Bendix 9 Brake System
05-11-2009, 09:17 AM
#16
CF Veteran
I keep looking and every article/write up I find or someone sends me is for a standard brake system to the Grand Cherokee upgrade. If I find one that is ACTUALLY for the Bendix system I will definitely post the link OR if someone knows if the procedure is the same pleas pipe up.(I know we have some Techs on this forum)
05-28-2009, 02:29 PM
#17
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Year: 1989
Model: Cherokee
Engine: 4.0
Does anyone know where to get the High pressure brake line that runs from that actuator along the firewall to the proportioning valve? Mine is leaking and the stealership wanted 300 dollars for one high pressure brake line!! and they wonder why Chrysler dealers all around are going under?
06-16-2009, 04:53 PM
#18
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Year: 1989
Model: Cherokee
Engine: 4.0
So, I'm still looking for this stupid high pressure brake line for my crap bendix system. I've talked to stealerships from Milwaukee to Chicago. No one can help me. Everyone says this parts not available.
One shop told me to try to put a steel line in there as a quick fix. Any suggestions anyone?
One shop told me to try to put a steel line in there as a quick fix. Any suggestions anyone?
06-17-2009, 04:11 PM
#19
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Year: 1989
Model: Cherokee
Engine: 4.0
I found a small bit more information on the Bendix 9 ABS system:
rings mounted on the axles. The Bendix 9 system control module is under the back seat attached to the floorpan. On 1989 and 1990 models,
isolated simultaneously by a single solenoid.
Brake pressure in the isolated brake circuit(s) is then released by energizing the
819 - Open circuit at diagnostic connector
accurate fluid level reading. The procedure goes as follows:
The bleeding sequence for this system is right rear, left front, right front and left rear.
The Bendix 9 ABS system on 1989 to 1991 Jeep Cherokee and Wagoneer is an integral ABS system that
combines the master brake cylinder with the hydraulic control modulator and two accumulators. The pump and
motor are a separate assembly, but work with the master cylinder and hydraulic modulator assembly to provide
power assist as well as braking.
Bendix 9 is a four-wheel, three hydraulic channel ABS system. During normal braking, the brake hydraulics are
split diagonally. But during anti-lock braking, both front brakes are controlled separately, while the rear brakes are
controlled as a pair. The modulator assembly contains nine solenoid valves: an isolation valve, a decay valve and
a build valve for each of the three ABS circuits.
Four -speed sensors (one for each wheel) are used. Front sensors are on the steering knuckles, with the
sensor tone rings mounted on the axle shafts. Rear sensors are on the rear brake backing plates, with the sensor
combines the master brake cylinder with the hydraulic control modulator and two accumulators. The pump and
motor are a separate assembly, but work with the master cylinder and hydraulic modulator assembly to provide
power assist as well as braking.
Bendix 9 is a four-wheel, three hydraulic channel ABS system. During normal braking, the brake hydraulics are
split diagonally. But during anti-lock braking, both front brakes are controlled separately, while the rear brakes are
controlled as a pair. The modulator assembly contains nine solenoid valves: an isolation valve, a decay valve and
a build valve for each of the three ABS circuits.
Four -speed sensors (one for each wheel) are used. Front sensors are on the steering knuckles, with the
sensor tone rings mounted on the axle shafts. Rear sensors are on the rear brake backing plates, with the sensor
rings mounted on the axles. The Bendix 9 system control module is under the back seat attached to the floorpan. On 1989 and 1990 models,
the mounting angle of the module is important because the module contains a mercury switch that monitors
vehicle deceleration. This allows the module to adjust anti-lock braking to better suit slippery driving conditions
when the vehicle is being operated in four-wheel drive. If the module is removed or replaced, it must be reinstalled
at exactly the same angle as before so the mercury switch will function correctly. On 1991 models, the module is
mounted on a bracket that holds it at the proper angle.
vehicle deceleration. This allows the module to adjust anti-lock braking to better suit slippery driving conditions
when the vehicle is being operated in four-wheel drive. If the module is removed or replaced, it must be reinstalled
at exactly the same angle as before so the mercury switch will function correctly. On 1991 models, the module is
mounted on a bracket that holds it at the proper angle.
BENDIX 9 PRESSURE SWITCHES & VALVES
The integral master cylinder, hydraulic control modulator and accumulator assembly contain a "boost pressure
differential switch" mounted on the pressure modulator. It has a single terminal, is self-grounding and is normally
open. This switch performs the same function as a differential pressure switch in a conventional brake system (it
illuminates the BRAKE and ABS warning lights in the event of fluid loss from the brake system). The relays for
both warning lights are located on the drivers side of the engine compartment near the master cylinder/modulator
assembly.
