Mechanical L-10 to 2006 EGR ISM CM875 repower
By Robert Reed
Here it is. It took me from April 10 to May 10 2006 to finish this beast. It was a mechanical STC Pt pump L-10 275 mated to an Allison HT700 hydraulic automatic transmission that is cable shifted and had a cable step modulator feedback to the mechanical throttle linkage.
The task was to repower this old 1990 bin loader garbage truck with a brand new, not recon, computerized digital full authority EGR ISM CM875 and figure out how to be able to step modulate the transmission in the absense of a mechanical throttle linkage, making the mechanical step modulating cable not possible to use. The transmission was a like for like swapout of the HT700 Allison. The old engine is pictured below.
The ISB, ISC and ISL engines have a programmable feature in the ECM and that ECM has an output wire for actuating the step modulator. But the ISM CM875 doesn't have this feature and no software calibration file has it for the ISM.
The step modulator was converted from cable actuation to a 12 volt servo motor that mounted on the transmission right where the cable was formerly attached. Step modulation (usually called "kick down") is an "either-or" function, in other words, it is either 12 volts on (actuated), or 12 volts off (relaxed), and nothing in between. The electric modulator is actuated "on" when the throttle reaches 80 percent increasing transient, and it de-actuates at 65 percent throttle decreasing transient. It lets the transmission know what the driver wants to do and where the engine is. It is the electronic equivalent of the cable modulator that attaches to the throttle linkage in all-mechanical setups. ISB, ISC, and ISL engines have this function that can be programmed and has an output pin to operate the modulator as mentioned above.
Everybody at Cummins figured the function was not included because nobody would be fool enough to mate an ISM engine type to a cable shift old-school Allison that has no data link capabilities. The assumption is that all auto tranny ISM's would be mated to Allison World or Voith Electronic automatics that can read a datalink.
Above: The finished project with the EGR ISM CM875. Too bad you can't see the engine for all the things in the way.
Part of the time burned on this project was researching and figuring out how to make the step modulator work. We toyed with ideas using throttle pedal mounted microswitches and other schemes. Nobody at Allison knew what an ISM CM875 EGR engine was, so they couldn't answer me, and nobody at Cummins had heard of anybody trying to mate one with a cable shift old school Allison. Ron Pasquetti at Valley Power Systems in Sacramento dug up some documents on interfacing the older M11's and ISM's with HT700's. He said it needed a device called a "data link translator" which is connected to the J1587 data link wires (which are usually the same wires as the J1708 data link), and also reads tach information from the engine ECM. The data ink translator listens full-time to the J1587 data link. It then turns the step modulator on and off by grounding and ungrounding a relay based on what it sees on the data link throttle position sensor information and engine speeds. It comes pre-programmed for the 80/65 throttle set points.
The second problem was splitting the Vehicle Speed Sensor output from the single signal mini gen on the tailshaft of the Allison. Allison transmissions use worm gear drives so you can't just put a 16 tooth tone wheel in it. ISSPRO makes a neat little box that takes one speed output and gives you five outputs all independent of each other, and any of them can be shorted to ground without affecting any of the other ones. The 12v power supply can be reverse connected without damaging the unit also. It works like a charm.
Other usual major repower related problems abounded, like converting the fan hub from the old non-serpentine style but microgroove to a microgroove serpentine belt. It was amazing that the hub worked for the serpentine belt. The fan mount was a wierd offset to the right mount to accomodate the offset radiator and engine mount schemes. Of course, after going through all the effort to make the hub work, I found out the fan couldn't be mounted after the engine went in the truck because the trailing edges of the blades hit the serpentine tensioner which the old engine didn't have, so I had to convert it to a Horton fan hub with a 1 inch spacer and move the radiator forward one inch.
Having to use the old fan hub mount made the new upper radiator neck on the EGR ISM unworkable, so I had to hack the new thermostat housing/radiator neck from one nice single part into 3 separate parts and then braze them back together so it would route out between the alternator and the EGR bullshit (you can see it in one photo of the RH side of the engine). Also, the CAC plumbing was a total fiasco, with major hacking of existing pipe into a totally new arrangement and routing, with about 4 feet of old pipe left over. Every change meant changing something else to make room or to make a mount, and the changes just never ended until they ended. Debugging after getting it into driveable condition was the stuff nightmares are made of but in the end I prevailed.
This was a living nightmare to get finished and de-bugged. It wouldn't let go of me. I spent about 25 to 30 hours of my own time on it on weekends just brainstorming and fabricating. Apparently this was an experiment by CWI to see if it could be done at all and have a useable vehicle. Heat rejection was a concern since these engines need about 10 to 15 percent more rejection capability from the cooling system. This truck has a front mounted PTO with a shaft that goes through a hole in the radiator like a forklift, and we had the radiator re-cored to a much thicker higher capacity core. It easily makes it to the top of Berry without any trouble. City Garbage told us that new vehicles intended for the same duty would cost them about a quarter of a million dollars, so that's why they did this seemingly ridiculous thing to an old garbage truck. These garbage trucks are getting too valuable to knock in the head.
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