Toyota Previa 1991-1997 Repair Information

Bleeding Brake System

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WARNING
Clean, high quality brake fluid is essential to the safe and proper operation of the brake system. You should always buy the highest quality brake fluid that is available. If the brake fluid becomes contaminated, drain and flush the system, then refill the master cylinder with new fluid. Never reuse any brake fluid. Any brake fluid that is removed from the system should be discarded.

It is necessary to bleed the hydraulic system any time the system has been opened or has trapped air within the fluid lines. It may be necessary to bleed the system at all four brakes if air has been introduced through a low fluid level or by disconnecting brake pipes at the master cylinder.

If a line is disconnected at one wheel only, generally only that brake needs bleeding. If lines are disconnected at any fitting between the master cylinder and the brake, the system served by the disconnected pipe must be bled.


WARNING
Do not allow brake fluid to splash or spill onto painted surfaces; the paint will be damaged. If spillage occurs, flush the area immediately with clean water.

MASTER CYLINDER



See Figures 1, 2 and 3

If the master cylinder has been removed, the lines disconnected or the reservoir allowed to run dry, the cylinder must be bled before the lines are bled. To bleed the master cylinder:



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Fig. Fig. 1: Fill the reservoir with the correct type of brake fluid



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Fig. Fig. 2: Depress the brake pedal ...

  1. Check the level of the fluid in the reservoir. If necessary, fill with fluid.
  2.  
  3. Disconnect the brake lines from the master cylinder. Plug the lines to keep dirt from entering.
  4.  
  5. Place a pan or rags under the cylinder.
  6.  
  7. Have an assistant slowly depress the brake pedal and hold it down.
  8.  
  9. Block off the outlet ports with your fingers. Be sure to wear gloves. Have the assistant release the pedal. Make a tight seal with your fingers; do not allow the cylinder to ingest air when the pedal is released.
  10.  



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Fig. Fig. 3: ... then, block the ports with your fingers and release the pedal

  1. Repeat three or four times.
  2.  
  3. Connect the brake lines to the master cylinder and top up the fluid reservoir.
  4.  

LINES AND WHEEL CIRCUITS



See Figures 4 through 7

  1. Insert a clear vinyl tube onto the bleeder plug at the wheel. If all four wheels are to be bled, begin with the right rear.
  2.  



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Fig. Fig. 4: Remove the rubber cap covering the bleeder plug

  1. Insert the other end of the tube into a jar which is half filled with brake fluid. Make sure the end is submerged in the fluid.
  2.  



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Fig. Fig. 5: Place a jar with clear tubing on the plug and begin the bleeding process

  1. Have an assistant slowly pump the brake pedal several times. On the last pump, have the assistant hold the pedal fully depressed. While the pedal is depressed, open the bleeder plug until fluid starts to run out, then close the plug.
  2.  

If the brake pedal is pumped too fast, small air bubbles will form in the brake fluid which will be very difficult to remove.

  1. Repeat this procedure until no air bubbles are visible in the hose. Close the bleeder port.
  2.  

Constantly replenish the brake fluid in the master cylinder reservoir, so that it does not run out during bleeding.

  1. If bleeding the entire system, repeat the procedure at the left rear wheel, the right front wheel and the left front wheel in that order.
  2.  
  3. Bleed the load sensing proportioning and bypass valve.
  4.  



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Fig. Fig. 6: Remove the bleeder plug on the proportioning valve ...



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Fig. Fig. 7: ... then bleed the valve

 
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