Be sure to bleed the brakes before going in to anything complicated on the lots of pedal travel thing. it could be just a little bit of air.

My next guess is that you have a master cylinder with too small a bore for the wheel cylinders. Assuming you have 3/4 and 1 ton stuff I would expect to see a MC bore around 1" to 1.25"

Then you may look at the linkage, unless it looks ____ed up / unsafe to start with, then fix that first.

Start simple and go from there....

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-