Troubleshooting Lucas Girling Hydraulic Brake Chambers

[MikePhua]

Background of Lucas Girling Brake Systems
Lucas Girling was a prominent British manufacturer of automotive and heavy-duty brake systems, with a legacy dating back to the early 20th century. Known for pioneering hydraulic and air brake technologies, the company supplied braking components to commercial trucks, buses, and military vehicles across Europe and North America. In the 1990s, Girling’s assets were absorbed into larger entities like TRW and later ArvinMeritor, which continued to support legacy systems under various product lines.
One of the more specialized components in their catalog was the hydraulic brake chamber—often referred to as a “hydraulic maxi pot”—used in parking brake applications on medium-duty trucks like the Ford F600 and F700 series. These chambers were unique in that they operated using power steering fluid rather than traditional brake fluid or air pressure.
Terminology Annotation

• Hydraulic Maxi Pot: A brake chamber that uses hydraulic pressure to apply or release the parking brake. It contains a powerful internal spring that engages the brake when pressure is lost.
  
• DuraPark Brake: A proprietary parking brake system used in conjunction with hydraulic maxi pots, often found on rollback trucks and vocational vehicles.
  
• Backing Plate: The metal plate that houses brake components such as wheel cylinders, shoes, and springs. Loaded backing plates come pre-assembled for easier installation.
  

Symptoms of Sporadic Fluid Leakage
In one documented case, a 1989 Ford F600 rollback truck equipped with Lucas Girling brakes exhibited intermittent leakage of power steering fluid from the passenger-side brake chamber. The leak would appear suddenly, then disappear for days, with no clear pattern. This behavior is often caused by internal seal degradation, temperature-induced expansion, or contamination within the hydraulic system.
The chamber’s internal spring can exert significant force, and any compromise in the seal integrity may result in fluid being forced past the piston. Sporadic leaks may also be triggered by pressure spikes during braking or steering maneuvers, especially if the fluid reservoir is overfilled or the return lines are partially obstructed.
Inspection and Repair Options
Upon investigation, three repair paths were identified:

• Purchase a rebuild kit for approximately $48, which includes seals, gaskets, and internal components
  
• Exchange for a remanufactured unit at around $126, avoiding the complexity of spring reassembly
  
• Buy a brand-new chamber for $344, offering full reliability but at a premium cost
  

Rebuilding the chamber requires careful handling of the internal spring, which can be hazardous if not properly compressed. For this reason, many technicians prefer remanufactured units, which eliminate the risk and save time.
Recommendations for Safe Repair

• Always depressurize the hydraulic system before removing the chamber
  
• Use a spring compressor rated for high-force applications if rebuilding
  
• Flush the power steering fluid and inspect for metal shavings or discoloration
  
• Replace both chambers simultaneously to ensure balanced braking
  
• Inspect the DuraPark brake assembly for wear, especially the wheel cylinders and linkage
  

Field Experience and Technician Preferences
Veteran service managers often avoid rebuilding these chambers due to the risk and time involved. Instead, they opt for loaded backing plates—complete assemblies that include new wheel cylinders, shoes, and springs. This approach simplifies installation and ensures compatibility with modern hydraulic systems.
In Knoxville, Tennessee, one technician recalled servicing dozens of rollback trucks with Lucas Girling systems. After multiple failed rebuilds, he standardized his workflow to include full backing plate replacement and remanufactured brake pots. This reduced comebacks and improved customer satisfaction.
Compatibility and Parts Availability
Although Lucas Girling components are no longer manufactured under that name, parts are still available through ArvinMeritor and specialized suppliers. Many truck parts distributors stock hydraulic maxi pots and DuraPark components, though diagrams and manuals can be difficult to source.
Technicians recommend:

• Using OEM part numbers when ordering replacements
  
• Consulting with Haldex or Meritor engineers for technical support
  
• Verifying chamber dimensions and mounting bolt patterns before purchase
  

Anecdotes and Lessons Learned
In San Antonio, a fleet operator shared a story about a 1991 F700 with similar brake issues. After chasing leaks for months, he discovered that the fluid reservoir cap was venting improperly, causing pressure buildup. A simple cap replacement resolved the issue, highlighting the importance of system-wide diagnostics.
Another operator in Oregon found that his chamber leaked only during cold mornings. The culprit was a hardened seal that contracted in low temperatures, allowing fluid to escape until the system warmed up. Seasonal fluid changes and seal upgrades resolved the problem.
Conclusion
Lucas Girling hydraulic brake chambers, while effective in their era, require careful handling and modern diagnostic approaches. Sporadic leaks often stem from internal wear, pressure fluctuations, or system contamination. Whether choosing to rebuild, remanufacture, or replace, technicians must weigh safety, cost, and long-term reliability. With proper maintenance and informed decisions, these legacy systems can continue to serve reliably in medium-duty applications.