Front brake problem

COOPer

New Member
I just bought a 2006 Mastiff. It appears somebody put new pads on the front and rear the rear work fine the front doesnt stop very well and when comes to almost complete stop makes a noise. Not a squeak but like a vibration and can feel it in the bars. Also in only a couple miles the rotor turns black. Its not hot and can wipe off also looks like fibers like the pad is coming apart or something. Cheap pads? Havent taken apart yet going to this week.
 

awg

Well-Known Member
I agree. Take it apart and see if indeed the pads are coming apart. Also check for brake fluid leakage around the pistons.
 

Sven

Well-Known Member
Here is the theory. Think about how old the bike is. Think about the maintenance needed swapping out oil with new fluid every two years is the servicing on the calipers and masters. Water is heavier than oil so moisture settles to the bottom. Heat wise, there begins a chemical reaction that builds in a groove where this seal lives.

The seal is called a quad-ring and has memory to return to a static position, as if the seal is sitting on a bench. The piston is round so the inside of the quad ring is that one side being flat. The other three sides sit in that groove that is machined square. There is nothing but fluid under that seal, but does not leak out that third wall, as well as the piston, correct? Imagine the piston is about to move and the quad more or less stands on its tiptoes as the piston pushes against the pad, pad against the disc.

When you release the lever, the quad moves back down flat footed back in that groove. That's what moved the piston back so there is no drag on the disc. So like a mold growing, it is that growth under the quad. It then locks against the pad and can't move back. Thus, the rubbing off of pad material. That powder between pad and disc causes the squeak to occur and disappear. More or less took the sheen off the surface of the pad.
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The Fix:
Here is where you remove the caliper, pump the piston out of the caliper, remove the quad ring, and super clean the white crust out of that groove. Break clean is showing who still remains when it evaporates. The clean is more using a dental pick so you clean the white crust out of the corners of the L of that groove. Plus, you never want to remove the finish off the caliper's machined bore hole. It has a very tight clearance so the piston does not rock. So brake clean and a paper towel is as abrasive as you get. Don't want to polish it because it too removes material.

Do you use the same quad ring? No. Replace with new. Can you clean it with your fingers and rub it off and reuse it? Only a leak knows for sure. Can't sand or do any other thing to the rubber surface but rub the white crust off by hand. Piston calls for the same paper towel finish on the piston surface as well. I clean my pistons by wrapping fiber type fishing line and wrap a loop around it and shine it like I'm a shoe shine boy going at with a towel and walk the line up the piston.

The pad surface smoothness needs to be rough again so I simply find a cement sidewalk, and use that as the abrasive tool. Couple of karate kid moves (round da floor/ up-down) and reinstall.
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Funny, but poor braking with softer pads would be the band-aid fix for low quality braking parts. Since you do not know the service history of the bike, you are looking at 14 years divided by 2 = 7 times the brakes needing that change since new.

And that's my drag story (pun) and am sticking to it (pun).
 
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