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 - 21 Dec 2025 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.

Hey Doc, I was fortunate to have talked at length about that time with Ray Dogget of AC. He was the marketing manager in the mid '60's. They had the upgrade to the D series in the 100's and the 190XT was not planned. The D21 was planned for the 100 hp unit. The problem was the horsepower wars and power demand got away from all brands, especially AC because of the lower production and lack of funding resources. They did know the first 190 which was a D19 basically, would not hold up long term especially with the harsher shifting power director. They had the slightly larger second tranny underway but the market and dealer feedback left him with a lose/lose decision. The turbo'd 301 was no issue - the tranny was. He had to weigh between putting out a product that would fail and have to be fixed with a fix that was 2 years away or stay where they were and lose out on the hottest segment of the market. The 4010/4020 806 and all the others.  He made the decision to build the units and suffer the cost of redos. Ray said about 40% never failed - the rest did and it was not pretty. The others in the market were not without their failures as well. AC's advantage was they at least had a plan - the others were caught by surprise when they broke in numbers. The memphis branch and others had techs working there that were keeping rebuilt exchange rear end assemblies on hand with the larger gears before the last sn 4 pinion change. They also discovered the fact that the shift rail set up was really bad and the units suffering from jump out were not completely shifting into gear. Billy Cruse and Bruce Derrington out of Memphis Branch made sure the remaan units were correct via moving the detent. The same fate befell the D21 . AC had no idea where the HP race would end. The hot 190XT's would out perform the first naturally asperated 426's. The tractor division had a target of 94 hp they agreed would meet market demand and tested the unit at Nebraska. The units on production tractors probably had a little more hp and they also had a torque screw that when backed out, yielded over 100 hp for most. This added to the tranny woes when tied to the ground with duals, fluid and weights. It also put the HP over the D21 in stock form which couldn't be turned up much w/o a turbo. It was much like the 7000 vs the 7010 - same hp with a couple of tons more weight. Then the tubo was added and the wider bull gears came into production and field retrofits required housing grinding without the modern tools we have today. The 220/210 were a stop gap waiting on the 7000 series that started engineering in the late 60's. Too much market move for a company built on WD/D series mentality.  It is amazing they did accomplish what they did without throwing in the towel. Then when they finally did get over the hump - 1980's farm economy came along.  It should also be noted they gave about all attention to high horsepower units and bought the under hp units as was the plan. The issue was they trusted Fiat. AC helped engineer a 5 speed power shift for the 6070/6080 and soon to be 6090 - I held a shifter in my hand.  After the sale Fiat stole the unit but now without the AC engineering help, never got it into production that I know of. OK this is too long and rambling but the football games are boring.       

I agree, actual history of our favorite brand of machines, as told by those who were there or by secondhand accounts from those who interacted with the pioneers of the brand, is incredibly interesting and rare. Thanks for sharing your experience. So many of the old timers are passing on, and this type of knowledge needs to be preserved and shared as much as possible. Swinford’s book is an invaluable resource, but so are you guys who have had many years of experience working for A-C, it’s dealers, or just using and repairing their equipment. Much appreciated!