M809 series 5 ton transfer case issues

There seems to be a constant stream of 5 ton transfer case questions/problems that pop up on this site. Any suggestions for a thread addressing the bulk of these questions so when new members ask, they can be directed to one post? Of all the systems on the 5 ton trucks, this one item seems to be the most misunderstood.

We have tried that in the Wkies or however you spell it.... People don't search so it would not matter if we posted it in the main page and you had to look at it every time you logged in... people still would by pass it and ask the same question 1000000000000 times.

Westech said:

We have tried that in the Wkies or however you spell it.... People don't search so it would not matter if we posted it in the main page and you had to look at it every time you logged in... people still would by pass it and ask the same question 1000000000000 times.

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Now now Westech do you realy think they would ask that many times.?.

I think it would be more like 100000000000 times at most.

No more M-800 series trucks in our motor pool so I can't speak for them; we've got the M-900 series trucks. Their transfer cases break pretty regularly if you try to use reverse gear while in low range. A big enough problem to have brought on low range/reverse lock-out kits and dash instruction plates.

We haven't had any other problems on an ongoing basis.
We get a pinched or ripped oil pump line now and then but that's usually from not securing them correctly. Air lines leak or electrical connections break down and suddenly the front axle won't engage. Rest of the time it's usually linkage adjustment problems.

Remember that lot of military equipment was deadlined for a month or better even before they went through the screening process and out the gate to GL.
Anything that isn't driven frequently will stiffen up with congealed grease, seals and bearings will dry out, air and oil lines will gum up or crack and leak, exposed parts will rust.
A regular PM program is the best preventative for most problems.

Well, I will give it a try, at least with the issues we have had, and how they relate to the transfer case &/or sprag shifting:

1) All M54/M800 trucks front axles are engaged with the transfer case when running and driving, if there is air to the shift valves on top of the transmission & on back to the shift cylinder located on the front of the transfer case. Some trucks have an added valve like a Deuce so the front axle free-wheels. The overrunning clutches (sprags) in the transfer case allow the front axle to run faster than the rear axles in a turn so there is little to no binding. There is always a slight delay before the front axle will "grab" due to the sprags engaging.

2) The sprags in the transfer case are controled by the shift valves (poppets) located in the shifting tower of the transmission. In any forward gear or neutral the forward sprag is engaged and the reverse sprag is only engaged when the shifter is in reverse. Never allow the truck to roll back with the transmission in neutral or any forward gear. A transmission change to a non-stock unit would require some type of shifting system to keep the transfer case engaged like the stock system. This is just one problem for an updated transmission installation in these trucks.

3) Any interuption to the air pressure in the shift system will affect the engagement of the correct sprag clutch. This was a issue we had with the water truck at first due to tar like oil in the transfer case. The transfer case must select the correct sprag or binding and much damage will happen.

4) An easy check of the sprag engagement process is to jack up one front wheel, make sure you have full air pressure in the tanks (truck off) and place the transmission in reverse. You should only be able to rotate the raised wheel backwards. With the shifter in neutral or any forward gear the same wheel should only rotate forwards. With no air in the system at all, including the shift valves, you should be able to rotate the wheel in both directions. This test assumes that you do not have a locker in the front axle. If so, just jack up both wheels. If you can't turn the wheels as noted something is wrong and the truck whould not be driven without removing the front hubs or drive shaft (completely). Any air leaks in the valves, hoses or the operator cylinder located at the front of the transfer case must be fixed or you risk a much worse problem with the internal parts of the transfer case.

5) The transfer case is nearly three times as large as the transmission, but only holds about 5 quarts of oil. All the gears are engaged when running down the road, so there is a lot of heat and "oil windage" inside the case at 50 mph. Of any compartment on these trucks requiring regualar lube service, the transfer case is the most important. We use a MIL rated GL5 gear oil and change it once a year at least, with checks in between to make sure that it is full all the time. This is very important, especially for guys that run at speed up and down hard roads.

The system as designed and built is really seamless and requires no thought, but you must follow the operators manual correctly.

When my transmission is in reverse, the front wheel can be turned in either direction, while it can only be turned in reverse when the transmission is in neutral or low. Could this be poppet valve air lines reversed?

If the truck has been driven with the lines reversed damage will have insued. Make sure the lines are not blocked and install them to achieve the operation as exactly outlined above by m139htotruck

Is it possible to work on the sprags without removing the transfer case?

I flushed my transfer case with diesel today and to my amazement my non working sprag works great now. I read where others had sucess with doing this. If the air valve and air cylinder is working correctley try this. I thought my sprag was broken and I started not to flush it out. I have a new sprag and I was just going to replace it. Im' Glad I gave this a try.

I mentioned earlier on that flushing with kerosene often frees up a sticky sprag, guess someone else agrees with me now. JT

Thanks, I will try the flush.

I filled the transfer case with 5 qts of diesel and took it to the beach sand and found that I now have a driven front axel! Thanks for the suggestions.

jacklegjim said:

I flushed my transfer case with diesel today and to my amazement my non working sprag works great now. I read where others had sucess with doing this. If the air valve and air cylinder is working correctley try this. I thought my sprag was broken and I started not to flush it out. I have a new sprag and I was just going to replace it. Im' Glad I gave this a try.

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How mush diesel did it take? my transfer case wont go out of neutral and im not sure how to fix it. I hope this works.

jasonjc said:

Now now Westech do you realy think they would ask that many times.?.

I think it would be more like 100000000000 times at most.

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Westech said:

We have tried that in the Wkies or however you spell it.... People don't search so it would not matter if we posted it in the main page and you had to look at it every time you logged in... people still would by pass it and ask the same question 1000000000000 times.

