Bobcat T630 Drive Motors Not Engaging – A Deep Dive Into Possible Causes

[MikePhua]

Symptoms and Initial Context
On a Bobcat T630 tracked loader, a reported issue involves the drive motors “not engaging,” while lift and tilt functions still operate normally. The customer also reports a very slow‑spinning cooling fan at idle, no error codes, and the machine being far from the dealer (in this case, 400 km away), making troubleshooting more challenging.
The T630 is a Tier‑4 (or Tier‑IT4) compact track loader with an approximate travel system relief pressure of 241.5 bar and standard hydraulic system parameters defined by Bobcat specs.
Likely Root Cause: Low Charge Pressure
One of the most common causes for drive motors to refuse to engage is a drop in charge pressure in the hydrostatic system. Charge pressure is critical: it’s the internal hydraulic pressure that ensures the hydrostatic pump and drive motors remain properly lubricated and can build torque. Forum responders suggest that the issue “sounds like … a charge pressure problem.”
Where to Look: Charge Filter
In many Bobcat compact track loaders (including the T630), there is a charge filter located on or near the cooling‑fan motor. Over time, this filter can become clogged with debris, restricting charge flow. According to a senior forum member:

“Remove the charge filter … and check for debris. … it may be a spin-on filter or the canister type.”

If that filter is blocked, the charge pump cannot maintain system pressure, causing the drive motors not to engage properly.
Possible Fault in Fan Solenoid
Another reported fix (by forum users) is related to the cooling fan circuit: replacing the fan solenoid. Suggested part numbers include 7316520 or 7010979.
The slow fan behavior could be a symptom or a contributing factor. If the fan circuit is compromised, it might indicate electrical issues that are also affecting the charge hydraulic circuit, or simply that the solenoid isn’t fully activating due to low system pressures.
Diagnostic Strategy Step‑by‑Step
To isolate and resolve the issue, here’s a practical diagnostic approach:

• Monitor Charge Pressure
  If your machine has the deluxe display, you may be able to view charge pressure in real time. A sudden drop or inability to maintain pressure under load strongly suggests a charging system problem.
  
• Inspect and Replace the Charge Filter
  Unmount the filter, inspect for metal particles or blockages, and clean or replace it.
  
• Check and Possibly Replace the Fan Solenoid
  Swap in a known-good solenoid to see if the fan behavior and system drive pressure improve.
  
• Verify Maintenance Records
  Refer to the Bobcat T630 maintenance schedule: the hydrostatic drive motor fluid should be replaced per the prescribed interval.
  
• Inspect Drive Motor Case Drain Filters
  Dirty or clogged case drain filters can cause back‑pressure in the motors, leading to internal leakage and loss of engagement. Common advice across related skid-steer models is to check these filters for metal flakes or contamination.
  
• Perform a Load Test
  With the machine on a stand, apply throttle and attempt to engage drive. Measure the case drain flow or check pressure drop to see if there is internal leakage or insufficient charge recovery.
  

Common Underlying Failures
Based on field reports and technical discussion, some of the next-level causes may include:

• Worn or failing charge pump — unable to build or hold charge due to wear
  
• Drive motor seal failure — leading to internal leakage and inability to build torque
  
• Poor preventative maintenance — infrequent filter changes or skipping case-drain service leads to contamination and premature failure
  
• Design or casting issues — historical reports (though more common in other models) describe problems with improperly machined internal castings or fittings in drive motors.
  

Real-World Implications and Cost
If left unaddressed, low charge pressure conditions can lead to:

• Drive motors not turning under load or at all
  
• Metal contamination as internal components wear, leading to more severe hydraulic damage
  
• Elevated risk of motor failure, requiring costly replacement or rebuild
  

Because the drive motor is a high-cost component, addressing upstream issues like charge filters, solenoids, or pressure problems early may prevent full motor failure.
Preventive Maintenance Recommendations
To minimize the risk of this issue recurring:

• Replace the charge filter at regular intervals consistent with Bobcat’s service schedule
  
• Inspect case drain filters for contamination, especially after any unusual behavior
  
• Monitor system pressures and temperatures in daily operation
  
• Maintain clean cooling and fan systems, since overheating or low fan output can contribute to fluid degradation
  

Conclusion
In a Bobcat T630 where the drive motors won’t engage, but the hydraulics for lift and tilt still work, and the fan is sluggish, the most likely culprit is a charge pressure problem—often caused by a clogged charge filter or a failing solenoid. Proper diagnosis involves pressure measurement, filter inspection, and possibly solenoid replacement. Addressing these proactively can save tens of thousands in potential drive motor rebuilds and avoid unexpected downtime.
If the issue persists after these steps, further investigation into the charge pump or internal motor leakage may be required. But beginning at the charge filter is the lowest-cost, highest-impact troubleshooting path.