The Stovebolt Site Forums The Parking Lot Big Bolts 1968 C60 brake issues

I've got some odd brake issues that I was chocking up to just believing these old trucks have poor brakes, but I misled myself.

When we hit the brakes the engine idle changes. There's a hissing sound but its not air brakes and it takes a crap ton of foot pressure to apply the brakes. I don't understand whats happening. I had the single on the firewall master cylinder replaced a few years back and when I reflect on it the brakes were good back then.


I'm gonna dig through the resources here and figure out how to get new soft brake lines, and a caliper just started leaking, but I need some advice on this hissing sound with the idle change.