M1078 A1 transfer case

Had some codes come up the other day on the transmission 2511, 2533, 5633. I pulled a cover that is next to the output shaft going to the rear axle. From what I can tell the gears look fine but something probably a bearing came apart and bounced around and you can see where the parts were hitting the case.

There was some metal around and on the sensor that is just inside the cover I pulled, which explains the codes.

I am going to further investigate just wanting to know if anyone has taken one of these apart or has ideas or best ways to go about it. Should’ve taken some pictures when I had it open today but didn’t will get some in a few days when I open it back up.

2511- output speed sensor @ 0 in 1st
2533- “ “ @ 0 in 3rd
5633- 3rd range verification test

Are the bearings you’re finding about 1/16” diameter x 3/16” long?
That’s the size of broken bearings I found in mine attached to the output speed sensor.
Before discovering them, I trouble shooted Everything else imaginable. Then discovering the broken bearings and contacted different companies that could rebuild the transmission priced $6,000-$8,000 plus freight.
so I decided to just source a used transmission/tcase out of a crashed Fmtv
For $2,500.

No they are small slivers and pieces about or a little smaller than pea gravel not many of them. Best price I’ve found thus far on transmission pricing is 5k for a Allison reman. But I would like to try a repair myself before going that route.

Bowhunter0311 said:

No they are small slivers and pieces about or a little smaller than pea gravel not many of them. Best price I’ve found thus far on transmission pricing is 5k for a Allison reman. But I would like to try a repair myself before going that route.

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Was it making noises also?

Yes it was right at the end before I parked it.

I need to go take some pictures, my phone died yesterday when I was working on it. I have found bearings in the bottom of the transfer case but I have not found which bearing came apart.
I have the output housing going to both the front and rear axle taken off, as well as the transmission pan and valve body.

Bowhunter0311 said:

Yes it was right at the end before I parked it.

I need to go take some pictures, my phone died yesterday when I was working on it. I have found bearings in the bottom of the transfer case but I have not found which bearing came apart.
I have the output housing going to both the front and rear axle taken off, as well as the transmission pan and valve body.

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Isn't that valve body fun!

The valve body was a bit of a bear. The cab of the truck is gonna smell like ATF for a while. Lol.
I have a few questions as to the next steps in the dissembling process as to either split the t-case in place or pull off back of the transmission then split it.

I woukd swap the whole trans as one. If your solenoid pack is reusable I would save it. There are differences even in wtec2 transmissions. Different wiring on the solenoid pack.

I want to try a overhaul on the t-case first just bearings and gaskets. It’s only about 8-10 bearings not counting the planetary.
What I’m not sure is to separate the case from the first yellow line closest to the back of the assembly or the one towards the front of the truck.

The two share fluid you have to make sure none of the little pieces made it into the trans. A friend had an issue years ago. There is a chat here screen above the solenoid pack it was full of bearing parts. I have trans here but I’m in CT. I know someone else who did a t case swap and something went wrong and it grenaded on the highway test drive. The military parts manual does show a good breakdown of the trans.

Bowhunter0311 said:

I want to try a overhaul on the t-case first just bearings and gaskets. It’s only about 8-10 bearings not counting the planetary.
What I’m not sure is to separate the case from the first yellow line closest to the back of the assembly or the one towards the front of the truck.

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What was the outcome of your fix?

Well, currently still in progress. Upon further inspection one of the roller bearings was forced through one of the walls on the case. Just so happens that where it went through the wall was a oil passage otherwise I would have welded it and went on. So I bought a hopefully good used transfer case from Superman on here, which I bet it is. Now trying to schedule time with my wife, I mean life to go flush and install it on the truck.

Bowhunter0311 said:

Well, currently still in progress. Upon further inspection one of the roller bearings was forced through one of the walls on the case. Just so happens that where it went through the wall was a oil passage otherwise I would have welded it and went on. So I bought a hopefully good used transfer case from Superman on here, which I bet it is. Now trying to schedule time with my wife, I mean life to go flush and install it on the truck.

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Thanks for the reply. Our truck recently got the same transmission codes you did and our output speed sensor also has roller bearing pieces stuck to it. I am interested in hearing what you've learned. Thanks again.

Bowhunter0311 said:

Well, currently still in progress. Upon further inspection one of the roller bearings was forced through one of the walls on the case. Just so happens that where it went through the wall was a oil passage otherwise I would have welded it and went on. So I bought a hopefully good used transfer case from Superman on here, which I bet it is. Now trying to schedule time with my wife, I mean life to go flush and install it on the truck.

