Chevelles and their A-Body cousins were the rowdy kids of the late 1960s and early 1970s. Performance was all about going fast in a straight line. Chevelle, GTO, GS Buick, Tempest, LeMans, and 442 cars did that very well. Braking performance wasn’t completely overlooked, but it certainly was not given all the attention it deserved. After all, speed was about going fast, not stopping fast.
GM midsize cars have become very popular with the muscle car crowd. The powerful Chevelle tops the list for many enthusiasts. These models can be found at the drag strip, on the road course, on the surface streets in Everytown, USA, and at the autocross course.
It wasn’t until the adolescence of the muscle car when the first front disc brake option finally became available. However, with the main focus on big-blocks, transmissions, and gearing, disc brakes remained a rare option and perhaps were even thought of more for the fledgling road-racing series than as a serious component for the strip and boulevard bully.
One way to do a budget upgrade is to use modern calipers from different models to take advantage of technology without spending a lot of money. This 1969 Camaro was fitted with a set of Z06 C6 Corvette calipers.
In this article, our focus is on a budget-friendly installation of a four-wheel disc brake upgrade on a first-year Chevelle. The test car is a manual-brake, single-reservoir master cylinder car that was fit (similar to all Malibus of the first few years) with drum brakes on each corner. Stock wheels were standard Kelsey-Hayes welded steel 14×5-inch models with a 1-inch offset.
Classic Performance Products (CCP) offers brake upgrades and complete kits for a number of Chevrolet models and applications. The kit we installed was supplied with new rotors, spindles, single-piston calipers, brake hoses and rear lines, brackets, the master cylinder, and booster. Most of the CPP kits for these GM A-Body cars include a choice of booster size from 7, 8, 9, or 11 inches. Drop spindles are an option for those wanting to lower the stance and center of gravity but still maintain full suspension travel. The overall result is improved ride and handling characteristics. Slotted and drilled rotors can also be had for an extra cost. These kits are about as complete as they come.
This upgrade consists of a complete kit from Classic Performance Products (CPP) along with the addition of power assist via a vacuum booster. CPP went through a lot of work to assemble all of the required components so an average do-it-yourselfer would be able to complete the installation with basic hand tools and maybe a little help from a buddy over a weekend.
The kit is based on single-piston calipers that were used on thousands of vehicles from the late 1980s. We will cover these calipers in greater detail under the disc and caliper sections. For now, it will suffice to explain that these calipers work in conjunction with 10-inch rotors that fit most 15-inch wheels.
Wheel fitment is a vital consideration when you’re upgrading the brakes on your muscle car. Remember, many of these cars from the muscle car era were fitted with 14-inch wheels from the factory, so wheel clearance is one of the critical aspects to check prior to choosing a brake upgrade kit.
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BEAT THE DRUMS
Drum brakes have their place but are better suited to the more pedestrian cars of the day, such as a four-banger Chevy II. When you could order a 375-hp 396-ci 4-speed Chevelle with 4.10:1 gears direct from the factory, those spindly 9.5-inch drums were severely outmatched. When brand new, the drums worked well for the average driver. As those enthusiasts lucky enough to have lived through that era will attest, the cars did brake acceptably well considering the rather rock-hard tires of the day.
The secondary (trailing) brake shoe on the left is much longer than the primary brake shoe on the right. The secondary brake shoe provides more of the braking force.
The question wasn’t if these cars would stop in a decent distance. The better question was whether they could muster the effort more than once. Freeway antics in today’s world can easily create a situation where a panic stop from 70 mph to a standstill is quickly followed by acceleration back up to 70 mph that almost immediately calls for another dramatic slowdown. If insufficient time has passed to allow the brakes to cool, that second effort might call for some evasive maneuvers in a Chevelle with front drum brakes.
For purists who feel the need to retain those drum binders, there are not many brake shoe options available as upgrades. The early Chevelles and their A-Body cousins used a 9.5-inch drum set in the front with a 2.5-inch-width brake shoe, while the rears were the same diameter but narrower at just 2 inches.
