low / soft brake pedal

[portworks]

68 swb, captain fab short booster bracket, s10 booster,73 corvette dual disc master cyl. Stock distribution block ,original style one into two front and rear lines. 9" ford disc rear end, and 1985 front disc.
I am aware of how to bleed properly with a stock distribution block and have pressure, vacuum, and manual bled.double and triple checked push rod lengths.
Any other ideas I'm missing ??? Possible ratio problem from removing stock under dash brake leverage arm/ bracket assy and hooking pedal directly to booster ?

[portworks]

Does anyone have any input ?

[88Stanger]

i am not the best at brakes, but i can tell you that i have been having a issue with hard pedal, i had to really shove my foot on the brake to get it to stop. I measured my vacuum and due to my cam i only get about 13" of vacuum and i really need 17 to 18 for properly functioning brakes as i am told. So i bought a vacuum pump.
do you have good vacuum? just trying to help.

[portworks]

No vaccum pump. The pedal is soft and low with engine off also.

[Boog]

A soft low pedal is normally due to air in the lines. Also possible is the rubber lines are swelling if they are very old. Front and rear.
How will the vacuum brake booster work under boost?

[portworks]

Lines are 1yr old, boosters have check valves

[weq92f]

Sounds like it's not the usual suspects then. If these brakes work as is and function safely, then I would still suspect the usual things mentioned. Does the pressure you can apply to the pedal produce enough clamping force on the rotor to stop the vehicle? Without knowing that, well... there's an old saying about py$$in in the wind...

Someone also said once that if you eliminate all other possibilities, whatever is left, however unlikely, is your culprit. My guess is you've got some issue with the travel you are managing to apply to the plunger with your modified interior parts.

-klb

[jessemthompson]

Is this a new setup? The reason I ask is because I have put in a new master cylinder that was bad. Same symptoms. Just out of curiosity, why such a hodgepodge of a setup?

[Marine-58]

Tough one. Sounds like you have looked at most everything. An earlier post mentions older rubber lines which could be the issue, maybe bad out of box parts, that will happen occasionally. You didn't mention replacing the steel brake lines or the distro block.

It may be a long shot but if the fluid that was left in these is pretty old, it can become contaminated or just break down. I have seen that a couple times over the years. The fix for this is to completely vacuum each line and refill with new fluid. On the good side, if you do that, you can use dot5 synthetic fluid if you choose. You probably already know this but for safety sake I have to mention that you never want to mix dot 3/4 with 5.

Good Luck with chasing this down. Please post when you find it. Probably a few of us are curious as to the cause.

[portworks]

Thanks for all of the replies. I an going to try something with the Distribution block which I had taken apart and unstuck once before. Just curious if I should go with a proportioning valve with having an adjustable for the rear already ?