2006 Stewart & Stevenson/BAE 6x6 Build

[anthonyca]

Any updates on this?

 

[charlieaarons]

2 questions in my mind:
1) does the lack of a 2 speed transfer case cause problems in something as big and heavy as a MTV?
2) as far as I can see the "mode" function locks the interaxle diffs but not the diffs between the wheels. If true this is a big problem. Of course Detroits would cure this issue. To
Charlie

 

[anthonyca]

2 questions in my mind:
1) does the lack of a 2 speed transfer case cause problems in something as big and heavy as a MTV?
2) as far as I can see the "mode" function locks the interaxle diffs but not the diffs between the wheels. If true this is a big problem. Of course Detroits would cure this issue. To
Charlie

These are great questions.

How fast can this truck comfortably cruise for long distances?

 

[Coachgeo]

2 questions in my mind:
1) does the lack of a 2 speed transfer case cause problems in something as big and heavy as a MTV?

You know how they say if you're thinking in about how a petrol engine works, is repaired etc. when discussing a diesel..... you just won't get it cause it is a totally different bird. Well it is the same with this. Don't think traditional Transfer Case 4wd or you just won't get it. This is a totally different bird.

That being said I will anyway try to cross the two to help understand this all.

.This is an AWD and it is done by Peter (front of T-case sending power to front wheels) stealing power from Paul (Rear of Tcase sending power to back wheels). This occurs all the time. In normal "Drive mode" the computer manipulates some clutches in T-case allowing Peter to steal 30% of what Paul has to offer. Peter uses this to drive the front wheels. In..... Ruff Terrain mode..... the computer allows Paul to steal even more. 50% total infact. Both front and rear now get 50%.
. In Ruff Terrain Mode at 50/50 split now consider it in effect..... 4wd HIGH when in SOME of the upper gears.
. Did that SOME just really confuse you? They say this is a 7-speed transmission....... well actually if you count the ratios that is true....... but... in other ways..... it's sorta NOT true. The transmission this is based on only has 6 ratios. So it is a 6 speed. Inside the T-case though is an additional ratio that is made accessible thru some magical manipulation of things I don't understand. Allison chose to call this fist gear. The actual transmission's ratios they call 2nd-7th. It's less confusing if you think of first gear as a Granny Gear that Magically appears in the Ruff Terrain mode ONLY. It is used at no other time. You take off in second gear in Normal mode.

My understand is when all ratios are looked at the comprimises between them sorta negates a need for a LOW/HIGH 4wd selection especially when adding the granny/first gear into the mix.Think of it like.... SOME of the gear ratios are low enough they operate in the range a typical trucks 4wd would call low range. Then SOME of the other gears available are typical ratios of a HIGH gear range. Course to confuse you one more time. Allison decided soldiers sometimes are not too smart. So to save wear and tear on the transmission and Tcase they programmed it so that in Ruff Terrain Mode the top 2" ratios (or is it just the top one..... I forget right now) are locked out.

So in the end this leads too:

ADVANTAGE TO THIS SET UP - You in round about ways get access to both a High Range AND Low Range ratios on the fly and you have to do absolutely nothing to make this happen. (except getting into granny?)
DISADVANTAGE TO THIS SET UP- You have no neutral between a typical T-Case's High Range and Low. Thus towning requires pulling of the drive shafts (or for rear pull axle shafts). Also you supossedly can't drive out on front axle only if you experience a broken rear something. In theory... but seen it done for 1200 miles and the theorized damage to the front clutches of The Tcase showed no issues in a later tranny rebuild buttt...... Don't Try this At Home.

2) as far as I can see the "mode" function locks the interaxle diffs but not the diffs between the wheels. If true this is a big problem. Of course Detroit would cure this issue. To
Charlie

no on the 4wheeled AWD group. Charlie is spot on for the 6x6 AWD as discussed in this thread.

Pretty sure in the 6wheel drive group the rear of the Tandem Axle pair is powered when in ruff terrain mode as charlie says. Not real up to speed on this but think the rest of the time the rear most axle is a tag axle. Might be wrong there. It might get activated in other settings too such as in the MTV's used as Tow Trucks. This is controlled by computer... which simply controls an air solinoid on the Offset Gear Box. Off set gear box on the MTV is bolted to the the first of the axles in the Tandom Axle pair. The air soliniod activates a Power Divider inside this offset gear box same way any modern Tandom rear axle truck does. Some tandom trucks have a manual switch. (older ones) Others like the MTV this is computer controlled. Again, the front axle of the pair does NOT have a diff lock. NOR does the rear one. Now to confuse you could think of it as having a THIRD differential. (As Charlie said..... the Interaxle) It is inside the off set gear box on the MTV as I understand it. It also works like a typical diff. in that it allows for some tires to roll differently between others.. in this case the two axles are allowed to roll differntly when needed. BUT... petty sure there IS NO LOCKERS . Again, the "power Divider" is part of the offset gear box. Maybe think of this as the "Power Divider" activates Tandom (with a little Differential action between the pair), or making the rear axle just a Tag along and that is it?

