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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
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Experience:  ASE Certified Master Technician
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I have a 95 Z71 ck1500..brakes..000 miles

Resolved Question:

I have a 95 Z71 ck1500. The brakes have never been very good, and now seem to be getting worse. Truck has 87,000 miles. I bought it new and have maintained it well.
Submitted: 7 years ago.
Category: Chevy
Expert:  Mike S. replied 7 years ago.
Is there Ceramic or Semi-metallic linings on there?
Customer: replied 7 years ago.
I think they are metallic. The brake pedal has a lot of travel, and requires a good bit of force to stop the truck. I have a 2004 Trailblazer, and there is no comparison between the braking on the two vehicles. I pull a light trailer with brakes frequently (2500 lbs). stops better with the trailer than without. I had to replace a rear brake line a couple of years ago and bled that wheel well. I recently gravity bled all four wheels which made a slight improvement. Are there inherent problems with the brakes on this model truck? The linings could be an issue, but I do not recall any change in braking performance when I replaced them. I replaced the front rotors with the last front brake job. The pedal travel and force required to stop seems to point to system components away from the wheels. Have you seen similar symptoms on this model truck?
Expert:  Mike S. replied 7 years ago.

If they are rear drums and the pedal travels too far before braking you may want to adjust up the rear brake shoes. If the brake pedal is actually spongy, then there may be air in the system and the system should be bled of air. If there is a brake booster on it make sure you are getting good vacuum to it. Also, look for any fluid leaks down behind the master cylinder running down the front of the booster.


Bleeding the ABS System


The brake system must be bled when any brake line is disconnected or there is air in the system.

Never bleed a wheel cylinder when a drum is removed.

  1. Clean the master cylinder of excess dirt and remove the cylinder cover and the diaphragm.
  2. Fill the master cylinder to the proper level. Check the fluid level periodically during the bleeding process, and replenish it as necessary. Do not allow the master cylinder to run dry, or you will have to start over.
  3. Before opening any of the bleeder screws, you may want to give each one a shot of penetrating solvent. This reduces the possibility of breakage when they are unscrewed.
  4. Attach a length of vinyl hose to the bleeder screw of the brake to be bled. Insert the other end of the hose into a clear jar half full of clean brake fluid, so that the end of the hose is beneath the level of fluid. The correct sequence for bleeding is to work from the brake farthest from the master cylinder to the one closest; right rear, left rear, right front, left front.
  5. The combination valve must be held open during the bleeding process. A clip, tape, or other similar tool (or an assistant) will hold the metering pin in.
  6. Depress and release the brake pedal three or four times to exhaust any residual vacuum.
  7. Have an assistant push down on the brake pedal and hold it down. Open the bleeder valve slightly. As the pedal reaches the end of its travel, close the bleeder screw and release the brake pedal. Repeat this process until no air bubbles are visible in the expelled fluid.


Make sure your assistant presses the brake pedal to the floor slowly. Pressing too fast will cause air bubbles to form in the fluid.

  1. Repeat this procedure at each of the brakes. Remember to check the master cylinder level occasionally. Use only fresh fluid to refill the master cylinder, not the stuff bled from the system.
  2. When the bleeding process is complete, refill the master cylinder, install its cover and diaphragm, and discard the fluid bled from the brake system.
  3. Perform 3 function tests with the TECH 1 scan tool. The brake pedal must be firmly applied.
  4. On models with rear wheel ABS:
    1. Refill the jar with clean brake fluid and attach the bleed hose to the bleed valve on the Isolation/Dump valve.
    2. Have your assistant slowly depress the brake pedal and hold it. Loosen the bleed valve and expel the air. Tighten the valve and slowly release the pedal.
    3. Wait 15 seconds and repeat this procedure. Repeat bleeding the Isolation/Dump valve until all the air is expelled.

  5. On models with 4 wheel ABS, repeat Steps 1-9.


When you replaced the front rotors did you have them machined a slow fine cut to assure a good smooth surface?


Do you notice any leaks at the wheel cylinders or calipers?

I will check recalls.

Expert:  Mike S. replied 7 years ago.

I didn't see any recalls here.


Expert:  Mike S. replied 7 years ago.

I did find 1 complaint.

Complaints Summary


Year: 1995
Complaint Number: 517777

Crash : NoFire : NoNumber of Injuries: 0
ODI ID Number : 517777Number of Deaths: 0
Date of Failure:
VIN : 2GCFC29K851...

Is there any fault codes?

Rear Wheel Anti-lock Rwal Brake System

General Description


See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Rear wheel anti-lock brake system schematic-R/V Series

Click image to see an enlarged view

Fig. Fig. 2: Rear wheel anti-lock brake system schematic-C/K Series

The Kelsey Hayes RWAL system is found on Chevrolet and GMC products including Suburban and C/K Series pick-ups. The system is particularly useful because of the wide variations of loading the vehicle may experience. Preventing rear wheel lock-up often makes the difference in controlling the vehicle during hard or sudden stops.

