I've been working on a 1966 A II Gleaner.  I've been having problems with the variable speed drive...I can get the variable speed to get the ground speed to go faster but will not slow down.  Off the hydraulic valve stack there is a single hose that feeds the variable speed, so the oil is supplied and returned through the same line.  When I operate the valve spool stroke full in and out manually it supplies oil over the the variable speed but will not return the oil back, I have remove the oil supply line to relieve the pressure on the varilabe speed get it to return back to the slow position.  I guess my question is what is suppose to happen in the valve stack to allow the oil to return to the sump?  There is a poppet valve in the valve stack, but from what I can tell that is there to hold the pressure in the fast speed posistion...something has to tell the poppet valve to release the pressue when you want to slow down?  Just wondering if anybody else has run across this problem before or not...Thank you.

Remove the valve's spool rod(plunger)from it's body. There is usually a snap ring at it's front. The rear can be a hollow nut?. Once the spool is removed, clean/inspect all the dirty oil from within it. If you find more than just dirty oil(yucky solids?), then unbolt the valve body from it's valve stack(multiple valves sandwiched together?), if that is how its arranged? And, thoroughly clean all valves/springs/portals, etc.  Probably best to replace o-rings at this time?

Here's a copy of Gleaner AII Dealers Parts Catalog, Section II - Combine, March 1965, hydraulic control valve pages 138 & 139. I believe the valve you're interesting in is Valve #3.

Are the bearings good?  

So you have an AC Gleaner Service Manual? I do too. Maybe you haven't found it's hydraulic circuitry fold-out near the back of the manual? If not, here is a copy of my gleaner K/F hydraulic circuitry that shows the functionality of each component. It shows by colors how the Variable Speed Valve's internals function. In that same service manual's hydraulic section, try going to page 7 where it discusses in detail how the variable speed valve(VSV) operates.

It appears that you've addressed most every other avenue per your A2's hydraulic restoration? So my guess is that some item(s) within your VSV are either worn out, absent, or incorrectly placed? Hoping the above illustration helps you? You do restoration right? So do you have multiple gleaners setting about? If so, then remove an UN-touched VSV from one of parts machines & insert it into this A2's hyd system & see what happens. If that corrects the problem & you want to know whats up with this problematic VSV, carefully disassemble them both & compare.

Oldoug wrote: I have never operated this combine before…from what I can understand you should be able to push the variable speed lever ahead and the combine should maintain that speed with your hand off the lever…is that correct? If that is correct that means the number 18 poppet has to hold that oil pressure on the cylinder…so when you pull your lever back to slow down something has to push the poppet ahead to release the pressure to collapse the cylinder…what is supposed to do that?

Yes, the combine cab's VS lever has 3 positions (PUSH forward for faster, PULL rearward for slower, & neutral middle). To operate the VS, the combine's engine needs to be running & transmission in neutral or travel motion. Gleaner hydraulics are responsive to its engine rpms ~ high engine rpms->max hyd response, lower engine rpms->less hyd response. Sitting in the operator's cab seat with the cab door locked open, you can lean to your left & watch the VS belt operate as you push/pull VS lever. You will know that the VS belt's tension is properly adjusted, by seeing about 1/8" of outer sheave of the trans input shaft showing above the top of the VS belt when it is in slowest setting. There will be no slack in the VS belt at any setting. At combine startup, be patient for VS to speed up. It's oil takes a bit to travel from valve to VS cylinder, activate, & then belt response. 

Hydraulic oil used in Gleaner is RED automatic transmission Mercon II or whichever is latest version. Maintenance: new VS belt will stretch into norm after first day or so, then readjust tension via belt idler. Grease guidelines: CANISTER SPRING should be lightly coated with grease at clutch repair, INPUT SHAFT BEARING ON CLUTCH BELL HOUSING gets ONE SHOT per month or so. CLUTCH THROW-OUT bearing gets ONE SHOT once a week. INNER HUB of sheave on trans input shaft gets ONE SHOT per day. It contains orings that allow grease to be smeared across input shaft. Any EXCESS grease can be squeeze past inner hub bearing & lands inside canister spring ~ very bad! Don’t over grease it.