brake bias

[Nitro]

My 65 Malibu SS locks up the rears before the fronts. I've replaced everything inside the drums, except the backing plate. The wear pads on the backing plate have been dressed and lubed. The drums have been turned. I have replaced the single piston master cylinder, and single diaphram booster.
Everything is as it rolled of the line, I believe.
The 65 didn't have a proportioning valve. Proportioning was accomplished with larger wheel cylinders and wider front brake shoes.
The master cylinder has a single line that goes to a distribution block, with two line feeding the front brake, and a third line that goes to the rears. I know I could put a prop valve in the rear line, but it should work the way it came from Chevy.
The last time I replaced a rear brake line was 1969. I seem to remember finding a small piece that slid inside the double flare, that reduced the rear line way down. It was a long time ago!
Thanks, Nitro

[Hank70SS]

Both rear wheels? I'm sure you adjusted the rears but you could back off on the adjustment some. I know a bad brake hose can cause problems on one side. If your's is on both I guess crap in the line could do it too.

[Nitro]

The car had a two piston master cylinder and a dual diaphram booster when I got the car. The problems were even worse. Both front wheel cylinders were leaking, and the right rear axle seal was leaking.
I've replaced everything back to original, I think?
I replaced the front rubber lines. As I replaced them, the small steel line running from the distribution block to the rubber line broke. I replaced it. I haven't replace the longer steel line running to the right front. The car does brake straight, when braking normally. Under an emergency braking, it locks up both rears.