disc brake master cylinder problem

I have just fitted 71 Galaxie disc brakes to my 64 Galaxie. Brakes were excellent while I was using the original 64 master cylinder.
Fitted a 71 Galaxie master cylinder with all the correct lines, proportioning valve etc. Now the brakes perform poorly. ie: won't lock-up not matter how much pressure is applied, almost like they are not power assisted
Can anybody tell me what's gone wrong here? Just about ready to stick the original cylinder back on.

I'm just trying to take some educated guesses, but did you check the pushrod length, and bench bleed the master cylinder before installing it? Hope that helps

Okay, so you used '71 Galaxie front calipers, spindles, and rotors. So far so good.

And you had a stock single-circuit fruit-jar POWER master cylinder/booster assembly on the car, and everything worked well. Do you know what the bore of that master cylinder is?

Next, you changed to a '71 POWER master cylinder on the '64 booster. Do you know the bore of that master cylinder?

A few things come to mind:

a) Trapped air is one.

b) A change in hydraulic ratios because the new master cylinder bore is larger than the old one. Is the pedal travel noticeably shorter now?

c) Incorrectly adjusted pushrod not allowing sufficient master cylinder travel.

d) Screwed-up combination valve (okay, it's unlikely but if nothing else...)

<font size=-1>[ This Message was edited by: JEM on 1/22/04 5:40am ]</font>

I agree with the other posts. Check free play on the brake pedal. With the reservior empty you should be able to see the piston through the hole in the bottom--you should have some free play in the pedal before the piston starts to move.