engine swap

[123cambo]

Has anyone swapped a cummins 8.3 into an LMTV yet?
Also wondering about if the transfercase can be swapped for an Axletech T600?[h=1][/h]

 

[coachgeo]

Folk on boards like this are enthusiast of the vehicle... as it is. Same with Unimog Boards, Suzuki or Harley boards etc. Like those boards here you won't find too many who have done nor are interested in major changes....... least not yet.

As to T-Case.. it's an unknown..... so much computer involved on the tranny. Talked to Allison direct when my Tcase cracked up about a possible TCase swap suggestion and their response was basically.... don't even consider it.

 

[Suprman]

Transfer case is married to the transmission. And it's all wheel drive. But if you throw enough money at something anything is possible. Swapping perfectly good drivetrain components for others that may or may not work seems unproductive.

 

[NDT]

Someone swapped in a ISB 6.7, that was BAE right before the current outgoing administration gave the FMTV contract to a blue state.

 

[123cambo]

While I understand people are brand loyal,I dont understand why?
I believe every vehicle has it's weakness's , rock crawler may do well in very rough terrain ( unimog) but not cruise highways at 60-65 all day. I know you can get Unimogs to go that fast but they are not within my budget!
I have read a lot regarding various surplus vehicles and know they all have their very loyal followers that deem that vehicle perfect as it is ( same as suzuki samurai that I think is under powered). I don't agree.
Many owners of LMTV's have swapped axle centre sections for better highway gears,some want lockers....etc.
Fuel economy and engine reliability are 2 on the top of my list and personally see the cummins to be a better engine ( my opinion).
I understand why the military goes with the designs it does but that doesn't translate to civilian/overland travel for me anyways. A/C, sound insulation etc etc. all good improvements.
I am not asking anyone to agree with my choices nor am I asking for your opinions about the platform, just looking to chat with those who have done the mods I am considering. Thanks

 

[Rebuilder]

While I understand people are brand loyal,I dont understand why?
I believe every vehicle has it's weakness's , rock crawler may do well in very rough terrain ( unimog) but not cruise highways at 60-65 all day. I know you can get Unimogs to go that fast but they are not within my budget!
I have read a lot regarding various surplus vehicles and know they all have their very loyal followers that deem that vehicle perfect as it is ( same as suzuki samurai that I think is under powered). I don't agree.
Many owners of LMTV's have swapped axle centre sections for better highway gears,some want lockers....etc.
Fuel economy and engine reliability are 2 on the top of my list and personally see the cummins to be a better engine ( my opinion).
I understand why the military goes with the designs it does but that doesn't translate to civilian/overland travel for me anyways. A/C, sound insulation etc etc. all good improvements.
I am not asking anyone to agree with my choices nor am I asking for your opinions about the platform, just looking to chat with those who have done the mods I am considering. Thanks

NDT mentioned it above but BAE put a 6.7l Cummins in the civilian version of the LMTV (SD BRAZOS). Looks like they used the Allison transmission and transfer case too. http://globalxvehicles.com/gxv-sd-brazos-specifications/ . I had this same idea when I was bidding on an LMTV with a cracked block but I didn't win it so that was that.

 

[doghead]

FMTV purists...

 

[123cambo]

NDT mentioned it above but BAE put a 6.7l Cummins in the civilian version of the LMTV (SD BRAZOS). Looks like they used the Allison transmission and transfer case too. http://globalxvehicles.com/gxv-sd-brazos-specifications/ . I had this same idea when I was bidding on an LMTV with a cracked block but I didn't win it so that was that.

Thanks!

 

[123cambo]

FMTV purists...

Right?

 

[123cambo]

Personally I love the Allison, wish we could have 2wd and low range but whats a guy to do?
Imagine the fuel savings if you could run it in 2wd?? And hubs???
I know it's just not practical during confict to ask for a time out while you get out and lock your hubs lol.
My thoughts at this point will most likely be to run the Cat until it has issues then swap it out for the 8.3 ($2500 for a rebuilt unit). I also want to change over to the AT4000 axles,lower ratios, lockers and disc brakes.

