M51A2 stuck sprag not engaging air problem?

[Robo McDuff]

OK. I am stuck in a wet snowy peat meadow, and it looks my front wheels are not doing much. My problem is that the air pack is being rebuilt and I needed to move the truck. So the air line to the air pack is open.
1) does that stop the sprag from engaging?
2) can that become harmful for the compressor, running too long without counter pressure?

Problem is that here in the Czech Republic, I cannot find non-metric nuts or bolts that I could use to block the air line to the absent air pack.

 

[sandcobra164]

1. yes 2. no. I would find a cap that is close but slightly oversized and use a lot of teflon tape to cap the line going to the missing airpack. Might not work but I know I'd try it anyway.

 

[Floridianson]

1. yes 2. no. I would find a cap that is close but slightly oversized and use a lot of teflon tape to cap the line going to the missing airpack. Might not work but I know I'd try it anyway.

That would be the best way. #2 Call a friend with a big truck to pull you out. #3 portable air tank hooked to the poppets.

 

[BKubu]

A friend once drove an M923A2 with an air leak and it burned out his compressor. Comparing air leaks is like comparing most things without seeing them.

 

[Floridianson]

Don't think he want to drive it far without brakes just wants to get out of the field.

 

[BKubu]

Good point. I was thinking more generally, but, you are right...should not be a problem running it continuously for a little while.

 

[red]

Without air pressure the sprag can't engage.

Since you're only going a short distance on dirt. If you can't find a plug take some cloth (shop rag, paper towels, etc) and duct tape. Plug that line and tape it up. Should hold well enough to get it through the field.

 

[SETOYOTA]

How does air pressure lock up a sprag transfer case ?

 

[sandcobra164]

Air piston in the front of it engages the transfer sprag. Once he has air pressure, it should assist by engaging the front axle. It's not a direct engagement like the air shift in the M35's "equipped" or M939 series trucks. In the OP's case, he has to have air pressure controlled by the valve on the top of the transmission to engage the reverse or forward action of the sprag. There are 2 of them inside. Think of a ratchet wrench. You can spin it one way with minimal resistance but it's locked the other way. Flip the thumb switch and it goes opposite. That's why he needs air pressure and the very basics of how his transfer case operates. Someone smarter than me will chime in shortly.

 

[BKubu]

I asked in the other thread if his sprag worked. I never got an answer. John Winslow, a longtime truck dealer in NC (God rest his soul), used to tell me that a good portion of his 5 tons with sprags were bad. This often comes from allowing the truck to roll forward in reverse or reverse in a forward gear. It cautions against in this in the operator's manual. As far as I know, we don't know if his sprag is working in the first place

 

[red]

I asked in the other thread if his sprag worked. I never got an answer. John Winslow, a longtime truck dealer in NC (God rest his soul), used to tell me that a good portion of his 5 tons with sprags were bad. This often comes from allowing the truck to roll forward in reverse or reverse in a forward gear. It cautions against in this in the operator's manual. As far as I know, we don't know if his sprag is working in the first place

Won't know until air is applied. With no air the sprags default to neutral (no front wheel drive).

 

[Robo McDuff]

I asked in the other thread if his sprag worked. I never got an answer. John Winslow, a longtime truck dealer in NC (God rest his soul), used to tell me that a good portion of his 5 tons with sprags were bad. This often comes from allowing the truck to roll forward in reverse or reverse in a forward gear. It cautions against in this in the operator's manual. As far as I know, we don't know if his sprag is working in the first place

Saw that, it is one of the reasons I started this thread. From whatever signs I checked later, it looks that the front wheels were not involved in the digging in with spinning wheels, but just went down in the existing ruts. Did not try starting the truck yet, did not manage to get it going before last Saturday 4 PM deadline, after that no time yet to do something, will try this weekend taking all tricks mentioned here and the other thread into consideration. One problem with starting is that both my batteries are dead and gone, I have no $$ to buy good new batteries at this time, so I am depending on borrowing and using the batteries of my son's forklift and a friend's tractor. They are not always available when I want to try something.

Looking back, if I had realized the sprag problem earlier, I probably would have been out already. Too many things on my head to think properly.

 

[Robo McDuff]

Before I make the next mistake. I read that there was a risk for damage rolling backwards with the sprag in forward and vv. Does this apply only while rolling backwards with the gear in forward?

First direction we went with the truck with the air system open to the air was BACKWARDS with the gear in backwards. The terrain is too flat to roll by itself. Since then, I moved back and forwards several times, always under own power but with the air off. We did not spin much, I stopped quickly to avoid getting in deep.

Any change this hurt the sprag? Anything I can-should do apart from closing the system and get driving to avoid damage to the sprag or to whatever?

 

[sandcobra164]

The sprag is pretty tough. If it wasn't broken before, I doubt you've damaged it. The way to engage it without air is to remove the actuator housing on the front of the transfer case and pull/push the piston into position. I can't remember which way for which direction of travel. With a fully operational truck with air pressure, you should hear a distinct pop whenever you shift into reverse. You'll hear the same pop when you move out of reverse. Not so much a pop but sounds like an air dryer on a commercial truck releasing.

 

[Floridianson]

Reverse sprag engagement would be piston /threaded rod to the rear or in. If a sprag does get get locked up the truck will hop and you will feel a bad drag on the drive line.