ISUZU Amigo/Pick-ups/Rodeo/Trooper 1981-1996

Bleeding

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The EHCU/BPMV is the one component which adds to the complexity of bleeding the 4WAL brake systems. For the most part, the system is bled in the same manner as non-ABS vehicles. Refer to the procedure earlier in this section for details. But because of the EHCU/BPMV's complex internal valve design, additional steps are necessary if the unit has been replaced or if it is suspected to contain air. These bleeding steps are NOT necessary if the only connection/fitting(s) opened were downstream of the unit. These steps may or may not be necessary after master cylinder replacement. If in doubt (or without the necessary special tools) thoroughly bleed the system and see if a firm brake pedal can be obtained; if not, the EHCU/BPMV must be bled as well.

As with the RWAL brake system, the use of a power bleeder is recommended, but the system may also be bled manually. If a power bleeder is used, it must be of the diaphragm type and provide isolation of the fluid from air and moisture.

Do not pump the pedal rapidly when bleeding; this can make the circuits very difficult to bleed. Instead, press the brake pedal slowly 1 time and hold it down while bleeding takes place. Tighten the bleeder screw, release the pedal and wait 15 seconds before repeating the sequence. Because of the length of the brake lines and other factors, it may take 10 or more repetitions of the sequence to bleed each line properly. When necessary to bleed all 4 wheels, the correct order is right rear, left rear, right front and left front.


CAUTION
Do not move the vehicle until a firm brake pedal is achieved. Failure to properly bleed the system may cause impaired braking and the possibility of injury and/or property damage.

If the EHCU/BPMV requires bleeding, the following procedures may be used to free all trapped air from the component. The procedures differ because some models are equipped with external bleeders in addition to the internal bleeders. In either case, 3 combination valve depressor tools and a scan tool are required. The combination valve depressor tools are used to hold the internal passage (combination valve and EHCU/BPMV bleed accumulator) bleed stems open, allowing the entire system to be completely bled.

The combination valve tools are relatively inexpensive and should be available from various aftermarket companies.

The master cylinder reservoirs must be kept properly filled to prevent air from entering the system. No special filling procedures are required because of the anti-lock system.

When adding fluid, use only DOT 3 fluid. The use of DOT 5 or silicone fluids is prohibited. Use of improper or contaminated fluid may cause the fluid to boil or cause the rubber components in the system to deteriorate. Never use any fluid with a petroleum base or any fluid which has been exposed to water or moisture.

Finally, remember to always bleed the 4WAL brake system with the ignition OFF to prevent setting false trouble codes.

INTERNAL AND EXTERNAL BLEEDERS

See Figure 1



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Fig. Fig. 1: Bleeder valve on hydraulic unit

These models are equipped with a pair of internal bleeder and a pair of external bleeder screws. These external bleeders look like normal brake bleeders and are found on top of the unit. Like any bleeder screw, they MUST remain closed when the unit is not pressurized.

The internal bleed valves on either side of the unit must be opened 1 / 4 - 1 / 2 turn before bleeding begins. These valves open internal passages within the unit. The valve located on the left side (nearest the fender) is used for the rear brake section, while the valve on the right (nearest the engine) is used for the front brakes. Actual bleeding is performed at the two bleeders on the top of the EHCU module. The bleeders must not be opened when the system is not pressurized. The ignition switch must be OFF or false trouble codes may be set.

  1. Make sure the ignition is in the OFF position to prevent setting false trouble codes.
  2.  
  3. Open the internal bleed valves 1 / 4 - 1 / 2 turn each.
  4.  
  5. Install J-35856 or equivalent combination valve depressor tool on the left accumulator bleed stem of the EHCU. Install one tool on the right bleed stem and install the third tool on the combination valve (rear).
  6.  
  7. Inspect the fluid level in the master cylinder. Add fluid if needed.
  8.  
  9. Have an assistant slowly depress the brake pedal and hold it down.
  10.  
  11. Open the left bleeder on top of the unit. Allow fluid to flow until no air is seen or until the brake pedal bottoms.
  12.  
  13. Close the left bleeder, then have your assistant release the pedal slowly and wait 15 seconds.
  14.  
  15. Repeat these steps, starting with depressing the brake pedal (including the 15 second pause), until no air is seen in the fluid.
  16.  
  17. Tighten the left internal bleed valve to 60 inch lbs. (7 Nm).
  18.  
  19. Bleed air from the right bleeder screw on top of the EHCU in the same manner as the left screw.
  20.  
  21. When bleeding of the right port is complete, tighten the right internal bleed valve to 60 inch lbs. (7 Nm).
  22.  
  23. Remove the 3 special combination valve tools.
  24.  
  25. Check the master cylinder fluid level, and refill if necessary.
  26.  
  27. Bleed the individual brake circuits at each wheel starting at the right rear. Refer to the hydraulic brake bleeding procedure located in this section.
  28.  
  29. Switch the ignition ON and use the hand-held scanner tool to perform function tests on the system.
  30.  
  31. Evaluate the brake pedal feel and repeat the bleeding procedure if needed.
  32.  
  33. Carefully test drive the vehicle at moderate speeds; check for proper pedal feel and brake operation. If any problem is noted in feel or function, repeat the entire bleeding procedure.
  34.  

INTERNAL BLEEDERS ONLY



The ignition switch must be 1 / 4 - 1 / 2 turn before bleeding begins.

Because the EHCU/BPMV has no external bleeders, the unit can only be bled through the downstream bleeder screws (wheel cylinders/calipers). To accomplish this, the internal bleeder and the accumulator stems/combination valves must be opened to allow air/fluid to pass through the unit. The internal bleed valves on either side of the unit must be opened OFF or false trouble codes may be set.

  1. Make sure the ignition is in the OFF position to prevent setting false trouble codes.
  2.  
  3. If necessary, bleed the master cylinder assembly as directed in the hydraulic brake bleeding procedure found earlier in this section. Check and add additional fluid, as needed.
  4.  
  5. Open the internal bleed valves 1 / 4 - 1 / 2 turn each.
  6.  
  7. Install one J-39177 or equivalent combination valve depressor tool on the left accumulator bleed stem of the EHCU. Install one tool on the right accumulator bleed stem and install the third tool on the combination valve.
  8.  
  9. Properly bleed the wheel cylinders and calipers. Refer to the hydraulic brake bleeding procedure located in this section.
  10.  
  11. Remove the 3 special tools.
  12.  
  13. Check the master cylinder fluid level, and refill as needed.
  14.  
  15. Switch the ignition ON (engine not running) and use a scan tool to perform function tests on the system.
  16.  
  17. Repeat the wheel cylinder and caliper bleeding procedure to remove all air that was purged from the BPMV during the function tests.
  18.  
  19. Check for a firm brake pedal. If necessary, repeat the entire procedure.
  20.  
  21. Carefully test drive the vehicle at moderate speeds; check for proper pedal feel and brake operation. If any problem is noted in feel or function, repeat the entire bleeding procedure.
  22.  

 
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