JD 4020 Powershift idler gear

[Kensk]

Wondering what the significance is of this idler gear/shaft on the output of transmission planetary.

Brought home a 1966 model, drained hydraulic oil and a couple bearing balls fell out. Found the ball bearing on front of idler shaft is the source and the idler gear has a couple teeth damaged on rear of gear. Going to be a yard tractor for running grain auger and moving pallets around with loader. Have a 4020 SR since new so it will keep doing the other jobs outside of yard. I can always split this PS unit next winter, but would like to run it a season and see if there are any other issues like maybe PTO slipping under load before considering splitting. Yes, I see it would be a double split so rather not do it right now.

 

[Fixingfarmer]

So I had a sr one that the clutch housing was actual split around one of the shaft bearings it looked like previous owner had split it and put it back together too roughly.

It took a whole clutch housing

If there’s bearing pieces falling out it’s time to see why

 

[Kensk]

I can't see in the limited space available, mirror won't fit and can't get good angle with bore camera. All I know is the balls are out and I found at least one ball broke into pieces so I imagine that ball got into the gear teeth and is what wrecked those teeth and split the ball.

I don't understand the function of the idler gear. Other bearing looks fine so the idler gear should continue idling along as transmission output shaft turns it. Drove the tractor home 15 miles, no idea how many hours/miles on it with this issue. Previous owner likely never knew problem existed. Park pawl on other side is good so that wasn't a source of damage.

 

[Fixingfarmer]

What’s the bolt about ready to fall in the gear train? There was a chunk of casting in the bottom of the one I did

I’d take it apart the last one it took a 2500 dollar rear half a tractor to fix and I got kinda lucky. That again WAS NOT a powershift if you want any hope of not destroying it further I’d suggest pulling it apart and seeing where you are at or the tractor if it isn’t done now won’t be worth fixing.

 

[Kensk]

That bolt is part of the shift collar mechanism used to disengage the drive train for towing. I beleive it is a stop bolt to limit the throw of the disconnect.

I will likely take it apart next winter. It got 15 miles on it last month and may not get more than 30 miles on it in the next 10 years. Probably put a half mile on it this coming year moving auger around. Yes, something can change any time, bind up and break a case. I couldn't move the end of shaft with a prybar so it is fairly stable. I would better know the risks if I understood what it does. There is a tapered bearing on shaft going into differential so thrust is controlled one direction for sure. Maybe this idler gear helps control thrust in the opposite direction but I can't see that either based on the design. Really don't understand it's role other than service manual calling it an idler gear.

 

[used red MN]

Really don't understand its role other than service manual calling it an idler gear.

Hello Kensk, welcome to YT! Sort of an arm chair mechanic on these, been to long ago. I think you are looking at gears 17 & 26 in this diagram. JD 4020 PS reduction gear diagram
It then drives gear 6 on the pinion, use right arrow to advance to that diagram.
I think it is just a way to drop the power down lower to the level of the pinion shaft so it matched the level in the synchrorange. This kept the final drive geometry nearly the same as when it was introduced in the 4010.
FYI, that is the older online parts catalog, last I checked the upgraded one only goes back to the xx50 or xx55 can’t remember which, there are a few exceptions.

 

[Kensk]

Appreciate that information, now I can better understand it. I didn't notice the second pinion shaft on the ring gear. So essentially this idler gear spins a second shaft to also drive the ring gear and so reduces the torque on what I would consider the main pinion shaft (the shaft direct from transmission). Even with the parts breakdown it isn't obvious till I look closer at it.

The idler gear is meshed with two gears and is why it seemed quite stable when I tried moving the shaft with a prybar. I expect I will be fine for now as long as I don't do anything to put high torque on drive train. Not an expensive repair, but I would like to run this tractor for a season to see if anything else needs attention before tearing into it. Don't want to throw a bunch of parts at it like dismantle and rebuild the clutches just because it is apart if they don't need it. Right now I am not 100% sure how this unit will run with an auger at full capacity, only ran auger empty to know PTO works and hydraulic valves raise and lower auger.

