Chevelle Brakes - Whoa Down

Installing a Hard-Stopping, Hydroboosted Four-Wheel Disc Brake System

John Nelson Feb 26, 2008 0 Comment(s)
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Once our new upsized four-wheel discs were locked into place at each corner, we turned our attention to how we would activate the new arrangement, namely with a new master cylinder and proportioning valve and the leg-saving advantages of a pressure booster. The manual master cylinder and combination valve combo the car originally came with was designed to work with a factory front disc/rear drum combo and isn't up to the task of operating our new system.

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In this case, our quest for a new power-boosted master cylinder system started with a changeover to power steering, done at POL before we arrived to document the brake install. POL's setup is based on a standard ratio, GM 800-series power steering box (as found in later A- and G-body vehicles) and the appropriate Saginaw power pump. Space constraints in the big-block-filled engine bay necessitated use of a remote fluid reservoir; this unit from POL is pretty slick and makes fluid level checks a snap. Small-block guys could probably use a traditional pump/reservoir duo. The conversion goes for about $580.

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So why all the hoopla about power steering in a brake upgrade story? A typical brake booster uses engine vacuum to multiply the force your foot applies to the master cylinder, which creates vital line pressure. In this case, since engine vacuum is in short supply in this big-cammed Rat, Becker chose a Hydroboost to provide power assist capabilities for the new brake setup, and this unit relies on the hydraulic pressure in the power-steering system rather than engine vacuum. We preassembled the pieces of our new master cylinder/booster combo for this shot--the lines for the Hydroboost are in the background.

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The Hydroboost unit bolts in just like a typical vacuum booster--in most cases, it actually takes up less space. The blue canister on the side of the unit is an accumulator, aka nitrogen reserve. This canister stores hydraulic pressure from the power-steering system, providing back-up assist power for up to three brake applications if the engine stalls.

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The system was rounded out with a POL master cylinder/proportioning valve combos. Wheeler filled the master cylinder and let it soak for an hour before bench-bleeding it--an overnight soaking is even better. Chadick recommended a master with a 11/8-inch bore; with the amount of power assist provided by the Hydroboost, he was concerned that the brakes might be too sensitive if a 1-inch bore was used. It was a good call.

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The final step was to install the extensive line kit for the Hydroboost--in short, the power-steering pressure line runs to the booster and on to the steering box; the return lines, one from the Hydroboost and another from the power steering gear box, "T" together and run back to the pump. The extra effort here paid off big time at the brake pedal--we got immediate and powerful stopping action without having to use nearly as much leg muscle, stopping shorter, easier, and more consistently. CHP

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