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Racing Technology
Cheapskate race car brakes
by Wayne Scraba
Cheap brakes? It can be done. Reworked brakes using factory hardware are common place in Stock eliminator. In my initial research, I read and was told that a number of tricks are needed to set up the back brakes for a footbrake application, such as a Stocker or bracket car. After all the smoke and dust settled, I discovered that there were no tricks at all — just a mix of common sense and a cross section of readily available, inexpensive jobber parts. This shouldn't be news to seasoned Stock eliminator racers. Most Stock racers will tell you that so-called tricks simply boil down to hours of heavy research, only to find that the hot-ticket parts weren't so hot after all. A mix of stock parts will do just fine.
I was told that for a footbrake car, one should use a heavy-duty Cadillac return spring kit for back brake shoes on a GM 9 1/2-inch drum application. In my research, I found that Raybestos part numbers for replacement spring kits were all the same for the type of brake in use. I contacted several well-known brake specialty companies, all of which are drag racing hip, and asked them if there was a difference in return springs and if a heavier-than-stock return spring kit was needed. They all said to use a stock replacement kit and that the type of return spring has little to do with brake performance. When I poked and prodded other Stock eliminator racers, I found that they all simply use a stock replacement spring kit, too. Ditto for many turbo Buick racers — and these guys really punish back brakes by building boost on the starting line with the footbrake.
Tricks are for kids
Another false trick revealed was the need to physically gusset the shoes. Forget it. It's not required, and if the person wielding the welding torch gets things too hot, you can do more harm than good. Adding a series of gussets to the shoes to increase their strength might in fact compromise the strength of the shoe. The heat from welding can warp the shoe, and if it's not done correctly, it can actually weaken the shoe material. I've found, from several sources along with my own experience, that it's the type of shoe that's important, not the gussets.
Shoe on the right foot
What shoe is right for a footbrake application? At the back of the car, use a set of good old-fashioned asbestos-free linings. Many brake shoes fit the above description, but what you need is a set of premium bonded and riveted brake shoes. Most jobber linings are bonded, but Bendix (along with other companies) offers a line of premium replacement shoes that are bonded and riveted and are perfect for the application. For racers north of the border, Canadian Tire's line of premium shoes are manufactured by Bendix, so there's no difference between the Bendix premium linings and the Canadian Tire premium linings.
Sintered metallic shoes are not the answer for a footbrake car. Sintered metallic shoes work best when hot, and conventional shoes work best when cold. The cold launch on a drag racing car does not warrant the use of semimetallic brake shoe models.
The primary and secondary shoes on a back brake system are different sizes. The contact patch of the primary, or leading shoe, is smaller (shorter) than the secondary shoe. The Buick Grand National crowd has found that you can increase the holding power of your back brakes by using a long shoe on the primary (front) side of the brakes. You can buy two sets of shoes for the application and only use the long shoes. Everything fits; I've tried it.
Pedestrian parts
Stock wheel cylinders for GM applications usually measure 3/4-inch or 7/8-inch. Use the 7/8-inch jobs, which are stock on most vintage Chevys. Raybestos and other replacement-parts companies have a cross-reference chart in their catalogs that list wheel-cylinder sizes. According to several Stock eliminator racers, you can find slightly larger wheel cylinders (like 15/16-inch) by looking at early station wagon listings. Find a wheel cylinder that works for your application. When mixing and matching OEM parts, remember that playing with wheel cylinders, or bore sizes, has an effect upon the "feel" of the brake pedal.
Backing plates are important and are linked directly to wheel cylinders. Early GM 9 1/2-inch-drum brakes use a four-bolt mounting arrangement to attach the backing plate to the rear-axle housing. Late-model GM 9 1/2-inch-drum backing plates make use of a two-bolt system. If you use aftermarket axle bearings on your car, such as a C-clip eliminator kit or a weld-on housing end with a sealed bearing, you'll need the four-bolt backing plates.
Early-model GM backing plates use two 1/4-inch bolts to hold the wheel cylinder to the backing plate. Late-model backing plates use a clip for wheel-cylinder retention. Typically, the two-bolt, clip-on wheel-cylinder backing plates are much thinner and lighter than their earlier counterparts. Turbo Buick racers have found that when you really lean on the back brakes (with larger wheel cylinders and long shoes), these late-model backing plates can bend. Aside from switching to the earlier four-bolt backing plate, they have found that physically stacking two backing plates, one on top of the other, can solve the bending problem.
Almost any mid-'60s through late-'70s GM compact or mid-sized vehicle has the heavy four-bolt, bolt-on wheel cylinders and long shoes. (Avoid the backing plates from Astro vans; they look right but are marginal in terms of material thickness.) If you use the early backing plates with an aftermarket housing end (I used a Mark Williams #58600 in the system shown), then you'll have to increase the size of the axle OD hole in the center of the backing plate so that the bearing clears.
Weight counts
Virtually all early GM brakes use an iron drum. There's nothing wrong with this, but the drum is heavy, which can have a significant effect upon quarter-mile performance. Finned aluminum drums from late-'70s to mid-'80s GM rear-wheel-drive cars are a better alternative. Swapping the iron drum with a set of aluminum drums can remove 10 pounds of excess baggage from the rear of the car.
These late-model drums have an outside diameter of 9.50 inches and are two inches wide. Taken individually, aluminum drums, including the cast-iron liners, weigh 9 pounds each, and conventional iron drums weigh 14 pounds apiece.
You can buy new aluminum drums from GM, but expect to pay a hefty price. A better bet is a local automotive parts recycler. The following is a list of cars that came from the factory with aluminum drums. Keep in mind that some cars in wrecking yards are old enough to have their drums replaced, and they might not have OEM aluminum versions installed.
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When you try to fit the OEM drums or aluminum drums to a rear end using an aftermarket axle and/or larger-than-stock-diameter wheel studs, a couple of changes must be made to the actual drums.
The wheel-stud holes must be enlarged for use with race studs. The factory stud on these cars is 7/16-inch in diameter. Studs used with race axles are 1/2-inch or larger. The other modification needed is to the hole in the center of the drum, or the register bore. Most aftermarket axles have a register bore that is slightly larger than the stock GM size. Again, the hole must be enlarged. Use your aftermarket axle register as a guide.
Other subtle modifications you can make to your back brakes so that they function better on the starting line and at the finish line are described in the photos. But remember, there are no tricks. It's all just a smattering of common sense laced with good old-fashioned premium replacement parts. (¬…