Re: Squishy Brakes. Continued.

[abbotts@xxxx]

If the fluid in the master cylinder reservoir is staying at the same 
level then you can rule out failed seals, whether at the m/c or the 
caliper.
You said that the rotors are warped. If the warping is sufficient it 
can cause brake pad "knockoff", where the warped part of the rotor 
pushes the pads (and hence the pistons) away from itself and back 
towards the caliper. When you hit the brakes, the pads are a small 
distance away from the rotor so the first bit of pedal travel goes 
into taking up the slack i.e. no braking effect until the slack is 
gone and the pads are once again touching the rotors. Race drivers 
often give the brake pedal a quick push just before they need the 
brakes in earnest. Even high cornering forces can cause "knock off" 
so they dab the brakes to push the pads back against the rotors just 
prior to the high braking areas on the track.

Cheers
Steve Abbott

--- In dmcnews@xxxxxxxxxxxxxxx, "therealdmcvegas" <DMCVegas@xxxx> 
wrote:
> Here is a bit more information to answer questions asked.
> 
> System wasn't just bled, but was power-flushed until fluid was 
clear, and all 
> air bubbles were gone. Which took almost 4 large bottles of GTLMA 
(old fluid 
> was BLACK). Also, the condition is the same, regardless of 
temperature. It can 
> be a warm afternoon, or cold enough that I've had to scrape ice off 
the 
> windscreen (last Saturday night), and the condition is the exact 
same.
> 
> Also, the fluid level inside the reservoir appears to be fine. When 
first filled, 
> the fluid touched both fill marks on either side, and a litte of 
the top of the 
> reservoir. Now, the level is slightly below, but if I tilt the 
reservoir from side to 
> side, the fluid will touch the "Full" marks on the top.
> 
> Glazing is most likely present, but not the root cause. The problem 
aside from 
> fade is that the brakes don't "grab" until the pedal is much 
farther down. 
> However, if you pump the pedal twice in rapid succession, the 
pedal "grabs" 
> much earlier. Although, the new brake fade is still present, it 
should remain 
> consistant, and should not be affected by pumping, which it is not. 
The main 
> concern is the "grabbing".
> 
> I've not been able to fully test for pull when braking. However, no 
force has 
> been noticed, and the car still feels and appears to be stopping in 
a straight 
> line. However, the front rotors are warped, so I'll need to find a 
set of calipers 
> to measure their thickness. Hopefully I'll have enough material 
left to turn 'em 
> so they'll be corrected, but that's another subject.
> 
> At this point, I'm more than convinced that the problem is 
hydraulic. But 
> wheather the issue is: 1. Blown seal(s) in new M/C, 2. Blown inner 
seal on 
> caliper(s), or 3. swelling brake hoses, I don't know. Or perhaps a 
combination 
> of one or more (these are the only things that I can think of that 
would cause 
> such a sudden pressure loss, and fit with my symptoms). Plus, gut 
instinct tells 
> me that I can't just replace the brake hoses, and leave the old 
calipers in 
> place. While it may be an unfounded fear, I'm not comfortable with 
forcing 
> more pressure on who-knows-how-old caliper seals with new SS 
Braided 
> hoses installed. And rather than replace a couple of seals, I'd 
also rather just 
> swap out for fresh rebuilt units (I don't trust old equipment).
> 
> Thanks again to everyone!
> 
> -Robert
> vin 6585 "X"