Masseynut(Australia)
Member
Your MF 399 will be a shuttle model incorporating a four wheel drive "pod".
The four wheel drive system in these tractors uses pressure oil directed thru a solenoid activated control valve to disengage the 4WD pod. Spring pressure holds the arrangement in 4wd.
You said your problem was intermittent engagement and dis-engagement of the 4wd while in motion. There are a few things to check here.
First, it must be remembered that this tractor has 4 wheel braking, meaning that when the brake pedal is depressed, it breaks the electrical circuit to the 4WD solenoid. Check to see that the brake light switch is working and adjusted correctly, (located above the pedals).
If this checks out ok, proceed to the 4wd circuit. Check that the 4wd switch is functioning correctly. A test light will help here. The 4wd solenoid may also be the culprit. I'd suggest swapping the 4wd solenoid with the diff-lock solenoid and test run the tractor again.
If nothing shows in these checks, I'd run a "hotwire" directly to the 4wd solenoid. This will deliberately supply 12 volts to the solenoid at all times, ensuring the uninterrupted power supply to the solenoid. This isolates the 4wd solenoid from the other electrical components. Run the tractor again and check if the problem is still occurring.
If you are satisfied that the electrical side of the 4wd is working correctly, the problem can then be attributed to the oil supply to the pod, or a mechanical problem with-in the pod.
Remember, you will not be able to rotate the front axle with the engine "off", because, as I said before, the pod needs oil flow and pressure to disengage the 4wd.
Hope this helps with your diagnosis,
regards, Evan.
The four wheel drive system in these tractors uses pressure oil directed thru a solenoid activated control valve to disengage the 4WD pod. Spring pressure holds the arrangement in 4wd.
You said your problem was intermittent engagement and dis-engagement of the 4wd while in motion. There are a few things to check here.
First, it must be remembered that this tractor has 4 wheel braking, meaning that when the brake pedal is depressed, it breaks the electrical circuit to the 4WD solenoid. Check to see that the brake light switch is working and adjusted correctly, (located above the pedals).
If this checks out ok, proceed to the 4wd circuit. Check that the 4wd switch is functioning correctly. A test light will help here. The 4wd solenoid may also be the culprit. I'd suggest swapping the 4wd solenoid with the diff-lock solenoid and test run the tractor again.
If nothing shows in these checks, I'd run a "hotwire" directly to the 4wd solenoid. This will deliberately supply 12 volts to the solenoid at all times, ensuring the uninterrupted power supply to the solenoid. This isolates the 4wd solenoid from the other electrical components. Run the tractor again and check if the problem is still occurring.
If you are satisfied that the electrical side of the 4wd is working correctly, the problem can then be attributed to the oil supply to the pod, or a mechanical problem with-in the pod.
Remember, you will not be able to rotate the front axle with the engine "off", because, as I said before, the pod needs oil flow and pressure to disengage the 4wd.
Hope this helps with your diagnosis,
regards, Evan.
