Anti-Lock Braking System
1989-1992 Thunderbird SC ABS Systems
by Duffy Floyd

Background

The Anti-lock Braking System (ABS) as we early model owners know, is a sometimes exasperating system which is very expensive to have a dealer fix. Unfortunately, it is also a critical sub-system since if it goes bad, more than likely the braking performance will be severely impaired. There are though a few relatively common things which can be checked or repaired on a DIY basis that can save some big bucks. Obviously though the scope of this article must be somewhat limited since the FORD Shop Manual contains over 100 pages of information on this system and it’s troubleshooting.

ABS was initially developed for aircraft applications and was toyed with periodically in the 50’s and 70’s in the automotive arena.

The system equipped on our SC’s is the TEVES Mark II ABS System. It was originally designed and manufactured by the Brake & Chassis Division of ITT Automotive which was based in White Plains, NY. On September 28, 1998 the division was acquired by Continental AG of Hanover Germany. The name of the newly combined company is Continental Teves AG & Co. The Germans must have liked what they saw since they paid US$1.93 Billion.

The TEVES Mark II ABS System has been equipped on many different cars of the 80’s Included in the list is the Pontiac 6000 STE and 88-90 Riviera and Reatta. The system also appeared on some SAAB, Mercedes-Benz, Jaguar, Alfa-Romero, and Lincoln Town Cars. Unfortunately for us though, ABS was usually installed as an option, a very expensive one at that so the number of car equipped with "our" system is rather limited when compared to more widely used systems like the TEVES Mark IV which the 93 and up SC’s came standard with. It does open up the chance though that there may be alternatives to FORD to purchasing some replacement parts. It appears though that there are minor differences in the design of each different car’s systems. Substitution should be done only after careful examination and comparison of the parts in question.

The main difference between the TEVES Mark II and Mark IV systems is that the Mark II is an integrated ABS System as opposed to the non-integrated system of the Mark IV. What that means to us is that our system contains all the controlling hydraulic components into one unit called the Hydraulic Actuator Assembly. This includes the Hydraulic Power Booster, master cylinder, pump and motor, valve assembly, and accumulator. On the Mark IV system the ABS system is basically piggy backed onto a conventional brake system to add ABS functionality to it.

Basic TEVES Mark II System Operation

The heart of the TEVES Mark II ABS System is the Hydraulic Actuator Assembly. This assembly is controlled by the Electronic Controller which is mounted in the Package Tray area of the trunk along side the ARC Computer,. Additional vital components include the Four Wheel Sensors and Indicator Rings.

Electronic Controller

If the Hydraulic Actuation Assembly is the heart of the ABS System the Electronic Controller is the brains. It consists of two parallel microprocessors which operate on the principal of two-channel redundancy for data processing and plausibility criteria monitoring.

The Controller monitors the system operation under normal driving conditions as well as during anti-lock braking. Under normal during conditions the microprocessors send short test pulses to the solenoid valves of the Hydraulic Actuator Assembly that checks the electrical continuity of the system without causing the valves in the Solenoid Valve Block Assembly to change position. When the Electronic Controller senses from the signals that is processes from the four wheel sensors that one or more wheel is about to lock up, signals are sent to the appropriate solenoid valves located in the Solenoid Valve Block Assembly of the Hydraulic Actuator Assembly to allow hydraulic pressure to be bleed away from the wheel(s) that are about to lock. The lock-up condition is sensed when one or more wheels is determined to be decelerating faster than the other wheels. The brake fluid pressure is then reapplied through cycling of the appropriate valves. This occurs at a rate in excess of 10 times a second. The cycling will continue until all wheels are decelerating at approximately the same rate.

Hydraulic Actuator Assembly (Figure 1)

The Hydraulic Actuator Assembly is made up of several sub components. These include:

1. The Hydraulic Actuation Assembly
2. Electric Pump and Accumulator Assembly
3. Solenoid Valve Block Assembly
4. Brake Fluid Reservoir and Level Indicator Assembly

Each of these sub components provides essential functions to the assembly as a whole. The system is a 3 channel system meaning that brake fluid can be controlled to each of the two front wheels independently and to the rear wheels as a unit.

