M818 front axle not engaging?

[Wastelander]

Hi, searched for posts to try and answer my problem but came up with nothing helpful, hopefully someone here can help me or point me to the proper post, I have a feeling my search terms weren't proper.

I've got an M818 tractor, no mods all stock, a couple months ago I got stuck in some muddy snow and had a **** of a time getting out. Right off the bat I know the non directional stock tires aren't great for snow, especially with no weight in the back, but I noticed I was only getting power to the two rear axles. I was in high range, 2nd gear if that makes a difference. I got it into low range after a little rocking and had the same issue with no power to the front axle. When I shift into reverse I can hear a short air hiss and a clunk which I assume is the air sprague engaging. Other than that the truck runs and drives great. Anyone able to diagnose my problem with that limited info? Much appreciated.

 

[Jakelc15]

You can check the sprag engagement by jacking up one front tire and seeing if it locks in. Engine off, air pressure up, the tire should only turn one direction for reverse and the opposite for any other gear and neutral. It's always locked in, that's why it's important not to drift backwards when in neutral.
Mine didn't want to engage fully a couple years ago when the temperature dropped. There was some water in the air cylinder that would defrost after driving for a half hour or so. Cleaning that out took care of it.

 

[Wastelander]

Much appreciated

 

[Wastelander]

So if I understand correctly, if the tire moves both directions when off the ground in reverse for example, the sprag is not engaging? Could it be as simple as disconnecting the air line and cleaning the sprag unit out?

 

[73m819]

FLUSH, FLUSH, FLUSH the transfer case with diesel till clean comes out BEFORE you do anything else, dump the gear oil, fill with diesel go down the road a bit (DO NOT PUT A LOAD ON THE TRANSFER), come back, drain, keep going though this cycle TILL the drained diesel is CLEAN, you will be surprised the amount of gunk that comes out, after the flush refill with gear oil, 90% of the time the flush fixes the sprag issue, the sprag (over running clutch) design has been around since early Egyptian times, it is mostly trouble free.

If, after the flush and you are still having issues, give me a call, Ron 703-389-6705

 

[Wastelander]

Excellent, thanks!

 

[KsM715]

Try using first gear, don't go from reverse to second.

*edit* never mind, in the TM it says when starting off in soft soil or sand to start in low, second gear to avoid digging in. I don't know why I was under the impression the you had to shift into first gear in order decor the sprag to engage forward.

However, when sitting in the truck with it running you should be able to hear that same hiss and "thunk" if you sit with the clutch in and shift back and forth from first to reverse, should hiss and clunk both directions