Ford Vans 1961-1988 Repair Guides

Diesel Brake Booster Vacuum Pump


Unlike gasoline engines, diesel engines have little vacuum available to power brake booster systems. The diesel is thus equipped with a vacuum pump, which is driven by a single belt off of the alternator.

Diesels are also equipped with a low vacuum indicator switch which actuates the BRAKE warning lamp when available vacuum is below a certain level. The switch senses vacuum through a fitting in the vacuum manifold that intercepts the vacuum flow from the pump. The low vacuum switch is mounted on the right side of the engine compartment, adjacent to the vacuum pump on E-250 and E-350 models.

The vacuum pump cannot be disassembled. It is only serviced as a unit (the pulley is separate).


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Fig. Fig. 1 Brake booster vacuum pump-diesel engine models

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Fig. Fig. 2 Exploded view of the vacuum pump mounting

  1. Remove the hose clamp and disconnect the pump from the hose on the manifold vacuum outlet fitting.
  3. Loosen the vacuum pump adjustment bolt and the pivot bolt. Slide the pump downward and remove the drive belt from the pulley.
  5. Remove the pivot and adjustment bolts and the bolts retaining the pump to the adjustment plate. Remove the vacuum pump and adjustment plate.
  7. To install, install the pump-to-adjustment plate bolts and tighten to 11-18 ft. lbs. (15-24 Nm). Position the pump and plate on the vacuum pump bracket and loosely install the pivot and adjustment bolts.
  9. Connect the hose from the manifold vacuum outlet fitting to the pump and install the hose clamp.
  11. Install the drive belt on the pulley. Place a 3 / 8 in. drive breaker bar or ratchet into the slot on the vacuum pump adjustment plate. Lift up on the assembly until the proper belt tension is obtained. Tighten the pivot and adjustment bolts to 11-18 ft. lbs. (15 -24 Nm).
  13. Start the engine and make sure the brake system functions properly.

The BRAKE light will glow until brake vacuum builds up to the normal level.