7 hours ago
The Challenge
In older Ford F-series trucks (like the 1995 F-700), the Lucas Girling hydraulic parking brake system uses brake “cans” attached to the backing plate. When the caging bolt—intended to compress and hold the spring—is broken, or if there's no resistance when turning the bolt, removing the can becomes tricky and potentially dangerous. The spring inside is under significant tension and could release suddenly. One operator, attempting to diagnose brake drag, discovered a lack of resistance whilecaging the spring when the engine was running and the brake engaged—until they cycled the parking brake with the engine off, which then allowed the spring pressure to be safely relieved and the bolt to function as expected. This revealed that the system's pressure state, not a physical break, was causing the issue .
Why It Happens
The engine running and brake applied pressurizes the hydraulic system, holding the brake spring engaged and preventing the caging mechanism from functioning. It's only when the pressure is relieved—by turning the engine off and cycling the parking brake—that the spring can be safely compressed again via the caging bolt .
Procedure for Safe Removal
System Background
Lucas Girling parking brakes rely on internal springs that wedge between piston components to apply the brake. Hydraulic pressure, supplied either via a pump or motor, compresses those springs to release the brake—a reverse of typical spring brake logic. Caging bolts are a manual backup method to hold the spring in the compressed (released) position, but they must only be used when the system is not under pressure .
Operators have warned that these springs hold tremendous energy—enough to cause serious injury if released unexpectedly .
Troubleshooting and Tips
Removing a Lucas Girling parking brake can without damaging components boils down to the system’s pressure state—not just mechanical malfunction. A thoughtful sequence—engine off and cycling the brake—relieves internal pressure, restoring caging bolt function. Understanding this behavior is key to safe and effective maintenance.
In older Ford F-series trucks (like the 1995 F-700), the Lucas Girling hydraulic parking brake system uses brake “cans” attached to the backing plate. When the caging bolt—intended to compress and hold the spring—is broken, or if there's no resistance when turning the bolt, removing the can becomes tricky and potentially dangerous. The spring inside is under significant tension and could release suddenly. One operator, attempting to diagnose brake drag, discovered a lack of resistance whilecaging the spring when the engine was running and the brake engaged—until they cycled the parking brake with the engine off, which then allowed the spring pressure to be safely relieved and the bolt to function as expected. This revealed that the system's pressure state, not a physical break, was causing the issue .
Why It Happens
The engine running and brake applied pressurizes the hydraulic system, holding the brake spring engaged and preventing the caging mechanism from functioning. It's only when the pressure is relieved—by turning the engine off and cycling the parking brake—that the spring can be safely compressed again via the caging bolt .
Procedure for Safe Removal
- Turn off the engine completely.
- Apply and release the parking brake a few times to relieve internal hydraulic pressure.
- Only then attempt to turn the caging bolt—you should feel spring resistance at this point.
- Once caged, the brake can can be removed without the spring force released suddenly.
System Background
Lucas Girling parking brakes rely on internal springs that wedge between piston components to apply the brake. Hydraulic pressure, supplied either via a pump or motor, compresses those springs to release the brake—a reverse of typical spring brake logic. Caging bolts are a manual backup method to hold the spring in the compressed (released) position, but they must only be used when the system is not under pressure .
Operators have warned that these springs hold tremendous energy—enough to cause serious injury if released unexpectedly .
Troubleshooting and Tips
- Don’t assume the caging bolt is broken. Hydraulic pressure can mask its resistance.
- Cycle the parking brake OFF (engine stopped) to relieve pressure before attempting any physical release.
- If the bolt truly is broken (unlikely in most cases), alternatives include using hydraulic pressure techniques or properly routed hoses to balance pressure—but these are advanced and risky (the original poster didn't need them once the pressure was relieved) .
- Replace with new parking brake can assemblies if the old ones exhibit wear or damage.
Removing a Lucas Girling parking brake can without damaging components boils down to the system’s pressure state—not just mechanical malfunction. A thoughtful sequence—engine off and cycling the brake—relieves internal pressure, restoring caging bolt function. Understanding this behavior is key to safe and effective maintenance.