Certain applications of A-Bodies, especially with El Caminos, have 11-inch drums on the rear to improve braking due to higher anticipated bed loads. Of course, these demand their own set of shoes because the smaller 9.5-inch drums and shoes will not interchange.
DRUM BRAKE SHOES
A set of four drum brake shoes will come in the box and the first thing any installer must do is separate the shoes into primary and secondary versions. If you look closely at the shoes, you will notice that the secondary shoe uses a slightly longer length of brake material than its primary partner. The primary shoe always is installed as the leading shoe: facing forward. The secondary shoe is always located on the trailing or rear position.
The reason for this shoe placement is what the industry referred to as the self-energizing (servo) action of most drum brake systems. When the wheel cylinder is activated, the pistons push both the primary and secondary shoes outward.
Looking at the drum system for the left front for example, the primary shoe hits the rotating drum and is immediately forced into a counterclockwise motion. The adjustable link bar at the bottom of the shoe attaches to the secondary shoe and forces the larger secondary shoe into the drum with more force. This is why the secondary shoe is fitted with more friction surface area.
A common issue that crops up with drum brakes is when the installer fails to realize the shoes are different, ending up with a pair of primaries on one side of the car and a pair of larger secondary shoes on the opposite side. When installed in this incorrect fashion, the car will pull hard to the side with the secondary shoes whenever the brakes are applied. Of course, the best way to avoid this is to install the shoes correctly.
BACKING PLATES
While we’re on the subject of improving drum brake efficiency, high-mileage cars often suffer from grooved backing plates where the shoe slides across the backing plate during braking. These grooves restrict movement of the shoes, which reduces their effectiveness.
There are backing plates reproduced by Right Stuff Detailing, so replacement parts are available, but you can also repair original plates by merely MIG welding material into the grooves and then smoothing the weld back to a level surface. It’s a cheap repair and not difficult if you have access to a MIG welder.
If the plan is to rebuild a drum brake set, just consider replacing everything, including the drum. Complete rebuild kits with all the springs and small parts are still available through companies such as Raybestos or Wagner, and these usually include the wheel cylinders.
If the car has been sitting and the wheel cylinders are corroded, don’t try to rebuild the cylinders since they will just leak past the pitting in the cylinder. A small dab of white lithium grease on all brake shoe contact points will help the shoes slide across the backing plates.
DISCS
We won’t spend much time on the two-year-only 1967–1968 Chevelle front disc brake setup. This system resembles the early Corvette and 1967 Camaro disc brakes that used a fixed four-piston caliper. While this system worked reasonably well, it suffers from a significant design flaw.
The flaw is that hydraulic pistons use rubber seals located on the pistons, sealing to the cast-iron caliper cylinders. These calipers were bolted over 11-inch rotors. After a few years with brake fluid absorbing water like it is prone to do, these four-piston cylinders began to corrode, leaving rust spots that soon allowed brake fluid to leak past.
Later brake upgrades fixed the seal into the cylinder bore and sealed against the piston. The pistons generally are made of a harder material and don’t corrode as easily, so the system is less susceptible to leakage. These calipers are still available but require a specific 1967 or 1968 A-Body spindle because this design was carried over in the 1968 model year with the new Chevelle body style. As with many of these calipers, they are specific to the right or left side because of the bleeder screw location. If the sides are inadvertently swapped, the bleeder screw will be on the bottom and of little use for bleeding the brakes.
General Motors switched to a single-piston, floating caliper in 1969. This caliper design became a staple for GM models for decades.
It is possible to apply stainless steel sleeves to original factory calipers when doing a restoration. The first company to offer this option commercially was Stainless Steel Brakes, but other companies now also perform this task. One company we discovered is called RK Sleeving in Upland, California.
Starting in 1969, General Motors converted to the now-familiar large single-piston, floating caliper that became the standard for decades. The single piston is located on the inboard side and uses a mount that allows the caliper to slide along large metal pins that pull the outboard brake pad into the rotor. As you can guess, there is a quite a bit of compliance in this design, which places most of the load on the inboard pad, so these tend to wear more quickly.
