Hydro boost brakes fight back

[Brian Tucker]

I have purchased a 70 Loadstar 1600 Horse Van. I Have drove it around some, but it doesn't like to stop. If you hit the brakes once it will almost put you through the windshield. After a few seconds of brakes applied the pedal will begin to push back on me. Where do I start looking?

[Allan E.]

I'm thinking of a few possibilities. The only ones with hydroboost I have seen have been diesels. The gassers have been vacuum assist.

The first thing is to check the master cylinder. I can't think of any way for pressure to increase without the boost being involved, as in pressure entering from the booster to the master cylinder. In a vacuum assist booster, it would be sucking fluid out of the master instead.

[Brian Tucker]

This is a gasser, with the biggest vacuum booster I have ever seen. I have never owned anything but scouts so this is new to me. There is a small reservoir coming from the firewall. It has a single line that goes underneath the truck to a huge vac booster. What's the purpose of this reservoir? I will crawl underneath the truck and see what else I can find.

[Allan E.]

Brian, this is how they did the remote hydrovac after 66. The single chamber master cylinder feeds the dual chamber booster. I have an 81 like that with a 345. It's the same master cylinder used all the way back into the 50s, the same as on my 1960 B166, but that one only has the single chamber.

You can bleed the master to the booster, then bleed in the same way you bleed a on old car's brakes, but the first thing you want to do is adjust the drag on the drums. I had Eldon adjust mine and it made a huge difference, but now they grab because it went too long. It's not hard to adjust them. The fronts have a cam adjustment and the rears have two star wheel adjusters, like the rear brakes on a scout, but two slave cylinders. After you adjust, bleed the system.