T-1138 transfer case info needed

[kskrawler]

Ok guys if looked all over and no luck. I just got a T1138 transfer case and I'm trying to find a pdf file showing the breakdown of the case and the air hook ups and what does what. I counted the hose connections and there is 5 cut off hose connections. Any help at all will be greatly appreciated including operating psi required.
Thanks again in advance......

 

[Swamp Donkey]

Are you installing this case in a M939 series truck or something else? I ask because some of the air operated stuff will not be needed if going in a custom rig.

The exploded diagrams can be found in TM 9-2320-272-24P-1 starting on actual page 208-1.

The air diagrams are best veiwed in the P2P program because they are scattered all over the place in the TMs, and they don't show air flow.. The diagrams in the P2P program will be animated to show how the air moves to make things work. This might not be helpful if going in a custom application though.

The TMs and P2P program can be found in the link below:
http://www.steelsoldiers.com/showthread.php?79228-TM-s-for-the-939-series-trucks

Everything operates at full system pressure of 120 psi.

 

[kskrawler]

Thanks for a lead to look in too. It's going into a custom rig, I'm putting the 1138 with some 5 tons in a 2003 dodge ram 3500 on 43" tires and yes it's going to be street driven daily. The rpm's are perfect with this setup but if I can't get the transfer case air figured out then I have a huge heavyweight 2wd lol

 

[simp5782]

Thanks for a lead to look in too. It's going into a custom rig, I'm putting the 1138 with some 5 tons in a 2003 dodge ram 3500 on 43" tires and yes it's going to be street driven daily. The rpm's are perfect with this setup but if I can't get the transfer case air figured out then I have a huge heavyweight 2wd lol

I believe there is an internal way to lock it up with out using air. It would just always be engaged. Ill find the info when i get home . I know on the T138 you just weld the sprag up. I would personally go with something smaller that is most likely alot tougher like a BW13-39 or an old 203. Heck you can make a 205 bulletproof and still weigh half as much as the t1138. IMO. The weakest link on these trucks is the transfer case

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[tobyS]

Isn't the only air on a T1138 for putting the front drive in and out...with a two position air valve?

 

[Swamp Donkey]

You need 1 air supply line going to the transfer case and a dash valve like in the M939 trucks. The rest of that stuff is not needed.



The square cylinder behind the parking brake drum, in the picture below, engages the front output shaft. It is air engaged and spring release. You'll run a supply line from compressor to the valve, and a line from valve to this air cylinder. That's it. The valve will do the rest. Air is supplied at the switch and vented at the switch. You now have on/off 4x4 function.



This mass of T-fittings is not needed. It vented several things in factory configuration but you only need to vent case pressure here. A simple barb fitting with a vent line up high takes care of this.



The other air cylinder stays in place but be sure to remove the elbow and put a plug in the air supply hole.



The stuff in the other pictures can go, including the airlines and wires.





If you want to leave it locked in constantly as Simp suggested then just remove the 4 bolts holding the cylinder to the case behind the parking brake drum. Remove the internal piston and spring. Make a spacer that will fully depress the rod end when the cap is installed and then reassemble. Everything is then properly sealed and no major disassembly was required.

 

[Swamp Donkey]

Isn't the only air on a T1138 for putting the front drive in and out...with a two position air valve?

The air also operates the shift lock cylinder on top of the case. Definitely not needed here, and in my opinion, not needed on anything but the M936s in stock configuration. I plugged the one on my truck last year and have enjoyed silky smooth shifts ever since. Really just personal preference though.

 

[kskrawler]

I believe there is an internal way to lock it up with out using air. It would just always be engaged. Ill find the info when i get home . I know on the T138 you just weld the sprag up. I would personally go with something smaller that is most likely alot tougher like a BW13-39 or an old 203. Heck you can make a 205 bulletproof and still weigh half as much as the t1138. IMO. The weakest link on these trucks is the transfer case

The reason I'm wanting to run the 1138 is for the extra overdrive gearing in high range. With the 0.73 high range paired to my 6 speed transmission and my tire combination it puts my rpm range perfect within 50 rpm of how the truck was bone stock so I'll put total power to the ground.
The numbers on the left are as my truck was bone stock. On the right it's with the 1138 t case - 6.44 axle gears and 43" tires.

 

[simp5782]

I believe there is an internal way to lock it up with out using air. It would just always be engaged. Ill find the info when i get home . I know on the T138 you just weld the sprag up. I would personally go with something smaller that is most likely alot tougher like a BW13-39 or an old 203. Heck you can make a 205 bulletproof and still weigh half as much as the t1138. IMO. The weakest link on these trucks is the transfer case

The reason I'm wanting to run the 1138 is for the extra overdrive gearing in high range. With the 0.73 high range paired to my 6 speed transmission and my tire combination it puts my rpm range perfect within 50 rpm of how the truck was bone stock so I'll put total power to the ground.
The numbers on the left are as my truck was bone stock. On the right it's with the 1138 t case - 6.44 axle gears and 43" tires.View attachment 655426

Are you going to be able to find a correct spline yoke/flange to use? I know you aren't going to want to use the wing joints that are 400$ each.