Even with this sliding caliper, the system is very robust and retained the 11-inch rotor diameter from the original 1967 four-piston calipers. While many performance brake companies downplay this system, it includes the widely used GM D52-style brake pad. What’s good about this popular brake pad is that just about every brake pad company in the world makes a pad for this application, so a lot of choices are available when it comes to pad selection.
SPINDLES, RESERVOIRS, AND BOOSTERS
This system was retained throughout the Chevelle era from 1969 through 1972 and makes an easy conversion for earlier A-Bodies. The spindles don’t even need to be changed. Later spindles used larger bolts to attach the steering arm that will have to be drilled out with a hand drill or drill press. The disc brake floating calipers work well as long as the cast-iron slides do not become corroded and the large pins remain clean.
For early Chevelles and A-Bodies, this conversion will also demand dumping the original single-reservoir master cylinder and replacing it with a dual reservoir, which also requires some custom brake plumbing. A standard 1-inch nonpower master cylinder for a 1969 Chevelle will bolt in place of a standard nonpower early single-reservoir master cylinder, so that’s a no-brainer, although we don’t really like the high pedal effort.
Some enthusiasts think that disc brakes also require a power booster, but this is not entirely true. It’s possible to use a nonpower master with front disc brakes and the only real cost is slightly higher pedal effort.
My experience with early Chevelles revealed that using a 7/8- or 15/16-inch-diameter piston master cylinder dramatically increases the line pressure to the front calipers and also to the back brakes. This reduces pedal effort but also increases pedal travel to make up for the lost volume using the smaller master cylinder piston.
To some people, this extra pedal travel can make the pedal feel mushy when in reality it is just additional travel necessary to move the fluid. While a small point, it is noticeable and some may find it objectionable. For everyone else, you become acclimated pretty quickly.
The size of the master cylinder piston has a direct effect on the amount of pressure created by the effort placed on the brake pedal. A smaller piston creates more pressure with the same pedal effort than a larger piston does. (Photo Courtesy Wilwood Engineering Inc.)
The physics behind this move is simple: a smaller master cylinder piston creates more pressure with the same amount of pedal effort. How much is this worth? We’ll save you the math and just give you the numbers: With a typical 75-pound load applied to the brake pedal with a 6:1 pedal ratio, this applies 450 pounds of force on the master cylinder. A 1-inch master will generate 573 psi of brake line pressure, while a 7/8-inch master cylinder piston will bump that pressure up to 748 psi, a 30-percent increase in line pressure. You will notice that immediately.
Conversely, adding a larger 11/8-inch master using the same pedal forces as above will reduce the line pressure from 573 psi to 454 psi, which is a 20-percent reduction or drop in line pressure. That means you will have to step on the brake pedal 20-percent harder to apply the same braking force to the tires. This could easily set up a condition where it would be nearly impossible to lock the brakes with the larger master cylinder.
What all this means is: if you are considering changing master cylinder sizes, even a 1/16-inch change in piston diameter can have a drastic effect on braking performance.
PROPORTIONING VALVE
Of course, adding a front disc brake system to a drum brake car also requires some type of brake pressure proportioning system to reduce the higher hydraulic pressure to the rear brakes. If a proportioning valve is not employed, the high pressure will prematurely lock up the rear brakes under heavy braking.
Many inexpensive front disc brake conversion kits come with a factory-style combination valve that reduces the rear brake pressure. While this is certainly better than no valve at all, it does not and cannot account for the dozen or so variables that are integrated into your particular application. Let’s look at an example.
The combination valve usually incorporates an isolation valve in the system. The isolation valve is controlled by the front and rear incoming brake pressure. This valve has incoming brake pressure acting on each side of a piston. If the pressure on one side of the piston is more than the other side, the piston will start moving toward the lower pressure. At a predetermined point of piston movement, the brake light warning switch is triggered.
