D-18 and then D-19 development

Looking back, this is how I think things probably went down from 1958 until late 1961 for the AC tractor division. It was determined that a tractor larger than the D-17 was needed. How many $$$$$ that are allotted to the design engineers has a direct effect on what you'll get. A clear direction from the Sales Dept and upper/upper management on what they want is also extremely important. So, the D-18 proto, from the instrument panel forward to the front axle began as a D-17 diesel. Nothing more. Nothing less. The first change was to use the existing 6-cylinder B-series gasoline engine at 262 cubes. The diesel engine, as I understand it, got bulked up on the bore/stroke combo to around 290 cubes, naturally aspirated.  Both engines were then rated at 2,000 RPM. This placed the HP output at far less than they eventually wound up with. So, everything inside the torque tube, including the hydraulic pumps basic design, was pretty much the same as the D-17 tractor. Little $$$ spent so far. The transmission, ring and pinion and differential were also the same as the D-17, just inside a new housing. Again, very little $$$$ spent. The rear end housing/casting was indeed all new, and housed the new inboard final drives, so a bar type rear axle could be used. They spent some $$$$ on that, and for the most part, I have no issues with what they did. I've never had any failures of the new design final drives or axles/bearings, etc. The drawbar area was also strengthened and was pretty good. A 3-point hitch wasn't ready when the tractor was first released and that was too bad. Their 3-point was finally as good as anyone else's at the time, just not ready from the beginning. That, is how I feel the D-18 tractor came to be. The hydraulics still weren't "live" or more than 6 GPM's in flow. They did however have a new tripe spool hydraulic valve. And, the HP levels were found to be lower than sales demand was going to be.  The 100 HP D-21 was clearly a different and separate project and may have been started the day after the John Deere 4010 was shown to their dealers in August of 1960.

Edited by DrAllis - 1 hour 6 minutes ago at 11:00am

Series 4 D-17 was on the right.  D-21 was also on the right. They were "live" hydraulic pumps.  All the other D-series valves to the left of the seat (optional except for D-19) had to be on the left, so you could release the hand clutch to stop tractor movement with your right hand and then operate the hydraulic levers with your left.