1. The Hydraulic Actuation Assembly

• This assembly consists of two sections. The master cylinder and brake booster. These are arranged in two parallel bores with the master cylinder being below the brake booster. The brake booster contains a main control valve which is operated by a lever connected to brake pedal rod. During normal braking when the brake pedal is pushed, this lever causes the control valve to modulate the amount of pressurized brake fluid applied to the rear brakes via a proportioning valve. The control valve also ports brake fluid to the master cylinder pistons which applies braking pressure to the front brakes. The source of this pressurized brake fluid is the accumulator which will be detailed later. Also the fluid must pass through normally open Load Solenoid valves in the Solenoid Valve Block Assembly. The operation of this assembly will be detailed later as well.

Figure 1 Hydraulic Actuator Assembly

• During the Anti-lock braking mode, the main control valve actuates allowing pressurized brake fluid to enter a chamber behind the master cylinder pistons and into the front brake circuits through the appropriate solenoid valves as required. The pressurized brake fluid also exerts force against a reaction sleeve which raises the brake pedal. This allows a 70% stroke of the front brake master cylinder pistons in the unlikely event of an anti-lock malfunction. The Actuation Assembly, Master Cylinder, booster and main valve are serviced as an assembly.

2. Electric Pump and Hydraulic Accumulator Assembly (Figure 2)

Figure 2 Electric Pump and Hydraulic Accumulator Assembly

 3). Solenoid Valve Block Assembly

4. Brake Fluid Reservoir and Level Indicator Assembly

• The Brake Fluid Reservoir and Fluid Level Indicator (FLI) Assembly is a translucent, plastic container that is mounted on top of the Hydraulic Actuation Assembly. The reservoir is connected to the pump inlet by a low pressure hose, and to the master cylinder by a sealed feed port. The FLI provides a warning signal visa the red Brake Light should the brake fluid level fall below the proscribed minimum. If level continue to lower this will cause the Amber Anti-Lock warning light to illuminate as well. Additionally the Electronic Controller will stop the ABS System from operating. The reservoir and FLI are serviced as a unit.

Wheel Sensor and Indicator Rings

The ABS Unit uses four sets of variable reluctance sensor and toothed speed indicator rings. These two devices work together to determine the rotational speed of each wheel. The work under a magnetic induction principle. As the teeth on the indicator rings rotate past the stationary sensor a signal proportional to the rotational speed of the wheel is generated. This voltage is an analog AC signal which is fed to the Electronic Controller via coaxial cables, one for each sensor. The frequency of the signal is dependent on how fast the toothed indicator ring is passing by the stationary sensor. It is the frequency that is used to determine wheel speed by the Electronic Controller. On the front wheels the toothed indicator rings are mounted on the back side of the Hub Assembly. On the rear they are mounted as part of the inner CV Joint assembly. The front sensors are attached to the front spindle and on the rear to the axle housing. The indicator rings and speed sensors are serviced separately. A fine point to be aware of though is that only the correct speed sensor can be installed at each wheel location. If you decide to get replacements from the junkyard, make sure you mark the sensors front to back and left to right and only install the sensor at it’s proper point in the system.

Electrical Operation of the ABS System

I examined the FORD Electrical & Vacuum Troubleshooting Manual for the 89 through 92 model years. The electrical system for the ABS System was virtually identical between all model years. Lets describe what happens to power this system.

When the ignition key is placed into the start or run position, power is applied to a portion of the ABS Control Module (Electronic Controller) via the 10A CLUSTER Fuse. The ABS Control Module applies power to the Anti-Lock Power Relay when the Ignition Switch is placed into the START Position. This relay closes it’s contacts allowing power to flow from the ABS MOD 30A Fuse in the Primary Distribution Box (inside the engine compartment) to the rest of the ABS Control Module. This relay is a "seal-in relay" in that it continues to be closed even when the Ignition Switch is released to the run position. The purpose for this relay is that it allows a relatively large amperage load to be powered but not directly from the ignition switch. This way up to 30A of power can be supplied to the system without relying on the contacts in the ignition switch to do it. After the system is energized it performs a self test. If you place your ignition switch to the run position without starting the car you can watch this test being run. This self test will check electrical continuity of the system as well as the Electronic Controller for proper operation. The Amber Anti-Lock light will illuminate for approximately 4 seconds and then extinguish if all is well with your system. If you then place the switch to the start position and start your car you should see the following cycling of lights. The Amber Anti-Lock and Red Brake Light should illuminate. The Hydraulic Pump Motor most likely will run since the pressure sensed by the Pressure Switch in the system is probably low (below 2030 PSI)if the car has been sitting a while. The Pressure Switch will allow power from the ANTI LOCK 10A Fuse to cause the Hydraulic Pump Motor Relay to close it’s contacts allowing power to flow to the pump motor from the ABS MTR 40 A fuse. It will also cause the Anti-Lock Warning Light to be illuminated. The pump running will pressurize the hydraulic accumulator to around 2650 PSI at which point the pressure switch contacts will open, the Hydraulic Pump Motor Relay will drop out and the pump will stop as well as the red and amber lights will extinguish. For all applicable model years the Anti-Lock Power Relay and the Hydraulic Pump Motor Relay are located on the passenger side firewall area. When facing the engine bay these relays are located as follows:

