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Brakes - Master Cylinder or Caliper or ....?

Perk

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Had a great ride this weekend.... in spite of having almost no brakes. Jumped on my sled and went to back it off the deck and grabbed the brake. Felt mushy and pulled all the way into the bar. I could pump it up and it would work but would bleed off quickly and then could not pump it up again until the next time I would use it. I tried bleeding it last night. No go. Would always act the same. Could pump it up, brake fluid would come out of the bleeder as long as I cracked it right away when it had pressure. Strange thing is, if I pull the brake handle in slowly, it collapses all the way to the bar and does not have hardly any resistance. If I pump it fast, it will build pressure but will bleed off in about 3 seconds. Fluid in the master cylinder is full, cant find any sign of a leak (traced the line all the way down to the caliper). The diaphragm in the master cylinder looks ok, cant see any holes in it. Brake fluid look like someone dumped a bunch of grey powder in it and if I pull the handle slowly with the cap off the master cylinder, you get a little disturbance (like a burp) in the fluid and it looks like chocolate milk. Fluid contaminated? Ride before there were no issues with the brake and nothing out of the ordinary. So my question is - go after the master cylinder first or does this sound more like a caliper issue?
 

05900

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Sounds like faulty master cyl. If you have the hose pinch tool pump it up and pich brake hose, if it looses caliper clamping rotor will free up..Still squishy Master bypassing..
 

kylant

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i have started to notice the same thing on mine, but not nearly as bad.

occasionally, the lever will have a little more pull than normal, but then normalize after a few squeezes. lever never goes more than 1/2 way to the bar.
 

kanedog

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J

jim

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You comments about the grey material and brown fluid leaking into the fluid has me agreeing that you may have a master cylinder problem. I would suspect a piston issue/leak. But, if you are losing pressure in the line, you are likely losing fluid somewhere. You might check the actuation boot (off of the rod from lever) to see if there is fluid in there.
 

GreenState

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We chased a similar issue on my buddy's Ski-donkey early this season.

At first thought it needed a bleed and that didn't fix it. It turned out that his brake pads were so smoked that the pistons had run out of travel.

I found a stuck caliper piston on my 800 that was causing one of my pads to wear much faster than the other one and had to to change pads a few weeks ago.

Check your pads and make sure there's plenty of and equal amounts of material left.
 

diamonddave

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We chased a similar issue on my buddy's Ski-donkey early this season.

At first thought it needed a bleed and that didn't fix it. It turned out that his brake pads were so smoked that the pistons had run out of travel.

I found a stuck caliper piston on my 800 that was causing one of my pads to wear much faster than the other one and had to to change pads a few weeks ago.

Check your pads and make sure there's plenty of and equal amounts of material left.



This is good info. And if worn pads are found, I'd chuck that rotor up on the lathe and check for flatness. Staring to hear about the oddball rotors that are out.
 

Perk

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it was the fluted seal on the piston inside the master cylinder. Cant buy a rebuild kit from Polaris - so $200 for a new master cylinder. OR you can get a rebuild kit for an M8 - part number is SM-5405. $20 shipped.
 

Perk

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Got the rebuild kit. Parts were an exact match. Put it back together and had a hard time bleeding the system. Could not get any pressure. Ended up filling a syringe with brake fluid and connecting it to a hose and then to the bleeder nipple (on the caliper). Forced the fluid in from the caliper up and then it would build pressure and could be bled.
 
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