Mazda 323/626/929/GLC/MX-6/RX-7 1978-1989

Power Brake Booster

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REMOVAL & INSTALLATION



The booster can be rebuilt, although several special tools are necessary. Refer rebuilding to an outside repair facility.

  1. Remove the master cylinder as described earlier in this section.
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  3. Disconnect the vacuum hose from the booster. On most late model cars, there is a check valve pressed into the vacuum hose that you will not be able to see. (On 626s and MX-6s with electronically controlled transaxles, and on 929s, the check valve is visible.) Before disconnecting the vacuum hose, note the direction of the arrow on the hose or on the valve. It should always be pointing toward the engine.
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  5. From inside the car, disconnect the push rod fork from the brake pedal by removing the clevis pin. Unfasten the attaching nuts, then remove the booster and gasket.
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  7. Install the brake booster with a new gasket and tighten the attaching nuts.
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  9. Connect the brake pedal linkage to the push rod fork. Grease the clevis pin.
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  11. Connect the vacuum hose in the proper direction and install the master cylinder. Bleed the system as described later in this section.
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ADJUSTMENTS



Pushrod Clearance

This procedure is required after rebuilding the master cylinders on 1983-89 models. It requires the use of a special tool since the clearance between the power brake unit pushrod and master cylinder piston cannot be measured when the two are assembled. For 1983-85 models, use Mazda tool no. 49-B002-765 or equivalent, and for 1986-89 models, use Mazda tool no. 49-F043-001 or equivalent. Since this is a simple adjustment, you might find that, if the tool is expensive, it would actually be cheaper to take the brake unit and rebuilt master cylinder to a qualified mechanic to have it performed. On 1986-89 models, you will also need a vacuum pump in addition to the special tool.

1983-85 MODELS

See Figure 1

  1. Set the unit on the end of the master cylinder with the head of the adjusting bolt upward. Make sure both legs rest on the master cylinder mounting flange, then turn the bolt downward until it just touches the bottom of the pushrod recess in the piston.
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  3. Turn the unit upside down and rest the other ends of the legs on the mounting flange on the power brake unit. There should be no vacuum in the unit. If there is any gap between the power brake unit pushrod, loosen the pushrod locknut and turn the pushrod until it just touches the head of the bolt. Tighten the locknut. This will ensure a pushrod-to-piston clearance of 0.016-0.024 in. (0.4-0.6mm) on the 626, 0.004-0.020 in. (0.1-0.5mm) on the GLC, and 0.004-0.012 in. (0.1-0.3mm) on the RX-7.
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Click image to see an enlarged view

Fig. Fig. 1: Install the power brake unit with clearance between the pushrod and primary piston (GLC shown, others similar)

1986-89 MODELS
  1. Set the special tool on the end of the master cylinder with the head of the adjusting bolt upward. Make sure both legs rest on the master cylinder mounting flange, then then turn the bolt downward until it just touches the bottom of the pushrod recess in the piston.
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  3. Disconnect the vacuum hose from the power brake unit and connect a vacuum source to the end of the hose. Apply 19.7 in. Hg (66.5 kPa) of vacuum to the power brake unit.
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  5. Turn the unit upside down and rest the other ends of the legs on the mounting flange on the power brake unit. Check the clearance between the end of the gauge and the pushrod of the power brake unit. There must be no clearance. Loosen the pushrod locknut and turn the pushrod until all the clearance is removed.
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