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Re: 4020 Power shift
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Posted by G/MAN on May 20, 2005 at 13:43:39 from (67.52.48.10):
In Reply to: 4020 Power shift posted by turnipman on May 20, 2005 at 12:28:25:
The "Powershift" tranny was an optional transmission for some models of John Deere tractor starting in '64. It has 8 speeds forward and 4 in reverse, and as the name suggests, it can be shifted on the go without clutching. It's roughly similar in operation to the automatic tranny in a car, except for it's not automatic. Every shift has to be made by moving the lever to another speed. On the 20-series powershifts, a transmission disconnect clutch is located on the rear of the flywheel. It can be disengaged to aid in cold starting by removing the load of the transmission on the engine. That's done with a lever on the side of the cowl. The "clutch" pedal is actually an inching pedal that allows you to modulate the transmission engagement for backing up to equipment and other close work. Pressurized hydraulic oil supplied by the transmission pump applies clutch packs and brake packs to achieve the various speeds. In good shape and properly maintained and operated, the Deere Powershifts are darn near bulletproof. The older ones can tend to shift rough, but that's pretty much just the way they work, since they rely on a mechanical means of controlling oil flow to the elements. The newer electronic powershifts are much smoother. I'd be wary of any tranny described as "weak". It could be as simple as the disconnect clutch I mentioned slipping, which would still require the tractor to be split, or as complicated as major problems in the clutch or brake packs, or a weak transmission pump. Those will require a lot more labor and money to correct. If you're considering purchasing it, have someone with familiar with the Deere powershifts check it out as much as possible. I'd check the system and lubrication pressures in ever gear at the very least. The transmission can be disconnected from the rear-end using the "tow" disconnect, so you can do diagnosis without the tractor actually moving.
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