Let’s say that we want to convert a 1964 El Camino from four-wheel drums to factory single-piston caliper front brakes by using a complete spindle and brake assembly from a 1969 Chevelle. While both cars share the same wheelbase, the El Camino is significantly lighter in the rear with its bed, putting less weight over the rear tires.
In this particular application, this 1964 El Camino happens to be equipped with larger 11-inch rear drums and taller 275/60R-15 rear tires mounted on 15×8-inch wheels with 5.5-inch rear backspacing. All of these are non-stock changes compared to a stock 1969 Chevelle combination valve and will drastically affect when the rear brakes lock up during emergency braking.
This really forces the issue to employ an adjustable proportioning valve for any front disc brake conversion. You’ve probably read a commonly used number that approximately 70 percent of braking effort comes from the front brakes under hard braking. Weight transfer from the rear of the vehicle to front makes braking force substantial on the front brakes.
Despite this common belief, my experience with high-performance brake systems on early GM A-Body muscle cars reveals that a very large percentage of braking efficiency comes from those tiny 9.5-inch rear drum brakes. It pays large dividends to apply as much braking energy to the rear brakes as possible.
UPGRADES
Several upgrades can be performed to the 11-inch Chevelle rotor and floating caliper world that do not require thousands of dollars to achieve. A quality set of performance 11-inch rotors attenuated with a set of performance pads, such as those from Baer Brakes, EBC Brakes, Hawk Performance, Performance Friction Corporation (PFC), Raybestos, and many others, is a great place to start. Look for a pad that has good street characteristics, such as good cold friction and reliable initial feel with a clean release, one that is not noisy or exhibits excessive brake dust because that’s just material you have to constantly clean off your wheels. There are several brake pad manufacturers that offer brake pads that fit this category, including EBC Brakes, Hawk Performance, PFC, and Raybestos.
Companies, such as Wilwood Engineering, offer several different brake pad lines. From the low- and mid-temperature/ friction lines for street use to full competition high temperature/friction use. (Photo Courtesy Wilwood Engineering Inc.)
Another simple upgrade is to replace the stock OEM rubber flexible lines with DOT-rated stainless steel hoses and fittings. These hoses do no deflect under pressure and will help deliver a more solid brake pedal feel. Several companies, such as Russell and Earl, offer affordable stainless steel hoses. Just the change to new brake fluid, hoses, and brake pads can make a dramatic change to braking performance while keeping the cost under just what a pair of 14-inch rotors would demand. Not everybody needs 14-inch four-wheel disc brakes with six-piston calipers.
ROTORS
Huge brakes have become the signature components of the Pro Touring push since the turn of the 21st century. They look amazing inside a set of 18- or 20-inch wheels and those slots, holes, and dimples just add to the bling. But what’s really going on here? Is all that really necessary?
Large rotor diameters do serve a useful purpose. Brakes are much like a clutch in a manual-transmission car. The larger clutch adds surface area which adds holding power. A larger rotor increases surface area (often called swept area), but more importantly, the diameter adds leverage. As diameter increases, this moves the caliper farther away from the spindle centerline, which gives the caliper more leverage over the kinetic energy of the moving vehicle.
Larger-diameter rotors also demand larger-diameter wheels to clear the caliper. These are not hard and fast rules, but a 12-inch factory rotor and caliper will usually fit inside a 15-inch wheel. A 13-inch rotor package will sometimes fit inside certain 16-inch wheels and certainly 17-inch wheels. The 14-inch rotor packages will demand at least an 18-inch-diameter wheel, so keep these relationships in mind when choosing a brake rotor size. Bigger almost always means more expensive, often in more ways than one.
Rotors with drilled holes are stylish and serve a purpose. Brake pads can outgas under heavy braking conditions. These drilled holes allow the brake gases to escape as the temperature rises.
Drilled holes are often thought of as stylish, but they do serve a purpose. Under heavy braking, brake gases need a place to escape as the temperature spikes. Unfortunately, these drilled holes offer an excellent starting place for stress cracks that will eventually cause rotor failure. Rotor technology and materials help fight this, but a better idea is rotors equipped with dimples or slots cut into the rotor face. These depressions perform the same function as holes but do not offer the starting point for stress cranks, which improves the rotor’s life expectancy. Most companies offer dimples and grooves as options for their performance rotors.
