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John_Lorenz

Update on Locked Front Brake during Hot Day

4 posts in this topic

I posted before the Old forum became the new forum and now the new forum is not old and this is new I guess :lol:

About my front brake just locking up during some Hot days here in Norcal.

Seems the issue was simple, but lesson learned. I installed an oversize roter, went back to the stock brake line routing and then decided to go back to the CR routing brake line.

In that I had been fiddling with the Brake lever itself adjusting it in and out. Seems that was the issue. I turned the Adjuster way in and this lead for no play in the handle or the plunger actuation. The hot weather simply expanded on that and locked the front calipers :thumbsup:

Well I think thats what happened.

Re bled the brake last night still stiff and hanging, started looking at the adjustment and backed it out and the front wheel now spins freely and the brake is working as it should.

:awww: Did not realize that the little adjuster at the lever would cause such an effect. :lol:

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I had a similar problem with the front brake...what happened to me was I had replaced brake levers and the new lever did not complete the "cycle" if you will. It wasn't releasing all the way. So although the line was bled there was still unreturned fluid in the line. When it gets hot like happened to you, the fluid expands. I hope the adjuster you backed out does it, but if not make sure the lever is completely returning....hope this helps someone!

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Oh Great now I am second guessing :awww:

Good point, What triggered my looking at the lever was a clicking sound what felt to be it hanging. In fact it was not returning ant the click was the adjusted repostioning itself on the cam thngy or whatever you call it. :thumbsup:

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Hydraulic brake master cylinders consist of 3 basic parts: the cylinder, the piston, and the reservoir. At the brake hose end of the cylinder, is a port leading to the brake caliper. a spring pushes the piston to the far opposite end of the cylinder, where there is a port leading to the reservoir. This port is positioned right at the edge of the piston assembly so that it is open when the piston is at rest, but the first 1mm of travel closes it off and begins to push fluid down to the caliper. When the fluid changes temperature, or the pads wear, all necessary compensation takes place simply by fluid moving up to or down from the reservoir. The same is true of a hydraulic clutch, and that's why they never require adjustment underway.

If the lever or brake pedal is adjusted so tightly that this port is closed in the "at rest" position, fluid heating could definitely apply the brakes for you, as the fluid would be trapped beneath the piston in that case.

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