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Hi Gang,
As many of you know, I traded my M925A2 for a 1985 M998. It came from a great guy in TX named Rick. It was an interesting 3-way trade where Rick got 19kilo's deuce RV, I got Rick's M998, and Dave 19kilo got my M925A2. The HMMWV is not quite home yet. It is currently in Memphis awaiting some PMCS at a vo-tech school, which is run by another Steel Soldiers member, Brian. Once it leaves Memphis, it will head to WV and into my garage.
The HMMWV is mostly complete and in good shape except for the engine. The current 6.2L has been stripped down and is in bad shape. Since the engine is junk, I will be taking this opportunity to re-power the 998 with a 6BT Cummins. I have a 6BT in the garage on an engine stand waiting for a new home. It is a 190hp/475lb-ft tq P7100 pump engine from a school bus and it has approximately 170k miles on it. It is a runner and shouldn't require any significant mechanical work. I am planning on some new seals, securing the killer dowel pin, swapping in 3k rpm gov springs, adjusting the AFC, installing a more aggressive fuel plate, and swapping in some stage 1 injectors. That should really get that humvee moving. The 6BT is significantly taller than the 6.2L so the 998 will require a 2" body lift to clear the valve covers. I'm not real keen on body lifts, but it worked well for the H1 Alpha and a lot of hard core off road guys run them too. I don't want to hack the body so it's really my only option.
I have several options when it comes to transmission/t-case setups. Option 1 is use a 4BT bread truck adapter with the stock TH400. That's the cheapest option, but no overdrive will be a pain on the highway and the adapter requires tilting the engine or the transmission 10*. Option 2 is use an adapter/flex plate from a company like DeStroked, which will run around $1400 and swap in a 4L80E trans. I'm not a big fan of electronic controls in military vehicle, but I know the late model HMMWV's run them with success. I could also use a manual valve body in the 4L80E, but that will require a lot of shifting and a vacuum source to modulate the line pressure. Option 3 is run a 47RH 4-speed OD trans from a 1994-95 Cummins Dodge Ram followed with a NV241D. The 47RH is hydraulically controlled and would be pretty simple to swap in. I could also use an inexpensive Dodge engine/transmission adapter with this option. It will require new cross-member as well as new drive-shafts like the 4L80E swap. I am leaning this way currently. Option 4 is run an Allison 1000 5-speed, but that would also require an expensive PCM and adapter. The take-out Allisons are pretty expensive compared to the 47RH and 4L80E as well. If money were no object, I would probably go with this option for sheer toughness.
Along with the Cummins swap and drive-train swap, I will also be putting on some 24-bolt rims. The 2" body lift will allow for up to 40" tires, but I will probably run the 37" Goodyears initially. I foresee the Cummins torque wrecking havoc on the stock CV's and geared hubs, so some 12k shafts and hubs will go in at some point. Also, the added weight from the winch I'll be installing and the Cummins will require some heavier springs up front.
This should be a fun project. I can't wait to get the 998 home so I can get the body off of the chassis and start swapping. I'll post more pics and info as things progress. I welcome any feedback about the transmission situation.
As many of you know, I traded my M925A2 for a 1985 M998. It came from a great guy in TX named Rick. It was an interesting 3-way trade where Rick got 19kilo's deuce RV, I got Rick's M998, and Dave 19kilo got my M925A2. The HMMWV is not quite home yet. It is currently in Memphis awaiting some PMCS at a vo-tech school, which is run by another Steel Soldiers member, Brian. Once it leaves Memphis, it will head to WV and into my garage.
The HMMWV is mostly complete and in good shape except for the engine. The current 6.2L has been stripped down and is in bad shape. Since the engine is junk, I will be taking this opportunity to re-power the 998 with a 6BT Cummins. I have a 6BT in the garage on an engine stand waiting for a new home. It is a 190hp/475lb-ft tq P7100 pump engine from a school bus and it has approximately 170k miles on it. It is a runner and shouldn't require any significant mechanical work. I am planning on some new seals, securing the killer dowel pin, swapping in 3k rpm gov springs, adjusting the AFC, installing a more aggressive fuel plate, and swapping in some stage 1 injectors. That should really get that humvee moving. The 6BT is significantly taller than the 6.2L so the 998 will require a 2" body lift to clear the valve covers. I'm not real keen on body lifts, but it worked well for the H1 Alpha and a lot of hard core off road guys run them too. I don't want to hack the body so it's really my only option.
I have several options when it comes to transmission/t-case setups. Option 1 is use a 4BT bread truck adapter with the stock TH400. That's the cheapest option, but no overdrive will be a pain on the highway and the adapter requires tilting the engine or the transmission 10*. Option 2 is use an adapter/flex plate from a company like DeStroked, which will run around $1400 and swap in a 4L80E trans. I'm not a big fan of electronic controls in military vehicle, but I know the late model HMMWV's run them with success. I could also use a manual valve body in the 4L80E, but that will require a lot of shifting and a vacuum source to modulate the line pressure. Option 3 is run a 47RH 4-speed OD trans from a 1994-95 Cummins Dodge Ram followed with a NV241D. The 47RH is hydraulically controlled and would be pretty simple to swap in. I could also use an inexpensive Dodge engine/transmission adapter with this option. It will require new cross-member as well as new drive-shafts like the 4L80E swap. I am leaning this way currently. Option 4 is run an Allison 1000 5-speed, but that would also require an expensive PCM and adapter. The take-out Allisons are pretty expensive compared to the 47RH and 4L80E as well. If money were no object, I would probably go with this option for sheer toughness.
Along with the Cummins swap and drive-train swap, I will also be putting on some 24-bolt rims. The 2" body lift will allow for up to 40" tires, but I will probably run the 37" Goodyears initially. I foresee the Cummins torque wrecking havoc on the stock CV's and geared hubs, so some 12k shafts and hubs will go in at some point. Also, the added weight from the winch I'll be installing and the Cummins will require some heavier springs up front.
This should be a fun project. I can't wait to get the 998 home so I can get the body off of the chassis and start swapping. I'll post more pics and info as things progress. I welcome any feedback about the transmission situation.
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Can't wait for the fun to begin once it gets to your house. Your builds are always well documented and interesting. Looking forward to it!!
