Posted by Owen Aaland on November 07, 2011 at 20:05:54 from (216.47.32.147):
In Reply to: 1486 t/a posted by IHMANKY on November 06, 2011 at 18:01:10:
You have the classic symptoms of a failing MCV pump.
Like Jim has already posted, the low side of the TA relies on a mechanical sprague clutch to dive the transmission. It also uses some hydraulically applied clutch disks to keep the tractor from free wheeling downhill. Those clutch disks also help keep the sprague centered so in your case it still works under load. The problem you have is that the MCV pump/hydraulic system is loosing pressure and that allows the sprague to get forced off center and it then slips.
The MCV puts out 12 GPM at rated speed of which 5 GPM is dedicated to the steering and then brakes, brake lube, TA control, hydraulic seat if so equipped, and finally TA lube. Steering has priority and the return flow from the steering is available for the rest. Each brake housing gets 1 GPM for lube leaving 3 GPM. The brakes have the next priority and they are limited to 1 GPM. That should leave 2 GPM for the TA and TA lube. The pressure rergulator valve limits the brakes and other controls operate to about 250 PSI pressure. The steering pressure depends on the load on the steering system and is limited to about 2000 PSI. When the pump is worn (or there is a leak) the flow from the pump will drop off as pressure increases. When you get to the end of the row and start to turn the pressure demand on the pump goes up and flow drops off. The result is that you no longer have the entire 5 GPM flow returning from the steering. Using the brakes also draws off more flow. If there is not enough flow the pressure drops off for the TA and it begins to slip. If TA pressure cannot be maintained the flow to the TA lube stops and the red light comes. Slowing the engine as you turn just makes the problem worse because it reduces the available flow from the pump.
When these symptoms occur there is a more critical problem that doesn't show up until too late. The flow is excess of 5 GPM from the MCV pump is routed to the oil cooler and then back through the MCV and back to lube the range transmission and ring and pinion gears. When the steering is taking all available flow there is no flow to the rear. If your MCV pump was only able to provide 4 GPM with small load from the steering you may not notice any problems with the steering, brakes or TA but there would be no flow to the rear frame.
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