Decreasing vehicular stopping distance has been a challenge near the top of auto manufacturers' engineering lists for the past two decades. As a result of automakers' efforts, brake systems now possess a level of sophistication that makes them much more effective, but much more difficult to service.

The past 10 years have seen remarkable advancement within the field of automotive on-board electronics. By teaming advanced hydraulics with the new wave of electronics, automakers are now confidently producing anti-lock brake and traction control (brake modulated) systems for most of their automobile lines across the board.

European cars aside, the first anti-lock brake systems (ABS) that U.S. independent shops really had to deal with at the service level were rear-wheel systems used on light trucks. The problems with the first systems involved testing and illuminated lights. Hard-core system failures were rare, but technicians did change a lot of those protective diodes.

Where I come from, whenever something shows up that cannot be readily understood or dealt with, fables that we refer to as "quips" turn up to explain the problem, and these go a long way toward suppressing technological progress by spreading mistruths!

For example: Back in 1988, many fleet owners intentionally disconnected the anti-lock controllers on rear-wheel anti-lock brake systems (RABS) because they felt that they presented some unknown danger to operators whose vehicles were heavily loaded or were towing. So why did the '88 and '89 GM full-size trucks wear linings in the front down to the steel back plate in 20,000 miles in many instances? Tests were conducted and theories were expounded, but after the dust cleared, real-world answers boiled down to a couple of choices.

First, towing with these units caused abnormal side-slip on curves because of the "push" effect from the loaded trailer. The ABS module translated this situation as a wheel slowdown and a "select low" correlation was provided to engage the anti-lock. Obviously, with a cyclic anti-lock effect happening for extended periods of time, the duty cycle for the rear linings was sometimes less than 30 percent of the front linings. All of the heat and wear was accumulative on the front.

A second premise given included the idea that drivers, when their vehicles were loaded down or towing, would stay close to the mat and push a lot harder on the service brake pedal. Combined with any side-slip or even trailer-hitching effects, this can send the system into anti-lock much more frequently than desired.

The term "quirk," or "quirky," seemed to fit all too well some of the aspects of anti-lock brake systems as they became more popular. Rapidly pulsing pedal feedback while driving on slippery surfaces, and buzzing, rattling, and clicking noises - are these factors considered "quirks" when associated with an anti-lock event? I would say so! Actually, these are the only facts that presented themselves to lead to the simple premise that over-use of the anti-lock brake system in a rear-wheel-only system can wipe out the front brakes.

Evolution and increased application led to newer units with the electro-hydraulic valve redesign. These had more cushion to prevent this problem. Also, of course, four-wheel truck anti-lock systems (4WAL) were introduced and designed to balance the anti-lock effect front-to-rear and side-to-side on the vehicle front axle where most of the adhesion takes place anyway.

Diagnostics using on-board assistance looked pretty grim in the mid-1980s, with rear anti-lock for the light trucks and Bosch mainline systems showing up on luxury cars at the time. The trucks could be checked by grounding the diagnostic link on the General Motors (GM) systems or by grounding/un-grounding diagnostic pigtails under the dash on the others. Bosch systems required extensive diagnostic charts and a breakout box, or special dedicated testers for each make or model with the anti-lock system. A spin-off evolution began to take place in the latter part of the decade. Some vehicles were coming out with anti-lock systems that integrated the power assist, anti-lock brake hydraulics and sometimes the electro-hydraulic controller with the service brake master cylinder into the same loop, and were referred to as "integral" systems. The "add-on," or non-integral, designs used a separate electro-hydraulic unit for the anti-lock. Most retained the vacuum power brake booster, but some used a totally separate hydraulic system for power brakes not linked with the anti-lock at all.

By the early '90s, insurance companies were trying to "shake off" what they perceived as a "hole" in their world called "no fault." The ABS bandwagon looked pretty good at the time, and so they hitched a ride. I mention this because the impetus to build a following of customers that are weaned on anti-lock ideals began here. Cars with anti-lock brakes could garnish discounts for auto insurance just by virtue of their existence on any given vehicle.

