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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When it comes to performance upgrades, we all want to make the number; if we're talking stopping distances, we want that number to be small. But it's too easy to focus on the end product rather than the nature of the improvement. For example, we often evaluate braking prowess in terms of simple stopping distance--how rapidly, measured in feet, does the vehicle decelerate from 60 mph to zero? And of course, we were looking for substantially shorter stopping distances when we called on Performance Online (POL) to outfit a big-block-packing Chevelle with its 13-inch big brake kit up front, accompanied by 12-inch rear discs to replace the factory drums, and the necessary master cylinder/prop valve combo to run it. And while we did cut our stopping distances, the fact that we converted this A-body from manual to power brakes by installing a Hydroboost hydraulic brake assist unit taught us that the effort it takes to stop short can be as important as stopping distance itself.

Our subject for this experiment, Jeremiah Becker's '66 'Velle, was fresh out of the paint booth when it graced the cover of our Mar. '07 issue. Becker's ride is actually well-endowed when it comes to suspension, since it's outfitted with a Hotrods to Hell Centerdrive Truckarm rear system, tubular front control arms, and a tall B-body spindle setup. Becker had also added some pretty good rolling stock to his ride, specifically Nitto NT555 Extremes, 245/45ZR17 up front and 285/40ZR17 out back. The braking setup, however, was not particularly high-zoot. The front package included the big single-piston B-body calipers, but these binders were backed up by the factory rear drum brakes and activated by a manual master cylinder. Even so, we actually got a stopping distance of 158 feet out of the old A-body in baseline form.

But it's not always about the bottom line. While we got the most out of the rear drums and B-body front discs and came up with a decent 60-0 number, it took maximum effort to achieve that figure: back arched against the back of the seat, left leg trying to drive the pedal through the floor, driver limping away afterward. More normal braking efforts--think a guy who's just pushing the pedal hoping to stop in a hurry as opposed to someone concentrating on maximum effort--produced considerably longer distances. The setup also faded when subjected to hard use. This is in no way a slam on the brakes our guinea pig came with; the old-school setup was actually pretty effective. Our results simply illustrate the nature of operating a power brake system as opposed to a manual setup. "You need line pressure to stop," says Performance Online's Jim Chadick. "And with a manual system, all you've got to provide it is your leg."

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For all our talk about braking effort and quality as opposed to bottom-line numbers, it was always a given that we would get out and measure before and after braking numbers. For this experiment, we utilized one of Tesla Electronics' G-Tech Pro SS performance meters. It would almost be easier to tell you what this device doesn't do rather than spell out what it does do. It's powered by a car's cigarette lighter or power port and attaches to the windshield with a suction cup. Brake testing is a snap. When performing a normal acceleration run--which is literally as easy as pressing a button and waiting for the signal to start--the unit flashes a red light when the vehicle hits 60 mph, allowing the driver the option of hitting the brakes or continuing on for a full quarter-mile run. The unit's triaxial accelerometer senses when the vehicle is speeding up or rapidly slowing and measures accordingly; the accelerometer also measure handling g-forces on three axes and can display the figures in real time. With a bit more setup, the G-Tech Pro SS can sense and display engine rpm and measure horsepower and torque, and it even has built-in sequential shift lights. This model goes for about $200; the RR model, which has even more features and can upload its data to a PC, is about $300.

It was a given that we'd be upgrading the brakes themselves when we showed up at Performance Online, ditching the old B-body discs for a pair of 13-inch platters clamped by two-piston PBR calipers and excising the drum rears in favor of 12-inch discs with matching PBR calipers. We also knew we'd be swapping out the master cylinder and prop valve, converting from manual to power assisted brakes. The easiest route would have been to install a typical engine vacuum-fed power brake booster unit behind the new master. The problem, as Chadick points out, is that the booster has to see enough vacuum to boost to be effective. POL considers 15-22 inches of engine vacuum to be the optimal level. The mondo-cammed 396 in our test bed was only pulling 5 inches at idle, which just isn't enough for the job.

The solution was to install a Hydroboost hydraulic brake assist unit in place of the typical power booster. Rather than relying on engine vacuum for its boosting capabilities, the Hydroboost relies on hydraulic pressure from a car's power steering system to provide assistance in braking efforts. In this case, that meant that Becker had POL convert his Chevelle to power steering before we arrived on the scene to document the brake installation--the Hydroboost system was then plumbed into the new system as part of the brake conversion. It took some extra effort and expense on Becker's part, but was it worth it?

