Questions and Answers

Ford 2-Ton Hydro-Boost Problem Q. Hi, I have a 1947 Ford 2-ton truck, 100 HP flathead V-8, 4-speed manual transmission, carbureted engine with Bendix Hydrovac boosted brakes. The brakes drag slightly all the time, enough that in five miles the drums are too warm to hold a hand on.

I have had the drums off, replaced one wheel cylinder, cleaned up another one, and all shoes and cylinders move freely and are properly adjusted. I have bled the system several times. The brakes work very well, but drag all the time. Is the Hydrovac unit likely to be causing this? What can I do short of buying a new unit for $150.00?

Jim in Maine

A. Hydro-boost II is a hydraulically operated power brake booster. The hydraulic brake booster consists of an open center spool valve and a hydraulic cylinder combined into a single housing. The power steering pump provides the hydraulic fluid pressure to operate both the power brake booster and the power steering gear.

A dual master cylinder is bolted to the brake booster and is operated by a push rod projecting from the booster cylinder bore.

This system uses a compressed gas accumulator as a reserve system to store sufficient fluid under pressure to provide at least two brake applications if fluid flow from the power steering pump is not available.

The booster is designed so that if a total absence of power assist occurs, the brakes can be applied manually, but somewhat greater pressure on the brake pedal is required.

If you disable the Hydro-boost, easiest way is to remove the power steering belt, and the brakes stop dragging, then you know, for sure, it is the hydraulic brake booster that's the problem.

If they still drag, then it is probably a bad master cylinder.