4840 hydraulic problem?

[Craig C]

Working on 4840 and evidently working on multiple issues. I?ve definitely got some type of leakage on the high side of the main pump, which process of elimination should figure out by blocking off SCVs, and I?m somewhat concerned that the hydraulic seat could be a source as it goes all the way up and won?t adjust. Looking for a loss in lube pressure. Also the hydraulic pump I can?t decide is acting up or if I?m dealing with a leak that is robbing all the flow. The transmission pressure is good, lube pressure is low when the rock shaft and steering/brakes are in the system. When I cap off the main hydraulic supply on right side under cab the lube pressure comes back in spec. I definitely had an issue with the pump not going in stroke, and I cleaned and put new filter in the stroke control as best I could with the pump on tractor. Main Pump is in spec and has pressure every time I put a gauge in the rear SCV. It?s not wanting to operate a two stage dump trailer cylinder, and I can?t decide if I?m fighting a leak in the rear or need to go back to the front. Increasing the rpms will make it dump and that should only affect the transmission pump, so I?m going around in circles. Guess I?m gonna have to block off the known bad SCV and see if lube pressure increases, I suppose even the hydraulic seat which wants to stay all the way up and rock solid could have an issue as well. This is a project tractor and we?ve been through the whole transmission, But my guess is, these issues where already here before the transmission puked out the clutch surfaces.

 

[Bob]

Start with the simple stuff, let the tractor cool off overnite, then start it and "feel" or use a temp gun on each and every hydraulic component after the main pump as it warms up.

Any component that heats up more/faster than the hydraulic sump (rear end casting) is likely leaking high pressure oil internally.

 

[JD Seller]

I would bet that you have multiple leaks in the high pressure side. The seat very well could be leaking but even full flow through it should not cause the issues your having. Since the main pump is creating pressure and will lift when revved up, It would seem to be doing its job. The only way to really 100% know is to check the flow with a flow meter. A leaking SCV could easily be dumping enough of the high pressure oil for the other SCVs to not work correctly. Also the rock shaft leaking can do it as well. You can block off components and try an locate it. As one other poster stated, let the tractor and oil cool over night start it up and start checking all the components with an inferred thermometer. The leak will create heat.