Brake Caliper - Seized Piston - Yellow Gunk Removal???

[mroberto]

Hello all,

I'm rebuilding the front calipers on a bike that I just picked up - a 1987 Honda CBR250R MC17. When I got the bike, the front wheel wasn't spinning freely. From what I see, it's because the pistons in the calipers weren't returning when I let go of the brake lever. I've taken the pistons out of the calipers and removed the seals. Underneath, I found this really hard yellowish gunk that seems to take whatever I throw at it and shrug it off. This stuff is really hard to remove. My guess is it's either dried brake fluid or the remnants of whatever lube may have been on the seals.

Do any of you gals/guys know any secrets for getting rid of this stuff? I've tried kerosene, methyl hydrate, Varsol, IPA, gasoline, Simple Green and Spray Nine. I've used a nylon brush, a delicate Scotch-Brite, a Dremel cleaning disc (the plastic kind) and a brass brush. I've gotten some of it off, but none of these solvents, cleaners or methods seems to be getting it all off. Right now they're soaking in a bath of Spray Nine.

If you have any suggestions, I would love to hear them! Thank you!

 

[Stewart]

i use a right angle dental pick to scrape out the grove and rinse with brake clean. that build up of crud presses against the seals on to the pistons preventing the pistons to retract. if you aren't replacing the seals... make sure you clean the backside of the seals with your thumb nail don't use anything sharp.

 

[mroberto]

Thank you Stewart! I soaked the calipers in Spray Nine overnight and that really softened up the dried gunk. What the brush wouldn't remove I then carefully scraped off with a dental pick. I then followed your advice to clean the seals and now it looks like everything is finally clean and ready for the rebuild. What a pain cleaning these calipers has been!

 

[clutch]

another tip, if the seals are deformed but still in good shape, is to dunk/soak it in recently boiled water.