Stuck in 6 wheel drive?

[5tonman1971]

Ok guys I've got a good one for your brains!

On my m813a1 I've been battling my front axle engagement for awhile now and I am about to give up.

I have rebuilt the shuttle valve, I have rebuilt the piston on the transfer case.
Everything seems to be working, with the truck fully aired up and shut off, you can hear the sprag fork rod moving from forward to reverse a real solid clunk when shifting from reverse to first. So my logic says that this should be moving the sprag clutch in and out of gear.

The problem is that, when I'm in forward gears my front axle is always engaged, tires chirp and pop when Turing on pavement and it won't go over 40-45 mph as the data plates say if you are in 6 wheel drive. When I press in the clutch it comes to a stop very quickly from 2-3 mph.

But in reverse I don't get any of this happening and when I press in the clutch at 2-3 mph it will roll freely for quite some time if on pavement as it should. When we had a lot of snow I tested to see if it would lock in the front axle if the condition were right so I back in to a huge snow pile the rears slipped for a second and then grabbed as the front axle engaged. If I remove the front drive shaft the truck is fine rolls good in both directions and can hit my top speed.

Is is it a possibility that the drift pin holding the sprag clutch fork on the shaft has wiggled out or broke cuasing the transfer case to keep the front axle engaged?

 

[Artisan]

I wish I could help, but is there a TM w/ a front axle / transfer case troubleshooting section?

Air all air lines routed correctly, something crossed? Do you have a pneumatic schematic?

I hate whodunits... there is a resolve, you will get to it.

 

[BEASTMASTER]

sounds like u got the air lines crossed to me.

 

[sandcobra164]

I would almost agree to airlines crossed but the truck rolls backwards fine and the OP hears a solid clunk when shifting between a forward gear and reverse with the truck sitting still. He also has had success with the sprag engaging correctly in reverse gear. I just think there are some demons in the transfer and I'm thinking about it as well. Somebody smarter than myself will provide the answer and I'll learn something. That's why I love this site. After I read the answer, I'll have something else to suggest to try to the next person who experiences this.

 

[73m819]

I would suggest that a GOOD flush with diesel BEFORE any other action is taken, drain the transfer case, fill with diesel, take the truck down the road and back DO NOT PUT A LOAD ON THE TRANSFER CASE, OR SPEED, come back and drain, REFILL diesel, do your road trip again, keep doing the drain/refill till it drains clean, (this will take a while) once you have clean drain refill with 80/90 gear oil. After the flush and you still have transfer problems we can go on to plan B

 

[5tonman1971]

Airlines were my first suspicious early on but I quickly eliminated that as an issue. The first problem was the shuttle valve it was not functioning so I fixed that and now the sprag is moving like it should or so it sounds but it is not acting like it should.

I have been been considering this diesel method of cleaning the transfer case but I thought that was is you did not get the clunk from the sprag moving Becuase from looking at the schematics of the transfer case if that rod is moving the sprags are moving. So I am wondering if my sprag has come apart bs is not being pulled out of the forward gear.

To to my knowledge the sprags clutch is like the synchronizers in a manual transmission where they are 2 pieces and I have a feeling the outter ring that is in contact with the fork has come apart.

 

[73m819]

FLUSH, FLUSH, FLUSH, when you drain, you will see if any chucks come out, you WILL be surprised what crud will do to the sprag, and you WILL also be surprised what plan old fashion crud will come out of the transfer case.

The sprag is nothing like syncos.

 

[Aussie Bloke]

G'day everyone,...


I was going to say sounds like transmission wind-up, if its under load it will not mechanically disengage.
Have you raised the front end so you can rotate the front wheels independently?
But you did say you removed the front driveshaft so any wind-up should have been able to unload unless its caused damage in the transfer case?

Just my thoughts.


Aussie.

 

[WOLF DOG]

Are all tires the same size ?

 

[5tonman1971]

Are all tires the same size ?

Yes the tires are all the same size 16.00s

 

[5tonman1971]

FLUSH, FLUSH, FLUSH, when you drain, you will see if any chucks come out, you WILL be surprised what crud will do to the sprag, and you WILL also be surprised what plan old fashion crud will come out of the transfer case.

The sprag is nothing like syncos.

ok I guess this seems to be my next option before I start taking the transfer case apart. I will try to do this over the weekend and report back.

 

[Artisan]

I took these screen prints from the TM's that are HERE.

As found in TM 9-2320-260-20

Does the TC Shift Lever hit anything? It shows a specific measurement
of 8.75" center to center on one connecting rod and all pivots lubed?

There is a "poppet valve" part #9 on the right side of the tranny that
connects to the TC, I wonder if it is a possible problem area, and
of coarse the piping needs to be plumbed correctly to and from the poppet etc.


TM -20 says;

 

[Floridianson]

I have to agree with Aussie it does sound like the sprag is jammed. Did you do any wheel hopping to make the sprag lock up last time the truck was used and before that she was running fine. If it turns out to be the sprag it can be replaced with the transfer in place I believe.

 

[swbradley1]

Question. How many members have actually put diesel in their sprag transfer case and and driven it?

 

[ClintA]

I flushed mine with diesel, but my fronts still will not pull

 

[73m819]

Question. How many members have actually put diesel in their sprag transfer case and and driven it?

I have talked to quite a few members on the phone about transfer case issues, from the feed back I have gotten, at least 50% if not more say that just doing a very good flush, getting the gunk cleaned out solved the problem.

There is almost no way for the shift rail to be out of adjustment, nor the poppet valves, the shift liver is ONLY for shifting H/L, has nothing to do the sprag, the sprag goes into reverse when the trans is put in reverse and comes out of reverse AS SOON as the trans is taken out of reverse. With the sprag WORKING in reverse, it should disengage the front just by its movement.

When you flush, stick a magnet in the pill port on the sprag housing an see what you fish out, a bunch of fines is normal (this and old gear oil is the goop you be flushing out)

 

[5tonman1971]

Does the TC Shift Lever hit anything? It shows a specific measurement
of 8.75" center to center on one connecting rod and all pivots lubed?

There is a "poppet valve" part #9 on the right side of the tranny that
connects to the TC, I wonder if it is a possible problem area, and
of coarse the piping needs to be plumbed correctly to and from the poppet etc.

My shift lever moves fine it moves freely.

The he poppet valve is what I'm calling the shuttle valve that I have rebuilt already and is working properly. I said that the sprag rod is moving from forward to reverse but I'm still stuck in forward 6 wheel drive but not reverse.