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| I've seen a number of posts on here that refer to steering problems on the Case 4490 and 4690 4WD tractors. Just thought I would give you my two cents on the issue.
On my 4690 the steering problem began as a bit of vibration that was hard to pinpoint. As the problem progressed, I noticed that the steering was oscillating slightly even though I wasn't moving the steering wheel. The problem was most noticable when going in a straight line. Took it to the dealer and they wanted to change the hydraulic pump but that didn't make sense to me so took it back home.
Did some sleuthing to figure out how the steering worked and discovered that Case used variable resistor sensors (also called potentiometers) for measuring the steering angle on the front and rear. This type of sensor tends to wear over time, especially in the area where it spends most of it's time (straight line steering, which is where my problem was). What had happened is that the sensors had developed a very small "dead spot" in the central position. If you test the sensors according to the Case service manual, they test OK. But if you do a very close check through the full range of motion, you find that the resistance doesn't change for a small angular distance which corresponds to straight line steering. This confuses the controller, since when it tells the wheel to move a bit from straight line steering (which the wheel does) the feedback from the sensor doesn't change because of the dead spot - so the controller tells the wheel to move some more. The sensor then gets out of the dead spot and the feedback from the sensor then tells the controller that the wheel moved too far, so the controller tells the the wheel to move back a bit. This goes on in a viscious cycle, which causes the tires to vibrate back and forth.
Bottom line is that the problem is probably a dead spot in the sensor, not the controller. You can test the sensors with an accurate ohm meter. If you're electronically inclined and understand how to calculate series and parallel resistances, you can actually solder an appropriate resistor in series with the sensor to move the dead spot out of normal operating range and correspondingly adjust the wheel sensor position (you may have to cut the plastic slots). | |
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4690 Steering
