Toyota Land Cruiser Brake Master Replacement and Upgrade
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|The Mammoth Project
Twisting it up
At one time or another, we've all experienced a mushy, sinking brake pedal. Often times, the culprit can be the brake master cylinder. The master cylinder is THE starting point in a hydraulic brake system. Mechanical force applied from the brake pedal is turned into fluid force from the master cylinder. This fluid moves in a path from the master cylinder, through the various steel (hard) and rubber (flexible) lines to cylinders located at each wheel. Nowadays, those wheel cylinders can be found as calipers in disc brake applications and wheel cylinders in drum brake vehicles.
Usually mounted to the firewall, and directly to the brake booster when power brakes are used, the master cylinder resembles that of one inside an engine. Inside the master cylinders bore is a piston. As the piston moves through the master cylinder's bore, fluid is transferred to the brake lines and distributed through the system.
What makes a brake master cylinder fail? Age: Over time, the rubber cups on the piston of the master cylinder wear and the cylinder will leak internally. This "bypassing" of fluid results in a spongy, soft-feeling brake pedal. Rust: Brake fluid attracts moisture like crazy. If left unchecked, rust can develop inside the bore of the master cylinder and cut the sealing cups.
In this article, we will discuss two items: replacement of the brake master cylinder and upgrading the brake system at the same time. For the purpose of this article, the vehicle is 4x4Wire's project vehicle, the Mammoth Project. The Mammoth Project is a 1987 Toyota Land Cruiser FJ60 that came equipped from the factory with a 7/8" bore diameter master cylinder. The time had come to replace the master as the brake pedal developed a mushy feel and braking performance had begun to suffer. As with any project, we saw the advantage in upgrading during this repair and set out to find a better replacement.
The beauty of working on Toyotas is their parts interchangeability. As in the case of our FJ60, we were able to upgrade the master cylinder without going outside of the Toyota family. After some research, we were able to find an original equipment Toyota master cylinder with a larger bore (1") that would bolt directly to the Mammoth Project's brake booster. As it turns out, the master cylinder from a 1988+ V6 4WD truck is the perfect application. This cast iron cylinder only required a slight bend in the front steel brake line and some simple re-wiring of the fluid level sensor located in the filler cap. Once installed, the larger bore of the V6 truck's master produced a firmer pedal feel. When the Mammoth Project's rear brakes are upgraded to discs, the larger cylinder will also move a bit more brake fluid. This is key to pedal feel and response as disc brake calipers require more fluid than do smaller drum-style wheel cylinders.
|Stock master cylinder installed||Original 7/8" master (L), New 1" bore master (R)|
Follow along as we replace the master cylinder on our FJ60 project truck and begin the upgrade process!
|Clean around master cylinder area||Removing retaining nuts|
Begin by giving yourself a clean and clear work area. Care must be taken to assure no contaminants like dirt enter the brake system. I like to spray the area around the fluid lines with a brake cleaning product prior to breaking them loose. Disconnect the fluid level sensor wiring that is integral to the reservoirs cap. Next, I remove all of the fluid from the old master cylinder. This makes the job a bit less messier. Place shop towels or rags below the master cylinder to keep any spilled brake fluid away from engine parts and paint. Brake fluid will ruin paint so use care and clean up spills immediately! Using a 10MM flare wrench (see picture), loosen the steel brake lines at the master cylinder. Using the correct wrench on these soft brass fittings is key to not rounding off their hexed edges. Gently bend the steel lines away from the master cylinder once they are free.
|10mm Flare-nut or "line" wrench||Removing fluid line fittings|
Depending on the vehicle, there may be some bracketry attached to the master cylinder. This bracketry may consist of electrical wiring or fluid distribution valve retainers. Regardless, study the routing of these items before removing them. In the case of the FJ60, a bracket is attached via the two lower (of 4 total) master cylinder to booster attaching nuts/studs. Using a socket and extension, remove these 4 bolts. Provided all of the above-mentioned items were removed, the master cylinder should be free from the vehicle.
|View of power brake booster with master cylinder removed|
At this point, it is time to prepare the new replacement master cylinder for installation. First, the master cylinder must be "bench bled." This process bleeds the air out of the master cylinder before it is installed. The master cylinder is clamped into a bench vise and filled with clean brake fluid. Bench bleeding kits that consist of hoses and threaded fittings can be purchased at most auto parts stores. Run the hoses back into the master cylinder's reservior. Activate the cylinder's piston by pushing it all the way forward with a screwdriver (See photo). Watch the fluid as it cycles back into the reservior. Keep pumping the fluid through until the large bubbles no longer appear in the fluid.
|Place the master cylinder in a vice||Bench bleeding master cylinder|
Once all of the air is bled from the master, it is time to install it. Slip the master onto the studs of the booster and install the retaining nuts and any additional items that were fastened to it. Snug the bolts down, then go to the steel fluid lines. On the Mammoth Project, the lines nearly lined up with the pick-up master cylinder. The forward line needed a slight bend applied to it. Thread the steel lines in and tighten with the flare wrench. The plug on the cap of the new master's reservior did not match the FJ60's harness. This was remedied by a simple wiring modification.
|Top view of modified cap and wiring||Side view of modified cap and wiring|
Once installed, the master will need one more bleeding procedure. With the aid of an assistant in the truck, push the pedal slowly all the way to the floor while cracking the steel lines loose. Any excess air will be bled out at this time. Be sure to tighten the fluid fittings before the assistant releases the brake pedal. Top off the brake fluid in the reservior to the "FULL" line and that's it! Be sure to test the feel of the brake pedal prior to a test drive. If the pedal still feels soft, additional bleeding at the master cylinder or wheels may be needed. Although rare, sometimes the master cylinder pushrod in the brake booster needs to be adjusted to either increase (not enough braking) or decrease (brakes dragging) braking application. See your repair manual for details and adjustment. There, one master cylinder replaced, step one of the Brake System Upgrade completed!