Looking for pictures of broken M939 series transfer cases for reinforcement/strengthe

[Jbulach]

I've seen a few pictures scattered around and I know it's been talked about before, looking for pictures to see if theres a typical break pattern that may be able to be reinforced, or to assess the difficulty of making a stronger case, especially when all the spares dry up.
Also if you could post what events caused the failure.

 

[tobyS]

I hope you find something on this but it appears to me (my opinion) that the position of the middle jackshaft is the problem and when in reverse, can force itself between the input shaft and the output shaft with a very low angle and extreme force. I can't see that there is a solution, but maybe someone with more experience can provide more info. I could be entirely wrong as I've only had a T-138 apart. I worry about this all the time with my M929A2, as I cannot avoid backing in low 6x6. Good luck.

 

[simp5782]

Some moron put the bull gear too close a tolerance to the case when It flexes under the torque it comes in contact with the case and proof. But this can happen in high or low forward or low reverse. Depending on the torque going thru it.

It always seem to bulge on that plate

 

[tobyS]

Notice how the center shaft is not in line with the input and output (on Wes's picture)? Forward moves that shaft out making more, not less clearance and reverse jams it in tight at a very low angle. It appears to me that having these shafts adjusted with light preload will be the best that one can do. Leaving them lose, especially the center, would seem to make the problem worse when backing as it has some play to wedge between the other 2 shafts. Wes's photo seems consistent with my observation.

 

[Gunzy]

Just modify and replace it with the Oshkosh 55000 transfer case from the HEMTT or HET series of trucks.

 

[Jbulach]

Just modify and replace it with the Oshkosh 55000 transfer case from the HEMTT or HET series of trucks.

Are they single speed, and do you have an “affordable” source for them, before Wes tears em all up? I’m going to need something more robust when I repower my truck with a trashed 8.3.

 

[simp5782]

The cases are getting hard to find. I have found plenty of cores. but No new ones are being sold on surplus. I mean i thought of buying a bunch of cores and take 2 or 3 to make one but I have only found 1 regular hemtt core. There are several Close Shaft versions of the case in civilian junk yards online.

One thing on the 55000 series cases is only the HEMTT version has the 1710 series yokes. The HET and PLS cases have 1810. The PLS has a rear PTO unit that would be handy however it also has a power divider unit on it which requires a different shaft to remove it and replace it with a normal 1810 or 1710 yoke. 1810 series yokes would be overkill for a 5 ton.

Mine lasted about 30,000 miles. I will be tearing it open maybe this weekend. luckily all the bearings and gears are available and hopefully its not too bad.

 

[99nouns]

Hey Wes, if you are willing to take some measurements and pictures while you have it a part I can attempt to draw it in CAD and I know you got good sourcing skills and we might be able to re design the flaws and get that case made somewhere if you think it is worth it.



I need a clear pic of the flange's mating face with exact measurements of the edges if you are interested, if you can place a some kind of ruler on the same plane as the flange would make it very easy for me.