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Dr.656

1066 MCV

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I have a 1066 with a couple issues. I don't believe the TA/MCV is behaving properly. The lube pressure light does not come on when the clutch is pushed. I have the dump valve adjusted as per the book. The only time I see the light on is before its started and about 5 seconds after its started. It hangs in gear some as well. When i put the plows in the ground, I can tell something is slipping. I cant tell if its the TA or main clutch. Running the tractor without a heavy seaward load, it does not slip. This tractor is new to us as I bought it with damage after a small electrical fire. I just got it running again so I don't know much history. TIA!

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First check inside the clutch housing for oil. If any engine or transmission oil gets on the engine clutch it will slip and make TA diagnosis more difficult.

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I took the inspection cover off and checked. Its what I would call damp with oil inside. There was not a puddle on the plate nor does it make a puddle on the floor from sitting. Although I suppose it wouldn't take much to make the clutch slip under heavy load.

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Far as the light not coming on, you need to put a gauge in that spot where sender goes to see what you actually have. Pressure should be about 20psi and should drop to zero when you put clutch in or just manually pull out the dump valve. It may only be a slow to operate sending unit, but it may actually have pressure with dump valve pulled. I have only seen this one time in my life and it was a badly scored up regulator valve that was letting enough oil into lube circuit so pressure would drop way down when dump valve was pulled out but not to zero. That is a four psi switch so doesn't take much to keep it closed.

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Far as the light not coming on, you need to put a gauge in that spot where sender goes to see what you actually have. Pressure should be about 20psi and should drop to zero when you put clutch in or just manually pull out the dump valve. It may only be a slow to operate sending unit, but it may actually have pressure with dump valve pulled. I have only seen this one time in my life and it was a badly scored up regulator valve that was letting enough oil into lube circuit so pressure would drop way down when dump valve was pulled out but not to zero. That is a four psi switch so doesn't take much to keep it closed.

I ran into the same problem a couple of times. I ended up using an engine oil pressure sender that was rated for 7 psi to replace the original 4 psi sender..

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Could having the oil cooler lines on backwards cause any of this? They were ruined in the fire and I had to try figuring them out using the parts diagram. I'm not 100% sure I got them right.

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I'm sure that there are a lot of tractors out there that have had the cooler lines reversed. The oil going through the oil cooler is already out of the circuit for the TA controls. There are three gallons per minute of oil that has priority for the steering and then the brakes and TA. The oil that is in excess of this 3 gpm is what flows through the oil cooler.

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Today I installed a gauge in the port for the tellite sensor. With the engine running it shows 20-21 psi. When either the clutch is depressed or the dump valve is operated by hand, the pressure drops to about 6-7 psi. Does this indicate anything? I would like to test the mcv as per the manual but I don't have the fitting for the regulator port on hand.

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The pressure should drop to 0 when you pull the valve out or step in the clutch. Does the light come on or the gauge go to 0 with the engine shut off? If it does you may have a scored dump valve or a bad gasket or oring in the mcv.

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Back in the day, I did a lot of studying of the oil flow in the mcv when this was happening to a tractor I was repairing. I decided the only thing that would cause this was a leak past the regulating valve into the lube circuit or it had a leaking gasket. As the pressures were normal in all other positions, I put in a new regulating valve spool and it cured the problem. Those spools get scored up and we polish them back down nice and smooth so they can leak past if enough of this takes place . On that one I had the mcv all apart before that so I am sure I polished the bore also. One other thing, to reduce the leak problems on the dump valve seal, I always make a groove across the tip of the dump valve. This allows oil to bleed off that leaks past dump valve , gets locked in due to the tip fitting against a dead end and goes back through the hollow valve and some times blows the seal right on out. First time I ran into this was on a newer 1086 and it would leak oil all over but not blow seal out. Of course by the time I got out to the farm to take a look it didn't leak because clutch had been depressed releasing pressure build up. Just luckily I was standing there, with it running, scratching my head and it started leaking. Blowing oil out, took a look and it was dump valve. Gave it the treatment and it never bothered again. I know some MCV's that got replaced because guys could not get them to stop leaking. Oh, this was a suggested modification from service school, not my own.

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Pete, you may have nailed the problem. After I posted the pressure readings I studied the diagrams of the mcv in the service manual. I pulled the pressure regulator since it appeared to be the pressure source for the dump valve. It does have some scoring. After reading your post I feel its worth replacing this valve. Thanks again Pete for your help.

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