Rewiring 939 Series 5-Ton to Eliminate Electronic Controls

I've had an idea rattling around my head for a couple of months. I am exploring the feasibility of eliminating electronic controls from my M923 5-Ton cargo truck. I like the simplicity of the deuce and think it is possible to replicate that system on most 939 series trucks.

I figure to keep solenoids, like for fuel shutoff, starter, air horn, but don't like the idea that an electronic component can fail and leave the truck operational.

Attached are a couple of diagrams that illustrate the complexity I would like to eliminate.

It wouldn't be as idiot proof for an inexperienced operator but then anything that heavy isn't anyway.

Comments?

they have survived a long time as is, I am not so sure I would re engineer something that may be more unreliable than the original system, just ask us Germans, we over engineer everything and that has taught me some things.

I have years of experience designing and retrofitting industrial control systems from the ground up. I have looked at process lines that weren't working correctly, interviewed the operator and designed new control systems that would make the process equipment do what the operator specified.

I prefer the most simplistic mechanical controls possible. Like Start/Stop.

The classic example of perfect controls to me is a start button to crank a diesel engine, and a cable to shut it off. Works every time.

I have thought about some of the same modification and also removing the air lock on the transfercase shifter, just less to fail

You have to REMEMBER that a lot of the interlocks on the 900s is NOT for safety but to keep the young and dumb from DESTROYING the truck, just like the control box on the 809s keeps you from trying to start if the truck is running, this makes it hard to roll start unless the the fuel shut off is turned in.

So I would guess you could get rid of at least 75% of the crap you are talking about and go back to the KISS principal, this is why I have been talking about GITTING RID of the protective control box for the 809s/900s and go back to how the m39 series is wired

So we have both been talking about it. How about we start doing it? I could sure use your help.

For simplicity's sake, I am going to start with the engine start stop circuit. In your experience with the NHC 250, is there a good place to connect a manual fuel shutoff? Can the emergency stop be modified to use for this? How about bypassing the fuel shutoff solenoid? Seem reasonable?

Any wiring changes I make, I will diagram them and post them here.

Every 855cid Cummins I've ever seen had an electric fuel shutoff and the manual screw in override. I'm not saying they don't make a cable control but I've never seen one.

The protective control box has been simplified in this mod, which was done for Chris's truck a few years ago.
Remember that a huge amount of the wiring is for the diagnostic system, even includes some shielded wires running to it.

m16ty said:

Every 855cid Cummins I've ever seen had an electric fuel shutoff and the manual screw in override. I'm not saying they don't make a cable control but I've never seen one.

Click to expand...

Even my '69 8x8 has an electric solenoid operated fuel cut-off and that's simply due to the fact that it would be more difficult to run a mechanical link to the IP.