tc40d fluctuating charge pump pressure

[jayhawk rv]

I have a tc40d and my charge pump pressure at the hydro filter is running at 110 and then drops down to 90 psi briefly and then back to 110 psi. gauge flutters when dropping pressure. Does anyone have any ideas? thank you Clayton

 

[Jerry/MT]

I have a tc40d and my charge pump pressure at the hydro filter is running at 110 and then drops down to 90 psi briefly and then back to 110 psi. gauge flutters when dropping pressure. Does anyone have any ideas? thank you Clayton

Leaking pump inlet tube or pump shaft seal allowing air to be sucked in?

 

[jayhawk rv]

Thanks,i was hoping it was something that did not require splitting the tractor

 

[jinman]

Please tell us how/why you are monitoring charge pump pressure? There is a charge pump pressure bypass built into the top of the HST filter when the oil is cold/sluggish. Perhaps this is lifting and causing a change in backpressure. A pressure shift from 90 to 110 is NOT dramatic.

Edit: The charge pump pressure can be as high as 200+ psi. Have you or someone else installed a pressure gage on your tractor?

 

[jayhawk rv]

I had some trouble about a year ago,the directional control broke and that lead to checking and replacing a weak high pressure relief valve.At this time I installed a permanent quick test port in the banjo bolt located on the oil filter base. I was leveling dirt by pulling a long beam and notice the tractor acting like it had a clutch and it was slipping,so i put the gauge on and notice the fluttering,hydraulic oil was at operating temp. Thought that i might be sucking air somewhere so I check the rubber T and tighten clamps,changed both filters and not any better, the books say it should be 114-170psi,the fluttering down in pressure make me very concern. Thanks for all your help and anything that you could point out that i might over look. Clayton

 

[jinman]

Clayton, the true test of pressure at your HST is the transmission test ports on top of the transmission. These ports will show full pressure of the HST before it goes into relief. That should be 5000 psi in all ranges. While your number is fairly close to what charge pump pressure is, it should also be measured at high rpm. If charge pump pressure starts to fail, you will see that the rabbit/turtle function is sluggish to shift since it uses charge pump pressure to operate. The charge pump relief valve is what regulates charge pump pressure.

I understand now about your pressure gage installation, but I think the true measure of performance is to measure the full HST pressure. If it can't make 5000 psi or it makes much less with the engine at 2600 rpm, you could have some wear issues.

 

[jayhawk rv]

Jim,I ran my test at 2600 rpm. I would think that charge pump pressure would not drop sporadic,I'm at the low end of the pressure aloud,if it was just low I wouldn't be so concerned but the dropping in pressure leads me to think that I'm sucking air somewhere. I do have some air bubbles on dip stick at rear of tractor. Are you not concern about about the pressure dropping? If I understand the charge pump relief valve right,it's for high pressure,could it be causing my pressure drop? Thanks for all your help Clayton

 

[jinman]

Clayton, while 90 to 110 psi is below spec, 110 psi is only 4 psi below the minimum amount specified. Is that enough to cause problems? I doubt it, but certainly am not sure. The repair manual suggests if the pressure is low, it's the main hydraulic filter, an air leak, or the charge pump relief valve in the HST has a weak limiting spring. The cooler bypass valve on the top of the HST filter that bypasses the cooler has nothing to do with charge pump pressure. The regulator in the HST is in the valve body of the HST just above and in the middle of the fwd/rev main relief valves.

BTW: The main hydraulic pump pulls fluid through the same main hydraulic filter and might change the suction characteristics of the HST charge pump with it's varied pressure demands depending on loader operation, 3PH, and remotes.

 

[jayhawk rv]

My test have been with not moving the loader or 3PH ,I will remove loader as soon as I can and see if that makes any differents.

 

[jinman]

I wouldn't remove the loader. As long as you aren't moving the joystick, there's not effect on the system. Saying the main system might have some effect is way out there anyhow. I just mentioned it because they use the same filter and feed pipe that Ts off to both systems.