This problem is still pissin me off, I believe some of the problem is still brake fade. Maybe because the pedal is not grabbing hard enough to stop, so it is just spinning, and creating too much friction, compounding the problem. Its hard to explain, but it really seems like the brake components are working right, however it is just shy of the capacity to stop the car. Like it needs 10%-15% more stopping power. I am aware this isn’t the case, just having trouble putting the symptoms into words.
I went ahead and replaced the master cylinder, and "bench bled" the new using the pedal while bolted to the booster but using the supplied plastic fittings and tubes, etc. Took several pumps but I’m 100% sure there was no air in the MC when I was done. To bleed, I go furthest to the MC, and did it twice (as in to rounds) for each corner. I use a coke bottle with some fluid in the bottom, with clear tubing coming through a hole in the cap, this tube fits snuggly to the brake bleeder. I can then open the bleeder and pump several times until clear fluid comes through with no bubbles whatsoever. Just thought I’d throw all that in just so I don’t get asked about are they bled correctly.
Ok! If I get the car to 60-70, and try and slow it quickly, the brakes become significantly (or scary) less responsive. They seem to go 90% to the floor “under power” (or feeling right and slowing the car properly) but the last 10% of travel seems hard, like it reaches a mechanical stop, but hasn’t stopped the car yet. This has me wondering if its a booster problem, because at low speed, if I apply lots more pressure (for that last 10%), I can make them lock up; but at higher speed, it brings on significant “brake fade” really quickly, and it will take a mile or so of light cruise (with very little brakes) before the brakes “come back” enough to make me even semi comfortable to drive slowly back to the house… And then if I let it sit for 15-30 minutes or so, they seem to act OK again, at least at low speed. I aint driving it right now just in case, but it does seem like it would drive fine in the traffic, unless I had to stop or brake aggressively on the interstate… just to further describe the problem.
I was originally concerned that there was leaking out of the rear of the MC between the MC and the Booster, as there was a few drips where they bolt together; but it really didn’t smell like brake fluid once I got it out, it was more like grime back there, so I am curious if it is more likely that there was some grease leaking out form the booster where the pushrod comes out although it doesn’t look like there is a seal of any kind in that area, it could have be leaking from?
So I’m at a loss now. Since I’ve done the swap (non-abs + mustang PBR calipers) the car seems to have stopped fine, just not very impressively. So the way it is acting is kind of “all of a sudden” though I believe there was a slight hint that it wasn’t acting 100% right when I first did the conversion to begin with.
Could the booster be bad? Could one of the rubber lines be failing, and “swelling” rather than delivering all fluid to the wheels (I would think it would have to be both sides if this was the case???) Or is there some air trapped in the calipers themselves???
I believe the pushrod length to be correct, I did have to use a screw with the head ground down to replace the original pushrod, as the original was allowing pedal movement before the pushrod really engaged the MC piston. As of now, the brakes do immediately respond, and there appears to be no slack in the pedal before the car begins to stop…
I don’t know what to do next…