The GMB Ferguson TEA20 position control

One of the snags with the Ferguson TE20 series of tractors is the rear linkage hydaulics only implements the "Ferguson System" or draft control, which is fine if you are ploughing but otherwise not so useful. Most tractors since then have the option of simple position control, which means that there needs to be feedback from the implement height to the hydraulic system. This is quite easy to do by cross-linking the rear arms to the control lever itself. This is how I did it on our 1948 TEA20.

The ball race thrust bearing is important as there needs to be very low friction between the wingnut and the clutch or it will undo itself. The 3mm piece of fence wire links the friction device to the control and is just about strong enough - the idea being that if things go wrong the hydrualics are so powerful that they will destroy anything that gets in their way so best not make it too robust! Note that the wire cannot link directly to the control lever arm itself because it has the wrong angular aspect with respect to the friction device, so the clamp on it offets the attachment point enough so that the friction lever operates from 45 degress left to 45 degrees right as the control lever goes from its top to bottom position.

To use the GMB position control, roughly adjust the implement level using the control lever, then as you get the height you want just tighten the wing nut, enough that the friction clutch is just strong enough to operate the control lever (mine was quite stiff) but not enough that you cannot override it. Once engaged you tweak the height up or down by moving the control lever a short distance in the appropriate direction. On my tractor the lever stays an inch or so before the upmost position, the point where the valve operates with no draft load on the top link.

Here is what it actually looks like.

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