Kubota 9540 steering drifts

[Dave M7040]

It never hurts to rule out some of the basics in vehicle tracking.
Ensure that tire pressure are the same assuming the tires are the same brand and age.
From my M7040 shop manual:Toe-in Factory spec. 2.0 to 8.0 mm 0.078 to 0.315 in.
Having a "toe out" condition especially where there is one wheel responsible for the out can produce wandering or pull to one side.
Others have dealt with the hydraulic side of the steering.
I regularly drive my M7040 for more than an hour on a mix of paved and gravel roads, sometimes with two wheels on the gravel shoulder and two on the pavement and am not having to be constantly steering it.
Dave M7040

 

[ruffdog]

Some people are talking about loose steering parts, some are talking about pulling to one side. What the OP is talking about is the steering wheel slowly working its way around while the tractor is driving down the road. These tractors have NO steering box connected directly to the front wheels. Instead, they have hydraulic lines going to a cylinder(s) that will turn the front wheels.

 

[MHarryE]

Some people are talking about loose steering parts, some are talking about pulling to one side. What the OP is talking about is the steering wheel slowly working its way around while the tractor is driving down the road. These tractors have NO steering box connected directly to the front wheels. Instead, they have hydraulic lines going to a cylinder(s) that will turn the front wheels.

That's right, and zero leak hydraulic systems are complicated to design, especially where there is movement (steering wheel turning) involved. I have had a machine with another solution, totally electronic control of hydraulic steering. Turn the steering wheel for a 30 degree turn angle and the wheels turn to the precise angle fed back by duplicate sensors. Return to straight and it is straight. Some very large tractors incorporate such a device. But a HMU (Hand Metering Unit) is going to have some leakage, and the higher the pressure involved in steering the greater the leakage.