Hydro Boost Brake System For Your 1972 Chevrolet Corvette C3 - Stopping Power

Hydraulic-Assisted Power Brakes For C3s, That Is.

Bob Wallace Nov 1, 2002 0 Comment(s)
Vemp_0211_01_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Aftermarket_braking_system 2/13

State of the art Corvette stuff is cool. State of the art Corvette stuff for older Vettes is even better. And state of the art stuff for vintage Vettes that is more advanced than what comes off the Bowling Green assembly line on brand new Corvettes is WAY cool!

For the most part, C5s are great examples of the best of contemporary high-performance engineering. They are, however, Chevrolets, which means that mass-production, high-volume purchasing, and in some instances using the least expensive component that will do the job is a fact of life. That doesn't mean that a particular part or system is bad; it just means that a more advanced but more expensive setup is passed over to save a few bucks (or even pennies) per-unit.

Braking systems have advanced drastically since the advent of disc brakes on Corvettes, starting with the 1965 models. With the exception of just 316 '65s that were ordered with RPO J61, the drum brake substitution credit, every Vette since has come with four-wheel disc brakes, and power assist (J50) increased in popularity (measured as a percentage of out of total annual production) every year from 1965 until part way through the 1976 model run, when power assisted brakes and steering became standard equipment. Each and every '65-76 with RPO J50, and every Corvette since has utilized a vacuum-powered booster to lessen the effort needed to operate the brakes.

Vemp_0211_02_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Vacuum_brake_booster 3/13

Here's a sight familiar to anyone who owns (or has owned) a '68-82 Corvette with power brakes-the bulky, stamped sheetmetal vacuum brake booster which we're going to replace with Hydratech Braking Systems' new hydro-boost hydraulic power brake booster system. Everything, with exception of a bottle or two or fresh power steering fluid and possibly some ibuprofen for your back, after you're done crawling under the dash twice) is included, right down to the braided stainless steel high-pressure lines that are prefitted with billet line clamps.

Overall, vacuum power brake boosters work fine. But vacuum assist does have its shortcomings-boosters are fairly bulky and cumbersome, and the feel (response and action) is not always consistent. Plus, if an older Corvette is equipped with both power assist brakes and has a "hot" (long duration) cam, the brake assist can vary from semi-marginal to damn near non-existent because a lumpy, lotsa duration cam does NOT produce much engine vacuum. Vacuum canisters are a common "band-aid" fix for this problem.

Hydraulic brake assist, or, as it's more commonly called, hydro-boost, is not new. It has a lot of benefits and very few drawbacks; the drawbacks being that power steering is a necessity (that could be an issue in early Sharks, when power assisted steering was not especially commonplace), and cost. A stamped sheetmetal booster and a few rubber vacuum lines and fittings are a lot cheaper to produce than a hydraulic booster unit and some high-pressure hoses.

Hydro-boost brake systems are a mystery to many people. Some associate hydraulic assist for brakes as something that belongs in big rig trucks; not the sort of thing one would install on one's Corvette. On the other hand, hydro-boost, which was originally developed by Robert Bosch GmbH, the highly regarded German automotive and industrial technology and engineering firm, is used on some very high-end European sports, ultra-performance, and luxury cars. Ford has been using a hydro-boost setup on all Mustangs-including the fearsome '00 R-model Cobra-since 1996, and on several of their upscale products.

Vemp_0211_07_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Brake_lines 7/13

After inspecting the master cylinder, the '72's owner, Loy McKenrick, removed the nuts attaching it to the brake booster and secured the master cylinder as far forward from the booster area as space and existing brake lines would allow.

Hydro-boost systems are commonly tied into the vehicle's power steering system, which is operated by an engine-driven hydraulic fluid pump that pressurizes either a boost-cylinder or ram (as on '63-82 Corvettes), a steering rack as on all '84 through '03 Vettes, or a boosted steering gear box (like the popular-for-street rods GM 605 box). The same pressurized hydraulic fluid that assists the steering boosts or reduces the effort needed to operate the brakes. There are no vacuum lines or large vacuum canister, no vacuum leaks, and no iffy brake response on a car with a long duration cam (which drops inches of vacuum way down). A hydro-boost booster unit is also very compact-the reason the blue oval crew went that direction when Ford's bulky 4.6 and 5.4L "modular" V-8s came into common usage. The fact that a hydro-boost brake assist system offers a better and more consistent pedal response as well as a smoother and more linear brake action under all conditions just happened to be a bonus. During my days on the editorial Dark Side (as a staffer on three different Mustang and Ford magazines) I drove a lot of Mustangs, stock, modified, race-prepped, long-lead press cars, and prototypes, and experienced a wide variety of braking systems of wildly divergent capabilities, assisted by both vacuum and pressurized hydraulic fluids, and developed a high level of appreciation for hydro-boost systems from those encounters.