Automakers also began to apply new technology to "tweak" systems and bring problem areas into line. G-force and/or yaw sensors had been developed for use in active suspension. Most of the hardware was an easy convert for use in tailoring specific anti-lock vehicles that needed the extra gear to function properly. The push was also on to develop less costly, more service-friendly systems that could be placed in use on even the most inexpensive model in a car line. Anti-lock brakes were in demand and the proliferation of designs have made technicians' lives more interesting ever since.

As the years have passed, the complexity of the newer systems has led to an increased use of scan tools and specialty "trinkets" that must be used to extract and/or erase codes; and specific and detailed bleeding procedures may also be required, which can be painfully difficult to deal with at times.

So, what are a few of the "quirks" that we find these days with the various systems? First, remember - from the beginning of this article the problems with the early RABS that were too sensitive or exhibited signs of an overactive anti-lock because of a heavy foot on the pedal of a loaded truck. Well, no one has ever said that systems were redesigned or revised to eliminate anti-lock engagements from occurring in certain situations where the anti-lock action really isn't needed.

The truth is that recent studies done at the consumer level, by the government as a follow-up, and finally by a premier automaker known for cutting edge European technology have proven that we are not getting the statistical data that we want. Furthermore, there is simply no hard proof that anti-lock brakes do anything to reduce collision incidents or keep the damage levels down when such situations occur.

How can this be possible, you say? The nuts and bolts of studies have shown that vehicle operators have adjusted their driving habits in two different ways due to the advent of ABS. In the first way, many operators drive with reckless abandon, maintaining a false sense of security, believing that the anti-lock brake system is magical and will save them from accidents and encounters in all but the worst situations.

The second change in driving behavior stems from the attitude that drivers don't want to push too hard on the brake pedal in order to avoid the "undesirable" anti-lock experience. This is sort of the same feeling many drivers have with regard to air bag usage. Most are glad they are there, but not many want to experience an air bag deployment firsthand.

Recent studies conducted in Japan point to the latter as being the real problem. It goes without saying that if you either can't or won't push hard on the service brake pedal, you will just never activate this safety system and will never enter the anti-lock threshold.

Other reasons seem to be centered on the idea that the system's redundant lockout features may be too complicated to provide a window for the anti-lock to be used, at least for low inertia incidents that occur in cites and close to home. Most serious accidents happen within 20 miles of home, which we all know is the "danger zone" that has proven to be of principal concern.

New technology has fortunately been brought to the forefront to deal with this concern, and Mercedes Benz Corp. has debuted an electronically controlled brake assist (BA) system. This system simply uses a wrap-around approach to brake assist for pedal effort. A microcomputer linked to the brake boost system recognizes a distinct grouping of pedal activities that it discerns as active emergency braking events. It then engages a solenoid which opens an air valve, filling the booster and immediately providing an increase in pedal effort to help shorten stopping distances and of course to enlist the help of traditional anti-lock systems. As soon as the driver releases the pedal, a reset occurs and the system reverts back to standard braking.

Nissan and Toyota are both involved in similar system development. Nissan's system is mechanical from stem to stern. The clever bell-shaped valve used in this system spreads apart so that as the pedal goes down and 75 percent of the travel is taken up, this results in the booster atmospheric port being exposed fully. The power assist is at maximum force and the resulting stopping distances have been decreased as well, and the anti-lock function is a "shoe in" with half of the input force produced at the pedal from an otherwise straight system with anti-lock only.

Toyota uses similar technology to that of Mercedes' endeavor, with the anti-lock function being constantly monitored electronically to digest any data that would call for brake assist to be called upon to add to driver pedal effort. The Nissan Brake Assist package is a snap to troubleshoot, with a couple of dozen diagnostic tree episodes to qualify a "pass or fail" status of the Brake Assist. In any event, the lower cost will make it a more ready changeover on a unit exchange basis once the items are in the supply system, according to Nissan dealers. Toyota and Mercedes systems require dedicated testing equipment, but also integrate traction control (TCS), and vehicle stability enhancement in Mercedes' systems.

