Note: This article has been published several times in various forms. This slightly revised version is for those that have not seen previous versions. This article is oriented towards drag racing. However, it is generally applicable to all cars.

FRICTION MATERIALS:

Asbestos, the cause of many health problems around the world, is also the cause of many of our brake problems. The health risk from asbestos in brake friction materials has spurred the development of replacement materials. Unfortunately, although some of the new materials are superior in many ways, none of them provide equal friction coefficient as asbestos at the same application pressure. Therein lies our problem. The brakes on most cars through the mid-70s were designed to work with asbestos linings/pads. The brakes on modern cars are designed to operate with the new lining materials and many of the available pads/linings for replacement use contain the new materials. The older brake systems simply do not have enough hydraulic pressure and/or lining surface area to work as well with many currently available pads/linings as they did with asbestos. What is the answer? Select your linings/pads carefully. The highest friction, best brake feel units now available are non-metallic pads/linings manufactured by reputable companies such as Bendix, Wagner, Raybestes, etc. This type of brake is the best choice for drag-cars or street/strip cars that do not see any severe road driving. Metallic or semi-metallic materials provide less friction but much better heat control to minimize fading under hard driving conditions such as mountain driving, road racing, or towing heavy loads. The factory brake systems that use metallic type linings usually incorporate higher hydraulic pressures to compensate for the loss of friction. Also, the metallic or semi-metallic linings tend to work better as they get hotter (and expand), just the opposite of what is required when doing a burn-out or staging at the drag strip. Never use “lifetime” or other extended mileage linings because they are extremely hard with a corresponding loss of friction. The new materials, such as Kevlar, are truly amazing in many ways but not in friction coefficient, so when you read brake sales advertising, read it carefully. Although I have no direct experience with such changes, I am sure that older brake systems can be upgraded with higher pressure brake lines, cylinders, and valves to work well with the new lining materials.

ADJUSTMENTS:

The last thing we want on a car at the drag strip or on the street is brake drag, yet we want the brakes to work reliably. Disc brakes, when working properly, should not cause drag. You should be able to spin the front wheel with your hand and have it turn at least part of a turn by itself. If it does not, the most likely cause of the turning resistance is the caliper assembly. Although rebuild parts for calipers are available, they do not always eliminate the drag caused by warped or misaligned cylinders. You usually are wise to buy new or rebuilt caliper assemblies.

The self-adjusting feature of drum brakes should be retained to assure that the brakes stay properly adjusted. However, it is possible for the adjusters to tighten the brakes too tight thus causing drag. To eliminate this possibility, bend the “adjuster lever” such that the lower part just contacts the star wheel at the outermost tooth when the lever is forced down. Normally, the lever contacts the star wheel several teeth higher on its periphery which causes the brakes to be adjusted tighter. This simple modification allows the retention of the self-adjusting feature without the risk of brake drag caused by overtightening. The return springs should be checked periodically and replaced as needed. The easiest method of checking return springs? Simply drop them on a concrete surface. A good spring will hit with a dull thud and very little bounce. A bad spring will ring like a bell and bounce off the floor. No, I didn’t say it backward. The bad spring has crystallized from the heat build-up and constant stretching. That, in turn, causes the ringing noise and erratic bouncing when striking a hard surface. A good functional indicator of a bad return spring is the tendency of one wheel to try to lock-up with light brake application after several miles of driving. The bad spring allows the linings to drag causing them to heat and expand, and upon light application, they grab.

FRONT WHEEL BEARINGS:

Wheel bearings are not normally considered part of the brake system but they should be carefully adjusted during brake service. The bearings should be packed with a non-fibrous, high temperature wheel bearing -grease and the spindle should be lightly coated with the same grease. I have read that oil or other thin lubricant in the bearings will decrease friction. That is theoretically true but it is highly unlikely that a 3000/4000# car will run measurably quicker with oil on the bearings rather than wheel bearing grease. It is likely that the bearings will be quickly damaged if oil is used. What is more important is proper bearing adjustment. Too tight and both drag and premature bearing wear can be expected. Too loose and wheel wobble and bearing wear will result. Wheel wobble will cause both drag and suspension wear. Pontiac states that the bearings should be adjusted for .001-.005 inches endplay (Looseness). To accomplish this, tighten the spindle nut (while turning the wheel) using pliers or other appropriate tools until the bearing is tight enough to cause the wheel to slow down due to bearing drag. Loosen the nut and repeat the procedure several times to assure the spindle/nut threads are smooth and not binding. Finally, tighten the nut with your thumb and finger as snug as possible with the wheel turning. Then back off just enough to allow the cotter key to be inserted. If you have to back off almost 90 degrees to insert the key, try another washer or insert a hardened washer between the original washer and the adjuster nut. You should get as close to 0 clearance as possible without overtightening.

BRAKE FLUID:

Disc brake cylinders absorb more heat than drum brake units.

This increased heat can cause the fluid to overheat and break down if proper fluid (for disc brakes) is not used. I have switched to Silicon brake fluid in my cars to minimize rusting within the hydraulic system and to eliminate the possibility of paint damage when brake fluid is inadvertently spilled on the paint. No adverse effects have been noted in the brake system or brake operation as a result of using silicone fluid.