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will1894

rear brake caliper problem

4 posts in this topic

Today I put new brake lines and pads on my 2008 yz450f the front went fine and I thought the rear was going good got everything on and bleed my lines but the rear caliper piston won't come back out after I compressed it to put the new pads in Iv bleed the line about a dozen times now and nothing the piston will move a little when I press the brake peddle and move back but I can't get it to come out to make contact with the pads any help would be very appreciated 

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Might be time for a caliper rebuild. I had the same thing happen to me on my RMZ. Ended up replacing the pistons and o-rings and it is as good as new. The piston and o-ring kit cost about $35, but I threw in stainless lines and fast/quick bleeders so all total it cost around $100. 

 

P.S. The easiest way to get the pistons out is to remove the caliper from the bike and spray 125 psi of compressed air into the port where the brake line goes. Just be sure to have the pistons pointed away from you (preferable aimed at the floor or into a pillow) because they will come shooting out like a rocket. 

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P.S. The easiest way to get the pistons out is to remove the caliper from the bike and spray 125 psi of compressed air into the port where the brake line goes. Just be sure to have the pistons pointed away from you (preferable aimed at the floor or into a pillow) because they will come shooting out like a rocket. 

 

Dangerous advice and unnecessary.

 

The hydraulic system the caliper is connected to is easily capable of raising more pressure than needed to push the caliper piston back out, and even if you get it back out, you'll have the same problem, which simply is that the system still has so much air in it that it's inoperative.

 

Start by filling the master.  Open the bleeder, press the pedal down semi-gently against its limit, hold, and close the bleeder.  Return the pedal and repeat this until it appears that there is no air in the fluid being exhausted from the bleeder.  During this process, it is important to keep the fluid level up in the master. 

 

Next, it's time to get rid of the giant bubble that lives at the banjo fitting where the brake line ties to the master cylinder.  Loosen the fitting, push down and hold the pedal, retighten the fitting.  You'll see air.  Repeat until you don't (usually 1-3 times).  The system should now be functionally free of air and capable of pushing the pads back out.  It may take several strokes of the pedal to run them back down, and you'll want to keep an eye on the level in the master.  At the end of the task, you want the level about three quarters up in the sight window, but not higher.

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Thanks y'all I don't think there is any air in the line but ill try messing with the banjo fitting and see if that works first, i was thinking of using a air compressor to get it out but i want to use that as a last resort but ya its probably time for a rebuild

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