Replace brake booster - 1996 GMC Jimmy

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The power brake booster is a tandem vacuum suspended unit. Some models may be equipped with a single or dual function vacuum switch which activates a brake warning light should low booster vacuum be present. Under normal operation, vacuum is present on both sides of the diaphragms. When the brakes are applied, atmospheric air is admitted to one side of the diaphragms to provide power assistance.
REMOVAL & INSTALLATION

1994-97 Models
See Figures 1 and 2

1. Apply the parking brake and block the drive wheels.
2. Remove the master cylinder-to-power brake booster nuts, then reposition the master cylinder and combination valve out of the way; if necessary, support the master cylinder on a wire to prevent damaging the brake lines.

1. Disconnect the vacuum hose from the power brake booster.

Fig. Fig 1: Common power brake booster attachment

1. From under the dash, remove the retainer and washer from the brake pedal on 1994 utility models. On all other models, remove the retainer and brake switch from the brake pedal.
2. Disconnect the pushrod from the brake pedal.
3. From under the dash, remove the power brake booster-to-cowl retaining nuts.
4. Back under the hood, remove the power brake booster and the gasket from the cowl.

1. Position the booster to the cowl using a new gasket.
2. Install the bo oster retaining nuts and tighten to 16 ft. lbs. (22 Nm) 1994 utility models, 24 ft. lbs. (32 Nm) on 1994 pick-up models and 27 ft. lbs. (36 Nm) on all 1995-97 models.
3. Connect the pedal pushrod and install the washer or switch and the retainer.
4. Connect the vacuum hose.

Fig. Fig. 2: Checking the piston booster rod using the gauge tool

1. For all vehicles cover ed in this guide, gauge the booster rod:
   1. Apply 25 in. Hg (85 kPa) of vacuum using a hand held vacuum pump or apply maximum engine vacuum.
   2. Chec k the maximum and minimum rod lengths using J-37839 or an equivalent pushrod height gauge.
   3. If the piston is not within limits, install a service adjustable piston rod and adjust it to the correct length.
2. Reposition the master cylinder and combination valve bracket to the booster studs, then secure using the retaining nuts. For details, please refer to the master cylinder procedure located earlier in this section.
3. Start and run the engine, then check for proper booster operation.