Found on both 2WD and 4WD vehicles, the RWAL system is designed to regulate rear hydraulic brake line pressure, preventing wheel lock-up at the rear. Pressure regulation is managed by the control valve, located under the master cylinder. The control valve is capable of holding, increasing or decreasing brake line pressure based on electrical commands from the RWAL Electronic Control Unit (ECU) or Electronic Brake Control Module (EBCM).

The RWAL ECU is a separate and dedicated microcomputer mounted next to the master cylinder; it is not to be confused with the engine management ECU. The RWAL ECU receives signals from the speed sensor. The speed sensor sends its signals to the Vehicle Speed Sensor buffer (previously known as the Digital Ratio Adapter Controller or DRAC) within the instrument cluster. The buffer translates the sensor signal into a form usable by the ECU. The RWAL ECU reads this signal and commands the control valve to function. If commanded to release pressure, the dump valve releases pressurized fluid into the accumulator where it is held under pressure. If a pressure increase is called for, the isolator valve within the control valve pulses, releasing pressurized fluid into the system.

The RWAL system is connected to the BRAKE warning lamp on the instrument cluster. A RWAL self-check and a bulb test are performed every time the ignition switch is turned to ON . The BRAKE warning lamp should illuminate for about 2 seconds and then go off. Problems within the RWAL system will be indicated by the BRAKE warning lamp staying illuminated.

If a fault is detected within the system, the RWAL ECU will assign a fault code and store the code in memory. The code may be read to aid in diagnosis.


System Diagnosis and Testing


See Figures 1 through 7

Click image to see an enlarged view

Fig. Fig. 1: Diagnostic circuit check-rear wheel anti-lock brake system

Click image to see an enlarged view

Fig. Fig. 2: Diagnostic test-brake light is ON

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Fig. Fig. 3: Diagnostic test-brake light is ON

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Fig. Fig. 4: Diagnostic test-brake light is ON

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Fig. Fig. 5: Diagnostic test-brake light is intermittent

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Fig. Fig. 6: Diagnostic test-brake light is flashing

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Fig. Fig. 7: Diagnostic test-brake light is OFF


If the vehicle is equipped with air bag (SIR) system, always properly disable the system before commencing work on the ABS system. Certain components within the RWAL system are not intended to be serviced or repaired. Only those components with removal & Installation procedures should be serviced. Do not use rubber hoses or other parts not specifically specified for the RWAL system. When using repair kits, replace all parts included in the kit. Partial or incorrect repair may lead to functional problems. Lubricate rubber parts with clean, fresh brake fluid to ease assembly. Do not use lubricated shop air to clean parts; damage to rubber components may result. Use only brake fluid from an unopened container. Use of suspect or contaminated brake fluid can reduce system performance and/or durability. A clean repair area is essential. Perform repairs after components have been thoroughly cleaned; use only denatured alcohol to clean components. Do not allow components to come into contact with any substance containing mineral oil; this includes used shop rags. The RWAL ECU is a microprocessor similar to other computer units in the vehicle. Insure that the ignition switch is OFF before removing or installing controller harnesses. Avoid static electricity discharge at or near the controller. Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test. Always wear a grounded wrist strap when servicing any control module or component labeled with a Electrostatic Discharge (ESD) symbol. Avoid touching module connector pins. Leave new components and modules in the shipping package until ready to install them. To avoid static discharge, always touch a vehicle ground after sliding across a vehicle seat or walking across carpeted or vinyl floors. Never allow welding cables to lie on, near or across any vehicle electrical wiring. Do not allow extension cords for power tools or droplights to lie on, near or across any vehicle electrical wiring.


Before reading trouble codes, perform the Diagnostic Circuit Check according to the chart. This test will aid in separating RWAL system problems from common problems in the hydraulic brake system. The diagnostic circuit check will direct the reading of trouble codes as necessary.


The RWAL ECU will assign a code to the first fault found in the system. If there is more than 1 fault, only the first recognized code will the stored and transmitted.

Trouble codes may be read either though the use of TECH-1 or equivalent scan tool or by connecting a jumper wire from pin H on the ALDL to pin A. If the jumper method is used, the fault code will be displayed through the flashing of the BRAKE warning lamp on the dash. The terminals must be connected for about 20 seconds before the display begins. The display will begin with 1 long flash followed by shorter ones-count the long flash as part of the display.

Sometimes the first display sequence will be inaccurate or short; subsequent displays will be accurate.

If using a hand scanner, note that if a soft code is stored, only the last recognized code will be retained and displayed on the scanner. Soft fault codes 6, 9 and 10 can only be read with a scan tool. Codes 1, 11 and 12 will not read on the scan tool; they must be read using the jumper wire method.

Never ground terminal H of the ALDL to terminal A if the BRAKE warning lamp is not lit. Doing so will set a false code 9 and illuminate the BRAKE warning lamp. With the brake lamp on, the RWAL system will be disabled.


