What is the cause of low or no brake pedal pressure on a 1964 Thunderbird when the master cylinder and all the lines have been replaced and bled?

I know you may think I'm wack, but you didn't mention brake fluid?

Just and idea Answer

Not sure of the question here but are you saying the brakes are soft and you can't get a resistance to your applying the brakes? Is this power brakes/ The vacume hoses may be bad. or the power assist chamber.

Just and idea Answer

Not sure of the question here but are you saying the brakes are soft and you can't get a resistance to your applying the brakes? Is this power brakes/ The vacume hoses may be bad. or the power assist chamber.

A couple more ideas...

Power brakes were standard equipment on the 1964 Bird. If your brakes just aren't working period, you've either got a fluid leak somewhere in the system or you need to bleed further...start by bleeding the master cylinder. Easiest way to do this is to take it off the car and "bench bleed" it. Put vinyl tubing into the ports where you would hook the brake lines up, then run the vinyl tubing back into the fluid reservoir. Main thing is to keep the reservoir full, or your bleed will be for nothing...the minute it sucks air, your back at square one. With the master clamped (gently) in a vise, actuate the master by pressing the piston in and then releasing it...until you don't see bubbles in the vinyl tubing. Leave the fluid in the reservoir after you're done bench bleeding; then install it back in the car (taking care not to spill any fluid..especially on the paint!), connect the brake lines, and finish bleeding the rest of the system. Not a bad idea to make sure the adjustment is correct on the rod between the booster and the master before you reinstall it. That can cause the brakes to be ineffective too.

Check your flex lines too...make sure they're not bulging when you press the pedal down. That'll cause the brakes not to work for sure. You mentioned that all the lines are new, but there are rubber flex lines....especially the one just forward of the rear axle. If they're weak or leaking, that could cause a low or no brake condition.

If the brakes work fine, but just seems like the pedal is too soft...or even too touchy, look at the brake booster, vacuum lines to the booster, and the vacuum connections on the booster. A bad booster can make the brakes feel too touchy or soft. These are just ideas from things I've run into on my own 64.

One more thing, make sure you keep your rear brake linings up to snuff and your emergency brake adjusted; if your master goes bad or your brake fluid gets too low, the brakes are gone completely...and you'll have to use the emergency brake to stop the car. Hope this helps.