69 Coupe Low Brake Pedal

[Doublej530]

I have been trying to figure out my brake issue for almost a year. I replace master cylinder. All brake cylinders and all 4 Drum breaks. All brake lines. Bled lines 100 times.bench bled M/C But pedal isn't hard and goes almost all the way to the floor. I replaced and adjusted( not sure if 100% correct but slight drag) brake pads. If I plug the proportioning valve on the front the rears seem ok. Hits at about 3/4 down on the pedal. Fronts seem to go a little lower. Not sure if the proportioning valve is bad. Tied changing with a used on but still same issue. Or if maybe my push rod on my M/c is wrong size. It looked about the. Same before I installed it. Thanks for your help.

 

[tos]

I had an issue like this. Converted to disc and dual bowl Mid 70s ? master cyl. Ended up being the pushrod was too long keeping the piston in the master cyl pushed too far forward so I wouldn’t get the proper amount of brake fluid pushed into the system.
I ended up cutting my rod shorter and making it adjustable. You can check it by disconnecting the rod at your peddle and letting the master cyl position the piston then hold your peddle up against the peddle stop and compare where the rod sits in comparison to the connection on the peddle. You shouldn’t have to push the rod in to connect it to the peddle or maybe just slightly. This will position the piston in the completely retracted position where it should be and give you full travel of the piston.

 

[Doublej530]

Thanks I will look into the push rod. As I recall it looked about the same length and the new m/c had the push rod installed and I didn't want to mess with it. And I don't recall having much difficulty lining up the peddle.
I took it out for a road test last night and it will slow down but need time to stop. Brakes don't lock up at any speed when I hit the peddle. Going to try adjusting the drum breaks again and look at the push rod and road test it again.

 

[tos]

Yeah the rods can be the same length but the pistons are different, just a thought.
Yeah your rear shoes could need adjusted too. They should be adjusted so they drag slightly when you rotate the drum by hand. Just make sure your parking brake is completely released before adjusting.

 

[Doublej530]

Ok thanks. I was also thinking maybe the proportioning valve is bad. Because i cant lock up the brakes. But might try taking off the M/C over the weekend and put the original push rod in the new M/C.