Front Brakes Building Pressure

Question

08 ZX6R, front brakes building pressure on their own. I just finished this restoration. When I got it, the front brake master cylinder was seized up. (Calipers were not) I cleaned and flushed the whole system. Over a week of sitting on stands, the system would build pressure and Lock the front wheel. I’d bleed it and it would be fine. So I rebuilt the master cylinder with all new internals. It would still build pressure but nowhere near as fast or bad. (Maybe 3 weeks but could still move the front wheel) I bled the system last night. I just took it for its first test ride and after about a mile it completely locked the front brakes. I had to open the bleeder to get it back home. What is causing this?


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Nick Tea 7 years 23 Answers 2456 views 0

Answers ( 23 )

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    Bad. Caliper

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      How would a caliper cause pressure to build?

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      Piston isn’t returning far enough when you let go of lever pads get warm and it locks up could also be air in the lines

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      But it would build pressure just sitting on stands without riding or even touching the brakes?

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    Ryan, the rear caliper the piston barely moves correct ? I know it moves but when I was looking over my brakes mine only moved maybe an 1/8″

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      When you press the pedal wheel stops when released should free spin but if there is any bit of air or the fluid seeps by a seal it will lock up

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    Oem levers? Or aftermarket?

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      Aftermarket.

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      How long have you had aftermarket ones on?. A lot Of the time cheap shortys arnt built 100% correctly and push on the plunger when they shouldn’t.

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      Since I rebuilt the MC. They were in the box of parts that came with the bike.

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      So if the plunger is never fully released, it will keep feeding fluid in but not let it return to the MC, correct?

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      Yeah. If it’s not milled correctly it will keep pressure on the brakes pretty much.

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        Quick way to find out is swap with a oem lever and take it for a spin. It’s way more common than you might think

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      I never thought about looking at the levels. You’re the man! Thank you.

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      If it’s not your lever giving you issues then I’m at a loss honestly. Good luck

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    I had the same issue and it was the aftermarket lever, put the oem on and problem was fixed

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    Have it checked out at a shop.one bubbly trapped in the breaks messed my buddy up at 30mph when it lockednup

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    whoever put china levers on the bike caused the issue.

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    Swollen cylinder valve seals ?

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    Bad seal on the master or caliper, its allowing fluid in past the master and down to the caliper without being engaged, the only problem it could be is a bad seal or check valve

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      Same as what I thought, the brake fluid cant flow back to the reservoir thats why it keeps building up pressure, could be a bad seal .. try pressing the lever a hundred times to see if the brake jams or not

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    Bad lines……rubber inside the lines dry rots and flakes….acts like a check valve or one way valve…..letting fluid go to calipers but not return. Last thing I ever thought it would be on my bike but sure as hell was…..hope this helps bro

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    bad cheap shitty levers they should be banned !!!

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