Cryogenics is another word that has crept into the high-performance lexicon. Some claim that this subzero exposure of the metals helps align iron crystals and improve the durability of the metallurgy, allowing the rotor to better withstand the heat of high braking temperatures. My research has led to no such results, and I have yet to find credible results that would lead to similar conclusions. While cryogenic freezing has its proponents, at this time many still remain skeptical. There may be better ways to spend your money.
CALIPERS
The main advantage of larger, multi-piston calipers is a combination of extending the swept contact area of a larger pad and adding pistons that can evenly apply the pad against the rotor. The main function of the caliper piston(s) is to generate clamp load. Brakes work by a combination of coefficient of friction of the pad applied with a given load over a given area positioned by the diameter of the rotor. Longer pads with more surface area require more pressure and multiple pistons make that happen.
Another advantage of multiple piston calipers is that the load applied is spread out over a larger area on the pad, leading to more even pad wear. This is one of the disadvantages of the original large, single-piston GM calipers. A recent innovation on multiple piston calipers is using a smaller piston on the pad’s leading edge followed by larger pistons toward the trailing edge. This also contributes to more even pad wear since the leading edge of any pad tends to accelerate wear and it digs into the spinning rotor.
Calipers with multi-pistons provide braking force that is evenly spread across the contact patch, resulting in more even pad wear. Almost every aftermarket brake manufacturer offers a multi-piston caliper as well as a single-piston caliper.
Most multiple-piston calipers are of the two-piece variety that are bolted together, often with a brake fluid transfer port that must be sealed. This two-piece construction makes the caliper easier to build. According to several brake industry experts, there are no real strength advantages to a mono-block or one-piece caliper design since the real test becomes the way the caliper is designed to resist the forces of pressure on both sides of the caliper, assuming a fixed-piston design that attempts to spread the caliper apart at the bridge where the caliper straddles the rotor. The bridge is any caliper’s weakest point. So there does not appear to be any real strength advantage to a mono-block caliper.
BRAKE PADS
This is an area that becomes a strange mixture of chemical concoctions that is heavily influenced by heat, pressure, type of use, and personal preference. It might seem that it would be easy to create a brake pad material that could do everything well, but as with most things in life, there are compromises. For example, brake dust, noise, cold performance, life expectancy, pedal responsiveness, and a host of other details are all variables that affect the decision on a pad material.
A brake pad with a very high coefficient of friction will certainly improve stopping power and may perform well at very high temperatures but might destroy a set of rotors in less than 10,000 miles. This is not a good choice for a street car.
There are literally a dozen or so brake pad manufacturers, and it isn’t possible to go into all the different configurations across all the major brands. If we were to break the pads down into categories, there are organic (non-asbestos) pads that are generally the direct-replacement pads, semimetallic pads, and ceramic material. The material differences generally follow increasingly higher temperature capacities for racing.
While some racing products can be used on the street, when it comes to disc brake pad material, these are best left for use on only road race or circle track applications. Higher-temperature pads as a general rule do not work well on street cars because it’s rare for a street car to generate the elevated temperature necessary to make a race pad perform properly. Other areas of importance for street-driven cars are dust and noise, which are nonissues with race cars. So, leave the race pads for the race cars and you’ll be better off.
Pedal Pulsation
One area that seems to garner a lot of attention is brake shudder or pedal pulsation. This is most often blamed on warped rotors. A white paper authored by noted race car builder Carroll Smith claims that rotors rarely warp and that the pedal pulsation is caused by a buildup of brake pad material on the face of the rotor that creates high spots that become extremely hard. These small peaks can be seen as hard blue spots on the rotor that cannot be removed by simple brake lathe cutting because these spots are incredibly hard. If the rotor is a two-piece design where the rotor can be separated from the hub, then the rotor can be Blanchard ground and the hot spots removed. Otherwise, the rotor must be replaced.
