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Seized Brake Caliper Piston

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I'm reworking an out of shape bike for the dunes and noticed only one of the brake pistons on the front caliper is working. From what I have gathered through the search feature, my piston is seized and I need to pull it apart to see if it can be reused with new seals. If not, I need to buy a rebuild kit. Is this correct?

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That's right. There's not much inside a brake caliper, but be very careful not to scratch the piston, just in case you can re-use it. Some people get them out with air, but I prefer to simply leave the brake line connected, take out the pads and pump the lever until the piston pops out. That method makes a bit more of a mess, but it sure beats getting the piston taken out of your forehead after you pressurize it and have it become a missle.

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I don't think the pumping would work because the piston is seized in the caliper. I don't know, though. Maybe you know something I don't.

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take the line off, and soak it in coke. yes i mean coke soda pop. Coca cola brand. in the red bottle. got it? ok soak overnight, see if it freed up, if not soak another day. It should free up and come out easy without scratches, then if it all looks good in there just clean and reassemble. Test it out and if needed then rebuild it with the kit.

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Pumping will work. The thing that you need to do is put the other piston in. Then put something between the piston and the caliper so the piston that moves can't pop out. The last time I did this, I used a big adjustable wrench. Something metal is good as the force it might experience is large, but wood should work too. Now start pumping. The moving piston will move out until it hits the wrench/wood. Now all the force will be on the non moving one. Pump and it will move.

When you get it apart check it carefully. Look for pitting on the piston and the bore. You can clean the piston up with some really fine 400+ sandpaper. If the piston has any significant pitting it's toast.

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Remove the hose, fit a grease nipple, make with the grease gun.

You can get enormous pressure on a grease gun and the grease helps lubricates things. I've only had this trick fail once, there was so much pressure the calliper casting split. I did once machine a piston out of a hideously expensive racing car calliper just to avoid damaging it, then had to sleave it anyway (the bore was corroded).

Luck dude, let's know how it goes huh?

Oh yeah, like cleonard said, you'll need to lock the free one in place but I suggest you use a G clamp over the piston side of the calliper (or put it in a vice), that way you're not straining the calliper frame.

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I had something similar happen on a RM250, I thought it was corroded but it was not. I apparently tagged a rock hard enough to knock the bore out of round. I used the same trick as Cleonard suggested to get it out. With a little bit of emery cloth I worked down the high spot. I put in new seals and the brakes worked great after that.

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The first time I ever took a piston out of a caliper, I tried to use vise grips. I got it out, but the vise grips scarred the piston bad enough that it wasn't useable. My Dad's the one that turned me on to the pumping method and I've used it ever since. Glad to hear it worked for you!

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How do you get the pistons back in and how do you get the seals out?

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the piston should push in.. if not then get like some card board and put it over the pistons and get a C clamp and push them in like you would it someone pumped your brakes like everyone of your friends do when you change tires and put em in. Make sure you get em in strait.

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Hi folks,

Searched and this was the closest thread I could find. Rebuilding a Honda 85 CR250 that sat for over 10 years and the front brake was seized. Got the inner and outer piston seals and after a lot of pumping out one piston, then the other, finally got both out. Took about 30 minutes...they were IN there!

One piston has a small nick/scrape from trying w/a rag covered pair of pliers (sigh), but both have some pitting where they rested against the outer seal. They're over $30 each, so I'd like to be able to re-use them if possible.

From those who've had these issues, what's the chances of polishing up the pistons so they'll work again? Saw the 400 grit paper suggestion (someplace, had seen that there's 1000 grit). Give it a try, or not a chance?

Thx!

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Small to none. Most have a hard plating. Once that is damaged and the surface pits or rusts, it continues. Would you sand a scored piston in the engine and reuse it.

Buy new pistons or source a complete caliper.

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take the line off, and soak it in coke. yes i mean coke soda pop. Coca cola brand. in the red bottle. got it? ok soak overnight, see if it freed up, if not soak another day. It should free up and come out easy without scratches, then if it all looks good in there just clean and reassemble. Test it out and if needed then rebuild it with the kit.

Ohhh, I thought you meant in cocaine.

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Been looking at/cleaning these:

- One piston's got only very small nicks/pitting/scratches...the other has a 1/8" inch mark about half-way around from where it rested on the the inner seal. Can't tell if it's pitted or just chemically messed up from bonding against the rubber seal all that time.

- The inner seal's deeper in one piston cylinder than the other! No idea why, unless to conserve space, but it looks like the piston w/the mark from the seal should drop into the other cylinder and that mark will be above the seal. May be in luck.

BTW...they're plastic, if it matters for trying to sand nicks out.

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Plastic? Then trying to sand them out is OK. either they will seal or they will not, you'll know PDQ.

They make the pistons of different diameters to cause one side of the brake pad to contact sooner and then the other provides more braking power.

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take the line off, and soak it in coke. yes i mean coke soda pop. Coca cola brand. in the red bottle. got it? ok soak overnight, see if it freed up, if not soak another day. It should free up and come out easy without scratches, then if it all looks good in there just clean and reassemble. Test it out and if needed then rebuild it with the kit.

Will coke eat the seals in the caliper?

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