Manual transmission LMTV?

[Off-Road-RV]

New here and I'm exploring the possibility of building a LMTV expedition vehicle.
I've been full-time RVing for the past 3 years, in an 5th wheel. Medical issues with my wife has us off the road for a while. Many hours have been spent on this site, and others getting educated and confused at the same time. Should I make this idea a reality, I want a highly reliable simple to repair. In the ability to get back to civilization without a Chinook. I haven't seen where anyone has put a manual transmission and manual transfer case behind a 3126 mechanical engine, in an LMTV. Does anyone have knowledge of this being done before?

 

[simp5782]

I've figured it all up before.

You would probably be using T1138 transfer case since it has an overdrive.

Any manual transmission setup you could use what the old cabovers used for the shifter linkage.


Clutch pedal would be a freightliner Cascadia setup that is hydraulic with an air assist slave.

With the T1138 and any 10spd I feel as though it would be too much speed on the shaft and it would throw em.

 

[GeneralDisorder]

Why would you do this? The auto is better in every single respect. 1st gear is your low range, and you have a torque converter so you can crawl at real low speeds.

3126b is not mechanical. It has an ECU similar to the C7.

3116 is the mechanical engine used in the A0 but the transmission still has a TCU. But these "mechanical" engine trucks had a host of other issues - PDP panel problems, poor charging systems, wiring harness issues, etc. And the 3116 is generally considered one of the worst CAT engines made. The 3126b is better, and the C7 is actually pretty decent for what it is. The MTBF of the A0 3116 trucks was not that impressive - something like 14k miles. The MTBF of the A1 and A1R trucks won awards from the US Army - they more than doubled it to like 35k miles. Mind you think is HARD military usage with Army personnel that are usually 18-24 y/o kids that treat them like you would expect a young kid to treat gear they don't own, and don't have to maintain or repair when they break it. Not RVing.

The late 3126b and C7 trucks have extremely reliable Allison 3700SP's. Carry an extra TCU with you (they are about 2lb and are the size of a couple decks of playing cards) if you are concerned. You give them good power and ground circuits and maintain them and the transmission will be the least of your worries. Army technicians regard the Allison's in these trucks as basically the most bulletproof part of them. With any reasonable amount of care they are SOLID.

 

[Off-Road-RV]

I'm thinking about the T138 stronger case but no OD. If I go with a 13 or 18 speed trans I'd have .73 OD and 3.07 rears, I'd run under 2200RPM at 65 MPH. Fast enough for me.

Thanks for the clutch info, hadn't given it much thought, only that it would need to be hydraulic.

Shifter, I'm thinking Kenworth K100e cable set-up might work.

With the 13 or 18 speed trans low would be 12:1 or lower, then low in the transfer case, where is the week link? I like that I could creep along at idle. But even that could twist a driveshaft or blow a rear.

I've figured it all up before.

You would probably be using T1138 transfer case since it has an overdrive.

Any manual transmission setup you could use what the old cabovers used for the shifter linkage.


Clutch pedal would be a freightliner Cascadia setup that is hydraulic with an air assist slave.

With the T1138 and any 10spd I feel as though it would be too much speed on the shaft and it would throw em.

 

[simp5782]

Why would you do this? The auto is better in every single respect. 1st gear is your low range, and you have a torque converter so you can crawl at real low speeds.

3126b is not mechanical. It has an ECU similar to the C7.

3116 is the mechanical engine used in the A0 but the transmission still has a TCU. But these "mechanical" engine trucks had a host of other issues - PDP panel problems, poor charging systems, wiring harness issues, etc. And the 3116 is generally considered one of the worst CAT engines made. The 3126b is better, and the C7 is actually pretty decent for what it is. The MTBF of the A0 3116 trucks was not that impressive - something like 14k miles. The MTBF of the A1 and A1R trucks won awards from the US Army - they more than doubled it to like 35k miles. Mind you think is HARD military usage with Army personnel that are usually 18-24 y/o kids that treat them like you would expect a young kid to treat gear they don't own, and don't have to maintain or repair when they break it. Not RVing.

