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Discussion Starter #1
A customer brought in their 08 700 because the rear brakes started on fire. ok, inspected, and replaced the rear brake line, rebuilt/replaced caliper piston seals, replaced brake pads. ever thing else seems kosher. Yet it won't build brake pressure. I have been power bleeding and hand bleeding the rear brakes to no avail, I can physically see the caliper working, but they are not getting enough pressure to stop/slow the machine and the hand lever squeezes right to the grip any ideas? I looked for leaks and bled at the master cylinder and where the hard line connects to the rear hose.
 

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I suspect a bad master cylinder.
 

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Discussion Starter #3
thats what we are starting to suspect, but at the same time we can't figure out why. the fire was localized to the rear brakes. Could the brake fluid have boiled and wrecked the seals in the master?
 

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Maybe, without knowing what caused the fire, its just a guess.
And I had a wheel bearing go bad, the rotor rubbed the caliper causing the fluid to get hot and the brakes were soft, I had to pump the level to get brake pressure. I fixed it before a fire.
 

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Before assuming anything, first make sure the inner brake pad is not catching up on the caliper mounting bracket. This is very common to happen. Most people miss it.
This causes spongy brakes. Usually it can fixed by simply adjusting the brake pad with a small flat screwdriver, to clear the bracket and sit square on the piston.
 

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Try clamping/keeping the piston bottomed in the caliper bore "c-clamp" while bleeding. It's common on the Grizzlys as the only way to bleed all the air out for some reason. It worked for me during a routine brake job.
 

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X2 dezz post...brake pads maybe hanging.
Fine tune the inside brake pads. The tang on the lower side sometimes needs to be filed to fit.

What caused the fire. Stuck brake pedal? Maybe debris in the master cylinder not allowing pressure relief. Could be why you can't pump them up. May need to rebuild.
 

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Discussion Starter #8
Ok, so the fire was caused by the rider resting his foot in the brake pedal, brakes got hot, the plastic rings caught fire. I did check and make sure the pads are not hung up, all is well in that department, I did double check and caliper seals on the right side, they where loose, i.e. the piston went in and out with very little effort. new seal kit for that should be here tomorrow
 

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Discussion Starter #9
update, rebuilt the master cylinder, a little improvement. really starting to think it also needs to rubber line coming off the master.
Personal rant: I really wish I was not handed this job halfway through repairs. The apprentice tech that started it was off for a bit with the rona so now it's my problem. Jobs like this are alot easier when you get them from start to finish right?!
 

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Discussion Starter #12
ok you helpfull scallywags, I clamped the pistons in(I left the pads on, but the pistons are all the way in) the right caliper looked like it bled real nice. The left caliper was not pulling ANY fluid, just air, although the level in the M/C was not going down. I am suspecting that the yamaha factory caliper rebuild kits are trash since I have already replaced one (right side) with an "all balls" brand kit and that is when caliper that bled nice. thoughts?
 
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