One might understand this better if it was thought of as having a separate gear box with a diff inside that sits between the axle pair that makes up the tandem axles. The "power Divider" connects or disconnects power to this separate box. With it connected the diff inside it will send some power to the rear most axle as well, creating a Tandom arrangement With "Power Divider" disconnected the rear axle is just a Tag axle.

Search google for Power Divider tandom axle for a more technical description.

Interlock for the Interaxle I believe is more like a typical locker in its function. Think of it as an ARB inside this third differential only. MTV does not have this.

As to Detroil locker or any other lockers for all other diffs (front, rear, rear most). Suposidly they exist but again NOT for the Off Set Gear Box's diff..... For the axles few have claimed to have seen them but as of this point they are just ghost we dream about. And like ghost we will probably NEVER SEE ONE.

 

[toylandcruiser]

2 questions in my mind:
1) does the lack of a 2 speed transfer case cause problems in something as big and heavy as a MTV?
2) as far as I can see the "mode" function locks the interaxle diffs but not the diffs between the wheels. If true this is a big problem. Of course Detroits would cure this issue. To
Charlie

I've driven the crap out of lmtvs and have never had an issue with power and a lack of two speed transfer case. 1st gear is pretty low.

 

[anthonyca]

I am a fan of the FMTV (4 and 6). I went to test drive one of the newer MTV 6x6 this spring/summer... On my test drive I go it stuck and had to be pulled out... It was both a little embarrassing and revealing.

1. The axles do not lock. If one side spins, the other side wont. If they did lock I likely would have been able to get out by myself.

2. Driver, know thy vehicle

3. Mode button changes split to 50/50 and cuts off gears 6&7... which didn't help me

So stupid to have an "off road" vehicle without lockers. They shouldn't even call them that.

 

[pairospam]

Just my PHO, but... isn't it a little sterile to go on with this thread if the owner does not update it since january 2012?

 

[Coachgeo]

Just my PHO, but... isn't it a little sterile to go on with this thread if the owner does not update it since january 2012?

Thread morphed into a general LMTV discussion. Nothing wrong with that. OP not here to complain of the hijack :coffeedrink:

 

[Tennmogger]

2 questions in my mind:
1) does the lack of a 2 speed transfer case cause problems in something as big and heavy as a MTV?
2) as far as I can see the "mode" function locks the interaxle diffs but not the diffs between the wheels. If true this is a big problem. Of course Detroits would cure this issue. To
Charlie

Hi Charlie,

The FMTV's aren't Unimogs, meaning of course that there are compromises with the FMTVs. Your questions are good ones. But, for a 'less than Unimog' vehicle, the FMTV's do very well.

As you know I have been around Unimogs a long time. Nothing beats the crawl ratio, portal axles, and locking diffs. But, the FMTV's have automatics with torque converter and a very low gearing "drop box" that compensates well for lack of a 2 (or more) speed transfer box. I have been impressed with the ability to hook up to the ground and pull hard.

Lack of diff locks is a major point. But, with CTIS and bead locks standard, it's easy to drop tire pressure to 20-25 psi for better traction.

I can do most anything with the LMTV that I'd use the U1300 for. I got the LMTV because most of my travels are on road, maybe gravel or dirt, but road. Deviate from that and better stick with Unimogs!

I really like the auto tranny. Guess I'm getting old but rowing through the gears on a city drive, while blocking traffic, bugs me. The LMTV gets away from the lights faster than most other traffic. Now I wait for slow traffic, not cause it. The LMTV is a screamer compared to a Unimog.

BTW, just finished a one month, 4600 mile trip out west with some of the mog group you know, had a blast, drove slow 50 mph 'Unimog speed' on back roads (when I could) because that's the way I like to travel and sight-see, and got 9 mpg.

Bob

 

[91AzXJ]

Here's an MK48/14 for sale
https://phoenix.craigslist.org/wvl/cto/5737227693.html