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Can some one count the zeros for me please, I get cross eyed after the 5th one and lose track. Thank you.

ldlambe said:

I filled the transfer case with 5 qts of diesel and took it to the beach sand and found that I now have a driven front axel! Thanks for the suggestions.

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Ouch

As I am adding to this old thread, you all can tell that I have run my query though the search engine.

Nearly all transfer case threads that I can find, are for the 939 series trucks with a smattering of deuce and a half questions. My question is related to the M809 series-

Here's what happened: Taking my M813 on its weekend 5 mile pleasure drive through the local neighborhoods, on the only stretch of open road, I hit 50 mph. After a few moments, I heard a loud sound that I can only describe as a screeching, rhythmic, banging sound. Fortunately, I was very close to my house by this point.

I limped into the neighborhood and the sound is definitely "rotational" in nature. My wife and I played "What's that sound?" where she stands on the street and listens as I drive past her. She indicated that the sound is equal with the tool box in location (the transfer case).

- I hit everything (hubs, brake drums, transmission and transfer case) with the IR temp gun. Nothing over 81F degrees. I could also touch everything easily.
- I observed that the transfer case shifts easily into low range, but is very difficult to get back into high range without a lot of fiddling.
- Although I didn't drive far, I noted that the noise only seemed present when driving in high range.
- I noticed a new leak at the rear of the transfer case, dripping gear oil. Not a lot, but definitely new.
- When the parking brake is released, I can grab the rear output drive shaft and there is noticeable play at the output of the transfer case where the new fluid leak is. Only a small amount, but I'm thinking that there shouldn't be any play at all.

Is my transfer case in the process of grenading?
Can they be rebuilt or are they too obsolete?
Can take-outs be had or are they getting rare? What's the market price these days?

Thanks for any help or advice.

Unhook the front and rear driveshaft and back off the emergency brake, so you know it's not the noise maker. See if the rear output shaft can be moved up and down by hand. Run the truck in gear and see if the TC is the noise maker.

Unfortunately when I had mine completely out and apart I couldn't find any interest in me fully documenting the tear-down and re-assembly, so I didn't. I asked several times and wrote up a little but there seemed to be no interest and management was not friendly. I've regretted it ever since as I inspected every single part, including the sprag and how it operates. My photo's would have probably just disappeared anyway...like when I search and can only get written description, links and pics gone.

You can take it out with a heavy tranny jack. The front of the truck needs raised on blocks to bring it out the side or front. It is a simple gearbox...don't get in a hurry and keep every part in an organized manner. There are jack bolts that will help with splitting it. I had a retaining ring fall through the pallet I was working on and had to split mine 3-4 times before i found the missing component....don't do that. I used aircraft form a gasket to reassemble...good thing since it was split several times. If all parts appear to be usable, assemble with the bearings on the three shafts loose. Then start with the input shaft when the TC is together (don't worry about the sprag at this point) and shim each shaft to the desired bearing tightness, one at a time. You want a light preload on them with enough room for heat expansion but not so tight they would bind when heated from use. There are lots of sophisticated ways to check the tightness but I did mine entirely by feel, rotating it until I felt it getting tight, backing off a little and then tightening down the plate to see if it changed.

Hey Toby,

I've already done the suggestions in your first paragraph. The rear output shaft can be moved around by hand, and there is a new leak from the rear output shaft seal. It looks like it ate the rear output shaft bearing.

I know it can repaired/replaced, but I don't think you can just yank out the shaft and bearing and jam a new one in. Your old post indicated that precise bearing pre-load adjustments are needed, and you have to open up the T-case for that, right?

I think this is what it needs: https://www.easternsurplus.net/PartDetails/6854/5T-986-T138-Rear-Output-Shaft-With-Gear

I have found a good, take-out transfer case for $500. I'm considering grabbing that, and having my original transfer case repaired and kept as a spare. However, if you say that swapping in a new rear shaft/bearing isn't difficult, I might just go that route.

What do you think?

If it ate the bearing, it has to be split. If it's only adjustment, which is what I would try first, you can probably try that in the truck.

I would have to do some research. It's several years now and I can't remember it the output is adjusted from the front or back.

The guy I bought my A3 from had a bad Allison. Hhe found a good, used and even guaranteed tranny, drove from Detroit to Iowa to get it, put it in and had the same problem. At $500, it seems like a good deal, if in fact it is in good shape. Can you try to move the input and output shafts and feel the play before you buy it?

If you have a parts breakdown drawing and patience, it's really not bad to split it and fully check it out...and well worth the effort, I think.

Notice how the bearings are on the shaft of the one you linked at Eastern. What we do to adjust the shaft tightness is making the outer tapered race to go together to tighten. There are shims behind a plate that act on the race and you may have to make or get get more shims to add to the shims already there. It's worth a try to see it will tighten up...if the bearing is shot, you will feel it while rotating.

jacklegjim said:

I flushed my transfer case with diesel today and to my amazement my non working sprag works great now. I read where others had sucess with doing this. If the air valve and air cylinder is working correctley try this. I thought my sprag was broken and I started not to flush it out. I have a new sprag and I was just going to replace it. Im' Glad I gave this a try.

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When you say you flushed the transfer case with diesel, could you elaborate that some more?
You drained the transfer case and then filled with diesel, did you drive it for any distance?

319cssb said:

When you say you flushed the transfer case with diesel, could you elaborate that some more?
You drained the transfer case and then filled with diesel, did you drive it for any distance?

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Drain the gear oil. fill it to the fill line with diesel. Drive it for about 50 miles, drain it and refill it with gear oil. Simple as that.