Got a caliper off ebay... turns out the piston is stuck in it also. In looking at the schematic on line for the "rear" caliper that is actually the middle caliper that grabs the transmission, there is a re-build kit with piston and seals. The confusing part is to me, they seem to show a caliper with parts on the back side that don't exist on mine. Mine is a solid housing with no rear access of any kind to the piston. Wondering if that rebuild kit will in fact work...? Says it is for a 1989 Big Boss but mine does not seem to have anything like schematic part #'s 16, 17, 18, 19 & 23 (Here http://www.mrcycles.com/fiche_section_detail.asp)

Guess I'll have to hope I can re-build it... but don't want to order a seal kit and have even more money into something that won't work. Hope you all can comment on this one. Thanks a lot, - Doug

 

If its the "transmission brake caliper" you can pull the pads by using a needle nose pliers to grab the two "pins" between the pads and push the pins toward the back of the caliper(may be a little rusty),then you can pull em out from the rear and the pads will fall out. After seal replacement,just set in the new pads,push the pins in from the back and through the holes in the pads and reinstall the caliper over the transmission rotor. Hope this is what you mean?? I believe you were looking at the "updated" caliper assembly on the 4x6 that has an adjuster **** assembly that can manually adjust the foot brake pressure and these parts are on the outside of the caliper,NOT the back side! You could have the one with out it. The seal kit should be the same. PLUS on the exhaust side on the square down tube should be an etched model number: ( W899627 89 Big Boss), (X898627 89 Big Boss 4x6), (W898627 89 Big Boss 4x6) parts on these machines will differ! WHICH NUMBER do you have??? (Hope its not ground off)
OPT

 

Gracias for yet another of your thoughtful replies! Actually, I am in the quandry over getting the piston out and the fact it appears it must come out the front only. The re-build kits show parts that seem to come off the back-side... On the one I bought and the original caliper, the casing/housing is solid in back. Does the piston come out the front only? Then back in with a new one and seals after inspecting for scoring? Obviously wet everything down with brake fluid.... Thanks, Doug

 

Yes the front only! You can pop it out by using an air gun through the brake hose connection on the caliper,but be careful!! Just remove the caliper brake line,place caliper face down on an old towel, and short short bursts of air into the caliper. Some are easy,some take a little time,especially if its a little dirty and corroded. OPT

 

OPT,

Had to use grease to force the piston out... ironically the piston seems very clean. Seals even seem O.K. There is a tiny bit of residue at the back wall of the cylinder. What would you use to hose out the grease? I'm a little hesitant to use wd40 as it might degrade the seals...? Maybe not, but I'd rather seek some more wisdom and use the right tools to clean out the inside of the cylinder area.

Also, whats the best method for replacing the piston back in the cylinder area? Thanks you for you tireless help. - Doug

 

If you are replacing the seals,just remove them and you can clean out the caliper with electrical or even brake cleaner and DRY thoroughly. Lube the new seals up with brake fluid and install,coat the caliper inside walls and piston with brake fluid and gently push piston back in with out distorting or damaging seals. may have to twist and turn to seat the piston. DON'T push the piston all the way back flush as it needs room for fluid behind the piston when you start to bleed the brakes when assembled. OPT