Thus, when I heard about a hydro-boost conversion kit being developed by a small group of performance-oriented automotive engineers for Third-Gen. Corvettes I was extremely interested-interested enough to contact the firm, Hydratech Braking Systems, about getting a unit to evaluate. I utilized friend Loy McKenrick's '72 "Size Matters" small-block coupe once again as our guinea pig (and, once again, Loy as installer) since Loy has owned and driven (on an almost daily basis) the old Stingray for around 25 years. I wanted the input from someone who is intimately aware of what his car is doing and would be sensitive to even slight changes in how the car drives, and for a C3 I don't know of anyone who'd fit the bill any better.

Before performing a conversion like this, the balance of the brake system MUST be in top condition and, seeing as how it is powered by the existing power steering system, ditto for the steering. Otherwise, it's a waste of your time and money. No sweat in this case-the steering was freshened up a couple years ago, we recently installed a Steeroids rack-and-pinion steering conversion (see the August '02 issue), and just a year ago we used Loy's '72 to evaluate Stainless Steel Brake Corp's then-new Force 10 system, complete with new hard lines and braided stainless flex lines.

Vemp_0211_10_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Brake_comparison 8/13

Here's a graphic side-by-side comparison of high tech and old tech. The clevis (arrow) must be transferred from the vacuum booster to the rod (at the bottom of this photo) on the hydraulic boost unit.

There are three variations of the hydro-boost conversion kit for '68-82 Corvettes; Level I utilizing a remanufactured boost unit, Level II also uses a remanufactured booster with the addition of a nitrogen reserve, and Level III comes with a brand new hydro-booster and the nitrogen reserve. Prices are $395, $495, and $595 respectively, F.O.B. Warren, MI.

According to Paul Clark, one of the principals at Hydratech, the nitrogen reserve helps to equalize the variations in hydraulic pressure so the pedal "feel" remains constant. It also acts as an accumulator, so if there is a pressure drop (like from a belt loss or stalled engine) there will still be some assist on brake application.

Vemp_0211_15_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Power_steering_system 12/13

With the car aloft on a hoist, Loy drained the power steering system of fluid.

We obtained a Level III system for the '72, then waited for a few weeks while Loy was treating the old Stingray to its first repaint in a couple decades. As soon as it was in driveable (but still not completely reassembled as in no hood, gutted interior, and for serious weirdness in our post-installation test drives, no windows!) form, we set aside an afternoon to give the car a boost. Seeing as how the instructions start by stating that removal of the driver's seat "increases ease of kit installation and is highly recommended!" we had a head start. It really didn't make any difference whether the hood was on or off.

The installation is pretty straightforward; the only real hassle is the part where the installer lays on his back, on the floor of the car, with his head and arm(s) beneath the dash to disconnect the brake pedal from the vacuum booster then unbolt the booster from the firewall, from the inside-and, of course, repeating the process in reverse with the hydro-boost unit. Do-it-yourselfers should have a good selection of standard and metric wrenches, a good floor jack, a quality set of jackstands, and a couple bottles of fresh fluid for the power steering pump. Plan on devoting at least two-three hours to the installation. We were quite pleasantly surprised to find that the kit, hoses, and all, hooked right up to the Steeroids rack-and-pinion-just as neatly as it would with an original-style steering system. No muss, no fuss, and no fabricating whatsoever.

The effort is well worthwhile. After topping off the P.S. pump's reservoir, cranking the engine over for a few seconds with the coil lead disconnected (to "prime" the system with fluid) and re-topping the system-we did this entire procedure a couple times, to get a constant fluid level-all the while inspecting for any leaks, it was time for a road test. First we ran the stroker 383 small-block for a few minutes, letting it warm up to its normal 185-degree operating temperature, then checked out the steering and the brakes once final time.

Vemp_0211_19_z Hydro_boost_brake_system_1972_chevy_corvette_c3 Power_steering_pump 13/13

Down below, the other end of the shorter line is connected to the power steering pump while the longer line is connected to the steering rack (or, on a stock steering system, the control valve), using the supplied control valve adapter.

Oops! No windows and no seats. A couple wadded up car covers would do for temporary seating, and who needs a windshield-we'd just have flow-through ventilation. Even as we were pulling out of Loy's shop, Auto Perfections, the difference in pedal feel was very noticeable. There was no vague or iffy assist, caused with the original booster by the low vacuum produced by the car's lumpy idling (relatively long duration) cam. The pedal-and thus brake system-response was smoother, more immediate and, on harder applications of brakes, more linear, than with the vacuum assist.

What about the guy who knows this old Corvette most intimately? "The brakes were already excellent after we'd put on the new setup last year. (Editor's note: the SSBC Force 10 system, October 2001) But, as soon as I hit the pedal, the improvement on these already great brakes was immediate and extremely noticeable. It's a tremendous improvement, a three-to-one one improvement over the standard Corvette brakes"

We'd agree. The hydro-boost system works as claimed, plus it fit perfectly. Yeah, state-of-the-art stuff for vintage Vettes is definitely cool!

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Bob Wallace Nov 1, 2002

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