Hey all I’m new here. I just recently bought a1973 f600 with hydrovac brakes. I’m having troubles getting brakes. I have to pump them to get pedal and after about 5 pumps I get pedal. I drove it home this way on back roads and once I had pedal I had to stand on it to even get the truck to slow down any. The previous owner says he replaced the hydrovac booster which it looks new when I got under it. I can hear vacuum when I pump the brake inside the cab and once I stand on the pedal the engine isles lower until I release the brakes. Any ideas please

 

Starting at the pad on the pedal, trace the braking system through the pedal and it's mechanicals, to the firewall mounted master cylinder. Check fluid. Check the lines, especially any rubber line, to the frame mounted hydro-vac. From there to the wheels.

Now the fun part. Check the insides of the tires for any evidence of a leak. Tire sidewall will be dark, like you just cleaned and painted it with tire black.

Since I'm pretty sure you have a functioning system there, whatever issues you find in the way of leaks should be easy to correct.

Did I mention fun?

Pull the wheels and look at your brake internals. Check the shoes for contamination, especially if you see any oil around the real axle hubs.

You can pull the entire hub and duals by pulling the axle and taking off the retaining nut and keeper that holds the hub to the axle housing.

On the front, I can't recall what's easier, but unless you get real lucky, you are probably pulling all the hubs anyway as the drums get well attached.

There are no new drums to be had, so go easy there if you get the urge to smash things.

If this is beyond what you want to do, find a truck brake place.

A helper, a 1" impact wrench, and the appropriate socket, and a good 12 ton jack, wheel chocks on front and rear, and solid wood blocking to hold the truck up in a fail-safe manner are some of the essentials.

Google "hydrovac brake system troubleshooting" first, and check out the Bendix and other links.