6.7 Cummins manual transmission

Cowcatcher

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If any of y’all have a g56 manual trans behind your 6.7 Cummins I’ve got a warning for you. I’m currently have a transmission “built” after a failure in the shift tower wrecked some gears and shrapnel knocked a hole in the front transmission case. So yeah the hole in the case left me in a spot where I didn’t even have a good rebuildable core to trade in. It sucks. Mind y’all that the shifter worked correctly and there was no heads up until the damage was done. I went out and started the truck one day and heard a loud pop. I shut the truck down and the next day the ground was soaked in tranny fluid under the truck. Fluid was seeping out the bottom of bellhousing where it mates to engine. Pulled trans in hopes that mayyyyybe I had just lost the front seal. Nope. I can’t say how long the parts were “floating” around in the trans. I do know that for a year probably there has been a slight pop sound when I’m loaded a first start to go forwards or reverse. I’ve been checking for broken leaf springs, gooseneck bolts, drivetrain mounts, u-joints etc. The trans was operating normally so I guess I didn’t really suspect it. I put a clutch in it about 2 years ago and I know the shifter was complete at that time. I’m thinking these parts came off the shift tower and had done some gear damage that was producing the pop I had been noticing when taking off or backing up. Not a loud pop but noticeable. Mind you the truck is loud being 5” straight piped but I know what my truck sounds like cuz I listen to it instead of the radio. Anyhow, the day it made the BIG POP on start up the truck had been parked facing down a hill for a few days and I’m thinking shrapnel had been washed to the front of the trans and it was in the front bearing/gears on the counter shaft. That’s how the hole came to get punched in the front of the case. I priced at minimum 10 re-man transmissions in 4 different states and quotes ranged from $5500 to $6700. After visiting with several of these guys that rebuild the g56 they said the shifter coming apart and grenading the trans was fairly common. They also mentioned the g56 has a weak case to begin with. There is a company out in Tennessee that has a beefed up case they call the “awesome g56” but a reman trans from them in their awesome case would cost $7200. So yes I considered it but it seems at least in my case the shift tower was the weak link not the case. Oh that’s another sad part of my story in case you didn’t put it together……..a reman trans does not come with a new shift tower. So to recap lol, I have NO Good core so that’s an extra $1500-$2000 I gotta spend plus my shift tower is busted so I gotta spend $500-$700 on that in addition to what the usual trans rebuild/replace would cost. I did luck out (I think/hope) and a fella close by had a remanned g56 ready to go for a g56 BUT it was for a 2wd. He said he would take the output shaft out of my 4wd g56 and put in his trans and then I could pay him $3850 for the reman trans and I could keep everything else from my trans. His trans also includes a shift tower but I’m not going down that road again. I ordered a B&M shifter for it. Sounds and looks better made. I don’t know if I will like the 30% less throw or not but I can get used to it if I’m not worried about a little tack weld breaking loose on the factory shifter. The B&M cost $550. Anyhow just thought I’d share fellas. It only takes a few minutes to pull the shift tower and if I’d known it was a common failure I would have checked it sooner. I’ll include some pics below. The stuff you see on shop towel was found in bottom of trans. It was an expensive lesson but I’m thankful I learned it at home and not loaded with 20,000 pounds of beef on the side of the road.
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Thanks @Glock 40 to you and your son for coming out and helping me pull it last Friday.
 

Snattlerake

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Damn! That thing grenaded! Not knowing anything about a tower, Is the shift tower an addition to ease the throw of the gears? I am assuming this as you mention the 30% spacing is going to need getting used to. Can you fix it? Beef it up a bit if you can?
 

Cowcatcher

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The whole assembly that contains the shifter and then bolts to the top of the trans is what I’m referring to as the shift tower. The B&M is supposed a tighter pattern that results in 30% less travel of your hand when shifting is how I comprehend it.
 

Roy14

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I wish dodge had either kept the NV5600 or copied the ZF6. The G56 was not a good move. How many clutches have you put in that truck? Every time I see a 4th gen G56 for sale, it’s had a clutch done within the first 25k miles and usually another before 100k.
 

Mr.Glock

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Best Truck I had and screwed up selling was a 98 1/2 with the 12v 5 speed. I bought a full billet main shaft that was designed that put the 5th gear inside the tranny, that and an Southbend Clutch and it made the truck bombproof. When I was offered a stupid stupid price I had to sell it. It was at 976Hp at the wheel and the torque went off the chart.
 

Snattlerake

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Best Truck I had and screwed up selling was a 98 1/2 with the 12v 5 speed. I bought a full billet main shaft that was designed that put the 5th gear inside the tranny, that and an Southbend Clutch and it made the truck bombproof. When I was offered a stupid stupid price I had to sell it. It was at 976Hp at the wheel and the torque went off the chart.
Hindsight is always 20 20. But at the time did you walk away with a pile of cash smiling?

Back to the OP, you would think the B and M to be very well-manufactured unit and take care of the problem.
 

Snattlerake

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I can see the B&M unit is physically larger, and looks beefier. Looks to be machined cylindrical steel housing instead of a cast aluminum housing as is the factory unit.

I can't see where the factory unit failed? Am I missing an obvious crack? Or did it just drop parts down into the trans?
It looks like in post #1 the second picture the shell of the box just failed causing the parts inside to lose tolerances eventually spreading and come apart. Is that the diagnosis?
 

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