I just recently finished replacing the pads, rotors, and brake hoses on my '99 C2 and it was the brake job from hell. Never in my life have I had so many problems with a brake system. It appeared as though someone used an impact on the caliper bolts and buggered up some of the threads/bolts, thankfully a rethreading tap and new bolts fixed that. Also, whoever installed the line fittings way over torqued them and I ended up having to cut half of the flare nuts off and make/splice lines, because even after more than a week with penetrating oil and heat they just wanted to round off (I tried a whole slew of wrenches even SnapOn line wrenches). During the line repair process I was unable to avoid letting the master run dry, and didn't think a whole lot of it as I have bled many brake/clutch systems from dry in the past, without too much trouble, but not this car.

I initially filled it full and bled 2 liters through the brake system (speed bleeders & traditional 2 person method) and the pedal felt okay, so I dropped it down and went to bed the pads during this my stopping power was fine, but the pedal got increasingly soft, to the point I am pretty sure I could stop faster than before the brake job, but the first half of pedal travel did very little and took almost no effort. After the pedal got soft I drove it home and bled another liter of fluid through it with no improvement, so I drove it around again and in a safe spot activated the ABS a few times, as I heard that can help and then put it back up on stands and ran 4+ liters of fluid through it with a Motive power bleeder and was able to get a bit more air out, but my pedal still feels like garbage. Also, I have confirmed that all of my new lines/splices sealed up good and I have no leaks.

I have searched extensively about my issue and can't find much about '99s, but see cases where with the newer 996s with PSM they can need the ABS system bled with PIWIS, is it possible I am having a similar issue on my '99 with the pre-PSM traction control? I feel like the ABS has to be contributing to this problem some how, but am unfortunately not very experienced with ABS as this is only the second car I've owned with ABS, and the only other is my '93 F350 with rear only ABS and I never had any issues with that. I have also read several complaints claiming installing Hawks HPS pads contributed to a soft pedal, but I have a hard time believing pads could make this big of a difference in pedal feel, nor can I imagine anyone would buy them if they give this kind of brake feel.

Any help or advice would be greatly appreciated, because at this point I am at a bit of a loss.

 

You have air inside the hydraulic ABS/PSM module.
Without PIWIS or Durametric (not sure that can activate valves and the pump) you can resort to braking hard on a gravel road in order to activate the ABS. This will flush any air into the main brake lines, which you then just bleed as you've already done, to get the air out.
Watch your review mirror before you brake hard.

 

Doubt it’s an ABS issue. My guess is air in the MC, the Motive isn’t getting it out. Have you tried an old fashioned 2-person bleed? Pelican advises this after using the Motive, to get residual air out of the MC. You could also try pulling the MC, bench bleeding, and starting over.

Or, your MC seals are shot and you need a new MC.

The brakes on Carreras are known to have a soft feel even when properly bled so keep your expectations modest. If you need a new MC consider a GT3 upgrade.

 

I bled at least one liter of brake fluid through the old fashion 2 person way and another 2 liters or so with speed bleeders (they are a one way valve so you can open them and pump the brakes to get air out but not let more in).
​The car is isn't new to me I've owned it for 2 years and put over 25k miles on it and the brake feel was great when I bought it and fell off a bit as the old rotors got worse, or at least that's what I thought, but I suppose it could have been my master starting to wear out and running it dry was the final nail in the coffin for it.

I'm going to try getting the ABS to activate again like hardtrailer suggested and bleed more and if that doesn't yield any improvements, I guess I'll pull the master and inspect.

 

Porsche 996 brakes are the best factory installed brakes I have ever used. When free of air pockets they are exceptional.

Before you replace any parts try removing drivers side head lamp. You’ll find a proportioning valve there. Will have four lines and wire bundle leading to it. Remove your Motive power bleeder and top off fluid. Then crack the two fluid lines leading away from valve. Just let the fluid drain for awhile. Hopefully some trapped air will escape as well. Might want to loosen all four lines initially.

After some time tighten lines and bleed system at right rear. You can try to activate ABS with Durametric, while applying brake pedal repeatedly 10 times.
Of course pressurize with motive while doing this.
May have to run this exercise a couple of times.
If there is little improvement first time top off fluid leave reservoir cap loose and let sit over night then repeat .

 

The what now? My C2's pedal is almost as hard as my BMW race car (manual brakes, no ABS, twin Tilton MCs). Didn't think twice of it as the braking response and modulation are super crisp. Unless my booster is broken in just the right way or the car has a surprise GT3 MC...

 

Yeah, i never had any problems with softness in my 996 brakes except for the first time I boiled them at Road America back in 2005. But that was a twofold lesson. (1) don't brake too early and ride your brakes because they get real hot, and (2) always flush your brake fluid before a track day and run the best brake fluid you can get.

While I did eventually replace my oem brakes with a Brembo GT Big Brake Kit (355F, 345R), I never replaced my oem master cylinder with a GT3 master cylinder. Never needed it and after 22 years, it's still doing the job.

 

I had same problem, replaced ABS unit all is good.