 

[used red MN]

No, and hopefully you are just not misnaming things. Only one pinion as shown in diagram ST2299168 (you arrowed right for) gear 6 there is being driven by the idler.
The synchro trans has two shafts as most gear transmissions do with paired gears with different ratios for the different speeds. In a synchro the upper shaft is on the crankshaft centerline and drops power flow through the gears to the lower shaft which is the pinion shaft, see this diagram.JD 4020 synchro range pinion diagram
Since the Powershift transmission utilizes all planetary gear sets the upper gear in your photo, the output of the PS trans that shifts the gears, is on the crankshaft centerline. As I said above the idler just drops the power flow down to the pinion.
Edit to add: I would suggest to keep the use of that tractor to pull anything at zero. If that idler comes out of place it might be possible that it breaks the transmission or rear differential case. Probably okay for PTO work.

 

[Kensk]

Yeah, I see it now. Had to go look at tractor again, that parts manual breakdown doesn't make things very clear and showing two pinion shafts on same drawing with no additional notes didn't help. There is a drawing specific to the power shift transmission pinion drive shaft.

Power comes out of transmission, is transmitted to idler gear which then transmits to pinion shaft which is in line, but below the transmission output shaft, so the arrangement is used to accommodate a change in height as you noted. And all torque is transmitted to the idler gear and shaft so that shaft will move with no bearing to support one end. I understand where I am at now.

 

[buickanddeere]

How about repairs now $ instead of repairs later $$$ ?

 

[Kensk]

Yes, been thinking about it last night and will probably split it. Never split a tractor before but this looks not too bad. I have the time and if a PTO clutch is slipping then it is a single split to get back in to do that and wouldn't be so bad if I have the stands already made up. The transmission is fine, shifts positively through the gears with some drag from 6 to 7th and I beleive it creeps forward when in neutral so likely a pressure adjustment will solve all that. Probably should go ahead and do that bearing now and deal with other unknowns later as they come up.

 

[used red MN]

Yes, been thinking about it last night and will probably split it. Never split a tractor before but this looks not too bad. I have the time and if a PTO clutch is slipping then it is a single split to get back in to do that and wouldn't be so bad if I have the stands already made up. The transmission is fine, shifts positively through the gears with some drag from 6 to 7th and I beleive it creeps forward when in neutral so likely a pressure adjustment will solve all that. Probably should go ahead and do that bearing now and deal with other unknowns later as they come up.

Is the creeping with the shift lever centered in the neutral slot? If so the creeping should be minimal in that position if everything is right. One of the more prevalent causes of creeping in neutral is warped clutch pack plates not the pressure. You should get JD tech manual and go through the diagnostic pressure checks before you pull it apart, that way you know what you got. A buddy of mine had a 200 head dairy in the 80s. He had four 4020 PS and a few bigger 30 and 40 series all with the PS trans. I used to help him chop silage using the 4020s on the wagons. We rarely used the clutch/inch pedal. If you are slowing down and want to go to neutral without shifting through every gear simply pull the shifter down to neutral. Then in the same motion quickly center the lever in the neutral slot. If you pull it down and don’t center it or push the clutch there will be an internal binding that if you are going very fast will slide the wheels and then let go somewhat. I wouldn’t recommend playing around with any of this until you get that “gear reduction” (idler) shaft fixed.

 

[Kensk]

I did find that if I moved the shifter to be in line with the park slot that it stopped creeping. If I pulled it straight down from 1,2,3 etc then it would creep a little, a didn't even notice it at first. I drove the tractor around yard maybe 6 times and it's been in the shop since doing other things like pulling final drives off to check brakes due to stuck brake pedal valve and now load shaft is out doing seals and bushings. I may as well keep tearing it down since fenders are off, hydraulic oil is out, rock shaft cover off, etc. Final drives back together, everything looked ok except a warped brake disc, rebuilt the brake valve since rust had made pistons sticky.

I have a service manual so had been reading about checking pressures and symptoms so was thinking I may need to tweak something there. At the end of the day, I don't need much from this tractor but I will do that idler gear bearing now in case my other 4020 goes down then this one can do some rock picking or pull some wagons if needed.