Hello,
I read much of the treads regarding this subject but I still seem to be stuck. I have a 67 that was converted to front disk with all new components, including lines, prop valve, calipers, booster, and MC. The rear plungers are new also. I bench bled the the MC and have been careful not to allow the reservoir level to drop. I started at the rear RT side to start the bleeding process. With the engine off, I can get a small amount of fluid to pump through the bleed hose, but its very slow and no pressure seems to be building. With the engine on, its even worse. The pedal drops to the floor with little effort and no fluid appears to be moving. Just as the pedal hits the floor, you can hear a small gush of air escaping from the booster somewhere. The engine idle slightly increases then goes back down as if the booster is building back the lost vacuum. The booster vacuum is attached with a straight hose to the large port on the back of the 750 Holly. The rod at the firewall is attached to the lower hole of the pedal. Seems like I'm missing something fundamental. Any suggestion is appreciated no matter how obvious. Thx
Mark.

Mark..sounds like you still have air in the system.At this point in the game..I would crack all 4 bleeders..top off the master cyl and gravity bleed all 4 wheels.Watch your puddles.The largest one gets that bleeder screw closed first and then move on to the other 3..2 then 1.Finish off with a pressure bleed or a partner that can pump your pedal and hold while you bleed.

Thanks, I'll do this.

If you've pumped for a long time with the rear bleeders open and still aren't getting anything but a few drops of brake fluid, you probably have a clogged brake like line or fitting. Start at the bleeder screen and work your way back to the master cylinder, disconnecting as you go along until you get fluid to squirt.

Thanks for the input. I now have a fair amout of pressure while the engine is off, but still have to pump a bit to build pressure. I can accept I may still have air in the lines..... This part is strange however; when I push the pedal while the engine is on, about midway through the stroke of the pedel, you can hear air escaping somewhere out the booter just before touching the floor. Then with the engine off, I had a partner push the pedal with the MC disconnected from the booster. I noticed the rubber gromet will separate from the assmembly while the pedal is pushed. The problem seems like the gromet is being pushed out of its position even with the MC installed. Am I missing some part that keeps the gromet up against the booster? Seems like depressing the pedal will dislodge the gromet and all vacuum is lost. All parts were ordered new with my front disk conversion.
Getting desperate.
Thanks for any help..

Under the dash, there should be no rubber boot like a manual brake car would have. Air must be allowed to enter the rear of the booster or you will have no boost. When the pedal is pushed very hard, a valve inside the booster allows air to enter the rear of the booster past a felt or foam pad that moves with the pushrod.

If very little resistance is felt by the pedal, the valve in the booster will not open until resistance is higher. You won't get boost until it's needed.

There is a plastic accordion shaped tube that connects the booster rear to the firewall. This allows it to draw in clean air from the passenger compartment.
David

On some of the kits the rod from the booster to the master is too long by just a touch. It caused mine to have no preasure to the rears and the fronts would get tight as I drove. If you still have a issue after many many bleedings, try double nutting the booster and loosing it just a little from the booster. If the master piston cant return all the way, It will surly give you trouble.

The piston between master cylinder and booster
To short and pedal to low
To long and u will find the brakes lock on..even slightly
The diffence is only a couple mm

This cannot be 'compensated ' for by adjusting the pedal punger
Sonds like your plunger is to short...use a pair of verneers to check depth and length
A quick way to find out is to drop a small washer(s) to take up the extra length...then try
Do not use the washers as a fix...use the correct length plunger.