It could be different tire pressure. It could also be an alignment problem, or a coil
or shock that is broken. It probably is the brakes though.. Jack up the car and take a
look in there. If something is wrong it will show. Brake fluid leaking out. Metal filings
all over , broken springs ect .If you don't have a shop manual get one. There is no rocket
science involved in these things. Try to remember that working on them is part of the fun.
This is very common, It could be as simple as an ajustment or it may need to be completely rebuilt as in new hydralics, Hoses,cylinders, ETC. IF you have the original system i would suggest rebuilding the whole system, you can do reletivly cheap if originality is not a question.
IMHO brakes are not a place to be cheap, EVERYTHING is riding on the condition of your brake system including your life. On every "old" car i have ever had i have always replaced every part of the brake system, It only takes one leak to make the whole system fail. What I always say is "It is only as strong as it's weakest link"
That's interesting. . . My 67 pulls to the right when I apply the brakes, too. It is going up on the rack on Monday (my day off). The brakes were supposedly redone one year ago by the PO. I guess I'll find out. Good luck with yours. BTW does yours pull at any other time or just when applying the brakes? Mine does it only when the brakes are applied.