Tractor Repair: 2670 case powershift, piston seals, clutch packs

Question
Thanks for your time. I have an old 2670 case 4 wheel drive (aprox 4600 hr's) and I first noticed I was losing hydraulic pressure when in 2nd gear on the power shift. Later when pulling a # 60 cat scraper if I started in digging in 3rd then down to 2nd it would pull fine for the first few seconds (maybe 20-30) then would just stop as if I had depressed the clutch. Same sound even that you get when stepping on the clutch. Now I would step on clutch dropping the power shift to 1st and release and go again. When scraper get's full I could shift up threw 2nd to 3rd and everything would seem normal. But trying to dump in 2nd the hydraulics would be really slow.  I had a case dealership diagnose the problem and came up with blown gasket between valve bodies on top of trans but now that I have removed them they look fine and am not sure where to go from here. Don't want to pull engine only to find out to is something repairable from outside of trans. I'm a farmer not a mechanic but do most of my own repairs. Have the manual and notice 2 clutch packs are used in every gear and only have problem in one gear so I don't feel it is a blown clutch pack. Appreciate your help.  Thank You   Kevin

Answer
  If your hydraulics got slow in 2nd, that tells me there is an oil leak somewhere in the powershift circuit.  As you said, there are 2 clutch packs engaged at all times.

  Here is the pattern:

powershift 1, C1 and C2
powershift 2, C1 and C3
powershift 3, C2 and C3
reverse, C2 and C4

C2 is modulated by the pedal, and with the pedal down only C4 should be on.  

  The only accurate way to diagnose is by installing 4 pressure gauges on the control valve to check all clutch pressures at once.  The pressure should be 195-210 psi with the oil warmed up.  If any clutches show low pressure, there could be leakage in the oil distributor or supply tubes, the clutch piston seals, or the control valve.  Since C1 and C3 are used in other speeds besides 2nd, the clutch packs should be OK or it would slip in the other speeds also, so it is more likely an internal oil leak, which is also affecting the hydraulics.  By comparing the clutch pressures in powershift 2 with the pressures in the other speeds, you should be able to verify if there is a leak.  If C1 and C3 each have a small leak, it becomes a large leak when the two are applied at the same time in powershift 2.  If the control valve gaskets are OK, then inspect the control valve, spools and springs, the internal check valves in the control valve, and the oil tubes and o-rings between the control valve and the oil distributor.  If everything looks OK, then possibly the oil distributor and rings are worn, or the piston seals are leaking which would require removing the engine to repair.