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Discussion Starter · #1 ·
while doing some fast laps aroud a field, that include lots of braking, i lost brake pressure on the lever. it works fine for a while, but then you can pull the lever right down to the bar! could they just be getting way to hot and then not working?
 

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yeah, sounds like they get too hot, probably from dragging if the caliper is hanging up. the heat causes the fluid to boil and turn into a gas, which is compressible. if the gas just compresses then you dont have the force going to the caliper.
 

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x2 make sure your fluid is completely full, if it is not it will boil faster
 

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I found my brake fluid was not a liquid and was now near a solid. After X amount of years the fluid starts to gel and needs replaced. Yours is probably heat related but it's worth flushing it out if it got to the boiling point anyway.
 

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The O ring in the slave cylinder (caliper) is probably not sealing when it heats up, allowing the brake fluid to be pushed past it.

Boiling brake fluid uh? That is the most ridiculous thing I have heard in my life. Where do you people come up with this stuff?
 

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Big rigs use air brakes on the trailers, not the trucks themselves. The cabs have hydraulic brakes just like every other vehicle on the road.

Do you have any idea of the amount of expansion involved when a liquid is boiled into vapor? Apparently not. You seriously believe that a liquid can be boiled to a gas within the same volume that it occupies as a liquid? If you took a torch and heated a brake line enough to get the brake fluid to boil, something would have to give to release the HUGE amount of pressure that would be created. Most likely the line would burst.
 

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ACTUALLY semis use air brakes NOT hydraulic brakes for the cab.. if you really wanted to know and YES you can boil your fluid, ive seen/herd it one of my friends was on his brakes alot and we lost him a while back an waited, he finnaly showed up and was complaining about no breaks, we popped the hood and herd the boiling fluid, we packed snow around the caliper for 10 mins and he was fine,, tell me this? why would a semi ONLY run air breaks on the tailer? and then tell me this,, ever seen ice road truckers,, how many times have you seen them poring alcohol and other deicing fluids into there tractors air break lines............






http://www.aa1car.com/library/bfluid.htm
 

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ilive4snow700 said:
thank you bj.hardy.

old_school, ever looked at a bottle of brake fluid? it says the boiling point right on the front.
no problem!
 

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Discussion Starter · #11 ·
can i upgrage the brake fluid to a higher temp boiling point? what should i do to check the brake system?
 

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bj.hardy said:
ACTUALLY semis use air brakes NOT hydraulic brakes for the cab..
Oh really? Take a look at this Peterbilt 330 operator's manual, scroll down on the left and click on brake system.

http://www.peterbilt.com/uploaded/manual/Peterbilt%20Model%20330%20Operators%20Manual.pdf


bj.hardy said:
if you really wanted to know and YES you can boil your fluid, ive seen/herd it one of my friends was on his brakes alot and we lost him a while back an waited, he finnaly showed up and was complaining about no breaks, we popped the hood and herd the boiling fluid, we packed snow around the caliper for 10 mins and he was fine,, tell me this?
When break pads and rotor get red hot they become virtually useless. Also, when the slave cylinder in the caliper gets hot, and the brake fluid is thinner because it's hot, the fluid can be pushed past the O ring. This also happens with slave cylinders on cars and trucks. At that point the slave cylinder needs to be rebuilt.


bj.hardy said:
why would a semi ONLY run air breaks on the tailer? and then tell me this,, ever seen ice road truckers,, how many times have you seen them poring alcohol and other deicing fluids into there tractors air break lines............
Trailer brakes are air activated because they have to be coupled and uncoupled all the time. Even though they are air activated, many trailers have hydraulic brake systems with dedicated master cylinder and reservoir. They are air activated, but hydraulic actuated.
 

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no they use air breaks because they are more reliable and can get higher pressure's with them, i drive trucks, the only time you will find any hydraulic systems are on very light duty trucks,UNDER 26500gvw (depending on state) single axle VERY uncommon on a tandem axle, and i dont know why we are fighting about this because Ive been around someone who HAS had boiling break fluid on there snowmobile, ANYONE PIPE IN ON THIS has anyone seen a hydraulic break system on a tractor trailer 18 wheel or in that case a 4 axle dump milk truck etc.. and did you read the website i posted.. after mearly 3 years a break fluid boiling point is significantly lower, stating that it IS possible to boil break fluid.

TNT123 said:
can i upgrage the brake fluid to a higher temp boiling point? what should i do to check the brake system?
just replace with Polairs break fluid, you should be fine you can also check to see if your pads are good along with your rotor. depending on how long its been since they have been replaced it might be a good idea.
 

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I apologize. I was way wrong on the boiling break fluid thing. Should have researched it before chiming in. The pressure from expansion is released back to the master cylinder as vapor builds in the slave cylinder/caliper. I've seen brake pads and rotors get red hot and become useless, but I've never heard of brake fluid boiling. Learn something new every day. I was way out of line on this one, and again I apologize.
 

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Yes ....almost all highway tractors and trailers use air brakes. Should a line rupture or the trailer become uncoupled the emergency spring (maxi) brake will automatically apply. As stated above the hydraulic and hydraboost systems are utilized for the most part on light and medium duty trucks only. I am a certified diesel mechanic and earn my living as such. As for the fluid boiling it is definitely a possibility. Polaris brake fluid is rated at DOT 3 which should be adaquate for the application as long as it is in good condition. DOT 4 and DOT 5 (synthetic) fluids are also available which are rated with higher boiling points than DOT 3. As DOT 3 brake fluid ages it absorbs moisture which will lower it's boiling point which is why some manufacturers reccomend changing (flushing) the brake system every 2 years. A common problem with Polaris snowmobiles is a leaking jackshaft seal which will allow chaincase lubricant to contaminate the rotor and brake pads which in turn will cause poor braking , especially when hot.
 

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Main thing to remember, if the pedal/lever becomes spongy, but stopping power remains until you run out of lever travel, you are either losing pressure, or boiling the fluid. If the pedal/lever is firm, but you need to apply more and more force to the pedal/lever to get the same stopping power, you are overheating the pad material, or you have glazed or oil soaked pads.

Your snowmobile can use only glycol based brake fluid. I believe that limits you to DOT 3 or 4. DOT 5 is silicone based, and will not function with the seals in your brake system. Also, remember that brake fluid is hydroscopic, i.e. it absorbs water from the air. The more water that is present, the lower the boiling point of your brake fluid becomes. Once enough water is present that it cannot be held in suspension, your brake fluid's boiling point would become that of water. As was mentioned before, the water vapor/ boiled brake fluid is compressible, and that is why you start using up more pedal/lever travel to get the same clamping force at the pads.
 
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