It's always possible to get a bubble somewhere that just won't let go.
Motorcycle brakes are infamous for this because of the small system
volume, and we had very complex methods for bleeding. One of the
reasons I like speed bleeders so much. You can pump fluid through so
fast that there's a much lower likelihood of a trapped bubble. But if
you want to do it right, bleed from the top down, bleeding at every
connection under strong pedal pressure. It's messy, but it works. You
almost always gets some farting from the bubbles of the upper
connections.
I wouldn't discount the bedding issue either. On higher performance
race cars it becomes really obvious when brake pads haven't been
properly bedded--they go away very quickly and/or develop hot spots
that make the material fail, usually crazing and hardening the
surface but in extreme cases making the pad crumble. Follow the
manufacturers recommended process exactly, and afterwards pull your
pads and look for high spots. You need to transfer material from the
pad to the rotor and you need the pad to be flat on the rotor face.
High spots are hot spots. I see people all the time with pads that are
obviously not working. But I rarely say anything because no one wants
to hear that they need to toss them and do the bedding right.
You CAN sometimes reuse a pad that''s been tapered or has hot spots. I
use a method I copped from Kas--a cupped grinding wheel in a drill
press with a dead flat surface (an old piece of inconel plate from a
nuke plant that I've hauled around for thirty years) to slide the pad
on. Grind till it's flat. Wear a respirator. Then rebedd it.
If your manufacturer doesn't give a recco, here's the standard approach:
Get on the track, accelerate to a good speed, press the brake gently
and slow to nearly a stop. drive a little more without using the
brakes and let things cool a bit, get going fast and then brake HARD
to nearly a stop. Cool again, brake hard to nearly a stop. Repeat
about five times, cooling in between. Return to the pits, pull the
pads and look at them. If you have high spots (isolated, shiny spots
with no wear around them) your pads aren't flat or your calipers
aren't pressing evenly. If they got really hot then your seals aren't
drawing the pads away from the rotor or you have too much residual
pressure.
Don't assume you don't have residual pressure. The weird little
Triumph brake line junction is a residual pressure device, and many
master cylinders come with a residual pressure device installed.
The calipers are supposed to withdraw the pads from the rotors with
the elastic stickiness of the seal lips. Worn or hard seals, corroded
pistons, or bowed calipers compromise this.
Girling calipers suck, by the way. For as heavy as they are, they
don't have a lot of rigidity. A Wilwood ultralight is ten times
better, give you brakes that can stop on a dime and give you nine
cents change, but we can't use them. Sure are nice though.
On May 19, 2009, at 8:51 AM, toodamnfunky@comcast.net wrote:
> Michael,
>
>
>
> The masters and calipers are rebuilt with only two races on them
> prior to this
> past weekend.
>
> jg
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