 

[DiverDarrell]

It's just money but... sure it's all possible. Gut the engine, trans, drop box, axles. Fab up new engine mounts, new cooling system and hope it all fits under the cab. Drop in the new engine. Trans combo (programmed together, add the axletech transfer case, with its new mounts. Cut brackets off the axletech 4000's fab and weld on new ones. Also remember the at4000 come in two widths and two gear ratios know which to get. Mount the axles, get rims that fit them as the budd rims won't. Now figure out new drive shafts and due to the longer engine trans transfer case figure out how to deal with the steeper drive line angles. Next up adapt the steering to the new axles. Finally wire the whole thing up and adapt or replace electonics. Install compatible gauges, build custom exhaust, and in sure there is a ton more.

I would do the same if I had the time, equipment and money. But would the cost justify the airlockers, the maybe 11mpg, the true transfer case? I'd drive the truck a bit first and see if you really need The upgrades.

Ive thought about this a lot, but after driving mine, and seeing how little room there is under the cab, will be hard pressed to fit anything bigger in.

 

[coachgeo]

Personally I love the Allison, wish we could have 2wd and low range but whats a guy to do?

Imagine the fuel savings if you could run it in 2wd?? And hubs???
...
My thoughts at this point will most likely be to run the Cat until it has issues then swap it out for the 8.3 ($2500 for a rebuilt unit). I also want to change over to the AT4000 axles,lower ratios, lockers and disc brakes.

if one was to look closely at the gear ratios available in the present FMTV Allison setup and look at ratios other trucks with a Hi/Low have....... you'll see there really is no significant difference. Each pretty much has the same ratios available... Also you go about reaching the tranny ratios in about the same way... you push a button.... like any other modern truck. Sure the FMTV style trucks have different names for what your selecting compared to a more traditional truck... but so what. The process on the drivers part is similar and the ratios available to the driver are all about the same.

Granted in the FMTV line it is AWD instead of 4wd but to the driver.... not much difference. Sure a hardcore offroader will notice the differences more.... but if they just let their mind adjust to AWD just like long ago when the had to adjust from 2wd to 4wd. etc. they will be just as happy on the trail. Especially now with a locker available.

So IMHO changing transmissions or Tcase.... really is not where you will find any advantage except for feeling more comfortable with the old way of doing things.

The lower MPG is only cause the military specifications that were asked for really didn't give as much a shiat about that. If they did they probably would only have gone with a different engine. Probably also not a 2:1 gear reduction in the hubs but only a 1.5 and/or a different ratio R&P. Then again... could have done it simpler by keeping as is but with an addition of an overdrive between the engine and tranny. Which IMHO should be something one should really really consider if one wanted to do some modifications. An overdrive in this area is one way Unimog's have gone about it and it has worked really well. Such as go 8.3 Cummins to 1:5 or 1:2 selectable overdrive box to the existing tranny/Tcase. Might need to swap rear axle to the Intermediate axle like they went to in 2008 so the shorter rear driveshaft from that arrangement won't result in a steep rear drive line angle. That would be a SWEEEEEET set up

Don't have enough knowledge of AT4000 axles to comment. Are you sure that with hub reduction in the LMTV Meritor axle you'll end up any better ratio overall? Will clearance be any better? Strength? Do commerical trucks this heavy use Disk brakes these days?

 

[DiverDarrell]

Axletech 4000 axles have a true planetary hub. For our trucks you need the wide axles, but they come with a super low ring and pinion. So you also need to buy the narrow axles and swap the center sections to get the higher gear ratio.

 

[coachgeo]

Axletech 4000 axles have a true planetary hub. For our trucks you need the wide axles, but they come with a super low ring and pinion. So you also need to buy the narrow axles and swap the center sections to get the higher gear ratio.

adding overdrive between tranny and engine sounds like a much simpler and less costly upgrade solution then buying two sets of new Axletech axles to end up with the desired width and ratios. Course if the axletech 4000's are already in use on vehicles and your buying them used... then that's a different story.

 

[123cambo]

if one was to look closely at the gear ratios available in the present FMTV Allison setup and look at ratios other trucks with a Hi/Low have....... you'll see there really is no significant difference. Each pretty much has the same ratios available... Also you go about reaching the tranny ratios in about the same way... you push a button.... like any other modern truck. Sure the FMTV style trucks have different names for what your selecting compared to a more traditional truck... but so what. The process on the drivers part is similar and the ratios available to the driver are all about the same.

