5 ton t-case confusion

Alright. I have read every transfer case thread I can find. Between what's on this , the sprag in that , air-shift the do-hockey [!] , I have no idea how the 5-ton transfer case works :banghead: . I got the deuce transfer case figured out, I know the difference between air shift and sprag, the air lines that engage foreward and reverse, but the 5-ton's workings continue to evade me :boxer: .


So what I want to know is:



Are all 5-ton t-cases sprag type? My M-54 has an air switch on the dash that says "front axle lockout". Is this on all of them, or what? Mine still has the two lines leading to the transmission. Can someone please explain this to me, because I think I am overly-confused by something fairly simple. Also, what are the major differences between the 5-ton t-case and the deuces?

Ok...The M-39 series 5-ton trucks all have transfer cases with over-running clutches for the front axle engegement. (Commonly known as a sprag clutch but usually not, most usually they are roller clutches, but still an over-running clutch.) The clutch engages either in the forward drive or rear drive position by connecting to the poppet valve assembly on the low/reverse shifter rail of the transmission. This is where it gets different from the 2-1/2 case. The 5-ton front drive actually has 3 positions; forward, reverse and NETURAL. The 2-1/2 case with the "sprag" only has forward and reverse to my knowledge. HOWEVER, the only way to access netural is to bleed off all air pressuer on the control cylinder. (The manual indicates to open the air bleed to reverse tow the 5-ton.)

Now, the valve that has been ADDED to your dash. It is not an uncommon alteration to install a front drive engage/disengage valve from a 2-1/2 to allow the 5-ton transfer to be bled of air and operate in the netural position. (I have one and recommend it.)

Other than the above, size and rated torque are the only other differences. They still have a 6% overdrive on the front shaft, but problems with the over-run clutch locking-up like the plague of the M-35 front drive (pre-air shift) just does not occur. [ I assume that the fact that just the front axle on the 5-ton has over 75% of the total weight of a 2-1/2 on it combined with the specific caution of "DO NOT ALLOW TRUCK TO ROLL BACK" has a lot to do with the dependability of the front drive system.

Hope this helps.

Alright, now I am intrigued.

Can you elaborate more on this 5-ton "unlocker"?

1) Do you have to use a deuce valve or will any pneumatic valve work? I have a lot of 24volt soleniod valves from work - surplus industrial machinery.

2) Do you have any schematic or photos to show how to plumb the switch? Are there other components needed?

3) Once it is installed, was is the procedure for operation (engaging, disengaging)?

The deuce valve is the common approach, and it has the switch to indicate when the axle is engaged.
Any 3 port valve wil work, it just has to supply air, and vent the outlet when released.
The valve goes into the air line on the passneger (left) side ajacent to the transmission where it goes to the control valves on the shifter rails. This line has air pressure at all times when the system is charged, what you want to accoplish is to interrupt this air supply and vent the pressure off the valve system.

We have engage and dis-engaged at up to 20 mph with no ill effects, just be sure that you are moving in the direction that the transmission is in. (Roll back in forward and forward roll in reverse in a MAJOR NO-NO in the five ton, refer to the operators manual also.)

I operate the front drive in and out of my driveway (1/8 mile) every trip to keep the valves and clutches loose. When off-roading, I stop, flip the switch to ENGAGE, conform that the front propeller shaft slide moves with forward/reverse shift ing and head into the dirt or whatever.

Hope this helps some more. I can send you some pictures of the installation and plumbing if you want. Drop me your address.

How do you tell if your front prop shaft is moving? Is your 5 ton a Fred Flintstone special (ie no floorboards?)

I'd love to see a good write up on this as its a modification I want to do for my M813.

So, what is the difference between the sprag and roller clutches? Are they less self-destructive, because I hear alot of storys of stripped sprags. Also, what gears does the t-case engage in? 6x6 seems to function properly in 1st and 2nd, but after 3rd, the rears started spinning and the truck ceased foreward progression(I was driving in snow). Could this have been because the clutch operated stickily because of cold weather? I haven't gotten it into a 6x6 situation since it has warmed up to test this theory. Also, possibly another cold weather problem, 6x6 sometimes won't engage in high without shifting to low and back to high. Also, just to ask a stupid question, the "FRONT AXLE LOCKOUT" switch should be set to the "ON" position for 6x6, correct?

