Chrysler Full-Size Vans 1967-1988 Repair Guide

Power Brake Booster

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REMOVAL & INSTALLATION



Vacuum Assisted Booster

See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Transverse mounted power brake booster and related components-all models except B-350 school bus



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Fig. Fig. 2: Inline mounted power brake booster and related components-all models except B-350 school bus

  1. Remove the master cylinder.
  2.  
  3. Disconnect the vacuum hose from the power booster.
  4.  
  5. Disconnect the pushrod from the brake pedal.
  6.  
  7. Remove the power booster attaching nuts and remove the booster.
  8.  
  9. When installing the mounting nuts, tighten them to 16 ft. lbs. Connect the pushrod to the pedal. Coat the eyelet with Lubriplate® or equivalent.
  10.  

Hydro-Boost

See Figure 3

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Fig. Fig. 3: Exploded view of the Bendix Hydro-Boost power brake booster used on the B-350 school bus

Some 1981 and later B350 school buses and all diesel engine equipped vans use the Bendix Hydro-Boost system.

The power steering pump provides the fluid pressure to operate both the brake booster and the power steering gear.

The hydro-boost assembly contains a valve which controls pump pressure while braking, a lever to control the position of the valve and a boost piston to provide the force to operate a conventional master cylinder attached to the front of the booster. The hydro-boost also has a reserve system, designed to store sufficient pressurized fluid to provide at least 2 brake applications in the event of insufficient fluid flow from the power steering pump. The brakes can also be applied unassisted if the reserve system is depleted.


WARNING
Before removing the hydro-boost, discharge the accumulator by making several brake applications until a hard pedal is felt.


WARNING
Do not depress the brake pedal with the master cylinder removed!

  1. Remove the master cylinder from the Hydro-Boost unit. DO NOT DISCONNECT THE BRAKE LINES FROM THE MASTER CYLINDER!
  2.  

Position the master cylinder out of the way.

  1. Disconnect the 3 hydraulic lines from the Hydro-Boost unit.
  2.  
  3. Disconnect the pushrod from the brake pedal.
  4.  
  5. Remove the booster mounting nuts and lift the booster from the firewall.
  6.  


CAUTION
The booster should never be carried by the accumulator. The accumulator contains high pressure nitrogen and can be dangerous if mishandled! If the accumulator is to be disposed of, do not expose it to fire or other forms of incineration! Gas pressure can be relieved by drilling a1/16" hole in the end of the accumulator can. Always wear safety goggles during the drilling!

  1. Installation is the reverse of removal. Torque the booster mounting nuts to 25 ft. lbs.; the master cylinder nuts to 25 ft. lbs.; connect the hydraulic lines, refill and bleed the booster as follows:
    1. Fill the pump reservoir with ATF+3® II ATF.
    2.  
    3. Disconnect the coil wires and crank the engine for several seconds.
    4.  
    5. Check the fluid level and refill, if necessary.
    6.  
    7. Connect the coil wires and start the engine.
    8.  
    9. With the engine running, turn the steering wheel lock-to-lock twice. Shut off the engine.
    10.  
    11. Depress the brake pedal several times to discharge the accumulator.
    12.  
    13. Start the engine and repeat Step 5e.
    14.  
    15. If foam appears in the reservoir, allow the foam to dissipate.
    16.  
    17. Repeat Step 5e as often as necessary to expel all air from the system.
    18.  

  2.  

The system is, in effect, self-bleeding and normal vehicle operation will expel any further trapped air.

 
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