tc40d fluctuating charge pump pressure

[jayhawk rv]

Just brush hog for about an hour, charge pump pressure 90psi at 2600 rpm.

 

[jinman]

Clayton, did you say that it was the same with the pedals at neutral or forward and reverse? I'm not onto anything here, just curious. The highest HST fluid demand would be low range with the rabbit switch enabled and the HST pedal at full forward or full reverse. If there is no fluctuation or dropping in pressure, that would seem to indicate that the charge pump is delivering all the fluid the HST pump can use.

BTW: High range also has that demand, but the tractor would be moving so fast that you might not want to glance down at the gage.

 

[jayhawk rv]

Jim It's doesn't matter if I'm in neutral or I'm going forward or reverse the pressure is down to under 90psi and drops about 20 psi and then bounces back.The rabbit/turtle switch is working but seems to be engaging harder than before. As far as High speed goes I feel I have lost my top end in ground speed,and when you are in high at full road speed and pull a sight grade it boggs down more than it should. Have 1800 hr on tractor,I think I would give up my pickup before my tractor, use it daily. I would be in big trouble if its was down very long or cost a lot to fix! Thanks for your input

 

[Harry in Ky]

I've never been into the 2 speed hydros, so I'm a bit hesitant to chime in here, but I have been following along. It seems to me, if the rabbit/turtle function is operated by charge pressure, and charge pressure consistancy is part of the problem, the two may be be related. Fluctuating charge pressure can only have a limited number of causes. 1 Inadequate suction/supply 2 A varying leakage on the pressure/load side 3 Erratic performance of the charge pump itself. Any others? Some foaming of the fluid could come from air getting into the supply. A faulty charge pressure regulator/relief seems like possibility here, but an inconsistant leak in the rabbit/turtle circuit seems equally likely. I'm guessing here, but I believe the system operates on a movable swashplate on the drive motor rotating group, actuated with charge pressure, right? If so, a leak in that area could affect both pressure and the shifting process between rabbit and turtle. This system is controlled by a solenoid valve, right? Is either range a springloaded position, or do both hi and lo require charge pressure to maintain? Not sure, but someone out there knows. Just seems to me there are numerous possible places for the pressure to leak off internally, the question is how many would be inconsistant?

 

[DieselMonk]

Sounds to me like there is some solenoid valve weak or the whole HST pump getting weak, HST filter plugged.
I mean the book sez you should have 114 too 170 psi... and you got only 90? Something is not quite right. This said, I wonder if you have the correct fluid inside the HST transmission. Change in viscosity changes oil pressure... it probably not be the problem...