Offroad Issues

[Iggy913]

Hello Everyone, I've only had my 923A2 for a few weeks, I'm still waiting on the SF97 to return so I can really take it out and play with it. However, I had a few questions I wanted to ask that I didn't see the answers to right away:

I understand no low range in reverse, however what if your crawling around in low and need to back up? Are you really supposed to put the truck back into the high range, back up, then go back into low to continue on? I know reverse is really low in high range already, but say your already in low, stuck in a mud hole or in sand, and you need to back up to choose another line? If your stuck how easy is it going to be to even change the transfer case range since the TM says you should be rolling in neutral before switching to high/low?

I completely understand the warning that it could cause damage to the transfer case because of the torque of the motor and the super low gearing, and I'm not asking for permission to go out and destroy the truck like that. What I'm asking is just what have you guys done in that particular situation, I don't see that being that rare of a problem for the members who are out using their trucks offroad at all. Can you just use some sense and light throttle inputs to slowly move yourself backwards to choose another line?

Lastly what kinds of experiences have you guys had in using your trucks in sand? Are you running them in high or low? 90% of my offroad use will be in sand, both hard and soft and I'm curious what you all have seen for performance?

Thanks a lot

Iggy

 

[DJones]

From what I have read you can use reverse low if you don't put it under much of a load, like just backing up if you didn't make a corner or something. I haven't had my truck in any sand yet.

 

[Gunzy]

Mine appears to have a lockout on shifter for reverse when in low range. I can't even select reverse until I have returned to high range. Or I don't have a clue what I'm doing which is a possibility.

 

[tbone1004]

Not having one of these trucks, but being familiar with sand, the key is to keep your tires aired as low as possible to maximize flotation and minimize ground pressure. This is obviously a colossal pain in a truck that big, but with narrow tires and a lot of weight, you may have trouble in loose sand. Singles on the butt end would be better than duals for sand as well. Good luck with the T-case issue, if they did put a lock out on it it was probably because they lost a bunch of differentials and axle shafts due to the torque, that or the output torque actually exceeds the working limits of the gears, which doesn't often happen

 

[Iggy913]

Thanks for the information. I'm not a newbie to the offroad world, the truck has singles on it already so I'm not too worried about it's capability in the sand. The CTIS actually works in this truck, most of the time anyway, so I was going to select the "Sand" mode and see how she did.

I was just curious to guys who had been in the sand what they found worked the best as far as high/low range was concerned. In my personal pickup I can just air down to about 25psi and usually go right down the beach in 2wd, only needing 4x4 high in real soft areas or trying to climb a hill. My truck is however 1/3 the weight of these 939s with more hp, and I was concerned with their ability to forge ahead in soft sand in high range?

One other basic question I had, when you engage low range it's supposed to automatically engage the front axle, or you can engage the front axle through the dash switch for high range use. Is there anyway to confirm the front axle is actually engaged? In all my trucks they were manual hubs with a transfer case lever, which means so long as the hubs are locked and you pull the transfer case lever you were 99% sure you were in 4x4. Just trying to verify a way to check besides the dash light? I guess I could always put it in 4x4 and try and make a tight turn at slow speed to feel for the drag of the front end?

 

[tbone1004]

ahh, forgot those had CTIS, that's convenient. Manual says 25psi for sand/snow, and 12psi for emergency which is nifty

Manual also indicates that the front axle should lock up automatically when shifted into low which you indicated, but I don't think there is really any way to know 100% that the axle is being powered.... I guess if you can get the whole thing on a lift *good luck* you can test out the transfer case and see if it is locking up... I don't think I'd worry all that much with the dual rears though

 

[Gunzy]

I tested mine in sand. That will let you know it is engaging. I was tow baring a M932A2 with flat tire too.

