I bought a 1954 Mercury last year and have slowly been getting it road worthy. It has stock front brakes, and a rear axle/brakes from a 1966 mustang (I think). It had a disc/drum master cylinder on it when I got it (even though it's a drum/drum car). So I got rid of that, and put in a dual circuit master cylinder from a 1967 mustang with drum/drum brakes. There is no proportioning valve or combination valve. All 4 wheel cylinders are new, all rubber hoses are new. The two rear hard lines on the axle are new. I bench blead the master cylinder before installing. The hard line going to the rear axle is old, but it's not rusty and I blew air through it with an air compressor. When I try to bleed the rear wheel cylinders, I get low fluid flow. It just dribbles out. I'm not getting any air bubbles. The front brakes blead fine, and I get good pressure from them while bleeding. The rear brakes seem to do pretty much nothing when I drive the car. Any suggestions? Is there something I'm missing?
Did you inspect every inch of the metal line that goes to the back, to see if it's crushed? It could still have some rust/**** inside it that's restricting flow. Might want to bite the bullet and replace it.
Check your bleaders. They should be perfectly clean. The person inthe car should pump 3-4 times and hold with pressure when you crack the bleader with a 6 pt box wrench and a hose on the bleader into a bottle it should burst with fluid out of the hose with pedal going very quickly to the floor. Check every connection in the line including the hose from the frame to the tee, the tee, etc.
My thought is pedal rod length. I don’t think you are getting a full stroke to the front of the master. ( usually the rear brakes work off the front port )
Bleeders are clean. Old line is not crushed. Perhaps I'm wrong, but I was under the impression that you want to use the stock 1954 Merc push rod when you do this conversion? https://www.jalopyjournal.com/forum/threads/tonight-i-am-not-happy.1103171/#post-12515347
It would be easy to check. You could measure how far the rod goes in. Unhook the pedal and find a rod or something longer to push with, with a rear cylinder open, you should be able to push the long rod all the way home by hand. (when the rear bleeder is cracked) When it bottoms out, mark it. You can do this with an ***istant (bleeding) and see how much more fluid comes out of the bleeder. The rod may be long enough, but the push point may not be. If the pedal rod is going all the way, no change, then you know and you can move on to something else.
The stock push rod is almost perfect for a Wilwood MC but they recommend the adjustable Mustang from Summit, Jegs, etc.
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