MCV Valve Issues

I had posted about issues on my 706 Farmall. I finally Tested the MCV. I have 200 PSI at the bottom port. I rev the engine up and get about a 5-7 PSI Increase on the high side. When I shift the T/A lever back to low, I get no change in PSI. I moved it back and forth and no change in PSI. The Sensor port shows 0 PSI all the time. If you remember, I changed the brake valve due to a broken shaft. I got a replacement from a salvage yard. The replacement I was told was from a 766 but interchangeable. Owen talked about an orfice in the brake line? Where would I find it? When the tractor is running at first I hear a tap about three or four times in the MCV area, then it seems to go away. The sound is like a lead hammer contacting something. It will only do it at first. The other symtoms are the tractor will be going down the road and take off like you shifted from low to high, but I have not touched anything? The other symtom is when going down the road and you come to an intersection and push the clutch in and clear yourself without coming to a stop and let the clutch back out. The tractor coasts like it is stopping and then will jerk once or twice and take off again? But if you touch the brakes after letting the clutch back out it will re-gage and go?

Any thoughts or other Tests or things to look at?

Thanks for your time.

It sounds like either the TA is acting up or the pump on the back of the MCV is shot. There is a plug on the rear of the MCV just above the flow control valve. Remove it and install a pressure gage, and see if you get pressure there. At rated engine speed it should be either 1500 or 2000 PSI. If there is no pressure pump is suspect. If pressure I would look at TA.

You have the pressure reading in both ta and direct drive position , but did you try to get a reading in the middle between direct and ta. That reading is important and on a 706 should be 15 psi less than the other readings. If you do not have that drop it tells you the fluid is escaping in the regulated circuit, if you do get the drop your fluid is escaping in lube circuit. From your readings I think it is getting away in regulated circuit. It could be as simple as the sump check valve or seat leaking or as serious as broken or totally worn out rings on ta input shaft. If you have a good service manual it will tell you many different things that can be going on. Far as orfice in brake valve , it is right under the supply fitting going into valve. It might be missing as it screws out. Borrow or buy a service manual for that model, it has the best explanation of any manual ever put out on the complete workings of the MCV. It is called Basic hydraulic control or something to that effect for 7 and 806. I'll just throw this in also, MCV stands for Multiple Control Valve so the extra word valve on the end is redundant.

I did check the pressure in the middle of the T/A shift. I get no change in PSI?

In that case I would make sure the brake valve is not using excess oil. Just plug it off and recheck pressures. If that is ok you are looking at digging pulling mcv and doing some checking for blown gaskets, o-rings, leaking sump check, stuck regulator valve. In other words, I can't tell from here, only give you ideas.