I just recently switched over my manual drum to power assist. I'm happy with the stopping power but I'm not sure if this set up is supposed to have a prop valve or not....I've read some post that say yes....others say no. I don't want to blow wheel cylinders and I'm afraid I might have to much pressure to the front wheels. I switched over to a dual master cylinder for drum/drum and an 11 inch Delco booster. Any and all help would be greatly appreciated.

No prop valve in the stock system but the power brake master cyl used a different sized bore than manual in 66.......pbly all about bore size

Thank you for the reply. The reason I started to question is it, because I had to replace a wheel cylinder that probably didn't have a 1000 miles on it.

you need to use a proportioning valve with the dual circuit master cylinder...one from a 67 would work perfectly...

you need to use a proportioning valve with the dual circuit master cylinder...one from a 67 would work perfectly...

This is only true for front disc brake cars. '67 & up Chevelles with front drums did NOT have a proportioning valve. No need for one unless you convert to front discs.

My 66 all manual drum setup did not have any proportioning valves or other stuff in the system. Stone ax simple and works ok when horrendously worn out. I see no reason why adding the power booster would change that. Brake system pressure should be about the same, just takes less foot.

Thanks a lot for the info.....maybe I just got a bad wheel cylinder and the problem is resolved for now anyway.