I think its time to replace mine, My car stops, but my pedal is extremly hard, the stoping power is the same, just a very hard pedal. My question is what is the difference between single and dual diaphram models. How can you tell the difference, my local auto parts store needs to order it and cannot tell me the difference..
Oh and I replaced every other part on my braking system ie. Master Cylinder, rear wheel cylinder, rear shoes and springs, front pads, and blead the snot out of the lines.

Thanks
josh

make sure you have sufficient amount of vacuum going to the booster. It may be possible that a vacuum line is plugged or maybe a bad check valve. I had this happen to me, I ended with a hard pedal after replacing the entire system. Drove me nuts for a long time and it ended up being the check valve wasn't allowing any vacuum to the booster. -matt

thanks matt..I'll give it a "check" no pun intended

Ok I found it I have a dual diaphram power brake booster, unfortunately it wasn't the check valve, but thanks for the advice Matt, at least I know now.

Josh

Well at least you figured it out. Not knowing is very frustrating! I know I went through it! Good luck! -matt

Actually distinguishing between single and dual diaphragm is fairly simple...

If the general side profile shape of the booster is triangular it is single diaphragm. If the side profile is more tubular then it is dual.

I recently learned this while shopping for a better than stock booster for my '68 BB with tall valve covers at the boneyard. Pulled a dual version out of a '79 El Camino and have clearance now. Have not driven it yet so I don't know exactly how well it works though...