I was warned.....

[oldcarfart]

Originally Posted by 2tons of fun

my 56 c6500 had a similar hydrovac system, with that plus the 10 lug stuff and 6.17 that truck may have been a 40 or just flat out over built.

your original bed looks dead nuts like mine.

It was not uncommon to see GMC/Chevy trucks with suspension upgrades bringing the GVW into the next range for cheaper tag fee's, commonality on fleet orders, etc. The hydrovac provides the most line pressure for hydraulic brakes, the next jump would be air-brakes.