher back in high school, he made us do it, its pretty neat. the rag is important because it catches the piston to prevent it from hitting the caliper on the other side. if you domt have a compressor you should be able to do the same kind of thing with the bike. it will be very messy though. put the caliper back on the line and fill the brake fluid back up, and out the caliper in a bucket and just keep squeezing the front brake and the caliper will come out. hope this helps

[79XS11F]

If they are so frozen that air does not work or if you don't have access to air ....
Remove the rubber boots and spray penetrating lube around the area where the piston meets the piston bore. Use a C-clamp to push the piston back about an 1/8 of an inch. this will free it up if it is "frozen in place. Spray more lube and then work it out turning as you pull outward on the piston. If you have to GRAB the piston do so ONLY on the very top edge so as to not damage the dust seal grove. I use large slip jaw pliers and grab it right at the top 1/8 of an inch to work it out.
Once it's out hone the caliper bore using brake fluid as the hone lube to return the bore to an even and clean surface. DON'T get carried away ... remove only as much as is necessary.
Inspect the pistons closely. If in pretty good shape they can be restored and reused. If you want to save the paint on the calipers while honing you will need to protect that paint.
Rob

[Ken Talbot]

Another, slightly messier idea, is to adapt a grease fitting to the bleeder hole. Plug the hole where the brake line attaches and pump away. I've always found that air works quicker, and is a lot cleaner.

[fredintoon]

Air vs grease

Airline or grease gun? Air is quick & clean & safe if you keep your fingers out of the way. But you do need a compressor and compressors peak out at around 120 psi.
If your caliper piston is severely stuck 120 psi may not be enough.
OTOH the average side-lever grease gun will develop over 5,000 psi. You may have to clean up a really messy splurt of grease but if ~5,000 psi won't shift the piston, best you go buy a replacement caliper.

[AlanB]

Hi Da-Bubble,

Air is OK if you are truly careful, and the pistons are not tight. I have a thumb joint which does not work 'cos I used 180 psi to shift a frozen piston. When it blew (after 15 minutes under pressure, some heating and hammer-work) it took the edge off of the knuckle on its way out through the asbestos roof of the shop.

Never did find the piston............

Grease works OK, but is messy.

There is an easier way!

Just hook the line onto the filled master, pump the fluid down the line, than hook it back to the caliper. You don't need a perfect bleed job, just some pressure! If the parts are away from the bike, clamp the front master to an old handlebar (or any bit of 7/8 tube!) and pump out the pistons..... front master works best for all calipers!

Only real downside is the nasty, paint-stripping nature of brake fluid! I generally do this a long way from the bike.......

Be cautious about using ordinary oils and greases near brake parts; penetrating oils, axle grease, and most anti-seize compounds (we have copper-slip?) all do HORRIBLE things to the rubbers in brakes.

ONLY use brake fluid and "Brake Grease"... (Actually a type of red wax) on brake parts. Anything else is plain wrong.

AlanB

[fredintoon]

In light of Alan B's post, let me revise a previous post of mine:-
I said:- "Air is quick & clean & safe if you keep your fingers out of the way"
What I should have said is:-
"Air is quick & clean & safe, just like dynamite, but you really must know what you are doing."
And of course Alan is right, anything except brake fluid is harmful to the brake's rubber seals. If you do use grease to pump a caliper piston loose, best you discard all the old rubber seals that got grease contaminated and wash the grease off the metal parts with solvent then acetone then air dry before installing the new seals.

[AlanB]

Hi Fred,

Yup, what I did was stoopid, but I had actually given up on it moving, had put all the tools away, and was just reaching across the bench to disconnect the hose when it let go, without any warning.

The shop roof was nearly 30 feet high, and I didn't even realise it had got me until after I had come back in from searching the car parking area............. It happened sometime in 1980, but it a lesson I will remember!

Once air starts expanding, it will keep going!

AlanB

[Da-Bubble]

Thanks for the advice. I have a 150psi compressor. I just went and tried to blast it by sticking the blow gun in the bleeder hole. Obviously it doesn't build up enough pressure. Did you guys screw the air line into the bleeder hole somehow? I sprayed them with lube and tried twisting them too but I'm affraid to break something.

[Da-Bubble]

Also I tried pumping it out using the master cylinder but could never build up enough pressure. I have a brand new fr master from partsnmore. I wasted an hour and got brake fluid all over the floor of my shop. I was only trying to bleed the one side I was working on. The other was attached but sealed up. Should I have had to bleed both sides to get any pressure?

[fredintoon]

Hi Da-Bubble,
Duh, yeah. The line to the other caliper is most likely full of air. Any air anywhere in a hydraulic system acts like a cushion to stop the pressure building. Try connecting a single hose from the master cylinder directly to the seized caliper and bleed all the air out. The caliper don't have to be on the bike, just let it dangle. Once the shortened hydraulic system feels solid you will be able to get the full master cylinder pressure behind the caliper piston and hopefully that will be enough to move it.
One more thing, use a drip tray.

[Da-Bubble]

Well it took all three methods, Grease gun, propane torch and 150psi blast, but I finally got them loose! Thanks for the advice. It did tear up my grease gun though! The freakin hose fitting seperated and blew grease out. The air does make a very satisfying POP when it finally comes out. My wife had to come see if I was OK! Hehe! For some strange reason, she's always worried I'm going to blow myself up....

[egsols]

Glad you got them out with all your fingers in tact!!! When you rebuild them make sure you use lots of brake grease to put them back in otherwise you could end up scorring them bad and damaging the new seals.

[OpFlash]

I had similar problem in the past. Air took one piston out but not the other. I used the grease gun. I was amazed at how fast the grease gun poped the pison out. Yeah a little bit more cleaning involved BUT youre already tearing them down cleaning them up so just consider it part of the process. If you dont have access to air I have to say the grease gun was a tried and true method.