M923 Front Axle Engagement

[nf6x]

When I was driving my M923 around on my property last weekend, I spun the rear wheels quite a bit. At one point I flipped on the front axle engagement switch, and things suddenly got better. So, it seems that my front axle isn't automatically engaging the way it's supposed to in low range.

The M939 P2P program shows that if the front axle switch is still engaging the axle in low range, then the valve that's linked to the transfer range lever must not be actuated. A quick look under the truck showed that the valve arm was just barely moved by the plate on the transfer shift linkage that actuates it.

So, the fix looks obvious and simple: Just readjust the arm on the valve so that it gets actuated properly in low range. The thing is, I'm not sure that I want to fix it. I'm considering mis-adjusting the valve arm even further so that it doesn't deflect at all in low range, and so that it'll be obvious that it was deliberately disabled. Then I'd just engage the front axle manually in either range with the switch on the dashboard, and I'd be able to use low range without engaging the front axle... for example, on the rough-but-paved section of country road that I traverse on the way to/from my property, where low range would work better on the hills but the traction is good enough that I'd rather have the front axle disengaged.

Do you M939-series experts see any problems with deliberately disabling the automatic front axle engagement in low range?

 

[emr]

I have the same situation, I dont call it a problem because like U I am good with being the one who initiates the front wheel drive, I am happy just the way it is and dont need to make it more off i guess U are saying.

 

[m16ty]

I have the same situation, I dont call it a problem because like U I am good with being the one who initiates the front wheel drive, I am happy just the way it is and dont need to make it more off i guess U are saying.

I'd just leave it the way it is. I've thought about disabling the auto low range 6X6 on my M936. I'd rather have control of when the front end engages.

 

[nf6x]

Cool. I just wanted to make sure that I wouldn't break anything by leaving the automatic front axle engagement "broken". Thanks!

 

[fsearls92]

If its not in 6x6 in low range can you use reverse? If so I will definately make mine not engage in 6x6 low!

 

[m16ty]

If its not in 6x6 in low range can you use reverse? If so I will definately make mine not engage in 6x6 low!

It would probably make the low range reverse issue worse because all the power is directed to the rear wheels.

I've used low range reverse many times but I'm careful with it.

 

[nf6x]

Was there ever an MWO to add interlocks to prevent engaging reverse and low range at the same time? If so, have y'all seen the kits out there for sale?

 

[fsearls92]

I really don't understand why they designed it where you can't use low in 6x6. There are plenty of times when I need it!

 

[nf6x]

I really don't understand why they designed it where you can't use low in 6x6. There are plenty of times when I need it!

That's backwards; they made it so you always use 6x6 in low range. It's easy to change that, though. I just wish that the driveline was strong enough to use reverse in low range without breaking stuff.

 

[nf6x]

As long as I'm changing features that seem silly for my truck's new civilian career, is there any reason not to "fix" the emergency stop so it's not necessary to get under the hood to reset it? The pull cable has a locking feature, so either adding a return spring or adding another stop on the cable to make it push-pull should work.

I think I'll also replace the throttle and maybe brake pedal springs with nice brand new double springs. I've lost throttle springs while in motion twice so far... once in an electric car project in college, and once in an M109A3 that I used to have.

Just more fun ways to pass the time waiting for my SF97!

 

[wsucougarx]

Not working?

Today I decided to go out and check to see if the front axle was locking up. Looks like a no go for me. Troubleshoot here I come.

Scenario 1:

Jacked up the front axle so the tires can free spin.
Built up air pressure to 120 PSI
Shut off truck
Engaged manual Front Wheel Drive air switch (Axle lock light came on)
Front tires free spin....
Attempted to shift to Lo Range to see if the axle would lock up...nope couldn't get the lever to move.

Scenario 2:
Drained off all the air in the truck
Now she will shift to Lo Range
Started truck back up and got air pressure to 120 PSI
No front axle lock up light
Front tires free spin
Attempted to shift to Hi Range....nope couldn't get the lever to move again.
Drained off the air in the truck

Scenario 3:
Shift truck to Hi Range once truck was drained of air
Started the truck up and got air pressure to 120 PSI
Turned truck off
Crawled under the truck and moved the transfer case switch that locks up axle
No sound could be heard of anykind when moving the roller switch
Whacked it a couple times with a rubber hammer...nothing

 

[nf6x]

It's normal for the axle lock light to not come on when shifting to low range; it's only lit up when engaging the front axle with the dash switch.

Other than that, though, it sounds like you have a problem. Since there was no air sound when manually tripping that valve under the truck, I'd look at the air plumbing first. The M939 P2P program may help you understand how the air controls are supposed to work, so that you can figure out what's not working right on your truck.

 

[armytruck63]

I think I'll also replace the throttle and maybe brake pedal springs with nice brand new double springs. I've lost throttle springs while in motion twice so far... once in an electric car project in college, and once in an M109A3 that I used to have.

Just more fun ways to pass the time waiting for my SF97!

I remember the broken M109A3 spring. Mark was driving to meet me to pick up an M105 trailer and a comm shelter. He called me to tell me about the broken throttle spring. My deuce was nearby, so I pulled the spring and bought new identical springs at a hardware store. Both deuces got new throttle return springs, Mark's being repaired on the side of busy Van Buren Blvd.

Mark, are you in town this weekend, or are you going to Camp Roberts? PM me please.

 

[nf6x]

Thanks again for your help that day! The M105 has moved to a new home, but the commo shelter still lives on the back of my HMMWV.

This weekend I'll be at the West Coast Mil Radio Collector's Group meeting up at Camp San Luis Obispo. I'll be giving a talk on the AN/GRA-71 code burst keyer. Anybody with an interest in the mil radios is welcome, and MVs are welcome to visit, too. Details are on our web page:

MRCG-West Home Page

 

[wsucougarx]

Hmm, it appears I have a missing connection going to the capacitor. Can anyone verify? From the TM it appears both the transfer case lever switch wires are suppose to go to this thing. Not sure if there was a MWO or some kind of update that moved the wire elsewhere. I traced the two wires on my truck. One wire goes to this capacitor and the second one does to the bottom driver side of the transmission.
Could this be the reason I am unable to shift Hi/Lo range with air pressure?

 

[armytruck63]

Mike, that looks like the female end of a regular M-series wire connector to me, not a capacitor. I would think there is a male wire connector that is supposed to plug in here, unless it was disconnected per a MWO.

Edit: looking closer I saw the cap. Guess it's time for new glasses.

 

[wsucougarx]

Mike, that looks like the female end of a regular M-series wire connector to me, not a capacitor. I would think there is a male wire connector that is supposed to plug in here, unless it was disconnected per a MWO.

The unconnected wire comes out of the capacitor (long ruber looking black cylinder). There are a total of 5 wires coming out of this thing. They're all connected to something except this male connector.

 

[wsucougarx]

Anyone have their 5 ton close by to check on the capacitor? It's bolted right above the tranny against the bottom of the cab

 

[nf6x]

I don't see any unconnected plugs on my truck's capacitor down there. I doubt that open plug is the primary cause of your front axle problem, though. I think that the front axle engagement controls are all pneumatic.

 

[juanprado]

could be the capacitor for the 5th gear lock up pressure switch wiring harness?

see Tm 9-2320-272-24-1 Volume 1, 3-135 governor piping and capacitor maint & 3-138 trans 5th gear lock up pressure switch replacement?