7140 magnum

cs880 · Dec 7, 2009

I know this might be to new for this forum but thought i would try anyways. i have a 7140 that is dropping the regulated pressure coming into the shift valve from 275psi to 215psi as soon as you shift tractor out of park. have had all shift packs apart and rebuilt and also put in a new tran. oil pump and nothing helps. have rebuilt the shift valve also. anyone have any ideas?

pete 23 · Dec 7, 2009

If I get around to it tonight, I might pull out my old magnum training manual and take a look. I recall doing some modification work on those shift valve assemblies to over come some off the wall happenings but don't remember what they were anymore. Haven't worked on them for 15 years.

cs880 · Dec 7, 2009

that would be great! it is a early 7140 with two speed reverse and no creeper. tractor has around 8000 hrs on it and has never given any problems till now. if i unhook the sender all works fine and can not get anything to slip in any gear

pete 23 · Dec 7, 2009

I did some looking in manual, however, I have been away from this system too long and just never did enough work on them to have it ingrained in me. We always did a 7 gauge hookup when testing transmission and master clutch pressures to try to isolate a problem. I will say though that the main pump does indeed provide the hydraulics for transmision after power steering. The other two pumps are for oil cooler, lubrication, and charging the main pump. As you say it works with sender disconnected I am at a loss as to just what takes place. I know that if you lose engine oil pressure the automatic shut down for the engine will come into play but can't relate to how the low regulated pressure would cause transmission to not drive. Getting too old for this I guess. Sorry about that.

pete 23 · Dec 8, 2009

Been doing some more looking in the book. The sender does indeed hook into the auto shut down but that would shut engine off, not disable transmission if that is what you mean. I could not remember them doing that. I don't have a answer why pressure drops in that position though. It does vary to the master clutch circuit depending on what gear you have it in. Have you checked pressure as you move through all the gears.

Anonymous-0 · Dec 10, 2009

the pressure stays exact same through out the gears. the only time it does change is when i pull it out of the park position and then it drops and stays low and the same pressure till i put it back in park.

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