Granted in the FMTV line it is AWD instead of 4wd but to the driver.... not much difference. Sure a hardcore offroader will notice the differences more.... but if they just let their mind adjust to AWD just like long ago when the had to adjust from 2wd to 4wd. etc. they will be just as happy on the trail. Especially now with a locker available.

So IMHO changing transmissions or Tcase.... really is not where you will find any advantage except for feeling more comfortable with the old way of doing things.

The lower MPG is only cause the military specifications that were asked for really didn't give as much a shiat about that. If they did they probably would only have gone with a different engine. Probably also not a 2:1 gear reduction in the hubs but only a 1.5 and/or a different ratio R&P. Then again... could have done it simpler by keeping as is but with an addition of an overdrive between the engine and tranny. Which IMHO should be something one should really really consider if one wanted to do some modifications. An overdrive in this area is one way Unimog's have gone about it and it has worked really well. Such as go 8.3 Cummins to 1:5 or 1:2 selectable overdrive box to the existing tranny/Tcase. Might need to swap rear axle to the Intermediate axle like they went to in 2008 so the shorter rear driveshaft from that arrangement won't result in a steep rear drive line angle. That would be a SWEEEEEET set up

Don't have enough knowledge of AT4000 axles to comment. Are you sure that with hub reduction in the LMTV Meritor axle you'll end up any better ratio overall? Will clearance be any better? Strength? Do commerical trucks this heavy use Disk brakes these days?

A selectable reduction box is the same as a low range, the difference between the design used on these trucks is that first is a very low gear used for really ruff stuff and once you leave first you lose that gearing advantage , a low range divides all gears.

 

[123cambo]

Axletech 4000 axles have a true planetary hub. For our trucks you need the wide axles, but they come with a super low ring and pinion. So you also need to buy the narrow axles and swap the center sections to get the higher gear ratio.

Thanks for this info!

 

[123cambo]

I am hoping the axletech axles work out,discs and airlockers??? Would be a huge improvement over drums and open diffs!!

 

[coachgeo]

A selectable reduction box is the same as a low range, the difference between the design used on these trucks is that first is a very low gear used for really ruff stuff and once you leave first you lose that gearing advantage , a low range divides all gears.

correct.. and off road you do not really need ALL the gears of a 6 speed divided when in a situation needing low range. Some you will never use. You only need say 3 low range gear ratios.. after that High range works fine... just stay in the low ratios of high range.

Here is what I remember from last looking at the various ratio charts.. sorry didn't record my observations and now not remembering details. check it out yourself.
. the Allison ratio of this first granny gear seemed essentially same ratio as first gear tranny/with a low range box?
. the Allison ratio of 2cnd gear seemed essentially the same ratio as your you would be in typical low range/2cnd-ish.. 3rd-ish gear Tranny..
. the ratios of Allison 3rd sat somewhere between low range/3rd gear tranny and high range/2cnd gear tranny. .
. 4th and 5th of the Allison sit at around same ratios in any typical truck (this heavy) high range/3rd and 4th gears.

So in concept..... End result.... Allison has pretty much Same "needed" ratios compared to a truck with low range gear box... just reached them differently.

Maybe I read the charts wrong? had to pull from various places and it got confusing. Curious what someone else finds if they dig around and pull charts of low range gear ratios and High range gear ratios..... then compare those to the ratios in the Allison w/granny

 

[123cambo]

imagine those gears running through a low range set, heading into unimog gearing territory!
I don't see pursuing this idea as a realitity due to the fact the 7th gear is actually in the tcase,2 steps forward 1 step back.....

 

[coachgeo]

imagine those gears running through a low range set, heading into unimog gearing territory!
I don't see pursuing this idea as a realitity due to the fact the 7th gear is actually in the tcase,2 steps forward 1 step back.....

Thought it was the granny first that is in the Tcase and not 7th?
The mulit ratios one ends up with via Unimog Cascade boxes and Crawler boxes is NOT in most Unimogs... just the few that will be doing heavy work (Agricultural, trenching, truck rallying etc)

Thanx for helping folk hash this out.