Well, here are some of the answers to "quirky" problems that have shown up with ABS over the years:

• The quip: RWAL, RABS and vintage anti-lock systems can be destroyed by hooking up a trailer wiring package, including electric brakes. The fact: Properly wired lighting and electrical braking systems are compatible with ABS systems, including those light trucks equipped with rear-only systems. The quirk: Installing an incorrect rear vehicle light bulb very often causes problems, which turn on ABS lamps and or simply disable the system.
• The quip: 4WAL ABS systems are unreliable on light trucks; most four-wheel-drive vehicles disengage ABS while in the 4WD mode. The fact: '90 and '91 Kelsey Hayes equipped S/T and some GM vans have connector problems that are difficult to track down. These vehicles may set a string of codes that are phantom in nature, but chew up diagnostic time. Testing at the two-pin connection of the hydraulic modulator may confirm that problems are connector related. If codes are eliminated by powering directly from battery to modulator, and the amber lamp remains off, you have located the problem - i.e., bad connectors and voltage drop! The quirk: In all but a few basic system designs, 4WD engagement locks out ABS function. The reasoning behind this evolves from the radical activities that axles and wheel speed sensors go through in ordinary off-road usage. It is also a fact that some late model Jeep Wagoneers and Cherokees will disable ABS systems when traveling over gravel roads and side-slip is taking place. ABS function would possibly be erratic.
• The quip: Bleeding ABS systems requires factory bleed-out equipment. Systems can only be manually bled, or bled out with dedicated service scan equipment. The fact: Although many systems that utilize complicated ABS controllers are sensitive to air entrainment (e.g. TEVES 4WAL), any regimented bleed-out of the system can be avoided in all cases but those requiring electronic brake control module (EBCM) service or replacement. GM's Power-master ABS is also tough to bleed if you don't follow service manual instructions carefully. Scan equipment can make bleed-out of many GM systems very easy. This includes the ABS-VI, which has become a veritable "workhorse" for GM! Using vacuum bleeding equipment can shorten the procedure by 50 percent if technicians follow bleeder equipment instructions, bleeding from the "bottom up." The quirk: After pad, caliper or other minor services, "test driving" and actuation of anti-lock during "test panic stops" can introduce contaminated fluid or stir up debris from lower systems, causing problems in hydraulic sections of ABS. (Hint: when possible, pressure bleed during ordinary system service bleeding.) Vacuum bleeding from "top down" may be substituted, providing fluid replenishment is maintained during the entire service procedure. Failure to take the very basic precautions such as venting fluid overboard during caliper retraction can lead to problems mentioned in this quirk.
• The quip: Refinements in important electronics seem to have made European systems more adept at controlling most function system operatives as well as integrating ABS. The fact: GM has never stopped research and development with regard to ABS and safety system integration. A new ABS control unit produced by Delphi - to be released for production in August - processes wheel speed inputs for ABS through control of the hydraulic control unit (HCU), solenoid valves and pump motor for traction. The ECV controls HCU as well as passing a "request" for torque reduction to the power train controller.

Another notable feature of this new DBC-7 system is piggyback construction of ECU/HCU units, while using an internal "enable relay." System applications include monitoring of tire air pressure; engine-only traction control; engine and brake traction control; variable effort steering; dynamic rear proportioning; and vehicle stability enhancement, dubbed "Traxxar." The quirk: After the complicated route taken with Power-MasterIII and ABS VI, GM has accomplished all of the above utilizing a small compact design with an integrated hydraulic control valve. Only three chips - basically three complex integrated circuits - are used, and this amounts to a major cost reduction. Additional functions such as steering control are easily mated to ABS logic, providing a "constant alert" input for use during radical maneuvering.

Quirks, quips and myths aside, technical training and experience go hand-in-hand while preparing to tackle the realm of anti-lock brakes. Your shop training program should include a decent time block allotted for ABS training both in-house and at jobber clinics or training schools.

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