my rear brake piston is not receding back into the caliper after the brake is applied, ive took apart and rebuilt the caliper twice! with new piston seals and a bleeding afterwards, i tried to 'set' the piston by putting index cards between the pads and rotor to no avail, why would my brake grab great but not release???? please tell me what i am missing!!!

 

Air in da lines......

Air expands much more than does the Brake fluid,... as you use the brakes, it creates heat,... heat expands the bubble of air (wherever it might be) and thus the fluid seems to be the culprit,... but it's not,.... It's the air doin' it.

In the summer months this is not uncommon in braking systems of all kinds. (well,... not direct mechanical ones, I guess)....but you should be able to spend a little time and burp the brakes and bleed them till there's absolutely no chance of air in the lines or caliper..... No more stuck brakes.

 

yeah it seems like there is way to much pressure in the system i guess it could use a better bleeding? one thing that baffles me is this rubber boot inside the rear master cylinder it seems it takes up alot of space and i dont know why its there, i dont know if it should be filled with air or fluid, ill snap a pic tomorrow, thanks for the help

 

What you might want to do is get a bleeding syringe. Hook it up to the bleeder valve and open the valve. Then draw from the syringe (not push but pull) Do this a few times and then rebleed as normal. Be sure to keep adding brake fluid as you draw or you will just get more air in. I had to rebuild my piston and this was the quickest way to regain the pressure without air bubbles I have done. Their are a few hydraulic bleeders that are a little pricey but do the same thing. The gasket might need to be reshaped. If you drew a lot of air in it may look like a cone head instead of a rectangular seal. hope this helps.

 

Butch450 gave ya a great tutorial on bleeding brakes. One thing to remember if you are doing it all by hand; Make sure you keep the pedal/lever engaged until you have tightened the bleeder screw back up. If it isn't tight when you release the pedal pressure the system sucks air back in and will never bleed out properly. Additionally, that rubber boot is there to take up space. When you top off the reservoir, collapse the boot before installing it. When the system is in use, fluid levels will fall as the pads wear. The boot is pulled out by the system vacuum and keeps that empty space filled.

 

well guys i re-bled it today, and collapsed the boot like scooter said, the piston retracts slightly but not fully, and there cant still be air in the lines, seems like some sort of vaccum issue, im going to swing it by to my auto mechanic (friend of mine) to see what he says tomorrow, i guess im just baffled how i cannot fix something this simple

 

hey guys any advice before i start ripping into the master cylinder today? and does it need to be replaced or can it be re-built, i think this isnt just a caliper/fluid/adjustment issue, thanks

 

Its called the "master Clylinder Kit" $45 from this place.Part #2 http://www.cyclepartswarehouse.com/f...008&fveh=12846

Yamaha Part Number 5BE-W0042-00-00 on this 2008 YAMAHA
YFM45FXX. You did not mention what ATV you have though.

 

sorry, its an 07 yamaha wolverine 450, could it be possible for the master cylinder to have died in 3 years and 350 miles? dosnt seem right, but then again i cant build up much pressure by squeezing the brake lever, (its been getting progressively worse) which is why this leads me to believe it is the M.C

 

The thing is ,even if you have air in your lines the brake when released should not drag the wheel. Are you sure you bleed them OK? I never bleed them on a ATV and I,m a disaster at it with cars and trucks,I leave the bleeding to a friend afer I change a line.

350 miles is nothing but if air get in, it gets in.