89 Model Year (Left to Right) WOT AC Cutout Relay, Hydraulic Pump Motor Relay, Anti-Lock Power Relay

90 Model Year (Left to Right) WOT AC Cutout Relay, Hydraulic Pump Motor Relay, Anti-Lock Power Relay

91 Model Year (Left to Right) Hydraulic Pump Motor Relay, Anti-Lock Power Relay, WOT AC Cutout Relay

92 Model Year (Left to Right) Hydraulic Pump Motor Relay, Anti-Lock Power Relay, WOT AC Cutout Relay

Note: This information based on diagrams in the Ford EVTM’s for the appropriate year. If it is wrong, blame FORD not me.

The CLUSTER and ANTI LOCK fuses are located in the Primary Junction Box in the passenger compartment and the ABS MOD and ABS MTR fuses in the Power Distribution Box in the engine compartment.

Basic Troubleshooting

Most of the problems associated with this system seem to revolve around the electrical operation of the Hydraulic Pump Motor and the Accumulator. So lets describe what some of the common symptoms are and what you can do about it.

Hard pedal Amber Anti Lock and Red Brake Light always on.

• The hard pedal is indication of no power assist which we now knows means the Accumulator is not pressurized or the hydraulic pump is not running to pressurize the system. You should also realize that you don’t have ANY rear brakes too. Run the Self Test and see the Amber Warning Light goes out in 4 seconds. Have an assistant stand by the open hood to listen for the Hydraulic Pump Motor to run when you start the car.
• If the pump runs, most likely you have a bad Accumulator or the pump is not being supplied with fluid because sediment has plugged the low pressure hose leading from the reservoir. Check the hose is unplugged and if that doesn’t correct the problem replace the Accumulator. If this doesn’t fix your problem you are into a high buck Pump Assembly replacement. (You already replaced the Accumulator so don’t buy another one now). For reference you should be able to press on the brake pedal from 5-8 times without the Hydraulic Pump Motor running. If this is not that case you are due for an Accumulator soon.
• If the pump does not run you now most likely have an external electrical problem although it is possible the pump motor is shot. Here is how to tell what is what. With the Ignition Switch off depress the brake pedal 20 times to ensure the system is fully depressurized. Turn the Ignition Switch to Run the pump should run. If not disconnect the 4 pin connector on the pump. Use a multi meter to measure the voltage on the pins of the harness connector. The two positive pins are on opposite side of the connector as are the negative pins. Measure from one positive to one negative pin. (See figure 3).You should measure more than `10V DC. If you don’t, potential problems include either the Hydraulic Pump Motor Relay, The Pressure Switch or the wiring harness between them all.

Figure 3 Four Pin Motor Connector

Figure 4 Hydraulic Pump Motor Relay Schematic and Pin-out

The failure of the Hydraulic Pump Motor Relay is a common occurrence. The normal failure modes are the contacts welded themselves shut causing the Hydraulic Pump Motor to run continuous or the relay failing to close which prevents normal pump motor operation. To verify relay operation it would be possible to disconnect the harness connector to the Anti-Lock Pressure Switch and ground pin 4 of the connector to ground.(See Figure 5) This will complete the circuit for the coil of the Hydraulic Pump Motor Relay and should cause the pump to turn on. If the pump does not run most likely the relay is bad and must be replaced. If the motor does run the Pressure Switch may be the faulty part and should be replaced. The FORD Shop Manual states that if the Pressure Switch is replaced the Hydraulic Pump Motor Relay should be replaced as well.

Anti-Lock Warning Light and Red Brake Light come on after brakes applied.

• Most likely this is indication of a weak or bad Accumulator. If you have this symptom it is important to fix it as soon as you can because you are cycling the Hydraulic Pump Motor unnecessarily which will cause this high buck part to fail sooner than it needs to.