The modulator assembly also has a brake and switch, and an accumulator low pressure
switch for signaling the controller if accumulator pressure is lost. The accumulator switch is a single terminal, selfgrounding
switch that remains closed during normal operation. If pressure in the accumulator drops below 1,050
psi, the switch opens and the controller illuminates the yellow ABS light. If accumulator pressure does not
increase enough to close the switch within 20 seconds, the red BRAKE warning light will also come on.
The integral master cylinder, hydraulic control modulator and accumulator assembly contain a "boost pressure
differential switch" mounted on the pressure modulator. It has a single terminal, is self-grounding and is normally
open. This switch performs the same function as a differential pressure switch in a conventional brake system (it
illuminates the BRAKE and ABS warning lights in the event of fluid loss from the brake system). The relays for
both warning lights are located on the drivers side of the engine compartment near the master cylinder/modulator
assembly.
The modulator assembly also has a brake and switch, and an accumulator low pressure
switch for signaling the controller if accumulator pressure is lost. The accumulator switch is a single terminal, selfgrounding
switch that remains closed during normal operation. If pressure in the accumulator drops below 1,050
psi, the switch opens and the controller illuminates the yellow ABS light. If accumulator pressure does not
increase enough to close the switch within 20 seconds, the red BRAKE warning light will also come on.
TWO ANTILOCK BRAKE ACCUMULATORS
Two accumulators are used: a high pressure accumulator (nitrogen precharged to 1,000 psi and capable of
storing fluid at 1,700 to 2,000 psi) located on the master cylinder booster assembly, and a low-pressure
accumulator (precharged to 350 psi, but also capable of storing fluid at 1,700 to 2,000 psi) which serves primarily
as a fluid reservoir. Both accumulators work together to provide additional fluid pressure during anti-lock braking,
as well as power-assisted brake applications should the booster pump and motor fail.
The remote pump and motor assembly are on the passenger side of the engine compartment. The pump supplies
system pressure for normal power-assisted braking, as well as anti-lock braking. Power is supplied to the motor
through a relay and pressure switch located next to the pump and motor assembly.
The pressure switch is designed to keep system operating pressure between 1,700 and 2,000 psi. When pressure
drops below 1,700 psi, the switch closes and causes the pump to run until it builds up sufficient pressure to
recharge the accumulators. At 2,000 psi, the switch opens and the pump shuts off. Normal pump time for a
completely discharged system (zero psi) is about 60 to 80 seconds. The pump only runs when the ignition is on.
To protect the system from serious damage that would be caused by too much pressure, a pressure relief valve
and thermal fuse are included as part of the motor and pump assembly. The pressure relief valve is a simple
"blow off" valve that opens if pump pressure exceeds 3,000 psi. The relief valve does not reseat if it has been
forced open, and must be replaced. The thermal fuse will shut the pump off if the pump operating temperature
exceeds approximately 385 degrees.
Two accumulators are used: a high pressure accumulator (nitrogen precharged to 1,000 psi and capable of
storing fluid at 1,700 to 2,000 psi) located on the master cylinder booster assembly, and a low-pressure
accumulator (precharged to 350 psi, but also capable of storing fluid at 1,700 to 2,000 psi) which serves primarily
as a fluid reservoir. Both accumulators work together to provide additional fluid pressure during anti-lock braking,
as well as power-assisted brake applications should the booster pump and motor fail.
The remote pump and motor assembly are on the passenger side of the engine compartment. The pump supplies
system pressure for normal power-assisted braking, as well as anti-lock braking. Power is supplied to the motor
through a relay and pressure switch located next to the pump and motor assembly.
The pressure switch is designed to keep system operating pressure between 1,700 and 2,000 psi. When pressure
drops below 1,700 psi, the switch closes and causes the pump to run until it builds up sufficient pressure to
recharge the accumulators. At 2,000 psi, the switch opens and the pump shuts off. Normal pump time for a
completely discharged system (zero psi) is about 60 to 80 seconds. The pump only runs when the ignition is on.
To protect the system from serious damage that would be caused by too much pressure, a pressure relief valve
and thermal fuse are included as part of the motor and pump assembly. The pressure relief valve is a simple
"blow off" valve that opens if pump pressure exceeds 3,000 psi. The relief valve does not reseat if it has been
forced open, and must be replaced. The thermal fuse will shut the pump off if the pump operating temperature
exceeds approximately 385 degrees.
