M1028 Cracked Transmission Case

Just found a crack in the rear of the Transmission case on my 1984 M1028. Thinking of replacing the entire thing.

Any videos, links, advise is appreciated, thank you in advance.

MachoTime96 said:

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Yessir, I believe you will need a replacement case.
Did you "dog" your truck, or was it already broken when you got it?

Not sure was "dog" means but i dont believe it was broken when I got it. I drive it carefully on mostly pavement.

MachoTime96 said:

Not sure was "dog" means but i dont believe it was broken when I got it. I drive it carefully on mostly pavement.

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Okay, what about the motor / transmission mounts? Are they in good shape? Generally speaking, a transmission will only get cracked if it is under a load (torque) and maybe the mounting was loose. I can't imagine it just sitting there and getting a crack in it.

Fork lift loading to sell at auction has done that many time in the past.

Mullaney said:

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Okay, what about the motor / transmission mounts? Are they in good shape? Generally speaking, a transmission will only get cracked if it is under a load (torque) and maybe the mounting was loose. I can't imagine it just sitting there and getting a crack in it.

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You may be on to something. I noticed my rear drive shaft was dented. The previous put a tire weight to offset the dent when it spins. This could be a factor. Ive yet to check the motor mounts. But ive never noticed them being worn.

Last year my 1985 M1008 transmission had a crack at the rear of the case. The crack was on the top, close to where the transfer case mounts bolts to the transmission case.

I have owned the truck for close to ten years now. I don't off road it hard or tow much with it. It was my daily driver for the first four or five years I owned it. I did replace both the motor mounts and the transmission mounts when I first bought the truck.

I was lucky to find a transmission out of a CUCV in a junk yard a couple of hours away. The replacement transmission had HD cast into the bellhousing.

The transmission that came out of my M1008 did not have HD cast into the bellhousing. I believe the HD transmission case had reinforcements made to the rear of the transmission case, to help support the transfer case.

I can only guess that a previous owner had replaced the transmission before. And the weight of the transfer case cracked the transmission case.

Maybe you need the support rod for the transfercase? I don't know much about them but there is a thread on here about it.


Good luck.

You can also crack the transmission case by being in low range transfer case and hard pull in reverse.

Look for dents/scratches/marring on the frame near the dent in the driveshaft, I've seen many a bent one from fork lift loading. The off balance driveshaft may have caused the crack as well if it were severely out of balance, but I'd think you'd feel that going down the road. If you could post a pic of the driveshaft bend that might help us draw a better conclusion.

That small of a crack can be easily fixed by welding. I have repaired bellhousing cracks that were fully separated in 2.

I have another military case separated at the rear adapter flange that lost the upper bolts and left the bottom 2 that broke out.

It is beyond repair but hopefully all the heavy duty internals are worth the transfer to another case. The mainshaft spins true so until the case gets broken down to see any further damage will depend on what gets saved.

Finding a good core is getting harder by the day. Every military core I pay 100 bucks for broken or not.

The 4 wheel truck cases are different from the passenger car and light duty trucks. Turbo 400 and some Turbo 350's the inspection cover for the torque converter on the HD trucks get bolt on covers to make the case more ridged at the bellhousing and provide for bolt on reinforcing bars to both sides of the engine to each motor mounts. On the 205 cases GM used an additional bar that went from the transmission bellhousing bolt to the right rear outside of the T case, and if memory serves like Curtisje stated the 208 uses the same T-case bar.

And why the military trucks did not use one noone really knows.

cucvmule said:

That small of a crack can be easily fixed by welding. I have repaired bellhousing cracks that were fully separated in 2.

I have another military case separated at the rear adapter flange that lost the upper bolts and left the bottom 2 that broke out.

It is beyond repair but hopefully all the heavy duty internals are worth the transfer to another case. The mainshaft spins true so until the case gets broken down to see any further damage will depend on what gets saved.

Finding a

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I have had the same thing happen with 700R4 cases, I don't know if this would work but it's worth a look. The threads in the top two holes ripped out , I could thread a bolt in but it wouldn't hold. On the 700 those two hole are thru hole and there's just enough room to fit a nut behind it, IIRC there's no room for a wrench but it did kinda jam in there and not spin when tightening the bolt. The bottom two are blind holes but have enough 'meat' to drill and use a threadsert.
Hope this can help you and others save some money and parts, as a bonus this can be done IN THE TRUCK!

The bent drive shafts will break the tail section of any transmission. Finding cases for TH 400 transmission is not as easy as it once was. But any constant vibration at high speed was twisting that transfer case around and the weak spot is rear flange of the transmission. I seen it many times. Even not greasing the CV joint on the front drive shaft can crack and break the casting. I had one break at 55 mph on I 20. I watched the oil and pieces falling out in the rear view mirror. I had lock out that would not disengage on a truck I just bought that day and was traveling home from Georgia towing another CUCV. Roadside I had to get the one I was towing operational to get home. It worked great. Hot and dirty along the highway with 2 kids and my Wife with another chase vehicle. It all worked out. But a new balanced driveshaft would have been much less expensive then the transmission case problem. Good Luck. I still have a few TH 400 that I use for parts and mainly cases. This has been an issue on many of the CUCVs I have seen and run a snow plow trucks. Splitting the cases is common.