Cleaning Caliper Piston and Bore

I don't have access to a brake hone and can't afford one, but, I do have some 400 and 1500 grit sand paper. Can I use this on both the caliper piston and the caliper bore to remove the buildup inside?

 

that build up, if it's old dried up brake fluid, turns into white powder when touched by the flame of a propane torch
heat it use a wood stick to scrape it, repeat as necessary
finish it with that 1500, you don't want to remove any more metal than you have to
is this a wheel cylinder a master cylinder or a 82 dodge ?

 

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Be more specific in your write-ups. We need to know that YOU know the difference between a Caliper and Master Cylinder Bore ... because WE don't want to make a mistake.

If this is a Brake Caliper that you are cleaning-up. Fabricate a scraping tool and refinish the two Caliper Piston Seal channels right down to bare aluminum.

Exposing the Crud build-up to the flame of a Propane Torch WILL cause it to
turn into a dust that can be removed by scrubbing the surface clean with a Medium (Gray) ScotchBrite Pad.
Go heavy on the Elbow Grease until you have the Bore cleaned to bare aluminum.
The bore needs to be cleaned and shined.
The two Caliper Seal Locating channels must be completely cleaned right down to bare aluminum.

Go heavy on the Disk Brake Kleen Spray.
Use nothing but new, fresh, clean Brake Fluid to lube the surfaces and Seals when you reassemble the Caliper.

 

I would not advise you to use a hard abrasive on the sides of the the caliper piston. I probably wouldn't use anything more than a cloth rag, elbow grease, and Brake Kleen on the piston. If the cylinder has a large amount of crud or rust in it you'll need to clean the then check the piston for pitting, scars and/or other surface problems. You want the outside of the piston to be glossy and scratch free. The piston doesn't really have much contact with the inside of the caliper bore. It's primary point of contact is the square cut lip seal at the bore opening. Any problems with the surface of the piston can damage the seal and create leaks or worse. If you have problems on the piston that you can't clean up, now is the time to replace the piston.

 

With everyone's help I got it clean and back together, thanks. One thing that did happen is as I was reinstalling the caliper piston and when it was half way in I checked it and looked like it was going in even, when it was almost all the way in I checked and it looked like it was still going in even. When I was done it was off. Am I up the creek? What can I do? I tried using a block of wood and a hammer but that didn't work. It's about 1/16" maybe slightly more, less than 1/8". Will the hydraulic pressure of the brake fluid help straighten it when I remount it to the fork and get it all bleed?

 

Let's see if I'm reading this right. You have the piston installed in the caliper bore, it's practically all the way in the bore, and one side is a 1/16 of an inch out further than the other side? This sounds very unusual. Most of the time, when you depress the piston into the bore, once it starts going in, it usually pushes all the way to the bottom and will be flush with the bore opening. If this is indeed the case, I think I'd place a small block of wood in the caliper that will only allow the piston a 1/4 to 1/2 inch of movement, then slowly apply air pressure in the brake line mounting hole with a blow gun. The air blowing into the caliper should cause the piston to move out of the bore that 1/4 to 1/2 inch to see if the piston straightens up. (At this point watch for air leaking out around the dust boot or end of the piston bore. If it's leaking air then chances are you've rolled the pistons lip seal down the wall of the caliper bore. You'll need to remove the piston, check the lip seal for damage, replace it in it's channel if possible, and then try to reseat the piston. A liberal coating of brake fluid on the piston and in the bore especially around the seal and boot area, should help the seating process.) If the piston doesn't move, and you don't see an air leak, try to straighten it up in the bore by applying pressure to the highest point of the piston with a large pair of channel lock pliers or a large c-clamp. Then try the air movement procedure again.

Remember, anytime you're applying air to the caliper have a block of wood, or something sturdy and soft, (NOT YOUR FINGERS) between the piston and rest of the caliper. Pistons will come popping out of the bore and can be damaged when they bash into other things.

 

Did you try taking a C-Clamp and applying some pressure to the high spot?