Brake LIne Pressure Question

[Argess]

A little update. I decided to bleed the brakes once again and this time I removed the pads and re-surfaced them with sandpaper. I also scuffed up the rotors a little bit. A good improvement after bedding in the pads again. The nose of the car would now squat down significantly under heavy braking. The 0.64 G's I previously had mentioned was a one time thing. The repeatable number was 0.61 G's. Now I get 0.67 G's and it is repeatable.

Still curious, I mounted a tape measure under the car to measure the front master cyllinder stroke and found that it was bottoming out. I bought a Tilton rebuild kit and changed it out. The old piston and seal showed no signs of wear and the cylinder bore was immaculate. No difference after doing this.

Thinking something was yeilding anyway, I installed SS teflon lines. No difference after that. So it's air. Now I've bled the brakes both with the vacuum method and reverse bleeding. The last time, I removed the calipers and held them up so the flex line was vertical and tapped the caliper to loosen any air bubbles. The net result was 550 psi where before it was a little over 500, maybe even 540. Hard to be acccurate with such a small guage.

So, there's one fact I didn't ever mention, and now it's time to fess up. I'm using DOT 5 fluid which is known to hold air and can make brake bleedng difficult. Mind you the rear brakes seem to work OK. The rear tires actually locked up during one test as I hit a few tiny pebbles on the asphalt and I could hear the tires skipping on them. The rear brake cylinder only moves a small amount when activated, so the DOT 5 is working well with them.

Also, it should be noted that the front master cylinder seals showed no signs of being affected by 25 years bathing in silicone brake fluid. They were the same softness as the new seals and did not show wear. Neither the piston nor bore showed any signs of wear either; (only 9000 miles on the car, so not a lot of braking).

I am at a loss. I guess I could swap out the whole master cylinder, but I doubt very much anything will change. I could swap out the DOT 5 to DOT 4 or something. I hope I don't have to do that. I also bought some Yellowstuff front pads to obtain the best braking I can get with what I have, but until I can figure out how to keep the master cylinder from bottoming out, it makes me uneasy to rely on those pads.