The best way to avoid the formation of these hot spots is to properly bed in new brake pads and/or new rotors. This bedding-in process creates sufficient heat to transfer pad material from the pad to the rotor. This demands a gradual application of significant heat, and often the process will be noticeable enough that you will smell the brakes as they cook off the bonding agents present in the pad material.
The important point when bedding in pads is to avoid coming to a complete stop after heating the pads. A full stop at high temperature can create an imprint of the pad on the rotor, which could easily create the high spots the bedding process intends to avoid. So, it’s important that the specific brake pad manufacturer’s bedding process recommendation is closely followed.
Recommendations
It’s difficult to make any kind of a street brake pad recommendation since there are so many different pad materials and compounds. Companies with a solid reputation for quality products include Baer Brakes, EBC Brakes, Hawk Performance, Performance Friction Corporation, Raybestos, StopTech, Wagner, Wilwood, and many others. If you are abusing your brakes under autocrossing or track day exercises, talk with some of the more-knowledgeable participants about their recommendations, especially if the pad will be used for both street and mild race use.
The most important point is to choose a pad that will withstand the heat it will be exposed to yet still generate decent cold-stop characteristics so that the brakes will work well the first time you step on the pedal. This is a characteristic that most race pads do not display, and it is the main reason that race pads should not be used on a street-driven car.
REAR DISC UPGRADES
It’s important to not overlook the contribution of rear brakes to overall braking performance. Many enthusiasts tend to focus on front brakes while often ignoring the rears. For the average street car, rear drum brakes are fine but if you do want to step up there are some interesting and relatively inexpensive upgrades for the Chevelle and A-Bodies that will not only offer improvements in braking power but also look good.
CPP offers several different versions of a single-piston floating caliper kit, one in particular is part number 1012RWBK-SE-6467 that includes a rear parking brake kit that is outlined in photos and captions with this article. There are several iterations of this kit available depending upon completeness.
Among the least expensive rear disc brake swaps are several kits that use parts from the third- and fourth-generation Camaro. Summit Racing (part number SUM-BK1623) and Right Stuff Detailing (part number AFXRD01) offer similar kits that supply the rotors, calipers, pads, mounting brackets, hoses, and even parking brake cables. These kits are competitively priced at under $400. If you want to do the job yourself using a combination of used/junkyard parts and new components, it’s not very difficult.
The key component is the rear caliper mounting bracket that connects the rear axle housing to the caliper. The factory application uses two different brackets, but we’ve found that the large, heavy, cast-iron bracket works very well and bolts directly to the early 10- and 12-bolt A-Body rear axle assemblies. This will require removing the stock drum brake assembly, which means the hardest part of this whole conversion is removing the rear cover and pulling the C-clips to allow removing the rear axles. The new caliper brackets bolt in on the stock rear axle mounting flange. Slip the axle back in place, slide on the rotor and the caliper, and the main work is done. The only thing left to do then is to install the metric flexible hose on each caliper. These use a short flexible hose because the caliper is free-floating. Adapt the metric fitting in the end of the hose to the hard line tee on the top of the rear axle.
This conversion is not in the least the only way to adapt rear disc brakes to a Chevelle. Baer Brakes, Wilwood, and many others also offer aftermarket kits in various rotor diameters and caliper configurations. If you desire to maintain 15-inch rear wheels to mount drag race slicks, keep in mind that larger rear rotor diameters will demand larger-diameter wheels. This can sometimes cause difficulties when you want to run predominantly drag race–style 15-inch rear tires. The third-generation 11.5-inch rear disc brake kit mentioned earlier is small enough to accommodate a 15-inch wheel.
This article really just begins to describe some of the various disc and drum brake options available to the enthusiast. Not everybody wants or needs a six-piston caliper brake system or even four-wheel disc brakes. It all comes down to what fits your budget and your sense of how much braking you need for how you plan to use the car. The rest of it is just fashion.
Written by Bobby Kimbrough and republished with permission of CarTech Inc
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