The late 3126b and C7 trucks have extremely reliable Allison 3700SP's. Carry an extra TCU with you (they are about 2lb and are the size of a couple decks of playing cards) if you are concerned. You give them good power and ground circuits and maintain them and the transmission will be the least of your worries. Army technicians regard the Allison's in these trucks as basically the most bulletproof part of them. With any reasonable amount of care they are SOLID.

if you are saying an allison is better, stronger, more reliable than an eaton fuller 10 or 13 speed in a similar application then you must be making a joke right?

I'm thinking about the T138 stronger case but no OD. If I go with a 13 or 18 speed trans I'd have .73 OD and 3.07 rears, I'd run under 2200RPM at 65 MPH. Fast enough for me.

Thanks for the clutch info, hadn't given it much thought, only that it would need to be hydraulic.

Shifter, I'm thinking Kenworth K100e cable set-up might work.

With the 13 or 18 speed trans low would be 12:1 or lower, then low in the transfer case, where is the week link? I like that I could creep along at idle. But even that could twist a driveshaft or blow a rear.

You wouldn't want to run the T138 it's a sprag unit. Not a good choice you will have to put air to it for forward select or rear select. It also only engages when the tires slip. Time the tires slip its too late for a big truck its already down.
An 55000 Oshkosh unit is a reasonable unit. 2.66 low and .98 high.

You don't need an 18 speed if you have a transfer case. Not to mention the GVW of any FMTV is too low to even even need an 18spd for any reason. 18spds only split the low range. Really not needed with a transfer case.

A 10c eaton will work fine. Cheap. It can take double the power that the allison 3700 can handle.

You can flip the rear 2 gears on a 13spd and you get a .74 and .62 in 13th. Basically turning a RTO-14613 into an RTOO.

 

[Off-Road-RV]

I know Allison makes a tuff trans, and I’d be all over it if I wasn’t planning to take this vehicle far off the beaten path. I want to be able to start and drive out with out any electric. I’m even toying with an air starter.

CAT did make a 3126 "mechanical" engine, used in marine and industrial here in the USA. I don’t think it met EPA for OTR use.

I could use a PDP panel and wiring from a A1 truck, I’ll need to custom some of it anyway.

I intend to rebuild or replace every part on this vehicle, lots of $$$, I'm an old guy that worked hard for them, so I know how to take care of my things.
18-24 y/o kids won't even be aloud to touch it. LOL

Why would you do this? The auto is better in every single respect. 1st gear is your low range, and you have a torque converter so you can crawl at real low speeds.

3126b is not mechanical. It has an ECU similar to the C7.

3116 is the mechanical engine used in the A0 but the transmission still has a TCU. But these "mechanical" engine trucks had a host of other issues - PDP panel problems, poor charging systems, wiring harness issues, etc. And the 3116 is generally considered one of the worst CAT engines made. The 3126b is better, and the C7 is actually pretty decent for what it is. The MTBF of the A0 3116 trucks was not that impressive - something like 14k miles. The MTBF of the A1 and A1R trucks won awards from the US Army - they more than doubled it to like 35k miles. Mind you think is HARD military usage with Army personnel that are usually 18-24 y/o kids that treat them like you would expect a young kid to treat gear they don't own, and don't have to maintain or repair when they break it. Not RVing.

The late 3126b and C7 trucks have extremely reliable Allison 3700SP's. Carry an extra TCU with you (they are about 2lb and are the size of a couple decks of playing cards) if you are concerned. You give them good power and ground circuits and maintain them and the transmission will be the least of your worries. Army technicians regard the Allison's in these trucks as basically the most bulletproof part of them. With any reasonable amount of care they are SOLID.

 

[Off-Road-RV]

Thanks, hadn't came across the 55000 Oshkosh, looks good.

