Terex TA30 with ZF 6WG‑310 Transmission: Diagnosing Leaks and Preventive Maintenance

[MikePhua]

Introduction to the ZF 6WG‑310 Transmission in the TA30
The Terex TA30 articulated truck uses the ZF 6WG‑310 powershift transmission—an automatic, torque‑converter design with six forward gears and integrated hydraulic retarder and diff-lock controls. Built for durability in heavy off‑road applications, this transmission relies on properly sealed valve assemblies and hydraulic circuits to operate reliably.
Understanding Where Leaks Occur and Why
A common issue reported involves leaks from the so‑called "gear shift housing" on the right side of the torque converter case. Despite its name, this component actually serves as the retarder or converter cooling valve. It handles low pressures—typically below 6 bar (~87 psi)—which should not generate leaks under normal conditions.
The valve cover gasket (referred to as gasket #6 or gaskets 12/13 depending on layout) is often the source of leaks. Frequent thermal cycling, minor seal material breakdown, or improper installation can cause seepage. Because these seals are small and operate under spring preload rather than high hydraulic pressure, they’re rated up to around 130 °C.
Key Diagnostic Steps for Transmission Leaks

• Identify the component as retarder or converter‑cooler valve, not a gear shift module.
  
• Visually inspect for oil stains between the valve cover and transmission housing.
  
• Remove and reseat the housing cover using high‑temperature gasket material if original gasket is worn.
  
• Inspect cooling hoses and fittings from torque converter to cooler and retarder circuit—they may host minor leaks.
  
• Check overall cooler and lubrication circuit integrity; although pressures are low, vibration and heat may promote gasket failure.
  

Common Root Causes

• Aged or brittle gaskets exposed to high coolant temperatures.
  
• Improper fit or torque during past servicing, leading to gasket compression loss.
  
• Heat cycling over years causing seal shrinkage or warping.
  
• Hose connector leaks upstream affecting pressure in the valve assembly, even at low psi.
  

Technical Terms Explained

• Retarder Valve Assembly: A housing that controls flow through converter cooling circuit and retarder engagement—not a gear selector.
  
• Converter‑cooler Circuit: Hydraulic line routing transmission fluid from converter through a cooler then to retarder or sump.
  
• Gasket Material: High-temperature seal material used between mating housing faces to prevent fluid seepage.
  
• Spring Preload: Mechanism where a spring, not fluid pressure, holds the valve cover in place under light load.
  

Field Repair Example
One TA30 owner traced constant oil drip from the valve cover housing. After removing the cover, cleaning mating surfaces, and cutting a new cover gasket, the leak stopped. The small spring only applied preload, confirming no high-pressure forcing; repairing the seal resolved the issue without further teardown.
Maintenance & Repair Checklist

• Remove and reseat valve cover using high‑temp gasket material.
  
• Inspect cooler hoses and fittings for signs of seepage.
  
• Confirm that downstream circuits (to retarder or lubrication) are intact.
  
• Monitor operating temperatures; ensure coolant or transmission fluid not overheating beyond 130 °C.
  
• Record serial numbers and gasket types for future rebuild consistency.
  

Preventive Measures

• Replace small retarder or converter valve gaskets periodically during transmission service due to thermal stress.
  
• Use OEM‑recommended gasket material rated for high temperature.
  
• Inspect valve cover torque specs after thermal changeover periods.
  
• Flush cooler and converter circuits during routine service to avoid debris buildup around valve seals.
  

Conclusion
Leaks from the TA30’s ZF 6WG‑310 transmission are most often traced to the retarder/cooler valve cover gasket—an assembly not under high hydraulic pressure but prone to seal wear from heat cycling. Repair involves resealing the cover with high‑temp gasket material, ensuring fittings and hoses upstream are sound, and keeping operating temperatures within specification. Addressing this proactively preserves transmission integrity and avoids downtime for Terex operators.
Let me know if you’d like help sourcing gasket part numbers or reviewing other transmission-related fault signs.