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Power Brake Booster Replacement

Contributed By: Carl Farley

The other day I jumped in the Grand Wagoneer for a trip to the store and when I started the Jeep and stepped on the brake to shift to drive I heard a loud hissing noise. After consulting the FSJ list it was determined that the power brake booster was bad. I contacted several parts stores and finally located a rebuilt booster for approximately $100.00. Replacing the booster was fairly straight forward but the location of the four bolts holding the booster to the firewall made it more challenging. In this tech article I will try to explain how to replace the booster.

The first step is to remove the vacuum hose from the booster. The hose is held in place by a spring type hose clamp. A pair of slip joint pliers will work nicely to open the clamp and pull the hose.

Once the hose is removed the next step is to remove the brake master cylinder from the booster. There are 2 nuts securing the master cylinder to the booster and the length of the studs necessitates a deep well socket. Once the nuts are removed pull the master cylinder forward until it clears the studs and separates from the booster.

Now the fun part. The four nuts securing the booster to the firewall are located under the dash above the steering column. It is a whole lot easier to reach these nuts if you remove the driver’s side seat. This can take more time than the booster replacement. Use plenty of penetrant on the bolts on the underside of the Jeep and make sure your tools are high quality. I tried to use a cheap set of open end wrenches and they spread a little and started to round the heads of the bolts. The front right and rear left seat bolts are located so that you can use a deep well socket but the others require a wrench. Moving the seat forward, backward and up will allow better access. Once the bolts are removed you can tilt the seat back and disconnect the wire to the seat motor and remove the seat.

With the seat out you can now lie in the floor of the Jeep and reach up under the dash to remove the nuts holding the power brake booster. Because of the tight quarters under the dash you can just barely turn the nuts. A deep well socket will work on two of the nuts but the other two will require a standard socket with the ratchet barely inserted. Once the nut is backed off a little you can the snap the socket on the ratchet and continue removing the nuts. Removing these four nuts took me about thirty minutes. An air ratchet would have really been nice.

After the four nuts holding the booster are off you can remove the cotter pin that fastens the booster rod to the brake pedal. With the rod disconnected it is time to wrestle the booster from it’s place in the engine compartment. It is a tight fit and the master cylinder and wiring harness as well as the cable for the cruise control are in the way, but the booster can be pulled out without disconnecting any of these.

Once the booster is out of the vehicle there is a casting that must be swapped off the old unit onto the new one. After the casting is swapped the installation of the booster is the reverse of removal.

I found that it is not necessary to bleed the brakes after the booster is replaced. This would be a one banana job but because of the tight quarters and location of the nuts I give it two bananas.

Carl B Farley
84 Grand Wagoneer "PITA"-Pain In The A$$

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