John Deere 400 Sundstrand 15 Help

[Lee_K]

I posted here a while back about a weak transmission and hydraulics on my 400. This tractor has a sundstrand 15 and peerless gearcase. I decided to go ahead and replace the charge pump. While everything was apart I also replaced some seals and other parts in the transmission/differential. I got it back together and running yesterday. However, the hydrostat is weaker than before. Moving the control for the deck raise/lower will make the hydraulic cylinder move but pretty slow and the pump whines. This is with the cylinder disconnected so no load whatsoever. The cylinder will actually go slower and faster through out the stroke. After inspection the dipstick in the transmission has bubbles on it. I assume this is from the charge pump cavitating and that is the whine or groan sound I am hearing. The drive will move a little with the control half way up which is nowhere near how it worked before. I did not run it much and only at idle to quarter throttle

I did not change the transmission filter initially because I had just replaced it and was planning to replace the oil and filter again once it got a few hours on it. However, i went ahead and changed the filter, but the result was the same.

I assume it is the pump starving for fluid that is causing this. Is there some kind of priming procedure I need/should have done? I did try to fill the lines and charge pump house with oil the best I could before I put everything together. What would cause the pump to starve for oil? Any comments or advice is appreciated. Sorry for the long post, but I wanted to give all the information I had.

Thank you,
Lee

 

[Roger in Iowa]

Not much help here, but bubbles on the dipstick says the system is sucking air somewhere.

 

[kencombs]

I agree with the sucking air diagnostic. I thing the 400 has an external line from low one the gearbox to the suction side of the charge pump If so, be sure that the fittings and orings are in good shape and installed firmly.

 

[Lee_K]

One of the fittings one the pick up tube was loose. Thanks for the help. I'm glad it was something simple.

Thanks,
Lee

 

[Credysis]

(quoted from post at 09:41:25 12/15/20) Not much help here, but bubbles on the dipstick says the system is sucking air somewhere.

Sounds like it. I don't think it's something complicated, but better to have it checked if other issues arise with it.