Red Brake Light comes on when accelerating or braking or going around a corner hard.

• Probably your brake fluid level is a tad low. Angles and dangles on the car are causing it to pick up the level sensor. Make sure your system is pressurized when you check / add fluid since the Accumulator will "store" an appreciable amount of fluid. This will cause the level to go down as the system is pressurized at start up. Where did the fluid go you might ask? Assuming you have no leaks it probably is as a result of the brake pads in your calipers wearing. As they wear more fluid is required to keep the caliper pistons maintained in the proper position for braking action.

Figure 5 Anti-Lock Pressure Switch Pin-out

Other Problems that might be troubleshot by the DIY

Just like the EEC the ABS System has a Test Connector which may be used to download error codes from the ABS Electronic Controller. It is located on the right rear quarter panel trunk area. The types of codes present here will be basic system faults which will cause the Amber Anti-Lock Warning Light to remain lit even after 4 seconds have elapsed on the Self-Test. As far as I know, any aftermarket Code Reader that is compatible with the FORD EEC System can be used to access these signals. Two things to be aware of though. One, if the first code received is in the 20’s, service the indicated fault. No other codes can be outputted to the code reader if a 20’s fault exists. After servicing the 20’s code repeat getting codes from the Electronic Controller. Two, the memory can be cleared only by reading all codes present, all faults being corrected (anti-lock warning light off) and the vehicle being driven above 25 MPH.

The troubleshooting techniques used for these type of problems are more involved than what is commonly used, but I have included the Service Codes for those of you that are more adventurous. I have tried to give a short summary of what checks are made but if it is not something obvious you are going to have to get the manual or visit a dealer unfortunately. I included this to give you a direction to look for the obvious rather than becoming an ABS Expert Troubleshooter. There are other checks detailed in each Pin Point Check Section other than what I am listing.

Self Induced Potential Problems

Given that signals are generated from each wheel sensor that is proportional to the speed of rotation changes to wheel diameter may have a detrimental effect on the ABS System. This is particularly true for those that choose to run different tire sizes front to back. This difference in tire height will be seen as the wheels rotating at different speeds thus giving the Electronic Controller potential problems. This could cause the ABS System to actuate when neither warranted or desired or may prevent it’s proper operation when needed. Please be careful when making changes in tire sizes or brands of tires. Some TEVES ABS systems can be reprogrammed to compensate for changes made to the tire size on the vehicle. Unfortunately the FORD TEVES System is not capable of that.

Another area of potential problem is the manner in which the brake system is bleed. Since this is a High Pressure ABS System certain procedures must be followed to perform these operations. Front Brakes can be bleed in a conventional manner either with the Ignition Key ON and the system pressurized or with the system depressurized. Rear Brakes are a different matter altogether though. The Ignition Switch must be ON and the system pressurized to get this bleed operation to work. Be aware that the system will have a lot of pressure on it so the brake pedal does not have to be pressed very far to get flow to the rear brake circuit.

When you decide to change your own brake pads here is another thing to think about. When the brake pads are pressed back into the caliper, any "junk" in the lines will be forced back into the ABS Hydraulic Actuator Assembly possibly contaminating the system. My suggestion is to bleed the brake system before doing the brake job to flush out some of the contaminants from the system before they can do damage. An alternative is to clamp off the brake hose but personally I am not too fond of that method.

Choices in remanufacturing your ABS Hydraulic Actuator Assembly

Given that FORD wants in excess of $1500.00 for a new Hydraulic Actuator Assembly I think you better consider a rebuild of your present unit as an alternative. In preparation for doing this article I contacted two reman companies for out TEVES ABS System. The three choices are Cardone Industries, SIA Electronics and Prior Remanufacturing. I do not have much to say about what Cardone can do since even though I contacted their Marketing Department twice for information they did not provide any to me. I do know that they will not deal with customers directly preferring to deal through distributors only. I was unable to determine their entire network of distributors but do know that Car Quest is one company they deal with.

Our other choice at present is SIA Electronics. I contacted Mr. Bryce Elledge who was very forthcoming with information concerning what his company can do for us. I quote a portion one of the two E Mails I received from Mr. Elledge concerning their process.

