I searched the forums for my problem and didn't see anything that matched closely. I was going up a pretty steep gravel road and the rears started spinning. It turns out one of my front brakes was locked and the other one was dragging but I hadn't used my brake lever for quite some time. After getting to the top and parking it, I realized that I couldn't move the lever at all, it was completely stiff. I was going out hunting so I left the 4-wheeler and did my thing hoping the pressure would bleed off while I was out.

It did and seemed to work after I came out of the woods 4 hours later. It was still stiff but it moved about as much as it has for the short time I've owned it. I didn't use the lever going back down the hill and relied on the rear brakes only. I kept the engine off for about half way to listen to the rotors. The left front one was a little raspy but not what I'd call dragging. The rest were quiet though.

This 4-wheeler sat for a long while before I bought it. I'm going to pull it in the garage if I have time today and pull the front tires inspect the brakes and vacuum bleed both front calipers until I've got fresh fluid all the way through the system.

Is there anything Polaris specific about this brake system that may be causing this besides contamination or air in the brake fluid that anyone knows about? I'd like to check for all the causes while I'm working on it so I don't find myself stuck in the middle of nowhere WV with a locked up front end.

Thanks!

You can try a mity vac first and see if you can solve this if trapped air is a problem.If that doesn't help then the two biggest problem areas on brakes are that the hand brake master cylinder piston seals can wear over time and suck air in or leak down and also the rear caliper seals. The caliper is split and uses two small o-rings for sealing each half. They can seep or leak air as they age also. If the foot brake still works then the small rear master cylinder itself should be ok. Either replace the piston kit for 54 bucks or replace the whole master cylinder. Item#5.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse If that still doesn't solve the problem then the rear caliper piston seals and o-ring come in a kit. 1999 2002 Polaris Sportsman 335 400 500 Rear Brake Caliper Seal Repair Kit OS148 | eBay

Thanks OPT. I'm hopeful the bleeding works. If not, it's good to know the next steps.

Well, bleeding the front brakes did not seem to help. I took it out today to play in the snow and the brake system locked up about a 1/2 mile away from the house. All the brakes were affected and I'm starting to wonder if the rear part of the system is really the problem. The whole system freed up and then I had no brakes from either the lever or rear pedal and had to pump the front lever several times before I got the brakes back. I think I'll just order rebuild kits if they're available for the calipers and actuators.

Ok, the rear brake has nothing to do with the front brakes locking up. The handle bar master cylinder, however, has everything to do with the front and the rear. The rear caliper also has its own little master cylinder for the floor board brake lever. I would recommend bleeding them again using the handlebar lever, and the rear brake first. Then do the front calipers. Then bleed the rear caliper by using the floor board footbrake. If you still have issues, and are not leaking fluid anywhere, more than likely your handle bar master cylinder is plugged/gummed up.

I've been reading the service manual (probably should have started there first) and I think you're right fasteratv. Before I start spending money, I want to try as you suggest and check the reservoir vent. I'm also thinking the compensating port may be gummed up. When I bled the front brakes, the fluid in the reservoir had a heavier viscosity more like oil than brake fluid. If I take the piston out, does anyone know if a polaris piston installation tool is really required to put it back in? I think I'll need to pull it out to run brake cleaner through the ports. Maybe not though?

Change to Dot 4 or Dot 5.1 fluid especially if you haven't changed fluid and it's dark. You can change the piston and seals out without the tool but you have to be careful.Have plenty of brake fluid around the seal.Once you get the cupped seal in the rest is easy. Just use a small flat screw driver to work the cupped seal in. On priming the master cylinder either remove the brake line at the master cylinder and place your finger over the hole to prime or you can clamp the brake hose close to the master cylinder and prime it up that way.

Good for you, the manual is your friend... While actuating the brake lever in and out, I have ran brake cleaner thru many of them over the years, cleaning them, resolving the issue. You can clean and rebuild the MC without any specialized tools. The problem is that water accumulates, and the fluid goes bad/gels/and corrosion occurs as no one ever thinks/wants to change the fluid out. Anyway, you can get the air of the MC without removing it and I certainly do not recommend collapsing the rubber brake line from the master cylinder in away way, or form...vice grips, clamps....etc. As you progress, post your questions and I'm sure several will answer.

I've used vice grips on these old rubber lines for years to help prime up master cylinders and released them with no problems at all. Wouldn't use any form of caustic cleaner as this master cylinder has a replaceable reservoir and has a sealing o-ring under the bowl that can be damaged. Also check that the two bowl screws under the master cylinder are tight sealing this o-ring or the bowl can seep or leak. It's the first thing I checked whenever one came in for service as these screws will loosen over time. Once the system is bled you can pull the brake lever 1/2-3/4 way back and zip tie the brake lever and leave it over night. Any microscopic air bubbles left in the system will work there way to the top brake line close to the master cylinder and once the zip tie is released,the handle pumped,they will vent into the bowl.Usually you'll have a firmer brake lever. This is an old dirt bikers trick that many riders still do.

I use spray brake cleaner on a regular basis, instead of the far more caustic carb cleaner....and with no ill effects, however, this is a quick shot of cleaner ( the tiny straw ) basically to clear holes and break down the crud... followed by low pressure air, then adding fresh brake fluid and using care not to saturate any rubber parts. Normally todays spray brake cleaner will not harm plastic tho I do not allow the cleaner to get on a painted plastic surface....or a painted surface of any type. If you have a better way of cleaning, please, by all means, enlighten the original poster, and myself ( I'm certainly willing to learn and I'm fairly sure he is as well ), and state your preferred method of cleaning a brake reservoir/master cylinder, what did you use, or currently use because he will more than likely need to clean his master cylinder to resolve the issue he is having. In regards to totally collapsing a rubber brake line...in my opinion thats a bad practice when there are other non-destructive ways to accomplish the job of bleeding the air out of an ATV master cylinder. Simply fill it...pump it, then release the trapped air from the brake line attached to the M/C ( bleeding )...takes a few attempts but doesn't take long if the M/C is clean and in good condition. Then gravity bleed the entire system prior to the pump-bleed effort. Again only opinions here, different people, different methods...as with most things... Almost always more than one way to resolve mechanical issues.