Go LOW and you can't go back!

[JingoJohn]

I thought I had lost my mind and my reading ability when I read in the TM for my 923A2 that you can't back up in low range. Maybe "can't" is too strong; you just risk your fortune to do so.

Citations from the TM:
1-17f/1-34 and 3-4/3-9 and 2-10/2-87

WHEN would one NEED to back up in LOW range more than when one has ceased all forward progress in low range? Being 'verbotten' to back in low is RIDICULOUS!

I am a VERY newguy to 6x6 ownership. It seems this situation could be solved with a different trasnsfer case (TC). If the old hands here can help me find a better TC which does allow backing; I would gladly devise brackets to install same in our vehicles. Of course, I would share the bracket designs with SS guys!

There is probably more to a swap than mere bracket design. Everything from cutting cab floors to u-joints, ground clearance, relo of other components and gear ratios will come into play. The "domino effect" ALWAYS reares its ugly head when mods are in the making.

From my novice view point it looks like this:

1. TC that will allow backing in low.
2. TC that has, or can be modified to have, the correct gear ratios.
3. TC that will fit 900’s as they are.
4. TC that would be a reasonable fit after a 900 series is slightly modified.

There is a thread devoted to the MRAPS being scrapped. Would one of their TC’s work? Could we get those TC’s?

This is the time for the guys with the REAL knowledge, expertise and experience to shine! My idea of a swap is useless without you.

 

[patracy]

Moved to the 5 ton forum.

 

[wreckerman893]

I don't see a problem with not being able to back up in Low. Reverse is a pretty low gear anyway.

 

[hndrsonj]

I don't see why you would ever need to back up in low???

 

[gimpyrobb]

You could swap in a Tcase from an 800 series. I think they are the same size, but you'll lose the overdrive in high range. You gotta choose your battles!

 

[wdbtchr]

Wasn't it the M211 that you couldn't back up in high range? I thought it was a problem with the transmission rather than the transfer case.

 

[m16ty]

I back up in low all the time in my M939 truck. The key is not to be "dogging" it in low. If I'm going forward in low range, I don't bother with shifting the t-case if I'm going to back up.

I do my lime spreading in low range because I have to travel a certain speed and keep the RPMs up the get the proper spread rate. If I have to back up at the end of the field I leave the t-case in low. IMO the main reason that is in the TM is for foot heavy GIs that tend to push these trucks to the limit every chance they get.

I may break the t-case tomorrow and I'll hear "I told you so" but I haven't had any problems and I drive like I have some sense. I know the t-case is weak in low reverse and I take that into account.


On the M211, it was the trans that was weak. You had to back up in low to help take stress off of the trans.

 

[Floridianson]

I to have used low reverse when on solid ground with no problems. How much backing in low reverse do you need to do to warrent the tranfer case change? As said high reverse has plenty of whatever you should need.

 

[wheelspinner]

The "typical" breaking point is reversing hard in low, and then the front grabs traction first, too much shock load on the transfer case from the sudden front drive load. Simple fix is to disable the automatic front axle engagement device (remove the washer) and control the axle engagement manually. Then at least you can turn the axle off, if reverse in low is a must. On solid ground, no sudden shock, no break. I have a spare transfer case, and I was wondering these things, so I tested it. Seems to be ok this way.

 

[doghead]

You can change the tires back to 11.00-20 and avoid the problem.

 

[swbradley1]

Is it the rotational mass of the larger tires/wheels?

 

[emr]

This was a problem that was caused by thousands of drivers driving without proper instruction to the TACTICAL vehicle they were driving, and was all but gone when driving techinics changed, mostly do not use low in reverse, Why, in my OPINION it is a way to keep inexperienced and experienced drivers that think they are experienced from ruining a perfectly well designed vehicle, Low in reverse is used by me in allot of situations even in these trucks. Its been covered a few hundred times in other posts and a search should have answered these questions. These trucks are 1980s tech and awesome at that. And have stood the test of time, And with more miles than the famous Red Ball In Germany While serving in the first Gulf war and continuing. It is a proven truck with the ability it was built for, redesigning a 1980 model truck , saying they could have done this or that is silly, Sorry but it is. This is exactly what was ordered and for good reason, it is the best of the M series . The thing forgotten when discussing this is these are TACTICAL vehicle, Not spin around town trucks. For how low this truck is geared, If you slam it into reverse with the R"s still up you will cause severe damage, and that is driver error, This truck driving in low reverse will not explode, But understanding what it is and how to drive it is the answer, Not redesigning it. But hey if you have the money rebuild away. All the best. Drive it like the truck it is and you can do what you want. But like said earlier, there is almost never a reason for low in these trucks, But I do find it is an awesome tool, and use it allot.

 

[swbradley1]

Sounds like how I drive my wife's Jag now after swapping the transmission. Full and complete stop, engine idle THEN shift. I'm not buying another one.

I never understood the whole "slam and auto back and forth" thing anyway. Oh wait, except when I was going into the military and I used to go backwards and then slam my transmission into drive and floor it so both tires would smoke.

Ah memories.........

 

[doghead]

Is it the rotational mass of the larger tires/wheels?

Yup.

 

[JingoJohn]

"... I drive like I have some sense. I know the t-case is weak in low reverse and I take that into account...."

Yeah! me too! I drove my '72 Scout thousands of miles off road over some pretty rough terrain. I never broke anything. Some of these numbskulls that break expensive components on a regular basis drive like they had MANY mega-buck corporate sponsors! (They don't, but their wives work two jobs to support the breakage hahah)


Sooo, the cavaet in the TM is to "Troop Proof" the vehicles?

 

[patracy]

Sooo, the cavaet in the TM is to "Troop Proof" the vehicles?

Pretty much. *


*I make no guarantee your t-case won't break in low/reverse.

 

[JingoJohn]

In my “Scout days” I had been in many situations where I could make no further progress up hill or down hill. Using the ‘gear that got me there,’ in reverse, was the only way out….backtrack.

Maybe I found a solution that does not have a problem for 923A2’s IF DRIVEN WITH A HIGH DEGREE OF SANITY?

I will say this: The TM sure as **** “TROOP PROOFED” ME!

The 800 series TC has some appeal for me for one of my trucks. It will be primarily off road. The other truck will probably be used to haul stuff from civilization to my mountain top hideaway; the OD could save a few $$$.

 

[bchauvette]

follow

 

[Excuse Me]

I back up in low all the time in my M939 truck. The key is not to be "dogging" it in low. If I'm going forward in low range, I don't bother with shifting the t-case if I'm going to back up.

I do my lime spreading in low range because I have to travel a certain speed and keep the RPMs up the get the proper spread rate. If I have to back up at the end of the field I leave the t-case in low. IMO the main reason that is in the TM is for foot heavy GIs that tend to push these trucks to the limit every chance they get.

I may break the t-case tomorrow and I'll hear "I told you so" but I haven't had any problems and I drive like I have some sense. I know the t-case is weak in low reverse and I take that into account.


On the M211, it was the trans that was weak. You had to back up in low to help take stress off of the trans.

Need pics of the lime spreader please.

I'm building a sprayer puller, and will be doing some backing in low.

 

[wheelspinner]

Yup.

Doesn't the A0 trucks, which have the 11x20 tires have the same warning?