I am in the process of replacing all the brake lines in my 67 - I was cleaning off the Proportional valve and I noticed that the line going to the back is 7/16". I thought all the lines were 3/8" in the car. Now looking at the old brake lines they are too gooked up to notice the size. What size lines are supposed to be on it? The manual says 3/8", just want to make sure nothing is screwed up.

BTW - It is a manual drum/drum setup.

 

Standard brake line is 3/16". Here is what I found out when I replaced mine. Mine is a 65, but most likely the same as your 67. Several people have had great success using pre-flared sections of brake lines available from most parts stores. I could never get a flaring tool to work for me. The trick here is that the Mustang uses a bunch of different thread sizes, so you have to find several adapters to mate to standard 3/16" brake line. Once I found all the adapters and bought the right lengths of brake line, it was a cakewalk!! Or, you might be able to get by using the ones you already have. The whole job of routing the brakelines took all of about 90 minutes, and looks awesome! Following is the list of parts for the brakes (using stock Mustang master cylinder, front disk, rear drums, so you will have to adapt for your drum front.)

Passenger Front:
(2) 7/16"-24 double flare (DF) to 3/8"-24 DF adapter
(1) 72" preflared 3/16" line w/ std 3/16" DF fittings (3/8"-24)
Driver Front:
(1) 7/16"-24 DF to 3/8"-24 DF adapter
(1) 10mm-1 BUBBLE flare to 3/8"-24 DF adapter
(1) 20" preflared 3/16" line w/ std 3/16" DF fittings (3/8"-24)
Rear:
(1) std 3/16" brake line coupler -- NAPA/Edelmann 302X3
(1) 40" preflared 3/16" line w/ std 3/16" DF fittings (3/8"-24)
(1) 72" preflared 3/16" line w/ std 3/16" DF fittings (3/8"-24)

The passenger side front is a 'little' tight if you follow standard routing along the front X-member, but it works well. I used a 30" line for the driver front, but it was a little long, and I had to make a cute little loop at the end. 20" would be better I think. When you do the rear brakes, start w/ the 40" piece at the rear and the coupling will end up being hidden inside the rear control arm bracket! Another trick is to use a wire coat hanger to make a pattern of the bend areas then bend your line out from under the car. It's really hard to try to bend the line while under there.

 

Wow! Thanks for the detailed help! I'll try all that tomorrow.