4020 hydraulics problem found

[SVcummins]

I took the plug out of the back of the transmission case . Oil sprays out off the cover on rockshaft housing when I cycle a hydraulic function

 

[WTW]

That would do it. All make sense.

 

[wore out]

It is interesting that function return oil can flow BACKWARDS through the rockshaft return line and leak like that.

It would seem to me there should be a constant leak there of transmission pump oil even when there is no function return oil?

IIRC, you couldn't get the transmission pump to pass the tests detailed in the manual even after you replaced it, the rockshaft cover leak MUST be where the oil was being lost when you were doing that testing.

 

[SVcummins]

I appreciate the help through this .

 

[SVcummins]

Definitely been a servicemans puzzler thats for sure

 

[WTW]

You are welcome. DW

 

[Bgearl]

hello I have been following your problem also and thought now what would happen if you put the same check valve in the return line of the rockshaft that you tried on the other one to stop backflow. 3pt oil would either go like normal or spray back in sump?

 

[WTW]

Bg, A check valve in that location would stop the charge circuit from back feeding / leaking to sump and help a lot but, that was only part of the problem. Hydraulic pump relies on the return oil from rockshaft to also help replenish the hydraulic charge circuit in slow idle conditions. Rockshaft return oil is being leaked / dumped to sump short changing charge circuit. Return oil from rockshaft leaking to sump has to be picked up and repumped by the fixed displacement transmission / charge pump that already is maxed out. Leak still needs to be fixed to return rockshaft oil to charge circuit to make system normal. Later 30 series tractors and newer have a spool valve in the return manifold to prevent this from happening. The same later tractor have the SCV mounted on the rockshaft that return all their oil to same cavity and this same failure then becomes a bigger problem yet if cover pops or blows gasket. DW

 

[Bgearl]

wtw that is what I was thinking the 3pt oil would only bypass when using 3pt. the check valve would buy him some time for warmer temps.

 

[SVcummins]

I ordered the seal and found a used plate on eBay just in case the old one broke . Something made a pretty big pop when it happened. The load that broke it weighed 33000 pounds . Kinda strange it didnt lose all hydraulics then instead of slowly getting worse over time thats what I never thought anything of it

 

[buickanddeere]

Good catch .

 

[SVcummins]

Its been a rough job but with the help of the fine fellows on
YTASAP we got it , headed to the shop as soon as the seal
and new plate gets here also going to split and fix the pto
bearing

 

[SVcummins]

Its going in the shop as quick as the seal and plate gets here. Going to split it and fix the bearing on the pto While Im at it do a little painting and get the new front wheels put on and a few things like that to make it nicer again