Anti-Lock Brake Systems

Automotive Mileposts
Image: AUTO BREVITY - Anti-Lock Brake Systems
Slippery road, stop sign and speeding traffic ahead...the perfect time for anti-lock brakes!

Not often considered until you need them, anti-lock brakes were developed during the sixties using what was then state of the art technology.

They worked quite well and laid the ground work for today's more sophisticated, high tech braking systems.

As the American automobile industry entered the 1960s, automobile braking systems basically consisted of drum brakes at all four wheels. Large, heavy cars often came with power brakes, that reduced the amount of pedal effort required to stop the car. Compared to today's cars, these systems were primitive, but they did work and were dependable. In 1962, Cadillac introduced a dual-safety braking system on its cars that utilized a split master cylinder that provided independent pistons and brake fluid reservoirs for front and rear brakes. This created two separate systems that were not dependent on each other. So, if one failed, the other could still bring the car to a stop.

The most important safety feature in any car is the driver, and there is only so much automobile manufacturers can design and engineer into a vehicle to compensate for a bad driver. But one of the achievements that did so was the anti-lock brake system. Designed to prevent the vehicle from going into a skid during maximum braking, this system prevented wheel lockup which allowed the tire to maintain contact and traction with the road surface. The braking force of a tire with good traction is substantially better than one that is skidding across the surface.

Image: 1971 Imperial Sure Brake component diagramThe anti-lock brake system consisted of a series of magnetic wheel-spin sensors to monitor wheel rotation, an analog computer to monitor and control the system, and the necessary electrical wiring and vacuum lines to tie all the components together. These items worked with the standard hydraulic brake system to pump the brakes up to four times per second—faster than humanly possible—to avoid locking up the wheel.

The driver needed to do nothing other than to maintain control of the steering and keep his or her foot on the brake. Everything else was automatic. The computer made a cycling noise and a clicking or thunking noise when the ignition key was turned on, and until the anti-lock feature was needed, the driver would be unaware it even existed other than the designation on the foot brake pedal that the car was equipped with the anti-lock feature. When in operation, the driver feels a "pulsing or throbbing" sensation through the brake pedal.

Should anything go wrong with the system, it was designed to fail so as to not interfere with the vehicle's standard braking system. A problem requiring attention would light the "BRAKES" warning light on the instrument panel, just the same as if there were fluid loss in the system. This notified the driver to have the car serviced immediately.

The anti-lock braking system was one of the most thoroughly tested systems ever contemplated for an automobile. In fact, by 1968 it had been in development and testing by the auto industry for 10 years! One test during the spring of 1968 included closing one of the runways at Detroit Metropolitan Airport and covering the taxiway with a layer of foam, the sort used when an airplane is in trouble. A 1968 Thunderbird prototype built to test the anti-lock system was sent speeding over the slick surface and the brakes were applied hard by the professional driver. The result? The T-bird came to a smooth stop, in a straight line with no skidding, wheel lockup, or loss of control.

Ford tested its system in winter and summer, on dry road surfaces, wet pavement, loose surfaces, and under any condition they could think of that a driver of one of their vehicles might face one day. During testing, it was discovered that the anti-lock system shortened stopping time on every surface except sand or gravel. On those surfaces, a locked-up wheel actually dug in better and stopped the car in a shorter distance. Since most cars aren't driven at high speeds on sand or gravel, the benefits obviously far outweigh the negatives on these two surfaces.

Ford introduced its Sure-Track Braking System in 1969 as a mid-year option on the Continental Mark III and Ford Thunderbird. This system only controlled the rear wheels, as they are the ones most likely to lockup. (As a vehicle decelerates rapidly, the weight is shifted forward and the rear wheels can lose traction due to this shifting of weight.) Sure-Track became standard on the Mark III for the 1970 model year.

GM had planned on offering an anti-skid system for the 1970 model year, but only a handful of Cadillac Fleetwood Eldorado, Oldsmobile Toronado and Vista-Cruiser cars were equipped with it. GM delayed its introduction due to changes to the "black box" which controls the system. Cadillac General Manager George Elges said the option wasn't installed at the beginning of the model run because "we were just making sure the device is absolutely perfected before we put it on a car. But it's looking real good and our tests have been virtually trouble free. We look for a 15 to 20 percent installation rate."

For 1971, the Imperial offered a four wheel anti-lock system designed in conjunction with Bendix. Since all four wheels were controlled, this system was somewhat more effective than the other systems, but it was also more costly, and very few Imperials were ordered with it. It remained an option on Imperial through 1973, but was dropped after that due to lack of sales, making it too costly to update it for the all-new 1974 Imperials.

Image: 1975 Continental Mark IV Sure-Track Brakes

Above: 1975 Continental Mark IV with Sure-Track Brakes


Sure-Track (Kelsey-Hayes; rear wheels only)
Introduced: 1969 (mid-year)
Continental Mark III ($195.80)
Ford Thunderbird ($194.31)

Track Master (AC Electronics Division)
Introduction: 1970 (late introduction)
Cadillac Eldorado ($211)

True Track (AC Electronics Division)
Introduction: 1970 (late introduction)
Oldsmobile Toronado ($205)
Oldsmobile Vista-Cruiser ($205)

Sure-Brake (Bendix; 4-wheel system)
Introduction: 1971
Imperial ($351.50)

Image: 1973 Imperial LeBaron

Above: 1973 Imperial with 4-Wheel Sure-Brake System