First Short Drive in my New M923

[nf6x]

I just took my new M923 for its first spin. I got it over a week ago, but I haven't had time to play with it on weekdays, and I did a bunch of little stuff to it first like fixing some air leaks behind the dash, installing the cargo cover kit, adjusting tire pressures, cleaning windows, and so forth. I don't have it titled yet, so I just stuck to the dirt roads around where I live.

I found that I have a lot of trouble changing the transfer range when stationary. The lever easily pops into neutral, but then I have a hard time getting it to engage either range from there. I can hear the small air dump when pushing the button on the end with the engine off and the master switch on, and nothing suggests to me that I'm having trouble with any of the interlocks. It just seems to be hard to get it to engage either gear. I'll need to look into this further. I haven't tried changing transfer range while rolling yet. Low range is fine for my local dirt roads, unless I need to stop and back up; then I'd need to get it back into high range before shifting to reverse.

On some of the worse bumpy parts, especially when braking, the truck started bucking like a bronco. I'm not sure, but it might have been the ABS doing its thing? I got well-acquainted with the bottom stop of the spring ride seat, and I think I may install a rubber bumper there to keep it from slamming down so hard. Maybe I just need to crank the spring adjustment tighter, though. I wish the seat back would lean back a bit farther.

The power steering sure is wonderful when making tight turns at low speed!

Rolling out of my gate on my fairly steep and rough driveway, I actually ran the truck low on air. I think this was partly due to having the truck in high range, the engine RPMs at idle, and feathering the brake a lot. I think this will stop being an issue once I smooth out the transfer linkage and get the hang of being in the right gear and range. It's been a decade or more since I've driven anything with air brakes, and I expect that I'll need to recalibrate my foot and learn how this truck likes to be driven.

Unladen, that 5-ton can be a rough ride on my dirt roads. I wonder whether 2-3 tons of knuckleboom on the back will make that better or worse?

This was my first time driving an M939-series truck, and it was fun! For that matter, it was my first time driving a big truck with an automatic transmission. I like it a lot better than a stick-shift in off-road driving, since I grew up with auto transmissions and I'm just more comfortable with them. It'll still take a bit of practice to learn just what gear ranges my truck wants to be in on hills.

 

[Truckoholic]

Does your truck seem to downshift hard when you are slowing down? I put the 16.00R20's on mine, and I can't help but wonder if maybe the shift points need to be adjusted with the bigger tires or something if that is even possible. It just seems like it wants to be in a higher gear than it should be when I am driving it. I've gotten used to having to start out in 1-2, and run the RPM up in each gear before shifting into the next higher gear to get it to shift more like normal for an automatic. If I start out in 1-5 out on the highway, it will shift into 5th gear when I am still only going like 25Mph, which is way too high of a gear for that speed with these big tires on. It just lugs the engine down, and does not allow me to gain any more speed unless I manually shift down into 1-3 and then 1-4 and finally 1-5 when I get up around 40mph or so.

When I am slowing down to stop at a stop sign, it will shift abruptly from 5th into 4th, and then to 3rd, and hard into 2nd, and finally really hard into 1st when I get down to 9mph. I hate what it sounds like it is doing to my entire poor drive-train, banging and clanging as it shifts so hard! I've never driven one of these trucks before, so I have no clue if that is normal or not.

Do any of you know if there is a way to adjust the transmission to shift right after putting bigger tires on the truck? It came with 14.00's on it, so I wouldn't think 16.00's would require all that big of an adjustment, but it definitely seems like it needs something. If that hard shifting is normal, then okay, I will just deal with it.

 

[nf6x]

I still need to get off my lazy butt and get it registered, so I haven't had it up to road speed yet.

My truck has the 11x20 duals, but I think I'd like to single it out with 395/85R20 tires at some point. So, I'm also interested in whether the transmission can or should be adjusted with larger tires on the truck.

 

[goldneagle]

I still need to get off my lazy butt and get it registered, so I haven't had it up to road speed yet.

My truck has the 11x20 duals, but I think I'd like to single it out with 395/85R20 tires at some point. So, I'm also interested in whether the transmission can or should be adjusted with larger tires on the truck.

Why not just go with 14.00-20 they are cheap and you can get the hemmt rims for them cheap as well.

