975 versatile transmission - The Combine Forum
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post #1 of 7 (permalink) Old 05-10-2019, 08:09 AM Thread Starter
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975 versatile transmission

2 seasons ago I rebuilt this transmission in my shop. I installed a lube pressure gauge in the dash. I get about 15-20psi on startup then as the oil warms up itll drop to about 8-9psi while working. Depending what range I'm in. Ranges 2 and 4 must spin the pump a bit faster than 1 and 3.

Anyway, with the oil warm when I idle down my pressure is down to about 3psi. I'm not sure if this is getting worse than before. Maybe I'm just paying more attention to it.
The hose for the gauge comes off the very top rear bearing of the transmission.
The transmission light doesnt come on. So without the gauge I'd have no idea.

Is this too low of pressure?
My first thought is to put new oil in the unit.

Any advise?
Should I be worried?

Thanks,
Rod

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post #2 of 7 (permalink) Old 05-10-2019, 12:20 PM
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Was on hold on the phone when I saw your post so logged in here quick, your hot pressure seems low, IMO I suspect your pump is getting tired. Don't have time right now but somewhere in one of the books I have on these it gets into pressures, flow and more on the tranny pumps. Another thing I do remember reading somewhere is that one never wants to alter the length and sizes of hoses used as it seems Versatile relied on flow restriction to equalize flow to the various ports. I have often thought of putting a gauge on mine too, just haven't got that far yet. I have a series 3 with the electronic system but got gremlins and am adding mechanical monitoring as needed and that tranny pressure system in in the list.
Some of what I am recalling might have come from discussions and emails I had with Scott about the tranny in mine when I bought it, going back a few years now, sure do miss him, like so many, gone too soon.


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post #3 of 7 (permalink) Old 05-10-2019, 10:43 PM Thread Starter
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My 850 versatile pulling the NH3 rig shows 10psi hot while working at 1900rpm and 5psi hot idle. Me thinks I better order another pump for the 975.
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post #4 of 7 (permalink) Old 05-10-2019, 11:19 PM
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Think buck is bang on the supply hoses.
I read somewhere only use original hoses from parts.
Not a made up hydraulic hose.
Something to do with pressure.
I saw only one complete failure that was due to lube pressure.
It was an 875 and the lube pump shaft or coupler failed.
It wasn't a pretty sight, the top shaft bearing must have piled up and it split the top of the transmission case wide open.
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post #5 of 7 (permalink) Old 05-11-2019, 11:58 PM
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Well got one helll of a head cold and just didn't feel like going back out in field after supper and took a minute to flip thru a couple books in the shop. Was some good stuff in a binder of service school notes, I do have more info somewhere else but for now there is this...and this covers all models of the 12 speed, no matter which tractor, as only diff is number of teeth on a few gears between V8 and inline 6 engine models. Early trannies have the coarse splines on the shift collars and shafts, Series II and up have fine spline. I know about the gears and splines from looking into replacement tranny for my Series III 875. Bought a whole 750 Series II tractor with 5100 original hours but with a bent frame, cheaper than the wreckers would sell me just a tranny, still haven't changed it, everything still works in my old one, I just don't have the bottom four gears, about 4mph is as slow as we can go lol.

Operating pressure is supposed to be set max 15 psi. Pressure is set by what they call a spring loaded check valve which is supplied directly from the rear manifold and screws into tranny case either just above shift cover or into the top of the cover itself on the right hand side. It simply dumps excess oil directly to sump.

The warning system on them is triggered at 4psi, so in other words, anything 4 or lower hot at idle is below spec.

Not sure why they are so elusive about the tech on that lube system, but I have a couple more books yet and I know its somewhere in one of them about the hoses. Thinking the flow test numbers might have come from Scott so they be buried in an email somewhere I guess. I seem to recall operating pressure to be 12-15 psi when hot as well, where that memory originates I well just can't remember lol.

There are rebuild kits for those pumps, but might be better in long run to just get a new pump.

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Last edited by albertabuck; 05-12-2019 at 12:00 AM. Reason: added comment
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post #6 of 7 (permalink) Old 05-12-2019, 04:56 PM Thread Starter
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Well pressure is slowly getting worse at an idle. Down to 1psi hot. Still 8-9psi while working.
The pressure light still doesn't come on with 1psi on my gauge. As soon as I release the clutch it comes on.
I'm ordering a pump first thing in the am. Will update pressures with a new pump.
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post #7 of 7 (permalink) Old 05-17-2019, 02:06 PM Thread Starter
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Installed a new pump. I now have 12psi with oil hot and engine revved up. 7 psi hot at an idle. I think I'm good to go now. $1600 for a pump
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