[mgarblik]

1" vs 7/8" on these cars has been confusing for years. Recently I replaced a 7/8" MC with a 1" unit on a 66 Bonneville with power brakes. I could get a new 1" unit off the shelf at a local NAPA and the 7/8" one was going to take a week or more to order. The 1" MC with power brakes gave me a slightly higher pedal with slightly less pedal travel travel. Both the customer and I were satisfied with the results. Which is actually factory correct? Honestly not sure. I think the factory chassis manual for 66 says 7/8" for power brakes. But I would have to verify. You have a 1" unit coming and that's what you are used to. Should feel fine to you.

Side note: The new NAPA MC had a machining error on the MC piston hole where the pushrod installs. I had to remove a small ridge in the piston with a cartridge roll to allow the pushrod to install completely and bottom out in the piston like it is supposed to. The brakes would "self apply", drag and get the drums hot once the fluid got hot. The compensating port was blocked by this condition. You have to check everything!