I like the 13 speed idea.

if you are saying an allison is better, stronger, more reliable than an eaton fuller 10 or 13 speed in a similar application then you must be making a joke right?

You wouldn't want to run the T138 it's a sprag unit. Not a good choice you will have to put air to it for forward select or rear select. It also only engages when the tires slip. Time the tires slip its too late for a big truck its already down.
An 55000 Oshkosh unit is a reasonable unit. 2.66 low and .98 high.

You don't need an 18 speed if you have a transfer case. Not to mention the GVW of any FMTV is too low to even even need an 18spd for any reason. 18spds only split the low range. Really not needed with a transfer case.

A 10c eaton will work fine. Cheap. It can take double the power that the allison 3700 can handle.

You can flip the rear 2 gears on a 13spd and you get a .74 and .62 in 13th. Basically turning a RTO-14613 into an RTOO.

 

[Hummer Guy]

M820 maybe a better option for you if you want a manual and a very simple truck to work on

 

[B-Dog]

Enlighten me, I don't understand the PDP comments. Why would anyone prefer a printed circuit board (A1) over serviceable modular parts (A0)?

https://m.littelfuse.com/~/media/commercial-vehicle/datasheets/automotive-fuse-holders/powr-blok-modules-datasheet.pdf?la=en

 

[Guruman]

Enlighten me, I don't understand the PDP comments. Why would anyone prefer a printed circuit board (A1) over serviceable modular parts (A0)?

https://m.littelfuse.com/~/media/commercial-vehicle/datasheets/automotive-fuse-holders/powr-blok-modules-datasheet.pdf?la=en

oooh shiney. I did not know the A0 PDP was modular like that. Opens up some interesting opportunities for modifications.

 

[Ronmar]

Yea the A0 PDP is not the source of the power issues that I have seen. The weak link in the PDP are the cheesy circuit breakers IMO. Auto blade fuses work great….

Having helped a few people with electrical issues, i cant think of a single A0 PDP issue, but I have helped several localize to circuit board issues(bad solder joints, burnt circuit runs) on the A1 boards. The A1R setup with the modular boxes are nice, but the A0 panel is easy to work on in the field if you should ever have an issue. Being modular it is also easier to modify/customize…

I like manual transmissions also, but the gearing and TC on the Allison is hard to beat. I do wish it was programmed a little differently though, to not start out in second.

 

[B-Dog]

Yea the A0 PDP is not the source of the power issues that I have seen. The weak link in the PDP are the cheesy circuit breakers IMO. Auto blade fuses work great….

I'll second that. One of the first things I would do is replace the CB's with fuses.

 

[Off-Road-RV]

Yea the A0 PDP is not the source of the power issues that I have seen. The weak link in the PDP are the cheesy circuit breakers IMO. Auto blade fuses work great….

Having helped a few people with electrical issues, i cant think of a single A0 PDP issue, but I have helped several localize to circuit board issues(bad solder joints, burnt circuit runs) on the A1 boards. The A1R setup with the modular boxes are nice, but the A0 panel is easy to work on in the field if you should ever have an issue. Being modular it is also easier to modify/customize…

I like manual transmissions also, but the gearing and TC on the Allison is hard to beat. I do wish it was programmed a little differently though, to not start out in second.

Great info, I'm here to learn. Still undecided if I want to start with a A0 or A1. Thinking it would be nice to find a complete cab in nice shape, rolling frame, rebuildable 3126, rad and intercooler, and miscellaneous items.

 

[Off-Road-RV]

if you are saying an allison is better, stronger, more reliable than an eaton fuller 10 or 13 speed in a similar application then you must be making a joke right?

You wouldn't want to run the T138 it's a sprag unit. Not a good choice you will have to put air to it for forward select or rear select. It also only engages when the tires slip. Time the tires slip its too late for a big truck its already down.
An 55000 Oshkosh unit is a reasonable unit. 2.66 low and .98 high.

