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pma

Rear brake won’t stop after pad replacement

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pma

It was time to replace the pads, front and rear. Front brakes work beautifully with the new pads but the rear brake piston just won’t compress the pads enough to grab the disc. I pumped the lever for what seemed forever with no change in pressure. I did a quick bleed, no air whatsoever. What am I missing? Please help!

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cornerslider

I mean no disrespect, but did you put the pads in the right way (pad material against the rotor)? I did it wrong on a car one time- VERY embarrassing..... I NEVER thought that I could ever do something like that 😞

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pma
27 minutes ago, cornerslider said:

I mean no disrespect, but did you put the pads in the right way (pad material against the rotor)? I did it wrong on a car one time- VERY embarrassing..... I NEVER thought that I could ever do something like that 😞

None taken. We’re all capable of making epically silly mistakes. They are on correctly. I went and bled them again. Still can’t bring it up to pressure. I didn’t touch the brake lines once during the process, front or rear. This is a 2016 model, so no ABS either...

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mossrider

Did you clean it up nice with a toothbrush and some simple green? Everything will look and work better. Shims in correctly? Caliper puck in correct if it came out, flat, closed end into hole first? Here's a link to the schematic;

https://www.partsfish.com/oemparts/a/yam/55db251587a8660384734df2/rear-brake-caliper

Plenty of fluid in resivoir? Bleed correctly? Check slack in foot pedal too. If it had been adjusted at some point to compensate for worn pads, when new ones put in it will effectively limit the pedal travel, potentially too much.

 Should work

Spitballing...

Edited by mossrider
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pma
17 hours ago, mossrider said:

Did you clean it up nice with a toothbrush and some simple green? Everything will look and work better. Shims in correctly? Caliper puck in correct if it came out, flat, closed end into hole first? Here's a link to the schematic;

https://www.partsfish.com/oemparts/a/yam/55db251587a8660384734df2/rear-brake-caliper

Plenty of fluid in resivoir? Bleed correctly? Check slack in foot pedal too. If it had been adjusted at some point to compensate for worn pads, when new ones put in it will effectively limit the pedal travel, potentially too much.

 Should work

Spitballing...

Thanks for the schematic. It is most likely the shims then. I'll let you know tonight. Thank you!!

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pma
22 hours ago, pma said:

Thanks for the schematic. It is most likely the shims then. I'll let you know tonight. Thank you!!

So I did miss the shims. Still won't build pressure. Readjusted the foot pedal for its longest setting. Still nothing. Noticed a small amount of brake fluid at the rubber boot. It's not actively leaking where there's a puddle, but it looks like I'm gonna have to pull the master cylinder apart at this point.Is it possible that when I compressed the piston in the caliper the forced oil or air boogered something in the cylinder ?

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mossrider
3 minutes ago, pma said:

So I did miss the shims. Still won't build pressure. Readjusted the foot pedal for its longest setting. Still nothing. Noticed a small amount of brake fluid at the rubber boot. It's not actively leaking where there's a puddle, but it looks like I'm gonna have to pull the master cylinder apart at this point.Is it possible that when I compressed the piston in the caliper the forced oil or air boogered something in the cylinder ?

Anything is possible, but not probable. Before I tore a caliper or master apart I would unhook the rear caliper and elevate it and make sure there were no loops or dips in the line and re-bleed it (put something between the pads). I bet you have an embolism in there. I always eliminate the obvious and simplest first and work toward the impossible. Use a vacuum bleeder if you can.

 

.02

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pma

In the end I took apart the master cylinder and cleaned it out. Put everything back together and it works beautifully. Thanks for your advice.

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mcbrien

that's great that you got it fixed. Any idea what happened in the first place? I wouldn't expect a problem changing pads.

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pma

Neither did I. The only thing I manipulated was the caliper. I asked a friend who’s a mechanic, and he felt that when I compressed the piston on the caliper I pushed air bubbles or possibly even some dirt back into the master cylinder. Somewhat rare to happen. Totally frustrating, but a damn good learning experience.

Edited by pma
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twf

Next time take reservoir cap off and get some fluid out before compressing pistons. 

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