If you are interested on how the 5FG system works, it as follows:
-From hydaulic tank to pump, to lift /lower, tilt combination valve, with built-in in flow control (flow divider, 3.33 GPM mininum to steering/brake criciut). From flow control valve to brake booster (with internal flow divider to steering, I am unable to determine which has priority brakes or steering). The brake control valve has 4 connection: input from pump, to brakes (711 psi max for 2 ton and 996 max for 3 ton), to power steering and bleed off from brakes when the brake peddle is released. The flow from the brake control valve goes to the steering control valve then back to the hydraulic tank.

Checking out the pump:
Spec. 10 GPM at 1500 rpm (am not sure if pump speed or engine speed).
-Connect flow meter (in pump output) and check flow, Operate tilt to deadhead, keep engine is at same rpm, if flow seriously drops ( to to less than 7 gpm) pump is worn out.
- If you do not have a flow meter, the problem is more apparent at low engine rpms. Undo the plate that is on top of the hydraulic tank and disconnect the return hose from the control valve to this plate, connect a short length of pipe to the control valve return line and stick the other end in the gap between the plate and hydraulic tank so that you can see the oil flowing back from the control valve. Dead head the tilt and if you see a major drop in flow and the engine not loading up good sign that the pump is worn out. Also check the bottom of the tank for metal filings and the pump suction strainer.
Note: There is a return line to the hydraulic tank from the brake booster, oil should only flow when the brake peddle is released and only enough oil to drain the brake cylinders. If oil is flowing when the peddle is pressed then the brake booster is the problem.
I may be wrong but I think this machine was manufactured late 80s or early 90s, give me the serial number if you want the date of manufacture.
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