I know many people with f3 trucks switch to a different rear end (often dana 60)
My question is do you switch the master Cylinder at the same time to accommodate the rear cylinders?

 

Interesting question. I've upgraded an F4 to a Dana 70 while retaining the stock front brake configuration and stock size master cylinder. I, too have solid pedal but have not had an opportunity to drive the truck yet and it will be a while. I discounted the size of the rear cylinders having much effect, as the majority of the braking is from the front brakes.

 

Have you driven many non power brake vehicles? They take MUCH more force to work but I think your looking at this problem backwards. Why go through the trouble of adapting a different master cylinder when its easier to change wheel cylinders?

Time for some math:
Typical minimum pressure required for a wheel cylinder - 400 PSI
80 lbs of input force on factory 1.25" master cylinder = 400 PSI
If you were to equip a power booster - 800-2000 PSI
(Booster multiplication can be between 2-5 times depending on design but is an unpublished specification)

The Dana 60 was offered with wheel cylinders ranging from 15/16" to 1 1/8". The 48-51 Early F-3 used 1 3/8" and 51 Late -52 used 1 1/8".

15/16" wheel cylinder - 276 PSI
1" wheel cylinder - 314 PSI
1 1/16" wheel cylinder - 355 PSI
1 1/18" wheel cylinder - 398 PSI
1 3/16" wheel cylinder - 443 PSI
1 1/4" wheel cylinder - 491 PSI
1 3/8" wheel cylinder - 594 PSI

A word of note is the bigger the wheel cylinder, the longer the pedal travel. So if you make sure you have a proper sized wheel cylinder your brakes will improve, by how much I can't say as there are other factors like adjustment, friction material etc.

Also these trucks were typically driven using the transmission to slow down and the brakes only for final stop.

 

I have driven a few. My 73 VW Beetle (driven quite a bit) was 4 wheel drums and manual brakes but not anywhere near this heavy. I occasionally have driven my father's London cab based on a Bedford truck chassis was probably the closest weightwise and had drums and manual. Both of these stopped much faster than the ruck currently does. When it stops raining I will take the drum of the back and see exactly what I have for cylinder size. All you information is very helpful. I am wondering if by dealing with the master cylinder I could get something else I would like ie. A dual sump Master.