Front Brake building pressure - please help


4 replies to this topic
  • Robert_Brazil

Posted February 02, 2009 - 01:34 PM

#1

I just took my 1 month old WR450F for the 4th time out on a ride with my friends. Meanwhile riding I noticed that my front brake lever started losing that free tolerance of a few milimeters and that the brake pads started dragging on the disc. It seemed as it was pumping up. I stopped and bled the front caliper which helped to solve the problem (the free tolerance returned immediately) however after a few minutes the problem returned. The brake itself worked very well, there was no sign of air in the hose, nor did I over brake or caused the front brake to overheat, just normal enduro riding. I repeated the bleeding steps a couple of times , 4 or 5 or so, until my brake cylinder became empty, without being able to solve this nasty problem.

What is causing this problem?:? The brake lever is not pushing the cylinder, I already checked that. Its actually a AVS lever that can return all the other way around. I am wondering whether the oil fluid perphas was no good. I had it changed just before the problem occurred, but done in a very professional shop. Anyone that has an idea what happened?

  • brutus68

Posted February 02, 2009 - 01:50 PM

#2

Couple of things to look at, I just went through a nightmare of the same deal on one of my street bikes. It turned out there one of the calipers was misaligned causing metal on metal which wasn't making much noise but in short time would heat up the system and cause the fluid to expand thus slowly applying increasing pressure.

On my WR I did have a problem with one of the shoe brackets getting between the caliper and the shoe causing it to drag constantly.

I would pull the caliper off, douse it in brake cleaner, look for unusual wear (should be easy to spot on a bike that's been out 4 times) and look at the pads to see if they aren't seating on the rotor correctly and dragging on one part. Looking down from the top you should see daylight between the pads and rotor until you apply the brakes and it should be parallel (same distance across them). When cold the front wheel lifted should spin freely.

good luck!

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  • Usedup

Posted February 02, 2009 - 01:52 PM

#3

I'm still learning about these bikes. My .02 worth; the return hole in the master cylinder is stopped up. Happens all the time with my old Beemers. But, as I said I'm still learning about these bikes.

  • Krannie McKranface

Posted February 02, 2009 - 06:04 PM

#4

Add back the free play at the lever adjustment

  • WR450FGreg

Posted February 03, 2009 - 10:50 AM

#5

My .02 worth; the return hole in the master cylinder is stopped up.


I agree.

This happened to one of my old TZ roadracers one time. I'd get two laps in before the back brake would slow the bike to a standstill. The return hole was blocked.

Not sure about these newer Yamahas, but the only wire I could find that was small enough to clear the hole on the older bikes was a single strand from a wire brush.

Greg




 
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