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Do you happen to know already which bearing came apart? Where the roller bearings came from? We have talked to an Allison service tech and looked at the parts diagrams and can't figure out where in this transmission there are bearings this small. The threads I have found on this topic also don't indicate the source of the bearing parts.

Here are some links to other threads with a similar issue.


I think this is the one Suprman was referring to:




Some discussion about this problem starting with post #22 through about #26. (EDIT: post #s 22 and 25 are particularly important, as the filter screen discussed is where we found the bulk of our broken C6 thrust bearing parts.)

We took the transmission out of the truck and started taking apart the transfer case to try to figure out where the bearing parts came from. There was considerable damage in the C6 clutch housing. One of the reaction plates had a section ripped out of it, and it carved out the inside of the C6 clutch housing cover. The thrust bearing was destroyed, and based on the parts we found floating around in there, this is the bearing we originally found parts from on the output sensor magnet. We did not find any new needle/roller bearings, just parts of the bearing carrier. We took off the valve body to see if the roller bearings were in the strainer there, but there were none. Going to keep tearing things apart until we figure out where they went, and to see if anything else was damaged.

We ordered a replacement for the C6 thrust bearing that came apart. When it came in, we were mystified that instead of a bearing, Allison handed us a composite washer that looked nothing like the bearing that failed. Allison gave us an information sheet showing that the C6 thrust bearing failed so often that they updated the part. They said the old part # was 29544806 ("Roller Thrust Bearing Assembly"), and the new part # is 29545936 ("Composite Thrust Washer"). The Allison parts guy couldn't get the information sheet describing the update to print entirely (words are missing from the right side), but I'll attach a pic of it anyway. It explains that the washer is thicker than the old bearing was, but that it will still fit, and that no special tools are required for installation. Here's hoping.

I also want to give a shout out to Xcalliber Transmission (https://www.xcallibertransmission.com/commercial-home/) for selling us a good used C6 cover (what the arrow is pointing to in the pic), since ours was all carved up on the inside. It was still expensive (~$780), but a lot cheaper than than a new one from Allison (~$2600).

langstonhs said:

We ordered a replacement for the C6 thrust bearing that came apart. When it came in, we were mystified that instead of a bearing, Allison handed us a composite washer that looked nothing like the bearing that failed. Allison gave us an information sheet showing that the C6 thrust bearing failed so often that they updated the part. They said the old part # was 29544806 ("Roller Thrust Bearing Assembly"), and the new part # is 29545936 ("Composite Thrust Washer"). The Allison parts guy couldn't get the information sheet describing the update to print entirely (words are missing from the right side), but I'll attach a pic of it anyway. It explains that the washer is thicker than the old bearing was, but that it will still fit, and that no special tools are required for installation. Here's hoping.

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ask the Allison Parts guy to set the printer to landscape and try the print again? another option is to hit print... but change the default printer to PDF.... this will save it to any location he sets it to be saved (desk top would be easiest in this case) He can then email it to you. after email goes out... he can delete it off the desktop. Might work.

This, I hope, is the final post on our transmission failure.

When we discovered that the C6 thrust bearing came apart inside the transfer case, we decided it was necessary to take apart the whole transmission to see where the bearing parts went, and if there was any additional damage. Once done, we were relieved to find that the damage was exclusively in the C6 clutch, and that the rest of the transmission looked to be in great shape. We figured there were approximately 40 roller bearings floating around somewhere in there, and we found about 3 of them on the output speed sensor magnet, and another 30-something in the screen on the intake side of the scavenger pump. This screen is behind the elbow that the hose of the scavenger pump attaches to at the side of the transfer case.

We have a Stewart & Stevenson in Albuquerque, but they did not prove to be very helpful for military truck parts. However, they are also the Allison transmission distributor, and were very helpful in ordering the parts we needed for the transmission. They printed out all the parts diagrams and parts lists for the transmission after we gave them our serial number, and we were able to order replacement parts based on these lists. Xcalliber Transmission online also sold us some of the parts we needed; one part was used (the C6 clutch cover/housing), some were new Allison parts, and others were aftermarket, but made by Xcalliber. Allison genuine parts can literally cost a fortune, so we were happy to have an alternate source for them.

We put the truck back together yesterday and took it for a drive, and it seems to shift through all the gears just fine, with no error codes. We had never taken apart any transmission before, much less an automatic of this size, and used the TMs to do the work. We did have to buy a big transmission jack, a big engine stand, and a big impact wrench to do the job, but we like that better than paying for someone else's labor. Thanks to everyone on here who steered us in the right direction.