Stored trouble codes must be cleared with the ignition switch OFF . Remove the STOP/HAZARD fuse for at least 5 seconds, the reinstall the fuse.


Four Wheel Anti-lock Brake System

Component Testing


Vehicle Speed Sensor

Prefer to of this repair guide for VSS testing.

Wheel Speed Sensor

See Figure 1

  1. Elevate and safely support the vehicle.
  2. Unplug the sensor electrical connection.
  3. Check the condition of the sensor terminals and the wiring harness terminals. Repair as necessary.
  4. Check the sensor wiring harness for an open or short circuit. Repair as necessary.
  5. Using a Digital Volt OhmMeter (DVOM) set to read resistance, probe the sensor terminals.
  6. If the resistance is not as specified in the accompanying charts, the sensor may be defective.
  7. Turn the DVOM to the A/C voltage scale and spin the wheel, there should be a voltage reading. As the wheel speed increases, the voltage should increase. If there is no voltage present, or the voltage does not increase with wheel speed, check the tone wheel for defects. If the tone wheel is found to be in good condition, replace the sensor.

Click image to see an enlarged view

Fig. Fig. 1: Wheel speed sensor temperature versus resistance chart

Pump motor circuit

  1. Check the condition of the fuse in the relay center and replace as necessary.
  2. Unplug the pump motor electrical connection.
  3. Check the condition of the terminals and the wiring harness terminals. Repair as necessary.
  4. Attach the electrical connection.
  5. Using a Digital Volt OhmMeter (DVOM) set to read voltage, backprobe between the black (ground) wire and red (power) wire terminals of the harness . The voltage should be between 9-14 volts.
  6. If the voltage is less than 9 volts, set the DVOM on the lowest resistance scale, disconnect the harness and the positive and negative battery terminals. Connect one probe to the positive battery cable and the other probe to red wire terminal. Note the reading. Connect one probe to the negative battery cable and the other probe to black wire terminal. Note the reading.
  7. If the resistance is less than one ohm the wiring is fine and the control unit should be replaced.
  8. If the resistance is more than one ohm, clean and tighten the terminals or repair the wiring as needed.
  9. Attach all unplugged wires and recheck the voltage.
  10. Clear the trouble codes and road test the vehicle. If the trouble code returns, check the motor supply voltage again.
  11. If the voltage is now between 9-14 volts and the pump is still not functioning properly, replace the assembly.
  12. If the voltage is still lower than 9 volts, there may be a problem with the EBCM.

System Diagnosis


See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Functional test-2WD models

Click image to see an enlarged view

Fig. Fig. 2: Functional test-4WD models


System diagnosis begins with the diagnostic circuit check as given in the chart. If the chart is used correctly, it will aid in elimination of simple, non-system problems such as blown fuses of failed bulbs. The chart will prompt the reading of codes at the proper point in the diagnosis.

Some of the diagnostic or repair procedures refer to the performance of a Function Test. This test is performed with the scan tool; it operates all components of the EHCU valve and checks their function. The test cannot be performed without the scan tool.


Stored trouble codes are transmitted through the flashing of the amber ANTI-LOCK dash warning lamp. The system may be put into diagnostic mode with a jumper wire, however, the use of the TECH-1 scan tool or its equivalent is highly recommended. The scan tool will allow performance of the specific system tests called for by the trouble tree for each code.

On all models except 1996-98, the codes can be read without the use of a hand scanner. To read the codes, use a jumper wire to connect terminal H on the ALDL to either body ground or to terminal A. The terminals must be connected for a few seconds before the code(s) will transmit. Observe the ANTI-LOCK light on the dash and count the flashes in groups: a group of 4 flashes, a pause and a group of 3 flashes indicates Code 43. Codes 12 and 14 are not trouble codes, but may appear with them to indicate normal operation. Not all vehicles use Code 12 or 14.

After the trouble codes have been read, refer to the correct trouble tree for each code. After repairs, repeat the initial diagnostic circuit check to confirm normal operation of the system.


Stored codes may be erased with the hand scanner if available. If not using a hand scanner, codes may be cleared as follows:

  1. Turn the ignition switch ON but do not start the engine.
  2. Use a jumper wire to ground ALDL terminal H to terminal A for 2 seconds.
  3. Remove the jumper wire for 2 seconds.
  4. Repeat the grounding and un-grounding two more times. Each connection and opening of the circuit should last 2 seconds.
  5. Connect the jumper to terminals H and A for a longer time; no trouble codes should be displayed. If codes are displayed, the system was not properly erased.
  6. If no trouble codes appear, the memory has been cleared. Turn the ignition switch OFF .


Expert:  Mike S. replied 7 years ago.


Vacuum Leak Test

  1. Operate the engine at idle without touching the brake pedal for at least one minute.
  2. Turn off the engine and wait one minute.
  3. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.

System Operation Test

  1. With the engine OFF , pump the brake pedal until the supply vacuum is entirely gone.
  2. Put light, steady pressure on the brake pedal.
  3. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.
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