1965 Valiant low brake pressure

I don't know if this will help since it's a bit of a different system. When I worked on air cooled VW's they didn't have self adjusting brakes (there was actually a good reason for this, but I won't get into that now), so you had to adjust them on a regular basis. If you just adjusted them until the shoes dragged & then backed them off a bit you'd end up with too much free play in the pedal. If I remember right, the trick was to adjust them until the shoes dragged, then stomp on the pedal hard several times. This centered the shoes a bit in the drum & gave you some more room to adjust them. After a couple of times of doing this then backing the adjuster a couple of notches at each wheel you would still have a good pedal when you were done. Might be worth a try.