BENDIX 9 ANTILOCK SYSTEM OPERATION
The Bendix 9 Jeep ABS system has an unusual feature compared to other ABS
systems in that it does not become functional until vehicle speed reaches 12 to 15
mph. It is also designed to disengage at speeds below 3 to 5 mph, which may allow
the to chirp or skid slightly just before the vehicle comes to a complete stop
when braking hard. This is a normal condition for this system and does not indicate
a problem. It was designed to function this way to make it compatible with Jeep
Selec-Trac 4WD.
When the brakes are applied, the brake pedal switch signals the ABS module to
compare the relative deceleration rates of all four wheels. If ABS braking is
needed, the module energizes the appropriate ABS isolation solenoid to seal off
the affected wheel brake. If either rear brake needs ABS braking, both lines are
The Bendix 9 Jeep ABS system has an unusual feature compared to other ABS
systems in that it does not become functional until vehicle speed reaches 12 to 15
mph. It is also designed to disengage at speeds below 3 to 5 mph, which may allow
the to chirp or skid slightly just before the vehicle comes to a complete stop
when braking hard. This is a normal condition for this system and does not indicate
a problem. It was designed to function this way to make it compatible with Jeep
Selec-Trac 4WD.
When the brakes are applied, the brake pedal switch signals the ABS module to
compare the relative deceleration rates of all four wheels. If ABS braking is
needed, the module energizes the appropriate ABS isolation solenoid to seal off
the affected wheel brake. If either rear brake needs ABS braking, both lines are
isolated simultaneously by a single solenoid.
Brake pressure in the isolated brake circuit(s) is then released by energizing the
normally closed ABS decay solenoid. Pressure is reapplied by energizing the ABS build solenoid. This opens a
passageway that allows pressure from the pump and accumulators to enter the line. Cycling of the decay and
build solenoids will continue until the vehicle slows to 3 to 5 mph. At that point, the isolation solenoid is
deenergized and anti-lock braking is discontinued. The wheels may then lockup or chirp slightly as the vehicle
comes to a complete stop.
passageway that allows pressure from the pump and accumulators to enter the line. Cycling of the decay and
build solenoids will continue until the vehicle slows to 3 to 5 mph. At that point, the isolation solenoid is
deenergized and anti-lock braking is discontinued. The wheels may then lockup or chirp slightly as the vehicle
comes to a complete stop.
Bendix 9 ANTILOCK BRAKE DIAGNOSTICS
The ABS control module monitors all system inputs while driving. If a fault is detected, the controller logs a fault
code and illuminates one or both warning lights. The ABS warning light will remain on for the duration of the
ignition cycle and as long as the fault is present. When the ABS warning light is on, the ABS system is
deactivated, but normal braking is still available. If the red BRAKE warning light is also on, however, it signals loss
of hydraulic pressure or power assist. The accumulators normally contain enough pressure for 15 to 20 powerassisted
stops should the pump fail.
The Bendix 9 system does not provide manual flash codes, so a scan tool must be used to access fault codes.
Codes on this system can be cleared by removing the ABS BAT fuse from the fuse panel for 10 seconds. A scan
tool can also be used to perform a series of ABS electrical checks. If a failure or problem is detected during these
tests, the scan tool will display a fault code indicating which circuit the problem is in. The scan tool can also be
used to monitor various system inputs and outputs, including the wheel-speed sensors, the ABS solenoids and
the operation of the pump motor.
The ABS control module monitors all system inputs while driving. If a fault is detected, the controller logs a fault
code and illuminates one or both warning lights. The ABS warning light will remain on for the duration of the
ignition cycle and as long as the fault is present. When the ABS warning light is on, the ABS system is
deactivated, but normal braking is still available. If the red BRAKE warning light is also on, however, it signals loss
of hydraulic pressure or power assist. The accumulators normally contain enough pressure for 15 to 20 powerassisted
stops should the pump fail.
The Bendix 9 system does not provide manual flash codes, so a scan tool must be used to access fault codes.
Codes on this system can be cleared by removing the ABS BAT fuse from the fuse panel for 10 seconds. A scan
tool can also be used to perform a series of ABS electrical checks. If a failure or problem is detected during these
tests, the scan tool will display a fault code indicating which circuit the problem is in. The scan tool can also be
used to monitor various system inputs and outputs, including the wheel-speed sensors, the ABS solenoids and
the operation of the pump motor.