A 5 ton tractor may be in my future. So if i install the valve to "unlock the roller clutch" can i run desplined hubs on road trips? Will this cause any T-case trouble? Or would i need to pull the front driveshaft?

First question, the difference in a roller clutch and a sprag. The operation is the same, a stepless over-running clutch (read this as a one way clutch). A roller clutch uses spring pre-loaded rollers that climb small ramps to wedge themselves into the outer race. a sprag uses small hour glass shaped wedges that rock against pre-load springs, when they attempt to stand up they wedge into the outer race. In both cases when the clutch over-runs the roller moves down the ramp and the wedge rocks over and unlocks. The fron drive in the 5-ton is rated to drive the truck fully loaded all by itself, just using a lower speed. It is a far heaver unit than the 2-1/2 ton.

When does it work, always. does not matter if it is low range or high range, and the transmission gear has no impact. Yes they can slip if the oil is real heavy (thick) it simply keeps the rollers or wedges from moving into place. If the switch is in the ON positon the indicator lamp should light at around 30 psig and the poppet valves on the transmission are active. These valves are prone to sticking and NOT shifting the drive fork.

Lastly, If you install de-splined hubs with the "disengage" switch there will be no problems, but you have no available front drive, and without a load in the back these trucks will not pull squat, to many tires. (I got stuck trying to pull my trailer (empty) out a gravel drive onto the road, flip the switch and off we went..) I recommend if youwant to go that route check out the 5-ton locking front hubs (M35-Products is working on them) then all you have to do is hop out and lock them in.

Ryan....the front shaft always turns when you move unless the hubs have been de-splined or you have lockouts...you know that.

Yep...Still playing with trucks

Thanks for the info. My plan was to keep a set of hubs under the seat. On road trips i was looking for a way to help with the fuel milage. I didn't know they were working on some 5-ton lockouts. Looks like i better start saving$$$.

Hi Dumb A$$,
I have an M54A2, but it didn't come with a switch on the dash for lockout,
However, when I got the truck from Jim up in Washington, a friend of his
put a valve in the airline and closed it tight. said that that would deactivate the
front wheel drive. Good thing, because I had to drive it all the way to
Berkeley CA.
Hope this helps a little. You can see that your not the only Dumb A$$ out here....

Reviving an old thread

at least I searched......but I may be more confused than ever now.

I have been lurking through SS for a few weeks now, and I am very familiar with the 800 series 5-ton axles through my recently completed swamp buggy project, but I do not yet own an MV. I definitely have the "fever", and have narrowed my selection down (up?) to either an 800 or 900 series 5T. Hopefully, y'all can help me narrow my choice as I "need" to purchase one SOON!

I have been under the assumption that all the 5-ton cargo trucks had "full time" front axle propulsion. I see in this thread that there is the possibility of adding an air-bleed from a Deuce to the transfer case's control system, but I am wondering if any of the newer trucks (923s and 925s specifically) have such a system built into the truck already or at least added through a MWO? I plan on having my truck on-road quite a bit, and freeing up the front is almost a necessity. I thought I was going to have to pull the driveshaft for long trips, but I am relieved to see that there may be a much easier alternative.

Thank you, in advance, for any input that you might offer.

The 900 5ts have a air shift transfer, the 809s have a sprag, not full time but on AUTO demand as needed, the MWO cuts the air to the sprag f/r shifter, putting it neutral

OK, Somebody please show me in the operators manual where it says to not let the M813 roll back on hills. I have looked through several times and the only reference I can find pertaining to hills is to not let coast down hill with clutch depressed. Of course that warning has nothing to do with the sprag. It has to do with vehicle control.
I have also looked through the manuals on transfer case repair and really cant see why it would hurt it to roll backwards..maybe just missing something here. I drove them in the Marines and dont remember anybody telling us not to roll back. We used them in the mountains, no way to not roll back sometimes.
In my search on here have found some very good system operation explanations, but no real explanation why it cant roll backwards
Still thinking on this...

When you shift into reverse you hear air and a clunk, that is the shifter engaging the reverse sprag. If you let the truck roll forward with the trans in reverse then the front will try to turn the wrong way and bind up the wheels. Just the reverse if in low gear. I think once you leave first gear you no longer have six wheel drive.