 

[jw4x4]

My 932A1 sure surprised me with its calm road manners. I was expecting it to be far more harsh, esp. bobtailing. It floats along, only "bucks" a little going over wash-boarded roads or concrete roads with the joints at just the right intervals. I am pleased with the acceleration. And yes it does downshift kinda hard, but that is to be expected with the Allison under no load. The main reason I bypassed a deuce and went with this truck is the power steering and air brakes. I believe I am going to seriously enjoy it.

 

[juanprado]

I understand the a1 & 2 has a different speedo adapter for the bigger tires so you have an accurate reading but I have not heard about the tranny have a different shift pattern or adjustment?

The hemmit rims are much thicker flange at the lug face and have a slightly diff offset. the combat wheels or fmtv wheels are similar to the oe offset and not as thick on the front hub face.

 

[nf6x]

I'll consider the 14x20 tires, too. I'm just going by what I've read so far. Some folks suggest that the 14x20 tires decrease the power noticeably, and I don't expect to have the truck over 55 MPH much. The 395s sound like a compromise that would give me the single-tire look that I like, a little bit more top speed for passing, but not rob as much power as the 14x20. I don't think I want to go any taller than the 14x20 tires, but I'm still just guessing based on what I've read here.

 

[rrrr]

Does your truck seem to downshift hard when you are slowing down? I put the 16.00R20's on mine, and I can't help but wonder if maybe the shift points need to be adjusted with the bigger tires or something if that is even possible. It just seems like it wants to be in a higher gear than it should be when I am driving it. I've gotten used to having to start out in 1-2, and run the RPM up in each gear before shifting into the next higher gear to get it to shift more like normal for an automatic. If I start out in 1-5 out on the highway, it will shift into 5th gear when I am still only going like 25Mph, which is way too high of a gear for that speed with these big tires on. It just lugs the engine down, and does not allow me to gain any more speed unless I manually shift down into 1-3 and then 1-4 and finally 1-5 when I get up around 40mph or so.

When I am slowing down to stop at a stop sign, it will shift abruptly from 5th into 4th, and then to 3rd, and hard into 2nd, and finally really hard into 1st when I get down to 9mph. I hate what it sounds like it is doing to my entire poor drive-train, banging and clanging as it shifts so hard! I've never driven one of these trucks before, so I have no clue if that is normal or not.

Do any of you know if there is a way to adjust the transmission to shift right after putting bigger tires on the truck? It came with 14.00's on it, so I wouldn't think 16.00's would require all that big of an adjustment, but it definitely seems like it needs something. If that hard shifting is normal, then okay, I will just deal with it.

There is a shift linkage that attaches to the IP from the transmission. I would start with its adjustment. I don't remember where in the TMs the procedure is. I did an adjustment on mine due to an early shift into 4th gear. It helped a lot. I've included a picture. There is another post that discusses this as well.

 

[M35A2-AZ]

I understand about the dirt road ride. I live on seven miles of it before I get pavement.
As rrrr said about the shift linkage and you may make sure you have the return spring on it. It is the one on the right in rrrr pic.
All my trucks shift a little hard when you slow down.

Good luck with the truck they are great fun.

 

[jedawson1]

NHC 250 w/Allison 5 in mine, It down shifts just like you describe. I have the 14R20 tires and I don't feel they are too much of a drain on power though I would not go any bigger with the NHC250.

I have an extra 6 super single tires and rims (2000 lbs roughly) in the bed and that has improved the ride significantly. That and running 55psi. I drive mine a few times a week.

 

[Truckoholic]

Thanks guys! And thanks rrrr for the picture! I'm pretty sure that is the exact adjustment I need. Because one other problem I forgot to mention, is when I am pulling a steep hill, no matter how far I push the accelerator pedal down, the transmission will not downshift. And by adjusting that linkage in the picture, I can see how it would cause the transmission to shift sooner. And that would totally make sense that with the bigger tires, giving it a higher gear ratio, the transmission would think the truck is going faster than it really is, and therefore shifting into higher gear too soon before it should.

Okay, I just found in the TM where it talks about adjusting the modulator for correct shift points. TM 9-2320-272-24-4 5-60 C shows a diagram of at what RPM the transmission is supposed to be shifting in each gear. And then a couple pages below that 5-61 talks about adjusting the modulator. I am going to have to see what I can do, because it most DEFINITELY is not waiting til 2,000 rpm to shift like the diagram shows it is supposed to!