Slows down on one side when warmed up

puller270

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Jun 8, 2025
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My jcb 320t with about 2000hrs on it resent hydraulic oil and filter change
Slows down on right side after half hour with rotary mower left side is fine
Does anyone have suggestions where I look for problem
Thanks
 
Check the hydraulic lines and connections on the right side for any leaks or blockages. Also, inspect the right-side hydraulic pump and motor for any wear or damage. Lastly, ensure that the filter is properly installed and not causing any flow restrictions
 
Check the hydraulic lines and connections on the right side for any leaks or blockages. Also, inspect the right-side hydraulic pump and motor for any wear or damage. Lastly, ensure that the filter is properly installed and not causing any flow restrictions
Good tip! My brother's 2022 JCB 320T had the same problem, right side slowed down after about half an hour of mowing. He looked for leaks and found a bent hose near the motor. The filter was also not put in right after he changed it. After fixing both, it worked fine again.
 
Could be a weak drive motor starting to show itself, or possibly a case drain issue on that right side. Since it only shows up once it's warmed up, my guess is internal leakage as the oil thins. Before taking it farther, I'd say swap the drive hoses left to right and see if the problem follows and that's a good way to narrow it down to motor vs control side
 
This is a sign of a problem with one of the hydraulic drive pumps or the drive motor for that side. As the oil gets warmer and thinner, a pump or motor that is worn on the inside will lose efficiency and power. Explains why the machine works fine when it is cold and only has a problem after a while.

Another thing to consider is a faulty pressure relief valve. If the relief valve for the right side is opening at a lower pressure than it should, it will bleed off some of the hydraulic power. It is also possible that a valve is sticking when the oil gets to a certain temperature. Go check the pressures on both sides of the drive system to see if there is a difference.
 
Some JCB models use electronic proportional valves or sensors to control speed. If a sensor or valve acts up on the right, it might slow things down or cause jerky movements.
 
The issue is heat-related and is due to internal leakage in the hydraulic circuit for the right track. When the oil heats up, its viscosity decreases (it gets thinner), allowing it to bypass worn internal seals and components, leading to a loss of pressure and flow to the right drive motor. Check the non-hydraulic components first. This is the easiest.
 
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