Lost my rear brakes


10 replies to this topic
  • MaddogYZ

Posted January 24, 2009 - 11:57 AM

#1

Last time I went riding I noticed I had almost no rear brake. I could lock up the tire but only if I completly bottomed out the pedal. I got around to bleeding them today and found no air bubbles in the line and I still don't have any feel at the pedal. I have plenty of pad thickness left and there are no leaks at any of the fittings. I'm thinking I have an issue with the mastercylinder, what do you guys think? Anything else I can troubleshoot to pinpoint the problem before I go ordering parts?

Thanks

  • Krannie McKranface

Posted January 24, 2009 - 03:05 PM

#2

Last time I went riding I noticed I had almost no rear brake. I could lock up the tire but only if I completly bottomed out the pedal. I got around to bleeding them today and found no air bubbles in the line and I still don't have any feel at the pedal. I have plenty of pad thickness left and there are no leaks at any of the fittings. I'm thinking I have an issue with the mastercylinder, what do you guys think? Anything else I can troubleshoot to pinpoint the problem before I go ordering parts?

Thanks


-Cracked Banjo fitting
-Torn master bladder
-Cracked line.

It takes me 20-40 minutes of bleeding to get a tight hydrualic circuit. Or a power bleeder.

  • TRUE_2_YAMAHA_001

Posted January 25, 2009 - 10:44 PM

#3

there could be a particle or 2 in the master cyclender. try taking it apart. they are relatively simple in terms of brakes. it could be as simple as that. or your master could be shot. i would bleed it more to be sure that there is nothing cloging the lines.

  • matt4x4

Posted January 26, 2009 - 12:13 PM

#4

I've heard of the lines themselves fatiguing and expanding under the pressure - effectively reducing your braking power, might take a look into that.

  • MaddogYZ

Posted January 31, 2009 - 12:37 PM

#5

If I'm reading my manual correctly it says that the diaphram should put in to bleed the rear brakes. So my brakes won't work at all without the diaphram right?

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  • MaddogYZ

Posted February 01, 2009 - 09:40 AM

#6

I replaced the master cyclinder kit and I'm still not getting any pressure at the caliper piston, in fact the caliper piston won't compress in at all. I pushed the piston in to push air bubbles from the line up through the reservior. Now the piston won't move push out at all so does that mean my problem is at the caliper? Fluid will squirt out the bleeder so the master cyclinder is pushing fluid so what's going on here?

  • Frostbite

Posted February 01, 2009 - 10:32 AM

#7

I replaced the master cyclinder kit and I'm still not getting any pressure at the caliper piston, in fact the caliper piston won't compress in at all. I pushed the piston in to push air bubbles from the line up through the reservior. Now the piston won't move push out at all so does that mean my problem is at the caliper? Fluid will squirt out the bleeder so the master cyclinder is pushing fluid so what's going on here?



I had a similiar problem during my first ride on my 450, the rear brake went away. I had several problems that day due to the extreme cold, and assumed that the brake line had cracked from the cold. I rode home and found the line intact and the reservoir full - no evidence of leaks anywhere. The brake pedal pumped like there ws nothing connected to it. I bled the master cylinder and it did push fluid out of the bleeder, but weakly - not much pressure. If you have a lot of air in your system the first few bleeds will be weak pressure, but mine didn't get any better.
I thought it must be the piston seal leaking pressure, since there were no fluid leaks, just pressure loss. I had a spare from my 400 and popped that and it worked perfectly so I left it mounted. That was a year ago. I did buy a spare used 450 master cylinder, but haven't installed it since the other is working fine, and I still felt it may have had something to do with the cold.
I had very few cold issues with my 99 400, but the 07 450 seems to use less rubbery more plasticky stuff, so it cracks in the cold. The speedo wire snapped in half on the 450 when I rolled it out the door, before I even rode.
Was it cold when you lost your brakes?
Frosty

  • MaddogYZ

Posted February 01, 2009 - 03:29 PM

#8

I've been riding it this winter so yea I've been riding in the cold. Everything is pointing towards the master cylinder but I just replaced the internals and it's still not working right. I blew every orfice out with compressed air including the brake line, took out the caliper piston and cleaned it (it looked brand new), so this thing is driving me crazy. I gotta make sure the line's good now before I do anything else. I'll miss with more later this week.

  • TRUE_2_YAMAHA_001

Posted February 01, 2009 - 10:02 PM

#9

i have one for a 2001 wr 426 if you decide that you get fed up and just want to put one on that works. but if you get it figure it out, i will be interested to know what was going on with it.

  • MaddogYZ

Posted February 16, 2009 - 01:59 PM

#10

I finally got my rear brakes working and got to ride Sunday for a couple hours. The original symptom pointed to air in my line but there was no visible leak anywhere, I still think that was the orginal problem. For whatever reason I had a hell of time bleeding the brakes, the confusing part is that I would never get any air bubbles while bleeding, but I could never get any feel at the pedal. After rebuilding the master cylinder, cleaning the piston, and eventually replacing the brake line I got my brakes to work.

I tried sucking fluid through with a Mityvac, pushing fluid through with a syringe, bleeding the conventional way, all to no avail. The only method that worked was tieing the brake pedal down with a zip-tie and letting it sit for at least 4 hours, cut the tie and then strap it down again. The first time i got a weee bit of pressure at the end of the stroke, the 2nd more, and the 3rd time I had pretty good feel at the pedal. What a PITA, just glad I wasn't messing with this during summer, I would've smashed something.

  • kjr247

Posted February 20, 2009 - 07:32 PM

#11

Glad you got it fixed. My '99 had the same issue with the brakes. On mine the brake reservoir warped slightly from the exhaust heat making the cap not seat right. I fabricated a small aluminum heat shield and it stays cool. You still might keep an eye on this. I am not sure how hot or long you run yours but it happened on mine. Drove me crazy trying to figure that out. No air in the line that I could see? Go figure. Ride on. KJR




 
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