Mazda Trucks 1994-1998 Repair Guide

Bleeding The Brakes

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Navajo & B Series Pick-up Models

See Figures 1 and 2


WARNING
Vehicles with 4-wheel anti-lock brakes require an Anti-lock Brake Adapter (T90P-50-ALA) and Jumper (T93T-50-ALA) in order to bleed the master cylinder and the Hydraulic Control Unit (HCU). Failure to do so will trap air in the HCU unit, eventually causing a spongy pedal. The tools are not required for caliper or wheel cylinder bleeding procedures.

When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the lines and cause spongy pedal action (because air can be compressed and brake fluid cannot). To correct this condition, it is necessary to bleed the hydraulic system after it has been properly connected to be sure all air is expelled from the brake cylinders and lines.

When bleeding the brake system, bleed one brake cylinder at a time, beginning at the cylinder with the longest hydraulic line (farthest from the master cylinder) first. ALWAYS Keep the master cylinder reservoir filled with brake fluid during the bleeding operation. Never use brake fluid that has been drained from the hydraulic system, no matter how clean it is.

It will be necessary to centralize the pressure differential value after a brake system failure has been corrected and the hydraulic system has been bled.

The primary and secondary hydraulic brake systems are individual systems and are bled separately. During the entire bleeding operation, do not allow the reservoir to run dry. Keep the master cylinder reservoir filled with brake fluid.

  1. Clean all dirt from around the master cylinder fill cap, remove the cap and fill the master cylinder with brake fluid until the level is within 1 / 4 in. (6mm) of the top edge of the reservoir.
  2.  
  3. Clean off the bleeder screws at all 4 wheels. The bleeder screws are located on the inside of the brake backing plate, on the backside of the wheel cylinders and on the front brake calipers.
  4.  
  5. Attach a length of rubber hose over the nozzle of the bleeder screw at the wheel to be done first. Place the other end of the hose in a glass jar, submerged in brake fluid.
  6.  



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Fig. Fig. 1: Bleed the rear brakes first, ensuring that no air bubbles remain visible moving through the tubing



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Fig. Fig. 2: Bleed the caliper until you can see clean, air bubble free brake fluid moving through the tube

  1. Open the bleeder screw valve 1 / 2 - 3 / 4 turn.
  2.  
  3. Have an assistant slowly depress the brake pedal. Close the bleeder screw valve and tell your assistant to allow the brake pedal to return slowly. Continue this pumping action to force any air out of the system. When bubbles cease to appear at the end of the bleeder hose, close the bleeder valve and remove the hose.
  4.  
  5. Check the master cylinder fluid level and add fluid accordingly. Do this after bleeding each wheel.
  6.  
  7. Repeat the bleeding operation at the remaining 3 wheels, ending with the one closet to the master cylinder. Fill the master cylinder reservoir.
  8.  

MPV Models

Master Cylinder

Due to the location of the fluid reservoir, bench bleeding of the master cylinder is not recommended. The master cylinder is to be bled while mounted on the brake booster. If the fluid reservoir runs dry, bleeding of the entire system will be necessary. Two people will be required to bleed the brake system.

  1. Fill the brake fluid reservoir with clean brake fluid. Disconnect the brake tube from the master cylinder.
  2.  
  3. Have a helper slowly depress the brake pedal. Once depressed, hold it in that position. Brake fluid will be expelled from the master cylinder.
  4.  


CAUTION
When bleeding the brakes, keep your face away from the area. Spraying fluid may cause facial and/or visual damage. Do not allow brake fluid to spill on the car's finish; it will remove the paint.

  1. While the pedal is held down, use a finger to close the outlet port of the master cylinder. While the port is closed, have the helper release the brake pedal.
  2.  
  3. Repeat this procedure until all air is bled from the master cylinder. Check the brake fluid in the reservoir every 4-5 times, making sure the reservoir does not run dry. Add clean DOT 3 brake fluid to the reservoir as needed. All air is bled from the master cylinder when the fluid expelled from the port is free of bubbles.
  4.  
  5. Connect the brake tube to the port on the master cylinder. Add clean fluid to fill the reservoir to the appropriate level.
  6.  

Calipers
1994

See Figure 2

  1. Raise and safely support the vehicle.
  2.  
  3. Fill the master cylinder reservoir with fresh brake fluid. Don't let the reservoir run dry during the bleeding process.
  4.  
  5. Have an assistant slowly pump the brake pedal several times and then apply a steady pressure to the brake pedal.
  6.  
  7. Attach a clear flexible hose to the bleed screw and place it into a clear container partially filled with brake fluid. Loosen the brake bleeder screw at the brake caliper or wheel cylinder and allow the fluid to flow. Close the bleeder screw.
  8.  
  9. Repeat this procedure for each wheel, until no air bubbles appear in the brake fluid. Begin the bleeding procedure at the wheel furthest (right rear) from the master cylinder and then work toward the wheel closest (left front) to the master cylinder.
  10.  
  11. Lower the vehicle.
  12.  
  13. Check the fluid level in the master cylinder and add fluid, if necessary. Road test the vehicle and check the brake performance.
  14.  

1995-98

See Figure 2

  1. Fill the master cylinder with fresh brake fluid. Check the level often during this procedure. Raise and safely support the vehicle.
  2.  
  3. Starting with the wheel furthest from the master cylinder, remove the protective cap from the bleeder and place where it will not be lost. Clean the bleeder screw.
  4.  
  5. Start the engine and run at idle.
  6.  


CAUTION
When bleeding the brakes, keep face away from the brake area. Spewing fluid may cause physical and/or visual damage. Do not allow brake fluid to spill on the car's finish; it will remove the paint.

  1. If the system is empty, the most efficient way to get fluid down to the wheel is to loosen the bleeder about 1 / 2 - 3 / 4 turn, place a finger firmly over the bleeder and have a helper pump the brakes slowly until fluid comes out the bleeder. Once fluid is at the bleeder, close it before the pedal is released inside the vehicle.
  2.  

If the pedal is pumped rapidly, the fluid will churn and create small air bubbles, which are almost impossible to remove from the system. These air bubbles will accumulate and a spongy pedal will result.

  1. Once fluid has been pumped to the caliper, open the bleed screw again, have the helper press the brake pedal to the floor, lock the bleeder and have the helper slowly release the pedal. Wait 15 seconds and repeat the procedure (including the 15 second wait) until no more air comes out of the bleeder upon application of the brake pedal. Remember to close the bleeder before the pedal is released inside the vehicle each time the bleeder is opened. If not, air will be introduced into the system.
  2.  
  3. If a helper is not available, connect a small hose to the bleeder, place the end in a container of brake fluid and proceed to pump the pedal from inside the vehicle until no more air comes out the bleeder. The hose will prevent air from entering the system.
  4.  
  5. Repeat the procedure on the remaining calipers in the following order:
    1. Left front caliper
    2.  
    3. Left rear caliper
    4.  
    5. Right front caliper
    6.  

  6.  
  7. Hydraulic brake systems must be totally flushed if the fluid becomes contaminated with water, dirt or other corrosive chemicals. To flush, bleed the entire system until all fluid has been replaced with the correct type of new fluid.
  8.  
  9. Install the bleeder cap on the bleeder to keep dirt out. Always road test the vehicle after brake work of any kind is done.
  10.  

 
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