I am always trying to come up with ways to check components after repair and before installation on the cheap. When I repair hydraulic pumps and motors I place gorilla tape over the inlet and outlet ports and manually turn the shaft, if it pulls and push the tape with nothing but air then I know it will pump or turn. Of course this does not work in all applications such as hydrostatic drive pump with intrigal charge pump because you would be only checking charge pump operation. Also there is the tried and true method of air checking transmission clutch packs. I have bulit a Dyno(I use that term lightly because there is no load test) to check the pressure on Cat transmissions I have built to ensure the clutches are engaging as necessary. It is A contraption and difficult to set up. So I had this thought about this about pressuring the clutch packs through the control valve with a potapower to system pressure and then measuring leak off time to establish at least the hydraulic condition of the clutch engagement. The question I have is without the shafts turning would the leakage at the shaft seal rings be greater with the shaft stationary? Please include any other "Dyno" tricks you guys have developed and want to share.
I don't have arrangement numbers for the transmissions i would be checking. But two versions would be in a 3kx00420 and 52500714 machines.
Been many years but local Cat dealer had a "test bench" set up they used to pressure test transmissions. As I recall it was basically a electric powered pump that supplied oil to the inlet the machines pump would be connected to. Then they could manually shift the gears while checking clutch pressures. oil that drained out of the case was then sucked back through a filter to the electric pump. Now the best set up the dealer that worked mainly on Euclids had set up to test Allison transmissions from the Euclids was I believe a 4-71 Detroit. Most of the Allisons back then were remote mount and driven with a drive shaft off the machines engine. It was a simple matter to connect them to this test engine and power it up. The only thing they could not do is load test the transmission but they would used the parking brake to put a little load on them to know they were passing along power. If nothing else you got to listen to that little Detroit sit there screaming while checking clutch pressures and looking for leaks!
The cat dealer I used to work for bench tested transmissions with no load on the output shaft . They had an electric motor spinning the trans input and had pressure gauges to test pressure. Transmissions without internal pumps needed an external pressure source. The trans should be spinning while tested due to the rotating shaft seals on some clutch packs. I always air pressure test the trans when I build it just before I bolt the valve body on. Most pistons will move pretty good with air
I remember in the 80s a local Allison dealer using an old 332(?) Ford "Y block" engine to do the same thing. They had the exhaust manifolds upside down without mufflers, just 3-4' of pipe. I think the guys just liked to play with the old Ford.