Help! Complete brake failure - Polaris ATV Forum
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post #1 of 10 (permalink) Old 08-17-2016, 07:31 PM Thread Starter
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Help! Complete brake failure

I purchased a used 1998 Sportsman 500 about 8 months ago. It sat in a older guys garage for years but was in great shape and only had 1500 miles. I used it to plow snow last winter with no problems. A few weeks ago i took it camping for the first time. While on a very short ride with my 3 year old son in front and wife on back, (combined weight approx 320 lbs) and descending down a fairly steep hill I suddenly lost all brakes. My hand brake would pull all the way to the grip with no pressure and the foot brake also lost all pressure. Needless to say that without an engine brake, shiftable transmission, or any sort of emergency brake I had absolutely no way to stop 500 lb. machine on a steep descent. Long story short we're lucky to be alive, particularly my 3 year old. I absolutely cannot believe that whoever designed this ATV made it possible for a single part failure to result in complete brake failure, especially on a machine without engine brakes or gears. Strangely after we thundered down the hill and finally crashed to a stop brakes mysteriously began working again (but not for 5-10 minutes after this whole ordeal).

I got the ATV back to camp, bled all the lines (there was no air in any of them), checked fluid (completely full in both reservoirs), checked pads (all we're good). I'm at a total loss. My best guess is that something went wrong with the rear caliper since that is the only place the hand and foot brakes intersect. Each have their own master cylinder & bleed screw on the rear caliper. I just can't believe that there is any chance both brakes could fail at precisely the same time, and then both mysteriously begin working again at the same time.

Had anyone here ever heard of or seen this in another machine? I I've been around and worked on ATVs my whole life. Now I don't dare take my son on it anymore, which kind of defeats the purpose for me. I've been thinking of plugging off the rear brake line at the 4-way junction in front of the fuel tank to completely isolate the hand brake from the foot brake, any thoughts? Has anyone done this successfully? I spoke to three different dealerships about the problem but none of them exactly inspired confidence. I feel like I need to be 120% sure I the brakes won't fail again before I will let any of my family anywhere near it again. I'm also reluctant to sell it for fear of someone else getting hurt. A $2000 machine just isn't worth it.

Apologies for the novel, I know there are a ton of experts on this forum. Any thoughts or help would be very much appreciated! Thanks in advance!!
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post #2 of 10 (permalink) Old 08-18-2016, 02:18 AM
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Welcome to the forum. Glad everyone is ok. Did you happen to service the brakes, change out the old brake fluid? It is an 18 yr. old machine. Might need to rebuild the master cylinders and calipers after sitting for yrs. 3 people for a single seat machine is quite a bit.

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post #3 of 10 (permalink) Old 08-18-2016, 06:38 AM
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my opinion,
your brake fluid is old and get too much water in,the water starts boiling and you have no brakes after 10 min cooling the brake works again.
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post #4 of 10 (permalink) Old 08-25-2019, 11:23 AM
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Originally Posted by cariboo View Post
my opinion,
your brake fluid is old and get too much water in,the water starts boiling and you have no brakes after 10 min cooling the brake works again.
So I have something like this too where the brakes come and go, except that when it happens it seems as though at least the rear brake is partially engaged. In fact one time there was smoke coming from where the back rear (Magnum 330) brake line meets the brake. The rotor was hot.

I’m baffled really. I don’t really even use the brakes much, so I’m not sure why things would be boiling.
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post #5 of 10 (permalink) Old 08-25-2019, 12:07 PM
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If a caliper sticks or you take off and forget the park brake is set partially on the fluid will boil in just a few minutes.
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post #6 of 10 (permalink) Old 08-25-2019, 03:05 PM
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The master cylinder can cause the problem - if the foot brake pedal or hand lever does not move freely, it may not fully release the brake - old brake fluid can be the cause of a sticky MC piston and old (or no lube) may cause the lever or pedal to stick.

I would start with changing the fluid - first in the foot brake system and then in the hand brake system. Sometimes you can change the fluid by gravity - remove the cap from the reservoir, sop out all the old fluid and fill with new DOT 4 or DOT 5.1 (personally I use 5.1 - it has the highest boiling point) - connect about 1.5 to 2 foot of clear plastic tube to the bleed screw on the caliper press down on the foot pedal and open the bleed screw 1/2 to 1 turn - you should see old discolored fluid in the tube - hold your finger over the end of the tube or close the bleed screw and release the pedal - you should feel a slight suction on the tube and the fluid level in the reservoir will fall the same amount as the amount of fluid in the tube - repeat this process until the tube is full of fluid and keep an eye on the reservoir to make sure it never goes dry - once the tube is full of fluid, you can position the end of the tube below the caliper and let gravity siphon fluid through the system until you have nothing but clear fluid in the tube - now close the bleeder and you are done. Repeat the procedure for the front master cylinder bleeding all three brakes starting with the caliper farthest from the MC.

If you want to do a professional job, remove the caliper and brake pads and press the piston into the caliper before starting the flushing process - leave the piston depressed while bleeding - pressing the piston removes all the old fluid from the caliper and forces it back to the MC reservoir - not only does this push the old fluid out of the caliper, it may expose other problems - if the piston resists being pressed into the caliper, leave the c-clamp under pressure and feel the pedal and lever - if either is 'tight' it may indicate the MC needs serviced.

When done, let set over night and re-bleed the brakes using your favorite tried and true method to remove any residual air trapped in the system - if gravity flushing does not work or is too slow for you, use pressure, vacuum or manual bleed techniques to accomplish the task.

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post #7 of 10 (permalink) Old 08-25-2019, 03:54 PM
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I wasn't even using the brakes, only just to test them to see if they were working. But if old brake fluid can both cause the loss of brakes and sticky brakes, then that would explain what is happening.

First step is to change the brake fluid. I'll post again if that doesn't fix the problem. Thanks.
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post #8 of 10 (permalink) Old Today, 01:43 PM
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I found that the piston for the foot brake master cylinder was stuck in which is probably why the rear brake was being engaged ending up with "smoke" coming off of the housing where the brake line goes into the caliper. I replaced it and changed the brake fluid.

The only problem I see now is that the back rotor still seems to be getting mildly warm (before it would get hot) so I'm guessing the brake is dragging a little.
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post #9 of 10 (permalink) Old Today, 02:15 PM
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So this is a good time to mention, "EXERCISE THE REAR BRAKE FOOT PEDAL ONCE A RIDE"!!!!!!! The foot pedal system has a far share of issues because of the lack of use. Personally I lock the rears up just for fun. Just keep it under control people, getting over zealous will get your wheeler on two wheels and eventually on its side if you aren't careful .

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post #10 of 10 (permalink) Old Today, 02:44 PM
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Motorcycle and ATV brakes run true - there is no run-out to push the pads away from the rotor so a warm rotor with no use is a good thing - if you can touch it without getting burned, it's fine

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