We have a 2004 Sportsman 400 that slowly loses brake pressure. It will still stop on a dime. But if you set the parking brake on a slope, it will start rolling after a minute. If you give the the hand brake a hard squeeze, you will feel plenty of resistance. But if you keep doing that, the lever will eventually close to the handlebar grip. There doesn't appear to be any external brake fluid leaks. I'm guessing this is master cylinder problem, but I wanted a second opinion. If you think that's the problem, should i replace the master cylinder or just get a rebuild kit? I appreciate any help.

 

Can be air in the lines,seals leaking, pads worn down pushing calipers pistons out to where they can start leaking,or a bleeding down master cylinder seals. Air in the lines,seals either leaking in the master cylinder/calipers which can cause the air to get in the first place. Try bleeding the brakes first after inspecting that the pads are ok and don't need replacing. If bleeding doesn't help,could be the master cylinder leaking,but no rebuild kits offered for this model. Either replace it or get an after market one on ebay.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Caliper piston seal kits are available for front and rear calipers if needed.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Plus here's a cheap Chinese master cylinder.For Polaris Sportsman 335 400 450 600 New Left Front Brake Master Cylinder | eBay Hope just bleeding the system solves the problem.

 

Thanks for your, Polaris Tech. I will start with bleeding the lines. The brake pads look like they still have some miles left on them, but it wouldn't hurt to replace them. If the calipers were pushing out too far, wouldn't I see signs of fluid leaking?

 

Sometimes seals can just distort enough to allow air in and leaking may not be visible. Especially if the small piston seal in the master cylinder is worn. Again hope bleeding solves the problem. Plus check the small master cylinder on the foot brake. They're bad about seals drying up/cracking from non use. If you can't get it to build up also,seal kits are available now for them instead of buying a 100 buck master cylinder.http://www.ebay.com/itm/1998-2009-Polaris-Sportsman-Rear-Foot-Brake-Master-Cylinder-Seal-Repair-Kit-/281685808329?hash=item4195c854c9&vxp=mtr

 

Great! Thank you so much for your help with this problem, Polaris Tech!