91 Z28, PBR rears, non-1LE fronts, bendix MKD154 titanium semi metallic front pads and bendix MKD413 rears. T56 conversion with 4th gen brake pedal. Earls' hyperfirm stainless brake lines.

my braking performance is fine. the car stops well and does not pull. Braking effect starts nearly right at the top of the pedal travel, and increases more or less linear with pedal travel. E-brake works fine too.

the problem is that the brake pedal feel is absolute crap. It feels like a sponge sometimes, and like it has a mile of travel. I can come to an aggressive stop (say 65% of max braking potential before lockup begins to occur) and you'd think the pedal would feel pretty solid, but nope - you can press harder and the pedal sinks what feels like a significant distance.
Have replaced the master cylinder with a new one from napa, no change. MC was bench bled OK. have run almost a full bottle of fluid through the system, bleeding all four corners. no change.

If I come to a stop with the engine running and pump the pedal 20 times, it will feel a little different every time. sometimes it goes a little farther, sometimes it feels and sounds spongy, sometimes it feels almost acceptable; and almost always feels very "low".

Actual measurements are:

engine running, full vacuum in booster: 3 1/4" travel from top to bottom
engine stopped, vacuum booster drained: 2" travel from top to bottom

as contrast:

my 71 camaro (front disc / rear drum) has:
vacuum booster drained: 1 3/4" travel, top to bottom

and my 88 fiero (4 wheel disc w/ GM's quick-take up master) has:
engine running: full vacuum boost: 2 1/4" travel from top to bottom
engine stopped, no vacuum boost: 1 1/2" travel from top to bottom.

both the fiero and even the ancient 71 camaro have FAR superior brake feel to my 91. The brakes on both cars respond quicker as well - a quick stab on the brakes results in an abrubt braking action, whereas the 91 is slow to respond.

Any ideas? Other than to continue bleeding and replacing parts?

 

Are you running steel braided break lines? If not, do that next.

 

yes, I'm already running Earls' hyperfirm stainless brake lines.

 

I would like to know this too. I probably have some worn out parts, but my dad (ASE mechanic) cannot explain why my pedal will feel so different, just like 91L98Z28. I put loaded front calipers on it about 5 months ago. The only additional things I have done to mine is new prop. valve, new rubber hoses and LS1 rear brakes....stock fronts. Im stumped now because he replaced his master cylinder and it didn't help. I hope it fixes mine.

 

I would like to know too.

I had an 86 buick witht he same symptoms.

It was my moms car and she took it to two shops including dealership.

After still no brakes I decided to fix it myself. Ended up replacing the whole brake system one piece at a time.

Still had bad pedal. Felt like you were pushing your foot into a bucket of goo. No feed back terrible modulation.

Sold Car to fix problem.

 

Couple of ideas, may or may not be: check the front wheel bearing end play. If excessive the hub/rotor will move around pushing the caliper and piston around.

Check the amount of movement of the booster & mastercylinder when the brake pedal is stepped on (hard). Could be loose mounting bolts or a cracked firewall.

RBob.

 

ABS equipped? Possibly in the ABS system...air, issues in general. If you have ABS and didnt bleed it a certain way depending on your car, you may still have some air in that system...just an idea...sounds like you tried everyting else.