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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Answers ( 23 )
Bad. Caliper
How would a caliper cause pressure to build?
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
But it would build pressure just sitting on stands without riding or even touching the brakes?
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″
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
Oem levers? Or aftermarket?
Aftermarket.
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.
Since I rebuilt the MC. They were in the box of parts that came with the bike.
So if the plunger is never fully released, it will keep feeding fluid in but not let it return to the MC, correct?
Yeah. If it’s not milled correctly it will keep pressure on the brakes pretty much.
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
I never thought about looking at the levels. You’re the man! Thank you.
If it’s not your lever giving you issues then I’m at a loss honestly. Good luck
I had the same issue and it was the aftermarket lever, put the oem on and problem was fixed
Have it checked out at a shop.one bubbly trapped in the breaks messed my buddy up at 30mph when it lockednup
whoever put china levers on the bike caused the issue.
Swollen cylinder valve seals ?
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
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
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
bad cheap shitty levers they should be banned !!!