Posted by Owen Aaland on September 26, 2011 at 21:10:34 from (216.47.32.147):
In Reply to: 706 clutch posted by RodInNS on September 24, 2011 at 15:10:10:
Quoting Removed, click Modern View to see
No. It most likely will make no difference at all.
The front hydraulic system uses a 9 GPM pump mounted on the inside of the Multiple Control Valve (MCV) assembly. When the oil leaves the pump it goes to a 3 GPM orifice and the rest of the oil is routed through the oil cooler in front of the radiator. From the oil cooler this oil returns to the MCV and then is routed back through the center section casting, through the reverse idler shaft in the range transmission and then to the the ring and pinion and then through the pinion shaft to lube the low range gear bushing and the front pinion shaft bearing. The 9 GPM flow is at rated speed. At idle the flow from the pump will be less than half that amount so the flow to the range transmission varies with engine speed.
The 3 GPM flow through the orifice is the priority flow so that amount stays constant from low idle to high idle. This 3 GPM is routed first to the steering and then returned to the MCV where it is regulated to about 250 PSI by the pressure regulator valve. If the steering is placed on high demand and the pressure rises to about 2000 PSI the steering pressure relief valve will open. This bypassed oil is routed to the same port as the steering return flow. The oil is then routed to the brakes where there is a 1 GPM orifice. On the 706 the brake control valve is an open center valve so the 1 GPM flow is returned to the reservoir and is not available for the TA and lube. Later tractors used a closed center brake valve so the 1 GPM is bled off only when the brakes are being used. After the brakes the oil goes to the TA spool valve where it is directed to either the high side or low side clutches. The oil is next available for the lube circuit where another pressure regulator valve drops the pressure to about 20 PSI. Any excess oil that is not needed to maintain the 20 PSI is dumped to the reservoir. The lube oil flow is routed into the TA to provide lubrication the clutch packs and bearings. When the clutch pedal is pushed in the dump valve dumps the oil in the TA circuit to reservoir so the TA clutches are released and there is no flow in the lube circuit. If the lube flow were to continue it could cause drag in the TA clutches resulting in hard shifting.
As the hydraulic pumps wear they are no longer able to maintain their rated flow. This flow rate will drop off faster the higher the pressure demand placed on them. In your tractor what is happening is that when the steering is placed on demand the pressure rises and the flow from the pump drops off. The pump is not able to maintain the 3 GPM flow through the orifice and the pressure in the control circuit in the MCV drops low enough that the brakes and TA control do not have enough pressure to continue to work. Since the TA clutches are releasing in your tractor we already know that there will be no lube flow so connecting the dump valve will not make any difference to your problem. Also since the steering is affected when put on high pressure, we know that the 3 GPM flow is not being maintained and since that flow has priority the flow though the oil cooler will be zero so the range transmission and differential are not being lubed.
It is possible that the pump may not be the only problem. If you have a blown O-ring between the center section and the MCV that may be the cause of the loss of pressure/flow through the system. A stuck priority flow divider valve may also cause similar conditions but in those cases the problems will occur at low engine speeds and be much better at higher speeds. The MCV needs to be removed and inspected. If no other problems are found, replace the pump.
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