What do I clean master cylinders with? I clean with the same thing that's been running through them for years. Brake fluid. If the master cylinder bores are corroded might as well throw em away. Bore cleaner brushes,solvent almost never work or doesn't last long when you install new m/cy pistons and seals kits. I've tried cleaning corroded bores on the old Polaris red handled master cylinders that were bad on this and so have many other people over the years.On these I talked most people into upgrading and using better fluid.The newer models are less prone,have better metallurgy that are used,but I still clean the same way. That's also why I recommended jumping to the either Dot 4 or Dot 5.1 because they have been proven to attract less moisture,less corrosion and also have a higher wet and dry boiling point than plain old Dot 3 that's a dinosaur now.Yes everyone has a different way off doing things and this happens to be mine,same on hose clamping for the past 23 years and never a problem.

 

Good news: Well, I took the master cylinder apart and cleaned it. The compensating port was blocked. It was a mess but no corrosion, pitting, or scarring and the seals looked good. It went back together fine with no problems and only minimal frustration.

Bad news: Rear pads gone (got a set of pads on order), Fluid leaking from the rear caliper, and rotor doesn't look too happy. I took the rear caliper off and tore it down to see what I'd need. It looks like one of the piston cups is deformed as best I can tell. If I read cyclepartswarehouse correctly, a new piston is $60. With seals it would be about $80 to rebuild. A new caliper is $186. The rotor is a little over $100. A used caliper isn't much cheaper. I can't believe there aren't rebuild kits for these. I guess I'll try the dealer on Monday to see what they've got available.

 

There are at least seal kits on ebay along with rotors I believe. Plus complete caliper assemblies,but may be more than you want to pay.Polaris ASM Rear Brake Caliper with Pads Sportsman Disel Worker 335 400 500 | eBay http://www.ebay.com/itm/Polaris-Spor...FSwNqw&vxp=mtr Unless pistons are trashed I've been able to reuse them. May not be able to in your case. On some items no aftermarket parts are available yet. Just have to bite the bullet and get them from online parts houses or see if the dealer can cut you some slack. Best thing is to not let one get this bad in the first place,but if it's a used machine you have to take the good with the bad when you tear into one. One last thing is that Wilwood supplies a lot of brake parts for atvs. Never tried to track down parts,but worth a try.http://www.wilwood.com/Calipers/Cali...0SC2%20/%20SC3