Rockwell T138 transfer case questions

[B36Peacemaker]

I have recently volunteered to assist a museum restoring a 1953 O11A American LaFrance Air Force Crash Truck. There are many issues to be addressed some of which I have already found guidance from this forum.
When we acquired it the wheels were almost buried so had to be dug out. They got it started and pulled it out partly under it’s own power with help from a pickup truck and tow chain. They drove it about 50 yards and left it to return the following week with a tow truck. At that time they started it in an attempt to move into a better position to hook up the tow. Moved about 20 feet in reverse and stopped, it wouldn’t move any further under its own power. It was flat towed about 50 miles to the museum and that’s when I got involved.
Right I need information about the transfer case. This is apparently full time 6X6 drive since the transfer shift only indicates Hi or Low with no neutral. The only ID I have for the transfer case is casting # 5876W205 which seems to indicate it’s a Rockwell T138. We can start it, engage the clutch, the input drive shaft spins but no movement to the front or rear output shafts.
The actual shift linkage is disconnected, but we can move the lever by hand and it seems to engage something both ways.
Looking at the attached picture of the front output, the speedometer cable on the left in the fore ground and there are two airlines. What do these do? Where do they originate?
Also does the transfer case have some sort of differential between the front and rear? Seems like that would be necessary.
I would appreciate if someone could share a parts breakdown or overhaul manual for the transfer case. Also any advice would be most welcome.

 

[gimpyrobb]

I think a 138 is a 5ton sprague T-case. One air line is to put it in forward, the other is to put it in reverse. They might have screwed it up.


Try to lift an axle or two to un-bind the load on the T-case clutches. Be careful, the wheels might kick!


Edit, that case should have neutral! It will be in between high(in) and low(out). I think, its been a while since I've tinkered with a 5ton.

 

[NDT]

You are correct, the O11A used the T138 transfer, same as military 5 tons 1950 to 1980. If you do not have power going through it with high or low range firmly engaged, something is wrong inside and internal repair is required. The air cylinders control the engagement of the front axle. Does your Oshkosh still have the huge Continental 6?

 

[B36Peacemaker]

Any ideas on where to find an overhaul manual? As far as I know the engine is the original Continental S6820, it is big and loud. I would upload a start & run video but I think it's too large.
Thanks so much for the reply

 

[NDT]

Splitting that transfer open and repairing it is very difficult. Most people just find a good takeout. That engine is 820 cubic inches and I think 300 hp.

 

[B36Peacemaker]

I looked through a bunch of manuals for 5 ton trucks. Found what we needed in TM-9-2320-211-35 5 ton multifuel 6X6 Maintenance.
I will soon need information on the engine. Do you know of any other vehicles that used the Continental S6820 (so I could find the specs etc)? Per those manuals a lot of them used R6602 which is smaller for sure but how else would they compare?

 

[NDT]

The 820 is like a 602 that grew up. Same OHV configuration. I believe that your crash truck is the only military vehicular use of that engine. I'm sure the engine had numerous civilian applications.