"THE THREE MAIN HYDRAULIC COMPONENTS (PUMP, VALVE BLOCK, & MASTER CYLINDER) ARE BROKEN DOWN CLEANED AND REBUILT. REBUILT MEANS REPLACING OF SEALS, O-RINGS, VALVES, SPRINGS, AND ANY OTHER NECESSARY INTERNAL COMPONENTS. UNITS SUCH AS THE ACCUMULATOR, PRESSURE SWITCH, MOTOR, LOW PRESSURE HOSES, HIGH PRESSURE LINES, AND OTHER COMPONENTS ARE TESTED AND REPLACED / REBUILT ON AN AS NEEDED BASIS. SOME OTHER COMPONENTS (RESERVOIR, FIREWALL GASKET, PUSH RODS, PLUGS, MOUNTING BOLTS, & OTHERS) ARE NOT READILY AVAILABLE TO US AND CAN NOT BE REPLACED.

THERE MAY BE SOME COSMETIC FEATURES THAT WE CAN NOT DO MUCH WITH, SUCH AS THE RESERVOIR, AND BROKEN PLASTIC ON PLUGS. THE REST OF THE UNIT WILL BE PAINTED A CAST COLOR FOR COSMETIC VALUE. ALL OF OUR UNITS WILL BE SHRINK-WRAPPED, AND PACKAGED USING A FOAM IN PLACE SYSTEM WHICH MOLDS AROUND THE UNIT TO PROTECT IT IN SHIPPING. IF THERE IS A CORE RETURN WE ASK THAT THE RESERVOIR BE DRAINED AND THE SAME FOAM AND BOX BE USED FOR THE CORE RETURN. THIS PROTECTS THE CORE COMING BACK TO US.

YOUR MEMBERS NEED TO MAKE SURE THAT THE UNIT THEY ARE SENDING IN FOR R&R IS HIGHLY PROTECTED FOR SHIPPING PURPOSES. THE SHIPPING COMPANIES DO NOT HANDLE THESE PACKAGES WITH CARE. WE HAVE RECEIVED SEVERAL UNITS WITH BUSTED PLUGS, BENT PUSH RODS, AND OTHER COMPONENTS DAMAGED IN SHIPPING. MANY OF THE DAMAGES WE CAN NOT REPAIR OR REPLACE. PLEASE STRESS THIS POINT TO YOUR MEMBERS. " (Emphasis added is mine)

SIA Electronic has been rebuilding the TEVES ABS Units since 1995. They are able to perform work on both the Mark II systems as well as the Mark IV’s of the later years. I quote from a second E Mail from Mr. Elledge which details their pricing structure. In addition SIA has offered a Club Discount pricing structure for multiple ABS Units sent in as a package for rebuilding. I defer to our President for details since he negotiated the price after speaking with Mr. Elledge. The costs shown below have also been discounted for the club and again I defer to Mr., President for the details.

FORD THUNDERBIRD ABS PRICING

This would seem to me to be a lower cost alternative for those that choose to have the work done. SIA Electronics can be contacted at 1-800-327-6338.

The final choice is the recommended one in my mind. Prior Remanufacturing (www.priorreman.com) has offered TBSCEC members a discounted rate not only on their Teves Mark II units but also the Mark IV Unit and all other Thunderbird/Cougar Master Cylinders and Power Assist Units. All reports indicate they do quality work and their Technical Department is willing and able to assist you with the details of installation. That is where my units will go when a remanufacturing is warranted. Their phone number may be obtained right off their website. They are located in Garland, TX, just outside of Dallas.

References

http://www.geocities.com/MotorCity/Downs/3837/absdebug.html
http://www.serviceinsights.com/main/tech/techarcv/0897brk6.htm
http://www.autotruck.net/library/brakes/breaks1.asp
http://www.serviceinsights.com/main/tech/techarcv/1198pond.htm

FORD Electrical & Vacuum Troubleshooting Manuals for the Model years 89-92
FORD Thunderbird Cougar Shop Manual 1989 Model Year.

Credits

I would like to thank the following people for their assistance in assembling the necessary technical information for this article.

Mr. George Davenport
Mr. Bryce Elledge
Mr. Lee Yaccarino
"SC Kido" Mr. Luis Garcia
"Kar Doktor" Mr. Craig H. Donor

Disclaimer: This article, and additional information, is for personal use only and for assisting owners in maintaining their vehicle. No publishing or reprinting is allowed unless by permission by the author of this article. The author is not responsible for any damage that occurs from the use of this information.