 

[Iggy913]

Does anyone know if the front driveshaft is always turning, even in 2wd? I ask because if it's not always turning I could put a zip tie on it long enough to come in contact with a neighboring piece of metal. Flip the dash switch or engage low range and listen for the sound of the zip tie striking, at least then you'd know the shaft was being powered. My guess however is the shaft is always turning being you can't unlock the hubs on the front axle.

I'm sure I can find a construction site near me and see if I get any pull from the front end. I'm fairly sure it works, it would just seem like a careless mistake to not verify it.

 

[tbone1004]

front shaft should always be turning due to locked hubs. You could also remove the rear drive shaft, lift the front end and engage first gear to test. Again, not the easiest thing, but shouldn't take too terribly long.

 

[ichudov]

Does anyone know if the front driveshaft is always turning, even in 2wd?

Front driveshaft is always connected to the front axle. But in 2WD, it is disconnected from the transfer case.

 

[Iggy913]

Maybe easier than pulling driveshafts: What if I got the front of the truck up in the air, put the transmission in neutral, released the brakes, and tried to turn the front driveshaft by hand? It should turn in 2wd right? However if I engaged the front axle I shouldn't be able to turn the tires at all since the rear would still be on the ground?

 

[tbone1004]

good luck turning the driveshaft lol... if you have a buddy with you to turn the other front tire that should work too. I honestly doubt you'd be able to turn that driveshaft by hand. almost a 7x1 reduction in the gears combined with the weight of the wheel/tire/brake combo that'd never happen.... With a buddy to turn the other wheel though you should be able to get the shaft to lock up

 

[Iggy913]

That's what I was referring to, turning the wheels rather than the driveshaft directly, I figured that was a lost cause. Thanks for the help on that everyone.

Still though, nobody uses their trucks offroad at all? I figured someone would have chimed in with some offroad stories by now. Like I mentioned in my original post, I know Low in Reverse is a technical no-no, but what if your crawling along in low and need to back up because of an obstacle/line change/get stuck?

Also what if your motoring along in High and encounter a steep grade or just need the extra grunt of Low, but you don't have the distance to throw the transmission in Neutral while still rolling to move the transfer case lever to Low? Is it not possible to change ranges without rolling?

Thanks again everyone for the help.

 

[Chief_919]

Mine appears to have a lockout on shifter for reverse when in low range. I can't even select reverse until I have returned to high range. Or I don't have a clue what I'm doing which is a possibility.

There was indeed an MWO that put a lockout on it that blocks reverse when in low range

 

[Chief_919]

That's what I was referring to, turning the wheels rather than the driveshaft directly, I figured that was a lost cause. Thanks for the help on that everyone.

Still though, nobody uses their trucks offroad at all? I figured someone would have chimed in with some offroad stories by now. Like I mentioned in my original post, I know Low in Reverse is a technical no-no, but what if your crawling along in low and need to back up because of an obstacle/line change/get stuck?

Also what if your motoring along in High and encounter a steep grade or just need the extra grunt of Low, but you don't have the distance to throw the transmission in Neutral while still rolling to move the transfer case lever to Low? Is it not possible to change ranges without rolling?

Thanks again everyone for the help.

You can do whatever you want.

But keep in mind lots of transfer cases are broken in low range reverse. I have seen it happen in flat ground. So nobody is going to sit here and tell you it will be ok to do it. That is your judgement call on your truck, all about how much risk you are willing to take.

 

[Iggy913]

I think I may be misunderstood, I certainly don't want to do any damage to the truck, and I'm not looking for someone to tell me it's ok to drive in reverse in Low, I understand the seriousness of the situation.

My main concern was the TM stating you have to be rolling in order to switch ranges. If I encounter a situation where I'm in Low already and my forward momentum ceases, I need to back up what are my options? Can you switch ranges from a stopped position?

 

[Iggy913]

Stand Down, I just watched that Army video done in the 90s when the 939 series first came into service. It said the transfer case can be shifted when moving less than 22mph or stopped. Question answered. Thank you all for the help.