John Deere 40U Questions

[RiverRancher]

Does the 1954 JD 40U need the 48 inch or the 72 inch coolant temperature gauge line? I’m going to order a replacement for my tractor and not sure which to order.

Did all JD 40U tractors with an hour meter have a wire going from the ignition coil to an oil pressure switch at the front of the engine below the generator? The man working on my JD said there is no second wire at the coil negative terminal and I know there is no oil pressure switch there. Were some 40U made this way or is this a previous owner’s modification?

Did the 1954 JD 40U come stock with the tall gas filler cap (AM3892T) or did some come stock with the short (normal looking) cap?

 

[Jim.ME]

Welcome to the forums.

A tape measure will give you an indication as to the length of capillary tube needs on the gauge. If in doubt get the longer one, it won't hurt and I doubt there is A significant price difference.

Many used the oil pressure switch below the generator to control the hourmeter. It could be wired to provide power or ground. How it was wired would say if there was a wire from the coil needed or not.

 

[Glen D Anderson]

Does the 1954 JD 40U need the 48 inch or the 72 inch coolant temperature gauge line? I’m going to order a replacement for my tractor and not sure which to order.

Did all JD 40U tractors with an hour meter have a wire going from the ignition coil to an oil pressure switch at the front of the engine below the generator? The man working on my JD said there is no second wire at the coil negative terminal and I know there is no oil pressure switch there. Were some 40U made this way or is this a previous owner’s modification?

Did the 1954 JD 40U come stock with the tall gas filler cap (AM3892T) or did some come stock with the short (normal looking) cap?

Our '54 40U has a regular style fuel cap.

Like Jim said you'll want to measure to confirm. & it'd only be a guess, but I'd say the 72" temp. gauge tube. You can always coil up the unused portion at the bottom of the operators stand / guage panel.

Our 40U never came with an hourmeter to my knowledge. FWIW our machine is 12V(converted from 6V)& I installed an hourmeter with the ground side controlled by a pressure switch(W/NO & NC contacts). I also used that same pressure switch to control an idiot light for oil pressure. Obviously it's not factory or period correct but it is functional.

 

[RiverRancher]

Our little workhorse is a JD 2720. The 40U is my wife's toy. She loves to hear the engine run: POP..POP............POP..POP. I am no longer able to go out and work on it, so I hired a local mechanic to put a set of points in it. Pretty bright young man, about 30 years old, quite familiar with a wrench. He couldn't get it started. The engine had no spark. Unfortunately, he is about as ignorant with a carburetor run engine as I am with a computer-controlled engine. I realized this when we were having a trouble shooting session at my kitchen table. After considerable discussion, I discovered that he had never seen a set of points before and had no idea how they work or what they do. He looked up the point gap and set the points to the correct gap....when they were supposed to be closed. So, with the points never closing, there was no way to get a spark at the plugs.

During the troubleshooting, I was following the factory wiring diagram and told him to put the meter probe on the coil terminal with two wires on it. He said that both terminals only had one wire on them and there was no other unattached wire nearby. At the time I just assumed that the 40Us were different than the rest of the 40s and the diagram didn't mention this. Being curious, I researched this and found the missing wire is supposed to go from the coil negative to oil pressure switch below the generator then to the hour meter. It seems like all JD 40s with an hour meter are supposed to be wired this way?