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[kskrawler]

The air also operates the shift lock cylinder on top of the case. Definitely not needed here, and in my opinion, not needed on anything but the M936s in stock configuration. I plugged the one on my truck last year and have enjoyed silky smooth shifts ever since. Really just personal preference though.

The way I understood it the air is to engage the front output same as t136 in a survey and the air also engaged a high lock and low lock depending on what gear the case was in. This lock is it the same as old 203 that when lock is engaged it truly locks the front and rear outputs insink with each other in rotation

 

[kskrawler]

Are you going to be able to find a correct spline yoke/flange to use? I know you aren't going to want to use the wing joints that are 400$ each.

Yes I'm actually going to mate the input of the 1138 to the output slip yoke off my stock dodge ram 271 t case and yes it will give me the selection of double low range. Adam gGates with Adams off-road performance makes a input flange to put on the 1138 that will bolt a 1485 flange yoke up directly to it

 

[Swamp Donkey]

The way I understood it the air is to engage the front output same as t136 in a survey and the air also engaged a high lock and low lock depending on what gear the case was in. This lock is it the same as old 203 that when lock is engaged it truly locks the front and rear outputs insink with each other in rotation

The high/low lock cylinder or shift lock cylinder only locks the selector shaft in place so the shifter can't be knocked out of gear. The selector shaft has detents too, which hold well enough, so it's really not needed. High and Low are still shifted manually. The front output shaft can only be engaged by air.

If you want this working then just run another line and valve like the other one to the cylinder on top. For it to be locked though, it needs constant pressure. You'd release the pressure to shift, then apply pressure to lock again when done shifting.

On Edit: If you build a mechanical shifter lock into the actual shifter you decide to use then you'll create the same lock without the extra plumbing. The problem I have with the shift lock cylinder is that if the internal seal leaks, you pressurize the T-case since it requires constant pressure to lock.

 

[kskrawler]

I'm going to run onboard air anyway for rear air ride, so that's not an issue. Someone said earlier they did away with the high / low lock and it shifted easier and smoother. Is this because it can hang up and not release fully. This truck is going to be a daily driver so if I can eliminate any hang ups I'm all for it, but I don't want the case to kick in and out when I'm needing it to stay in.

 

[kskrawler]

I'm going to run a semi truck air brake push pull switch with exhaust port. I ran them before on t136 cases and worked great. How much psi is needed to work the t1138 front output engagement???

 

[Swamp Donkey]

I'm going to run a semi truck air brake push pull switch with exhaust port. I ran them before on t136 cases and worked great. How much psi is needed to work the t1138 front output engagement???View attachment 655434

That will work fine too. The main thing is that it can vent the supply line which that one will do.

I'd say you need to aim for 120 psi. The return spring for the engagement rod is very stiff. I can't fully depress it by hand. This spring is what the cylinder has to depress to engage the front output. If only partially engaged I'm sure bad things will follow.

 

[Swamp Donkey]

I'm going to run onboard air anyway for rear air ride, so that's not an issue. Someone said earlier they did away with the high / low lock and it shifted easier and smoother. Is this because it can hang up and not release fully. This truck is going to be a daily driver so if I can eliminate any hang ups I'm all for it, but I don't want the case to kick in and out when I'm needing it to stay in.

See my edit in the previous post. Design the lock into your cab shifter to keep everything simple.

 

[kskrawler]

I know I was able to run 45 psi on a regulated supply for the 136 from a deuce and it worked great. Guess I'll have to play with it but don't want to much psi and blow seals and same goes I don't want to little and it not engage fully. Wish a manual was out there for specific information.

 

[Swamp Donkey]

Yeah some testing would help. I'm not saying that it won't work fine at lower pressures. I just know 120 psi is there on the M939s and I don't know what it'll do at lower pressures. Obviously, pressures fluctuate on the truck when the air brakes are used, so I'm sure you could safely drop at least 20 psi just from that observation. I'm sure there is a design minimum too, but I've never seen it listed so I don't know what it'd be.

 

[kskrawler]

I wish there was more gearing options for the 1138 so it would be like a 0.83 or so high range, which in turn would deepen the low range

 

[gimpyrobb]

I wish there was more gearing options for the 1138 so it would be like a 0.83 or so high range, which in turn would deepen the low range

Why would you think that? They are separate gears, hence the shifter.