On a power brake booster what is the difference between a single and dual diaphram? I have a 66 with a single reservoir M/C. I will be installing a dual reservoir M/C. Is my original booster a single or dual diaphram? Will I need a dual diaphram for my new front disc brakes to work properly?

The difference is one diaphram......

Ha Ha - Couldn't resist

All the stock 60's and early 70's Chevelle stuff is a single diaphram. The late model stuff comes with dual diaphrams to shrink the size of the booster and give more pressure and be easier on your leg.

So would it be to my advantage to install a new dual diaphram booster while I am doing a front disc brake conversion? I have a new M/C that I will be bolting on to the old booster. Should I just try out the old booster and see what happens or buy a new dual diaphram booster? The motor is a 355 with a Comp Cams .562 lift cam and 11:1 comp. pulling about 14" of vacuum. If I do decide to install a dual diaphram, is it a simple bolt on? Will I need to change my lines going to the pro. valve or to the distribution block if I do swap boosters?

Your mileage may vary...

Many of the boosters are comparable and the pressure adjustments needed for disc brakes are handled in the hydraulic system.

I recently converted from an original looking large diameter single diaphram booster to a newer smaller diameter dual diaphram booster. My application is a '68 El Camino with BB and drum/disc. I used a booster off of a '79 El Camino. To make it work I had to:

1. Make an adaptation of the pedal pushrod. I measured the original and then grafted part of the original to the part of the new to end up with just the right length.
2. Grind the mounting brackets off the old booster and massage the holes to bolt onto the "new" booster.
3. Slightly shorten my original booster to MC pushrod.

I used my original MC and brake lines. The lines do have to be bent a bit as the MC is moved further out from the firewall. Mine had enough slack and such to work but I could see where some applications might not reach.

I have about 10" of vacuum when I have a good idle and this is sufficient to give me plenty of boost. I wonder if I have too much boost as it takes very little pedal pressure to make things happen when braking. But I suppose the brakes should be just as overboosted as the steering, right? ;)

Note that the driving reason why I swapped was for clearance for a BB with tall valve covers. Otherwise the original single diaphram booster was satisfactory. Thus you could go either way. I would try it with the old booster first and see where that takes you.

Thanks vrooom!! That's what I wanted to hear.