Greetings to all!! I am a new member...Just joined, and I thought that I might pose a question. A few days ago, I bought an older John Deere 400 backhoe, 1960's model? used it for 5 minutes (I'm not kidding!), whereupon I lost all pressure and hydraulic oil began spraying from the front (or is that rear?) pump seal. I removed the pump and found that the seal had been pressed in too far thereby blocking the overflow back to the reservoir and causing the pressure to build up and rupture the seal. But I didn't think that answered my loss of pressure problem. Sure enough, I replaced the seal and reinstalled the unit... No more leaks..Also no pressure anywhere.. I then removed and cleaned the two top and bottom plugs from the control head at the front of the pump, being careful not to disturb the adjustments too badly and reinstalled them. Now I have pressure!... Too much pressure! When I started the machine it immediately burst the large hose going into the filter assembly.. I replaced the hose ($132.00 for a 6 foot hose, OUCH ) and started the machine again. It then burst the hose next to it! Also, it is very hard to start. I have to relieve the pressure by actuating any control to be able to crank the engine. Sorry for the long winded explanation, but my question is this: does anyone out there know how to check or reset the destroking mechanism on this machine? Could it be anything else? The pump and control head has no wires going to it, no solenoid. What I took out and cleaned did not look like anything that I have found in hydraulic schematics yet. I have already replaced all of the filters and fluid...twice. Any help would be appreciated. I cannot afford to keep replacing hydraulic hoses. Thank you very much guys!!
I would pull the pump and take it to the Deere dealer or local hyd pump shop, call first to make sure they can still work on a pump that old. Something's not right in the control head, it regulates the pressure in the pump housing, when it reaches the set pressure it increases pressure inside the pump and floats the pistons off the crankshaft.
Thank you very much, lantraxco for replying to my question. I appreciate it. Can I just remove the control head and take that into them, or do I have to remove the entire pump assembly and take it to them as complete unit. Also, when I had the pump off the first time I took it into them and they (John Deere) said that they could rebuild the pump, but that it would have to be adjusted for the proper pressure while it was on the machine. Since I have already put out about $700 since getting the machine (not including the purchase price), I'm trying to do this as cheaply as possible, but yet still do it right. Thanks again!
Been a long time since I worked on one of those Deere setups, the transmission pump feeds it so I suppose you do need to adjust pressure on the machine. Might ask them about the control block, if nothing else if you took it to them they could maybe see if it was all assembled correctly and nothing sticking open or closed.
They open again on monday, so I'll call them and ask..Thank you for your input, I appreciate the help..Any idea where I can find a hydraulic diagram for that old of a machine? It helps if I can be somewhat informed when I talk to them.