International 1086 hydraulic issue

Bought a 1086 and tractor looks good and starts good.
The problem is when I idle down and put it into gear tractor dosent move, if a rev engine up and let clutch out then it shifts smoothly. Three point also does the same thing, wont raise when idle but when reved up it starts to raise. Steering is also affected to. Tractor shifts and drives out good when reved up for hydraulic pressure. The TA is frozen up in direct drive. Idk if it will work in low drive, but can someone explain to me how this TA and hydraulic systems works. Hydraulic oil is past full.

Basic operation. The TA is a gear reduction unit that is between the engine clutch and the transmission input. The TA gears are housed in a carrier that spins with the engine clutch in direct drive, and is stopped when in gear reduction. the TA front clutch is a hydraulic multi disc clutch that is under pressure and locked up when in direct drive. This causes the engine to spin the TA gears and housing as a unit, transfering engine RPM to the transmission. There is a one way (overrunning clutch) at the rear of the TA when in direct, this clutch is slipping in its CW direction (looking from the front of the tractor)as it should. When the lever is moved to reduction (back) the front TA clutch is no longer pressurized, and is free to rotate. The gear reduction in the TA carrier now tries to rotate the TA assembly CCW, but the one way clutch locks it to the case of the main TA housing and stops that from occurring. The gears now rotate the trans input shaft CW but in reduction through the TA gears. There is also a small multi disc clutch at the location of the one way clutch. This clutch is applied when the TA lever is in reduction. it is not a strong brute of a clutch. its only job is to prevent the one way clutch from turning in its free direction. This is so the tractor does not coast down hills and overspeed from that coasting. costing loss of control. It is not designed to be downshifted into TA reduction as a braking action and will wear out if used that way. So it is best to use the TA while under pulling load, and never to slow down on the road. I hope this makes sense. Jim

Well on the 86 series depending on if it is and early or a late model depends on the hyd system . Early was and open center system and late was a closed center . The MCV controls your steering , brakes , T/A and your cooling and lube oil for the transmission and rear end. With the T/A lever stuck in high you can bet that the low side is OUT in the T/A and the cable is frozen . SOOoooooo with the low pressure on the MCV it can be that the MCV pump is toast or you have a massive internal leak either in the MCV or the T/A . This system also has a supercharges deal that sorta hooks the MCV pump with the rear hitch pump and has caused problems . The closed center hyd. system can be a nightmare as this system is not for the barnyard mechanic as it takes special equipment to work and test this system and i do not have the addition for my flow rater for this . There also could be a leak in the pick up tube in the rear end that at low speed the pumps will not pick up the flow till ya raise RPM . So on this you will more then likely end up spending some big money at a dealership that can do the testing . That addition to my flow rater i tried to get one at a closing I H dealership and drove for five hours to get the sale and chased to to over 3 grand and did not get it . BUT i did get a few things and two hot dogs and a pepsi .

The tractor is a 1978 year model
Where should I start at checking stuff?