You don't need an 18 speed if you have a transfer case. Not to mention the GVW of any FMTV is too low to even even need an 18spd for any reason. 18spds only split the low range. Really not needed with a transfer case.

A 10c eaton will work fine. Cheap. It can take double the power that the allison 3700 can handle.

You can flip the rear 2 gears on a 13spd and you get a .74 and .62 in 13th. Basically turning a RTO-14613 into an RTOO.

With the 55000 Oshkosh married to the RTOO looks like I'd be in the sweet spot of the power curve on the 3126.



If I ever need to get in a hurry I crank out 95 MPH before getting to the red line. LOL

 

[TheRealJohnnyB]

Hey Off-road! Any progress here? I'm looking at a similar situation myself. Did you land on a tcase that makes sense?

 

[eaw46]

Lots of real world info and advice on living and traveling off road here.

Expedition Portal

The global resource for overland and adventure travel.

expeditionportal.com

 

[bluesteel01]

I don't think anyone had gone forward. Any benefits are outweighed over the cost time and labour to change over an already very stout auto setup.

 

[Frugal Plinker]

New here and I'm exploring the possibility of building a LMTV expedition vehicle.
I've been full-time RVing for the past 3 years, in an 5th wheel. Medical issues with my wife has us off the road for a while. Many hours have been spent on this site, and others getting educated and confused at the same time. Should I make this idea a reality, I want a highly reliable simple to repair. In the ability to get back to civilization without a Chinook. I haven't seen where anyone has put a manual transmission and manual transfer case behind a 3126 mechanical engine, in an LMTV. Does anyone have knowledge of this being done before?

I realize the post is a bit old and this is a military vehicle group. However, a smaller, probably cheaper, and ready built option would be a Mitsubishi Fuso FG of the correct year range to get a mechanically controlled engine. Already has a manual.

 

[Ronmar]

Well having the eco hub calculations fresh in my head, What is the total ratio in one of these manual+transfer combinations? 12:1? That probably would not work all that well. You are probably only going to get ~200# of idle torque out of a 6-7L diesel, and the clutch won’t be happy trying to engage any more than that anyway… 200 X 12 / 2 X 7.8 / 2 / 1.942 = ~2400# of thrust per wheel, or 9600# total starting thrust. That is about 2/3 of what a 3116/allison with eco-hubs can deliver, and about 1/4 of what a stock 3116 powered LMTV can produce…

Wait, it gets better 700RPM@12:1 + 7.8:1 will yield ~12.4MPH at idle with our 46.6” tires. 24:1 Gearbox? Well that gets you to 6.2MPH. 48:1, well now you are getting down to a good walking speed, 3.1MPH. But thats a lot of ratio to shift thru, and 3.1 might still be a little fast for precise work/crawling over terrain. Anything less = slipping the clutch…

I love manuals, but there is a reason that a 6 speed Allison can replace a multi gear manual, and do things with heavy weight trucks that will destroy some other manual configurations. They built a better mousetrap, and the torque converter is the key, allowing application of anything between ~200# to 2X peak torque to a non moving vehicle. And the slippage provided by the TC allows you to provide that torque at any speed, allowing a true crawl to occur… Now a manual with a torque converter… Things that make you go Hmmm…

a manual also won’t address what I think is the biggest flaw in the LMTV drivetrain. With a 7.8:1 axle ratio, we are spinning our driveshafts at 2X the max rated speed for the driveshaft angles When at highway speed. 3.07’s help(6.14:1), but they still run significantly beyond the red line at highway speed. There have been numerous examples posted here and elsewhere of some pretty spectacular(and expensive) driveshaft failures…

 

[biscuitwhistler37]

Does it have to be an LMTV? An M35A2 with service van body would make a nice rv, but won't go very fast. Then you have a manual and a 2 speed transfer case and an all fuel engine that only needs electricity to start and have gauges. Basically everything you want out of an LMTV on close to the same chassis, just not a cab over. Just saw this post is from 2022, apologies if it's no longer a concern to you.