Help! Rear Brake Explosion!


3 replies to this topic
  • DirtJunkie450

Posted August 29, 2011 - 11:38 AM

#1

Just bought a '05 YZ 450 with a rekluse left hand rear brake setup.

Got out on the trail 2 miles from the truck and noticed something dragging the bike down, about that time I chopped the throttle and the bike slid to a stop with the rear tire locked up. With the bike in neutral I tried to roll it back and forth but it was locked up. So I grab my brake lever and it is TIGHT, won't move at all.

Kill the bike and while I'm looking at the rear caliper, it starts to smoke. So while I'm taking my lid off to get a better look, it starts to smoke real bad and then with a big puff of smoke it sprays brake fluid every where. :)

After letting everything cool off, it appears that it is leaking fluid where the banjo bolt attaches to the rear caliper. When I squeeze the lever (which goes all the way to the grip, no pressure at all) that is where the fluid is coming from. Did I blow the line? Did I blow a seal of some sort? Please tell me my caliper isn't toast.

I assume the brakes weren't bled properly. :) Any ideas?

Also, looking at the rotor, there is a real rough spot where it looks like the brake pad stuck to the rotor while it was 50,000 degrees. Rekon that will scrub off? Hope my rotor isn't warped.

:):banghead:;):banghead:

Oh yeah, the fork seal is leaking too FFFUUUUUUUUUUUUUUUUdge! :)

  • grayracer513

Posted August 29, 2011 - 12:22 PM

#2

Some part of your brake linkage was improperly adjusted, or your hand brake kit is incorrectly installed so that it pushed the master cylinder piston far enough into the bore to close the fill/expansion port off. When this happens, the heated fluid cannot push back into the reservoir, and so the captive pressure applies the brake. That, of course, heats things up and makes matters worse.

You will first need to locate the leak and fix it, then determine why the MC piston doesn't return all the way. Sand the burned on junk off the rotor and see how it works.

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  • DirtJunkie450

Posted August 29, 2011 - 03:37 PM

#3

Here is a pic of where it's leaking fluid. It's coming from the blue bolt where the line attaches. When I squeeze the lever the fluid just runs out from inside the bolt.

I took the bolt out and it has a hole through the bolt that appears as if it needs to line up with a hole in the brake line. That seems like a crap shoot to get that to line up. Any trick to that? Is it possible this was out of alignment not allowing the fluid to return?

In the next pic, is this the piston you're talking about needing to back out or release pressure? Or is there one in the Master Cyl by the lever that I need to look at?

Posted Image
Posted Image

  • grayracer513

Posted August 29, 2011 - 05:38 PM

#4

No, that's the caliper piston, which incidentally looks to me as if the brake pads are worn out almost completely. The master cylinder piston is in the master cylinder.

The bolt doesn't need to be aligned with anything. The "banjo" fitting it passes through has an annulus in it the allows fluid to flow around the bolt until it finds the cross hole. You need to determine whether the bolt is cracked, the washer/seals have failed, or the fitting is broken.





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