TH,
The original Doe had only a clutch connected to the back tractor. You put the front one in gear, set the throttle then went back to the rear tractor, put that in gear and away you went. The thing then developed to either electric shift or a system worked with car brake cylinders to work brakes, clutch and dif. lock as well as the gears. The ones I worked on had linked throttles so both tractors worked together and some had brakes on the front wheels as well as the back. The best one I ever came across was a Doe 130 which was two Ford 5000,s joined. It was a Selectospeed with a long cable from a lever about 3' long connecting front and rear gearbox controls. You watched the exhaust on the tractors and the one throwing out the most black smoke was in a different gear to the other so the lever had to be jiggled to get them both the same. but I have never seen a better pulling tractor. They made a version with a Ford 5000 in front and a Ford 7000 in the rear. This allowed the extra horse power to drive the hydraulics and power steering which were worked from the rear tractor. I loved to get one in the field on some really heavy work after I had serviced it. Just for a little test run you understand. :0) regards Brian
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