BENDIX 9 ANTILOCK BRAKE DTC CODES:
800 - No voltage at ECM
801 - No serial data from ECM
802 - No signal
803 - Warning lights inoperative
804 - Yellow ABS warning light inoperative
805 - Differential pressure fault
806 - Boost pressure fault
807 - Low accumulator pressure
808 - Pressure modulator fault
809 - Self-test failure
810 - Solenoid under voltage
811 - Relay fault
812 - Pump/motor fault
813 - Stoplight circuit fault
814 - Low fluid
815 - Right rear wheel speed sensor
816 - Left rear wheel speed sensor
817 - Right front wheel speed sensor
818 - Left front wheel speed sensor
800 - No voltage at ECM
801 - No serial data from ECM
802 - No signal
803 - Warning lights inoperative
804 - Yellow ABS warning light inoperative
805 - Differential pressure fault
806 - Boost pressure fault
807 - Low accumulator pressure
808 - Pressure modulator fault
809 - Self-test failure
810 - Solenoid under voltage
811 - Relay fault
812 - Pump/motor fault
813 - Stoplight circuit fault
814 - Low fluid
815 - Right rear wheel speed sensor
816 - Left rear wheel speed sensor
817 - Right front wheel speed sensor
818 - Left front wheel speed sensor
819 - Open circuit at diagnostic connector
FALSE CODES
One problem that is common on Bendix 9 is false codes. The ABS controller can sometimes be fooled by certain
driving conditions into believing a fault has occurred when in fact there is nothing wrong with the system.
Spinning the wheels on ice, water, mud, snow or gravel, for example, when starting out in the two-wheel drive
mode may cause the controller to think something is amiss with the wheel-speed sensors, causing the ABS
warning light to come on and a code to be set. Deceleration on a steep incline or when the transfer case is in fourwheel
low can sometimes set a brake code. A marginally low level may trigger the red BRAKE warning
light during hard deceleration or when driving on an incline. If the vehicle is driven over two to four miles per hour
with the parking brake set, a fault code can be set. To rule out the possibility of a real problem, always perform a
complete system check.
A different type of false code problem may be encountered on 1989-1990 Cherokees. The original ABS module
(P/N 56004028) may have been replaced by a later 1991 module (P/N 56004948). The two modules appear to be
identical, but communicate differently with a scan tool, resulting in false codes. The problem can be resolved by
jumping terminals three and four on the D1 diagnostic connector. This reconfigures the data coming out of the
newer module so the scan tool will read it correctly.
One problem that is common on Bendix 9 is false codes. The ABS controller can sometimes be fooled by certain
driving conditions into believing a fault has occurred when in fact there is nothing wrong with the system.
Spinning the wheels on ice, water, mud, snow or gravel, for example, when starting out in the two-wheel drive
mode may cause the controller to think something is amiss with the wheel-speed sensors, causing the ABS
warning light to come on and a code to be set. Deceleration on a steep incline or when the transfer case is in fourwheel
low can sometimes set a brake code. A marginally low level may trigger the red BRAKE warning
light during hard deceleration or when driving on an incline. If the vehicle is driven over two to four miles per hour
with the parking brake set, a fault code can be set. To rule out the possibility of a real problem, always perform a
complete system check.
A different type of false code problem may be encountered on 1989-1990 Cherokees. The original ABS module
(P/N 56004028) may have been replaced by a later 1991 module (P/N 56004948). The two modules appear to be
identical, but communicate differently with a scan tool, resulting in false codes. The problem can be resolved by
jumping terminals three and four on the D1 diagnostic connector. This reconfigures the data coming out of the
newer module so the scan tool will read it correctly.
MAKING REPAIRS
The Bendix 9 system is an integral ABS system so the accumulators must be completely depressurized prior to
doing any brake work. This can be done by pumping the brake pedal firmly at least 45 times while the ignition is in
the off position.
Do not open any brake line unless this has been done!
The Bendix 9 system requires a special fluid fill procedure because both accumulators must be filled to get an
The Bendix 9 system is an integral ABS system so the accumulators must be completely depressurized prior to
doing any brake work. This can be done by pumping the brake pedal firmly at least 45 times while the ignition is in
the off position.
Do not open any brake line unless this has been done!
