This is a 2 part question:

1974 Dart Sport, disc front, drum rear. Everything new, calipers, cylinders and brake shoes in the rear.

1: I have a really hard pedal if I pump my brake more than once.

Would this be caused by a bad MC?

2: I did install a line lock and they did work OK until the MC started leaking in the back between the MC and booster.

Has anyone else experienced a hard pedal with the line lock?

I have a new MC which I will bench bleed and install because of the leak, I just want to be sure to check for any other problem while I'm there.

Thanks in advance.

Yeah, but it feels normal on the first push, just like it should. It's only when I release and re-apply the brakes that the pedal gets hard.

Edit: Also it did not do it at first, it got progressively worse.

Anything else I need to look for or check while I have this apart?

Usually if you get a hard pedal is because of loss of vacuum.That or a bad booster.Does it have a bigger cam in it?On of my kids friends had a C body that I put a cam in.Same thing.Hit brakes once and good second time hard pedal because of low vacuum.Rocky

Yeah, it has a 340 cam in it, but my vacuum gauge tells me 15hg at idle. Now that I think about it I did mess with the tune the other day and the pedal got worse. I will check that out today. I hope to get the MC replaced today, but I have to work on the daughter's car first.

I've found PB work OK with 12-13" or more vacuum... sounds like you should have enough unless the tune changed it a lot.

Changed out the MC, bled some more and it's much better. Still not perfect, I think part of my problem is my vacuum is at 10in in gear. I was checking in park and it's 15. Set the line lock and it's holding better too. Time to go test it .

Sounds like you might need a vacuum can.Rocky

Yup, that what I was thinking.