It's been a long time. Two years ago (September) I was driving home and broke a valve spring into three pieces. Fed up, I just let it sit. Almost sold it.
My brakes have never been up to par. With the current motor in the car, I would have to stand on the pedal (pushing down so hard my leg hurt) just to get it to stand still. Most of the time I would just put it in Neutral at a stoplight. If I let off the pedal even a hair, you could hear the brakes creaking and wanting to let go. I just about had more torque than my brake system could handle.
In addition to the lack of holding power, the pedal was extremely spongy. I've been through five master cylinders, the last one being brand new. All of the calipers have been replaced with new ones. All of my rubber hoses have been replaced with steel braided hoses. And I've bled them God only knows how many times. In fact, I've put nearly two gallons of brand new fluid through the system since I put the braided lines on. Needless to say, the fluid is clear and absolutely no bubbles come out when I bleed them.
The one and only thing that hasn't been replaced is the combo valve, but I've read all over the place where they just don't seem to go bad. I don't want to buy a new one if I don't have to, but I'm at wit's end with the system and considering just going ahead and replacing it and the hard lines as well.
The pedal has nearly no resistance at all and the brakes don't start to grab until I've got about an inch or so of travel left. When I do stop, I have to come to a slow stop. If I have to panic stop, the only thing that's going to stop me is whatever I hit. The car just stops when it darn well feels like it.
I'm putting in a 355 with AFR 190 heads, a CC306 hybrid cam, and a Holley Stealth Ram - far more HP than the motor I have in there now. There's no way on earth these brakes are going to hold this car still.
What would you guys suggest?

 

i assume you have bench bled the master properly? A spongy pedal means air in the system. You can power bleed 10,000 gallons of fluid through the system and never get the air out of the master.

I know brake issues can be a real bitch to track down, i've been ****ing with mine for a couple months now, just found my issue, a rubber line with a vacuum leak, not at the ends, the actual hose! Found it completely by accident.

As for the new engine, i would recommend at least upgrading the front setup to at least a ls1/c5 setup.

 

Yeah, I've bench bled that baby quite a few times. And the shop I took it to on my last attempt disassembled it and then reassembled it completely submerged in a bath of brake fluid - they don't trust bench bleeding at all. No air anywhere. I just thought of something last night - the rubber hose that completes the circuit between the hard line and the rear end. I don't know why they don't give you a hose for that when you buy a braided hose kit.
So the only things left is the possibility that air is getting into the system via a pinhole somewhere in the combo valve, the hard lines, or the rubber hose on the rear end.
I'm thinking of testing the system in a way I saw someone reply to one of my previous posts. You unscrew the output ports on the combo valve and put plugs in them and test the pedal. Remove the next plug and test again. When you find which one causes the soft pedal, then you know where the problem is.
As for the upgrade ... I was considering that. I'm also considering buying a master with a bleeder valve built in so I can put an end to the bench bleeding.
It's bad, man. My vacuum canister doesn't even help.

 

the body to axle flex line is included in most flex line kits, wonder why you didnt get one. Its possible that if that line is shot, its just expanding instead of holdiong the pressure and letting it get to the brakes, that expansion, if severe enough, could cause a bad pedal.

 

I didn't think of it at the time. I can't find any information anywhere (part #, etc.) on that body to axle line. I'll pop an e-mail off to Russell and explain my situation to them. Hopefully they'll sell me one separately from a whole kit.
I do know that hose has been stretched. Could have a pinhole in it somewhere, or expanding like you mentioned.

 

I am assuming that you have the rear brakes properly adjusted. If not, this will cause excessive pedal travel and low engagement of all brakes.

 

Unless your engine isnt coming down to idle and/or your tq convertor is shot, you shouldn't be "making that much tq" that with the engine idling, you can't stop the car. Its got to be a brake issue, not a "too much power" issue.

 

that is what I thought too or motor may not make enough vacuum, could always go to hydroboost.

 

Even if the booster isn't getting enough vacuum, the pedal will be hard to push but you'll have brakes when you begin pushing on the pedal, still. He mentioned that he's not getting brakes until the pedal has traveled a lot.

 

hydroboost has alot more clamping force when it is working correctly. sounds like it has a hole in the line somewhere but why put alot in the stock setup when there is something that works better for not much cash.