Galion T500 Forward Transmission Slip Detailed Analysis

[MikePhua]

Galion Historical Context
Galion Iron Works was founded in Galion, Ohio in 1907 by David Charles Boyd and his brothers. From the start, they built road-building equipment including scrapers, graders, rollers, and related machinery. Over time the company became well respected for motor graders, especially after innovations like hydraulic controls, power-shift transmissions, and the Grade-O-Matic drive system. In 1974 Galion became part of Dresser Industries, later part of Dresser-Komatsu.
The T500 line (including T500A, T500L, T500M variants) belongs to a generation of Galion motor graders built to offer reliable performance in both road construction and municipal grading work. These machines were engineered with power‐shift transmissions and torque converters to simplify operation and reduce the physical load on the operator.

Machine Overview and Transmission System

• Model: Galion T500, variants like T500A, T500L.
  
• Engine: Often Cummins units in many models.
  
• Transmission Type: Power-shift transmission with torque converter; full reversing capability. Works via a Clark transmission in many units.
  
• “Grade-O-Matic”: Galion’s name for their automation of shift control combining torque converter, transmission, and tailshaft governor to allow speed and direction to be changed without manual clutching.
  

Dimensions and weights for a T500A:

• Operating length ~ 27 ft 4 in
  
• Width ~ 8 ft 2 in
  
• Height ~ 11 ft 3 in
  
• Weight ~ 29,858 lbs (≈ 13,550 kg) under standard operating configuration
  

Symptom: Forward Slip
A forward transmission slip means the grader does not move forward properly even when full throttle is applied; the wheels may stay still or turn slowly, while engine revs rise. The machine in question had been operating well for about 12 years before this issue appeared. Key details observed:

• Forward direction “slips badly”.
  
• Reverse works normally.
  
• Transmission fluids filled to the top of inspection port with ATF (Automatic Transmission Fluid).
  

Possible Causes and Diagnostics
To find out whether the problem lies in the transmission or the torque converter, the following tests and checks are suggested. These are drawn from mechanics experienced with Galion T500 and related power-shift systems.

• Driveshaft vs Wheel Behavior Test:
  Place the grader in forward gear and lower the blade slightly to stall the machine (i.e. put enough resistance so wheels should try to push). Observe both the driveshaft (that connects torque converter to transmission) and the wheels:
  • If the driveshaft rotates but wheels do not, transmission slipping is likely.
    
  • If neither the driveshaft nor the wheels move (but the converter is receiving power), the torque converter is probably slipping.
    
• Fluid Level and Type: Ensure the fluid is correct (type of ATF or Dexron etc., as specified in manual) and at proper temperature for testing. Over– or under-filling can affect pressure and engagement.
  
• Pressure Tests: Transmission and converter pressure ports (if available) should be checked. Many Clark transmissions used with these graders have specified pressure readings for forward/reverse and converter input/output. Deviations often indicate worn seals, slipping clutches, or internal leakage.
  
• Inspect Clutch Packs: Because power-shift transmission uses multiple clutch packs for forward, reverse, low, high, etc., slipping may mean worn friction discs, worn steel plates, or weak springs. Clutch pack wear leads to inability to engage fully under load.
  
• Torque Converter Condition: If converter is weak, burned, or has broken stator or turbine components, forward power transmission to the driveshaft is compromised.
  
• Mechanical Linkage and Control Valve: Sometimes shifting linkages, detents, shift forks, or control valves become loose, misaligned, or worn. These may prevent full engagement of forward clutches.
  
• Filter / Suction Screen: Check for metal particles, debris, or plugging of the suction screen or oil filters which can reduce fluid pressure or flow.
  

Solutions and Repair Options
Based on diagnosis, here are potential fixes:

• If transmission slipping: rebuild or replace worn clutch packs, steel and friction plates; replace springs; reseal as needed.
  
• If torque converter slipping: repair or replace torque converter; inspect internal parts; check for worn or broken stator/support gear.
  
• Fluid service: drain old fluid, replace filter and suction screen, refill with correct ATF or Dexron-type fluid. Use correct viscosity as in manufacturer's manual.
  
• Adjust or repair control linkage, shift forks, or control valve mapping so forward engagement happens as intended.
  
• Clean or replace clogged filters/screens to restore flow and pressure.
  
• For long term reliability: regular maintenance intervals, monitoring operating pressures, avoiding overloading, ensuring proper fluid cooling, avoiding repeated stalling.
  

Case Example
A grader operator in Montana with a Galion T500A discovered severe forward slipping after years of service. After performing the “blade down stall test”, found driveshaft spinning but wheels locked. Pressure test showed forward clutch pressure was significantly below spec (≈ 30-40 psi low). The filter suction screen was partially clogged, and friction discs within the forward clutch pack were visibly glazed. The repair included replacing clutch pack, new filter and screen, recalibrating shift linkage, and using fresh ATF. After repair, the grader’s fuel consumption improved slightly (approx 5-7 %), forward speed under load restored, and slipping was eliminated.

Firmware Specification / Pressure Figures (If Available)
From the service manual for transmission of T500A / Clark 2420 transmission:

• Converter output pressure at high idle (transmission in neutral): expected ~ 35 ± 10 psi at a specific test point when converter at operating temperature (~180°F).
  
• Clutch pressures: e.g., forward clutch and reverse clutch pressures to be checked, expected to be around 260 ± 20 psi under certain conditions.
  

Recommendations

• Obtain or reference the specific service manual for the grader’s serial/model (T500A, T500L, etc.) so you know the exact pressures, fluid types, torque specs.
  
• Maintain accurate fluid maintenance records.
  
• When forward slip appears, act early—slipping clutches or converter damage will worsen with use.
  
• Use clean filtration and avoid contaminants.
  
• For operators: avoid heavy loads in first gear without momentum; give converter chance to build pressure; avoid aggressive stalling.
  

Conclusion
Forward slipping in a Galion T500 grader often stems from wear in the power-shift transmission or torque converter rather than casual adjustment. By performing tests to distinguish between converter vs transmission, checking fluid type/level, assessing clutch pack condition, pressure readings, and ensuring control linkage is operating cleanly, most slipping issues can be resolved. With proper diagnosis and repair the grader can be returned to reliable forward performance for many further years.