Taking it solely by the numbers, absolutely. The new binders cut 10 feet off the Chevelle's 60-0 stopping distance, taking us down to 145 feet. Fade was nonexistent--our top-three average was 147 feet. But there's also the nature of the improvement to consider, and suffice it to say that the effort it takes to make this thing stop has been significantly reduced. Pedal response is immediate--when we say these brakes really bite, we mean it in a good way. We quickly learned to develop a light touch on the pedal--that was all we needed to produce consistent, short stops.

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This is the front brake we found as we got to work on Jeremiah Becker's '66 Chevelle. Given that B-body spindles and disc brakes were installed in between the Hotrods to Hell upper and lower control arms, this Chevelle was in better brake shape than when it rolled off the line, but it still had plenty of room for improvement. Performance Online's Mike Wheeler capped the brake line to keep fluid from getting all over the works before doing anything else.

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Wheeler wanted to use the ball joints and tie-rod ends already bolted into the '66, so he eschewed the pickle fork and relied on a dead-blow hammer and copper mallet instead. The ball joints were released by loosening--but not removing--the castle nuts, then striking the spindle with the dead-blow hammer until it dropped. For the tie rods, a copper mallet was inserted so that the tie-rod end could be hammered out without damaging it.

Now you can stop this thing hard-without limping away.

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Wheeler had already unbolted the sway bar from the spindle, so all that remained was to extricate the spindle/rotor/caliper assembly. Wheeler placed a jack under the lower control arm and lowered it until the loosened top ball joint was free; he then lifted the works up and off the lower ball joint (which had also already been loosened).

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POL's big brake kits rely on the tried-and-true PBR 38mm dual-piston aluminum caliper. These calipers were first introduced on the '96 Corvette Grand Sport and have been a staple for brake swappers ever since. They're a full floating design, lightweight yet rigid, and feature fins to help disperse braking heat. POL loads them up with Raybestos HP brake pads. Ceramic pads, polished calipers, and braided-stainless lines are available as options; we went for the upgraded hoses.

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The difference between the old-school one-piston caliper and the considerably more modern two-piston PBR unit is striking, but we took this shot to highlight the modifications necessary to adapt a factory spindle to the big-brake configuration. POL utilizes a special fixture that allows it to cut off the old caliper ears and correctly drill the new holes for attaching the caliper cage, properly aligning the caliper every time. Stock height and drop spindle setups are available.

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Much as we'd like to get into an extensive explanation of how the new brake system is installed, it really isn't necessary. POL's big brake kits come fully assembled: The hub, bearings, studs, drilled and slotted Raybestos HP rotors (we upgraded to zinc plated), and calipers are all in place on a powerdercoated caliper for your application (setups are available for Tri-5s, '58-70 B-bodies, '62-79 Novas, '67-81 Camaros, and '64-72 Chevelles). All Wheeler had to do was bolt the new spindle into the spot just vacated by the old setup, reattach the swaybar, and hook up the stainless brake line. Looks good, yes?

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After repeating the front brake swap on the driver side, we moved out back. The car is equipped with Hotrods to Hell's Truckarm rear suspension, as you can see, but the car's original 12-bolt rearend and drum brakes (albeit with really long studs) are equally in evidence. The downward force created under braking with a Truckarm setup allowed this Chevelle to make the most of its non-power drum binders; still, there was room for improvement.

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To complement our new mondo front binders, we chose one of POL's 12-inch rear disc conversion kits. This setup is also based on a Corvette-spec, internal parking brake rear caliper, and grabs Raybestos HP rotors. POL's Chadick calls the combination a matched caliper system: "They're all Corvette items, and they're engineered to work together." Given our results, we'd add that they're made to work well together.

Installing the new rear disc setup means that the old binders must first be excised, which of course means the Chevelle's C-clip axles must be removed so that the drum backing plates could be removed. The POL rear disc conversion kit comes with concise directions for installation, but we ended up improvising a bit. In most cases, the caliper mounting bracket would be placed so that the caliper sets to the rear; the Truckarm setup wouldn't allow it, so we faced the calipers forward; it works either way. Note that the rotor is firmly bolted to the axle using a couple of lug nuts (1). This is critical, since the caliper mounting bracket must be shimmed (2) so that the rotor is centered and parallel to the brake pad surfaces.

Once the caliper was properly aligned with the rotor and bolted into place, it was simple to plumb the brake lines and attach the new emergency brake cables. The POL kit comes with new hard lines that run from the center T-fitting out to the axle ends, where they make the connection with the brake hoses (arrow).

While we were primarily interested in improving this Chevelle's rear brake performance, it's fair to say that the new setup is a considerable upgrade in the looks department as well. This shot also shows the e-brake cable setup (arrow). The slotted cable ends connect to the activation levers on each caliper; the other end attaches to the factory parking brake equalizer near the front of the car. The cables were adjusted for proper tension at the equalizer, and voil, we had working e-brakes.

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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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