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Toyota Maintenance: Brake Booster Replacement

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Brake problems can manifest themselves in a number of ways. Shoes or pads can wear out, leaks can develop in the master or slave cylinders, or the power booster on a power brake system could fail. In this case, the problem was the brake booster leaking vacuum on a 1994 Land Cruiser FZJ80.

The owner complained of loss of braking and excessively hard pedal pressure. A local brake shop diagnosed the problem as failure of both the brake booster and master cylinder, simultaneously. I drove the Cruiser a bit and found that the booster and brakes worked fine when I first pushed the pedal. But, if you took your foot off the pedal and quickly reapplied pressure, the brakes would still stop the vehicle. However, it took alot more pedal pressure. What I figured was happening was that the booster was leaking vacuum when the brakes were being applied. Each time the pedal was released, the vacuum in the booster would build back up if given sufficient time (5-10 seconds).

I've seen other booster failures. Some will leak all the time when they fail and you can hear them hissing. This particular failure didn't hiss alot and it was only leaking during the time the pedal was pressed.

A replacement booster turned out to range in cost from very expensive at the dealer to non-available at the cheaper parts stores. We sourced a quality rebuild from the local NAPA store and it took a day or two to get it in stock.

When we got the booster we found it varied slightly from our original. There were two types of boosters used on these Cruisers and the one we got had the slightly smaller canister and the vacuum port was in a bit different location. We proceeded with the install due to lack of time to order another one.

Our failed brake booster The new rebuilt brake booster

Removing the booster was fairly easy. We removed the four retaining nuts from inside the firewall. Then we pulled the clip and pin holding the rod clevis to the brake pedal and removed the return spring. We also removed the four nuts securing the master cylinder to the brake booster and pulled the master off the booster and out of the way as much as the brake lines would allow. The rubber vacuum line was pulled off the booster and the booster slowly worked out of the firewall area. It was a tight squeeze but we got it out in a minute or two.

Four bolts retaining booster Pedal and linkage parts Removing the brake booster Old and new boosters Difference in vacuum ports

Before installing the new booster on the firewall, we moved the rod clevis from the old booster to the new one. With the booster bolted to the firewall we checked and adjusted the length of the pin between the booster and the master. If it is too short, the booster won't push on the master piston sufficiently. If the rod is too long, the master piston will have pressure applied to it even without having pressure on the brake pedal. With the rod adjusted, the master was bolted back onto the booster and the vacuum line reconnected. We had to do a little hose twisting and slight rerouting, but were able to use the same hose on the new booster.

Rod for pedal clevis Pin between master and booster New booster installed

We reattached the pedal hardware and checked the rod clevis adjustment to make sure there was a little freeplay at the pedal and checked the pedal travel to make sure the pedal did not travel too close to the floor. We also did a quick check to make sure the brake switch was properly adjusted.

The install took about an hour and required no special tools or skills. The replacement completely fixed the brake problem and the Cruiser was back on the road.

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