706 clutch

Looking at a 706 Farmall dsl. the issue is that when
I turn steering all the way left or right the
tractor stops like the clutch is disengaged. As soon
as I move steering off maximum turn, the tractor
jumps like I popped the clutch. Not too familiar
with Internationals. Any help appreciated. Thanks

Have you tried pulling anything with it? I'd guess that one of 2 things are going on.

1. clutch is slipping, check by hooking onto something that will be a load and going str8.

2. something with the hydraulics where the TA isn't getting the pressure it needs when at wheel stop turns making it disengage. That will more than likely require pressure testing the TA.

Rick

Used to run a international forklift, with more or less the same problem. Answer turned out to be, that one of the hydraulic valves in the bank, has to be drilled on a diagonal, to allow the priority to for to clutch, then steering, apparently there was a service bulletin, on the issue. If it has already been drilled, it might be something blocking the passage.

The classic example of what happens with a worn out MCV pump and a TA that has a worn out sprag clutch in the low side of the TA.

The MCV pump provides oil for the steering, brakes, TA, and TA and transmission lube, in that order. With no demand on the steering the oil just flows through and the pressure is regulated by the pressure regulator valve in the MCV to about 250 PSI. When the steering is put on demand the pressure rises until the tractor steers or it open the steering relief valve at 1800 - 2100 PSI. In a worn out pump the flow drops off as the pressure increases. When the flow drops off the TA no longer has pressure to keep the clutches engaged and so they release. If the sprag was good on the low side the tractor would down shift to the TA speed but keep pulling. Because it stops we can determine that the sprag is slipping. When the pressure requirements for the steering drop off the TA again receives oil and the clutches engage again with a bang.

When you pull the MCV off the center section you may find a blown O-ring or it is possible that the flow divider valve is stuck but those conditions can be seen after things are apart. If other problems are found it is possible that the pump may be OK.

A bigger problem can not be seen when you have these conditions. The excess flow from the MCV pump is used to lubricate the range transmission and differential bearings. Since the steering has priority if you do not have enough pressure to satisfy the steering there is no lube flow through the oil cooler and the rear frame.

That makes perfect sense as the TA is out and the
power steering seemed weak on this tractor. What is
the MCV pump and where is it located? One other
thing I was curious about was that there is a
smaller rod that is attached to the main clutch
linkage that was dangling loose (the pin that should
have held it in place was missing). what does that
small linkage activate and could that be an
indicator?
The clutch didn't engage until all the way to the top either. Wasn't much adjustment left either. Is that a totally separate issue? I was looking to puchase this tractor and wasn't too afraid to splt her and put a clutch in and possibly fix the TA. Thanks, all of these replies are great and very helpful.

Don't know what that rod is for without a picture but it could be for the TA dump valve.

Rick

The little rod is indeed for the TA dump valve. It is there to dump the hydraulic pressure from the TA clutches when the main clutch is released so that the TA does not lock up from having both the high side clutch engaged and the low side lock up the mechanical sprag clutch at the same time. That happens when the transmission input shaft reverses direction when you come to a stop. It also dumpd the lube pressure so there is no drag on the clutches from the lube oil. With a good TA it makes it very hard to shift if it is not working. In your case it doesn't bother you when it doesn't dump the oil because the low side clutch is out.

So if that rod is hooked up, would everything but
the TA work correctly? ie steering wouldn't be slow
and wouldn't stall out during a hard turn?

(quoted from post at 19:57:58 09/26/11) So if that rod is hooked up, would everything but
the TA work correctly? ie steering wouldn't be slow
and wouldn't stall out during a hard turn?

Click to expand...

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.

You can't get a better explanation than that. I was
looking at the tractor to buy, thinking I may have
to do a little work to get her in shape. Sounds like
there is a good possibility that transmission and differential are not being lubed. Think I'll move on
and keep looking. Thanks so much for all that info
and saving me from a possible disaster.

There is splash lubrication in the range transmission even if the MCV pump is weak. If the transmission oil is full the level is in the middle of the lower shaft so those gears will throw quite a bit of oil around inside the case. Problems from lack of pressure lubrication are more likely to show up in the larger horse power tractors. Tractors like the 706 are much less likely to have problems than those that are being run at 150 HP or more.