Allison HT740 to Allison MH4000 Swap
Posted: Wed Aug 16, 2017 7:53 am
To recap the history about my project, around 10 months ago (time flies!) I purchased a 1982 Eagle conversion equipped with an Allison HT740 transmission and a 1994 vintage Cummins N14 500 HP engine. I drove it back from the west coast to Ohio. On the way home I lost reverse and the remaining gears started slipping badly. After returning home I was able to find an Allison MH4000 transmission that had been mated to a Cummins ISX engine in a motorhome for a very reasonable price from a motorhome salvage yard in Missouri. The salvage yard included the TCU and the touch pad shifter along with a short amount of wiring harness.
I had the transmission tested on a dyno at an authorized Allison service facility. To prepare the transmission for the dyno the technician replaced the fluid, changed the filters and replaced the multi-pin connector that had been damaged after removal from the motorhome. I was charged approximately $1500 by Western Branch Diesel for the dyno service so at the present time I have around $2600 invested in a functioning World transmission that the salvage yard told me had low miles.
My plan is to remove the shift cable assembly, trace the control cable back to the engine compartment and hopefully use that cable to fish the transmission wiring harness from the driver's area back to the engine compartment. I spoke with the foreman of a local automotive electric shop who is willing to wire the touch pad and ECU into the bus at my location for a reasonable hourly rate. While speaking with him he just happened to have in his desk a wall chart wiring schematic for Allison World Series transmissions so I'm confident he has the knowledge to wire it correctly. Hopefully I'll learn something while observing him work. I have a large garage with a grease pit I can use to lower the HT740 down into. I checked around and can rent a 2000 lb capacity transmission jack from a local tool rental center.
I'm wondering if I can remove the transmission from the coach myself or if I will need a helper to assist with the process. I was told by Western Branch Diesel that the torque converter clearance needs to be checked when changing to a different model of Allison transmission. While the transmission is out it would be a perfect time to re-ratio the differential so I can use all 6 gears of the World transmission. Can I use the transmission jack to do it? Any advice from those who have experience with an Allison upgrade or differential R&R would be most appreciated! -Jim
I had the transmission tested on a dyno at an authorized Allison service facility. To prepare the transmission for the dyno the technician replaced the fluid, changed the filters and replaced the multi-pin connector that had been damaged after removal from the motorhome. I was charged approximately $1500 by Western Branch Diesel for the dyno service so at the present time I have around $2600 invested in a functioning World transmission that the salvage yard told me had low miles.
My plan is to remove the shift cable assembly, trace the control cable back to the engine compartment and hopefully use that cable to fish the transmission wiring harness from the driver's area back to the engine compartment. I spoke with the foreman of a local automotive electric shop who is willing to wire the touch pad and ECU into the bus at my location for a reasonable hourly rate. While speaking with him he just happened to have in his desk a wall chart wiring schematic for Allison World Series transmissions so I'm confident he has the knowledge to wire it correctly. Hopefully I'll learn something while observing him work. I have a large garage with a grease pit I can use to lower the HT740 down into. I checked around and can rent a 2000 lb capacity transmission jack from a local tool rental center.
I'm wondering if I can remove the transmission from the coach myself or if I will need a helper to assist with the process. I was told by Western Branch Diesel that the torque converter clearance needs to be checked when changing to a different model of Allison transmission. While the transmission is out it would be a perfect time to re-ratio the differential so I can use all 6 gears of the World transmission. Can I use the transmission jack to do it? Any advice from those who have experience with an Allison upgrade or differential R&R would be most appreciated! -Jim