The Bendix 9 system requires a special fluid fill procedure because both accumulators must be filled to get an
accurate fluid level reading. The procedure goes as follows:
1. Fill the reservoir to the full mark;
2. Start the engine and pump the brakes until the booster pump/motor assembly turns on;
3. Stop pumping the brakes and wait for the pump to shut off; and
4. Recheck the fluid level and add as needed.
2. Start the engine and pump the brakes until the booster pump/motor assembly turns on;
3. Stop pumping the brakes and wait for the pump to shut off; and
4. Recheck the fluid level and add as needed.
BENDIX 9 ANTILOCK BRAKES BLEEDING PROCEDURE
When bleeding the brakes either manually or with pressure bleeding equipment, the entire must be
bled, including the accumulators, pump and master cylinder as well as the individual brake lines. Depressurize the
accumulator by pumping the brake pedal 25 to 40 times while the ignition is off, and leave the ignition off while
bleeding the system.
When bleeding the brakes either manually or with pressure bleeding equipment, the entire must be
bled, including the accumulators, pump and master cylinder as well as the individual brake lines. Depressurize the
accumulator by pumping the brake pedal 25 to 40 times while the ignition is off, and leave the ignition off while
bleeding the system.
The bleeding sequence for this system is right rear, left front, right front and left rear.
Last edited by DirtDog; 06-17-2009 at 04:19 PM.
06-23-2009, 11:07 AM
#20
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Year: 1990
Model: Cherokee
Engine: 4.0L
I wanted a little clarification on this ... I'd like to disable the ABS. Can I just pull the connections and kill the dash light? Is there anything that needs to be done to the actual hardware?
-- KC
-- KC
10-22-2009, 04:30 AM
#22
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Year: 1995
Model: Grand Cherokee
Engine: 6 in line
The Accumulator holds the hydraulic fluid under pressure either with a nitrogen charge or air charge. To service an accumulator, that pressure needs to be depleted or it will simply mangle you to death.
02-28-2010, 08:20 PM
#23
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Year: 1989
Model: Cherokee
Engine: 4.0L I6
I have an 89 Cherokee Laredo with the Bendix 9 ABS system. My pedal goes near all the way to the floor before it does anything. I have replaced the MC, accumulator (I think that's what it is. It's the round tank to the passenger side of the MC), proportioning valve (again I think that's what it's called), and front two calipers. After all of this I bled the system like a normal vehicle (right rear, left rear, right front, left front). If I pump the brake pedal I get OK brakes, but still not as good as your average car or truck. Anyone have an idea of what the problem could be?
03-11-2010, 10:30 AM
#26
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Year: 1990
Model: Cherokee
Engine: 4.0
What i have been told to do since i am doing a 8.25 swap is... Pull ABS fuse from under dash and remove wheel sensors. if the light then bothers you all you have to do is pull the light out and u will still have " power breaking". My end result is to swap brake system out with a newer one. Thanks hope this helps.
05-06-2010, 04:04 PM
#27
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Model: Cherokee
So, I'm still looking for this stupid high pressure brake line for my crap bendix system. I've talked to stealerships from Milwaukee to Chicago. No one can help me. Everyone says this parts not available.
One shop told me to try to put a steel line in there as a quick fix. Any suggestions anyone?
One shop told me to try to put a steel line in there as a quick fix. Any suggestions anyone?
clint
06-22-2010, 08:37 AM
#28
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Year: 1990 limited
Model: Cherokee
Engine: 4.0
I found a place that makes the hose for 30 dollars. I also have 1 slightly used hose. I got a new hose about a month ago and the hyd pump went out. I am just finishing doing a brake swap with a 97 XJ. I can now lock my brakes up at 60 with no problem.
08-14-2010, 02:21 AM
#30
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Year: 1987
Model: Cherokee
Engine: 4.0
first do ur brakes still work? as in do they feel normal when you depress the pedal? second to get rid of the light pull the abs fuse =] (if ur brakes still feel normal this will probably disable them...i wouldnt really know mine never worked in the first place) finally take all that electronic brake crap out all undo the clip on the back of the pedal, four nuts on the master cylinder thru the fire wall pull it all out.....SAVE UR BRAKE LINES unless ur getting new ones pull the portioning valve off too u will need a new one if its related to abs under ur hood unbolt/un plug it pretty much...go to a junk yard find any other late 80's early 90's xj salvage booster/master/portioning valve from it (cost me 60 bux) bolt it in get new fittings for the portioning valve connect lines bleed brakes......its A LOT and believe me A LOT easier to convert to regular brake booster than it sounds.... from start to finish it was 2 hours consisting of going to the junk yard driving home pulling old stuff out putting new in going to CarQuest getting fittings back home back to CarQuest for more fittings back home bleeding brakes and driving the jeep id say 2hrs time and 80 bux for everything including new fluid and i had reliable brakes again! btw there is a write up on this........