If I remember correctly when air pressure is built up, with truck in neutral or a forward gear the forward sprag is engaged. When you shift into reverse, air is dumped from forward sprag and air applied to engage rear sprag. Thus the clunk sound.
Thanks for the reply, but still doesnt explain why. If all the wheels are connected together, why would movement in one direction or another cause binding. Again still thinkng here, must be some reason everybody says this, I just cant logicaly figure why!
Thanks again.

Found a good answer here on a post i must have missed, the 6% difference is what causes it..that makes more sense. They will turn at different speeds, thats the reason for the lock up. Now this was a reply to a M35 with srag question and the TM reference was also for an M35. Wonder if 813 is the same or because of the M35, everybody just assumes so

"The sprag transfer cases have a 6% overdrive on the front propeller shaft. When you get 6% slip on the rear, the sprag will engage and hold till the front shaft returns to overspeed. This makes them VERY effective on pulling the front through turns and maintaining control in slippery conditions. They can also provide reliable 6x6 operation on hard surfaces when slippery conditions are variable, because of this unlocking feature. BUT, the 6% overdrive means that when rolling reverse to the sprag selection that you have a mis-match of speeds and the transfer attempts to lock-up. In the 2-1/2 ton t-case the sprag is the weak link, what you hear is the sprag outer race popping over the "sprags" . (Not to be confused with a roller clutch that does the same thing.) Yes this will either lock-up the sprag or brake it. The air shift case does not have the overdirve and will not experience the lock-up, but can not be left engaged on hard surfaces due to no over-run provision."

Any Gear

73m816 set me straight on the questions of which gears will have six wheel drive.
ANY gear. When the sprag moves into position because the front and rear axles are turning at different speeds; the transfer case engages the front drive shaft and
you have those three magic words: "SIX WHEEL DRIVE".

Ditto on the posted experience of getting stuck easily with no weight on the rear
of the truck. I once got my Chevy 1-Ton 4x4 stuck in wet long grass while in two
wheel drive. I actually left the truck in creeper gear with the clutch engaged and
exited the cab to do a "walk-around" to scratch my head and determine what the
dickens was going on?? The rear wheels were spinning slowly on the wet grass
with no traction at all, the truck just sat there! I got behind the wheel, engaged the front axle and pulled away with no problem.

The most dangerous vehicle on the road in slippery conditions is a truck with no
weight over the rear drive axle(s).

In the 5t the sprag is STRONG, not a weak link in the drive train, the sprag is made up of TWO overrun CLUTCHES, by rolling backwards while in forward it will automatically (because of the way the sprag clutches are made) try to set the reverse sprag clutch while the forward is set, thus looking things up, and a BIG bang when things release, you will get the SAME if rolling forward while in reverse.

THE DO NOT ROLL against shift can be found in the -10, and in PMS mag

Yeah Ive heard everybody say the "do not roll" is in the -10..and i have no doubt its there..I just cant find it, except the TM for the M35..
Something I'm thinking on is, if the forward clutch [sprag] is engaged, and the shift fork has it in engaged, wouldnt the reverse clutch [sprag] be disengaged..would seem to me the sliding fork can only be in forward..neutral[with no air] or reverse...Looking at the Tms, I only see one shift fork. If the output shaft tries to turn the reverse sprag, rolling backwards, the outter part is not connected to anything..unless the fork is moved to reverse position at which time the front sprag is no longer engaged....I could be wrong, but thats what it looks like to me. And if you guys hear a big bang, something is going on..I just cant see what it is. Unless its the ratio difference someone mentioned but the post I read was on a m35.
Appreciate everyones thoughts.

F18hornetM said:

Yeah Ive heard everybody say the "do not roll" is in the -10..and i have no doubt its there..I just cant find it, except the TM for the M35..
Something I'm thinking on is, if the forward clutch [sprag] is engaged, and the shift fork has it in engaged, wouldnt the reverse clutch [sprag] be disengaged..would seem to me the sliding fork can only be in forward..neutral[with no air] or reverse...Looking at the Tms, I only see one shift fork. If the output shaft tries to turn the reverse sprag, rolling backwards, the outter part is not connected to anything..unless the fork is moved to reverse position at which time the front sprag is no longer engaged....I could be wrong, but thats what it looks like to me. And if you guys hear a big bang, something is going on..I just cant see what it is. Unless its the ratio difference someone mentioned but the post I read was on a m35.
Appreciate everyones thoughts.

Click to expand...

It is the way sprag clutches are designed, basicly a automatic clutch,