The Antique John Deere Transmission
Jumps Out of Gear
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Meli.... My problem. My 1945 hand start B jumps out of low range in any gear, when under load (ie. going up a steep hill, for instance). The range lever actually kicks over to the right so far that it interfers with the clutch lever (which can make for an exciting moment or two when on a very steep hill). When it is kicked over, it is basically between or out of gear. If I move the range lever to the high side, the tractor stays in gear and operates fine. 
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Yeah, I've had at least three tractors that did that. One had low range lever acting just like yours. One of them jumps out of second gear, but it does it on the main shift quadrant. And that's the gear I like to use to pull the disk harrow. Then there is a late styled 1950 B that jumps out of third gear when running DOWN a hill!
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| I have studied my parts manual, asked other B owners and have not been able to determine the cause. I removed the transmission cover and cannot see anything obviously broken. |
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I have never dug deep into the bowels of the the transmission to prove it, but I have been told that it happens due to wear on the gears, especially on the pair of gears that is used most often. They are spur gears (shown above and below). Notice that the faces of the teeth are parallel to the shaft. Here's what I picture is happening: two gears are not quite completely meshed, due to carelessness, poor adjustment, or some other maloclusion. One gear wears more on one side, the other gear wears more on the other side. Over the course of geologic time they become tapered, and tend to push each other apart, especially under load. The more they push each other apart, the worse the uneven wear gets, until the tractor comes down with "jumping gear syndrome". MY solution to this problem is to park my FOOT firmly in the spot where the shift lever goes when it jumps, to prevent it from doing so. Of course, the REAL solution to the problem is to take the transmission apart and replace the offending pair of gears with new ones, or at least with BETTER ones. I haven't been brave enough to try it |
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| I realize this is not much to go on, but I do not know enough about the inner workings of the transmission to diagnose the problem myself. |
| The Model B service manual has an extensive chapter on the transmission and I believe it would guide you through the assignment should you choose to accept it. You can get one HERE |
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