I have a Case 850B highlight, about 1980 vintage. The last couple times I have used it I have had real slow hydraulics on both the bucket and boom. They start off kind of slow. I have to give it full throttle to work. Later on, once everything warms up, they are almost worthless. I pulled the cover off to get a look at the main control valves. I can hear some fluid going through it while stationary, but cannot confirm which lines. I have checked and all the spools move freely. I am not completely sure how this system works. Could the pressure relief valve be opening? The parts list off the Case website does not show a pressure relief valve of any kind in the system. If so, where would I find it to check it. Tomorrow I hope to check hydraulic pressure in the system, once I buy an appropriate gauge. Also, what pressure should I expect in the system?
You really need to get info on The System Operation. Then even with out specs you can figure out what's not working right. Tune up to spec later. Later Bob
I agree with Bob, if you don't know how the system works, you need to get some info. The 850B uses a gear pump (positive displacement), so the hyd system would either have to be open center or some type of load sensing system. If you look at the inlet section of main control valve, I would wager it's a load sensing system given the amount of gizmos in that inlet section. Oh, by the way, the main relief valve is in that inlet section as well. Also, the spool sections have port reliefs and anti-cavitation valves, a lot of stuff going on with that control valve. If you determine pump is in good shape, problem is likely in that main control valve. But I'd take it off the machine to bust it apart on a bench. Even then, I'd be real careful and attentive disassembling it. Here's an illustration of the inlet section. >
Sure looks like that Wille. Sounds like something stuck with a system like that. Definatly a leak, fades off as warms up. Could easily be something jammed up. Take apart and check all before spending money on big items. Later Bob
Thanks for the info Atco. Could a circuit relief valve cause this problem, or would it have to be system related ( such as pump or main relief)? It looks like I may have to pull it out.
Not likely a port relief problem bpogue, that would only affect one function. From what you describe, you either have a failed pump or something wrong with that inlet section, there's a bunch of stuff going on in that inlet section. Just a guess on my part.
Normal main relief is 2 stage and will hold pretty steady pressure with one of the circuits bottomed out by holding the lever over releif. If you rev the engine up and down and the pressure remains fairly constant even if it is low the pump probably is not the problem. On the other hand if the pressure has a wide swing as you reve the engine up and down it's a pretty good indication the the pump is worn out, the other clue is that the hotter the oil the thinner it gets so a worn pump would even get worse with the increase in heat.
I assume I have a load sensing system, but am unsure. I put a gauge on the pressure line going in to the main valve. Pressure is bascially zero until you move one of the hydraulic levers. Then pressure will increase. Pressure seems to be around 800-1200 psi while in operation. RPM changes will affect pressure, to some extent. Even when I lose hydraulic power, pressure seems similar. What do you make of this?
pump failure seems to be evident.......Dealt with the same issue not so long ago....Good luck
I seemed to have missed this thread - hows the diagnostics going bpogue? Can you flow test the pump to check if it is OK.? P.S. - Do all the valve sections / circuits give the same main relief pressure reading?