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So, had a bit of an issue in my 16 SRT M6, just to provide background the motor is stock so stock power level, stock clutch. Mods are rear upper control arms, cradle bushings, CDV delete, differential brace.

I was driving it just as I have for the past 17,000 miles & after a rolling pull gears 1-3 i hear a rattling sound from below so I figured okay my clutch went. So i continue driving and about 5 minutes later BANG. Car wont move. Diagnosis is the transmission’s main shaft snapped. I was so suprised. Luckily it was replaced & i’m good now but I’m still baffled. I wasnt power shifting but was shifting like I meant it. Defective tranny or my fault? Thoughts??
 

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probably a flaw in the input shaft

I know folks that have M6 and go to the track frequently - these hold up
 

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I broke a mainshaft in a M22 Muncie many moons ago ........ it happens sometimes even to transmissions with a reputation for toughness so LARGE they get dubbed "Rock Crusher".

In the end you probably had a shaft that was one in a thousand or more......a simple stress flaw that shouldn't have made it through inspection somehow during assembly.

Main-shafts are always TOUGH pieces and breaking one is no small feat. In a street car this heavy you have one piece of the puzzle but you also need the power and the traction. If you'd been doing clutch "dumps" at BIG RPM at the track on slicks.......MAYBE.......but on the street with street tires ....you're ABSOLUTELY RIGHT to be asking ....WTF? ..... Why me? Sucks but it sounds like you're still under warranty.

I wouldn't spend much time worrying about it happening again....

Every summer guys with supercharged Hell Cats are putting slicks on a car with more power and just a tad heavier than yours. We aren't hearing stories of the main-shafts shattering a lot so I'd bet you just got that one bad one and the replacement is gonna be just fine.
 

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Discussion Starter #4
probably a flaw in the input shaft

I know folks that have M6 and go to the track frequently - these hold up
yeah i mean I'm honestly worried about it happening again. I wasnt driving the car super hard nor was I launching it which is why i was so surprised.
 

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I broke a mainshaft in a M22 Muncie many moons ago ........ it happens sometimes even to transmissions with a reputation for toughness so LARGE they get dubbed "Rock Crusher".

In the end you probably had a shaft that was one in a thousand or more......a simple stress flaw that shouldn't have made it through inspection somehow during assembly.

Main-shafts are always TOUGH pieces and breaking one is no small feat. In a street car this heavy you have one piece of the puzzle but you also need the power and the traction. If you'd been doing clutch "dumps" at BIG RPM at the track on slicks.......MAYBE.......but on the street with street tires ....you're ABSOLUTELY RIGHT to be asking ....WTF? ..... Why me? Sucks but it sounds like you're still under warranty.

I wouldn't spend much time worrying about it happening again....

Every summer guys with supercharged Hell Cats are putting slicks on a car with more power and just a tad heavier than yours. We aren't hearing stories of the main-shafts shattering a lot so I'd bet you just got that one bad one and the replacement is gonna be just fine.

Yeah I'm genuinely worried about snapping this one now, I was so surprised that it happened because i've heard of 600 horsepower challengers launching on a slick at the track and not breaking their transmissions & I grenade mine on a simple street pass?

I'm praying it doesn't happen again as 2 times will be hard to explain to the dealer. Thank God it was covered.


I typically dont launch the car much and when I do its nothing too harsh & I rarely if ever track it. All it is is mainly hard 1-2 and 2-3 shifts this definitely shouldn't have happened from that!
 

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Sounds similar to what happened to my Brog Warner T5 non world class (metal on metal, no roller bearings). I was going about 70 on the interstate when I start hearing this ticking noise. I roll down my window to listen when all of a sudden, the rear wheels lock. I was able to get to the side of the road. Had it towed back to my place where it sat for a few years before I decided to take it apart. What happened was the bolts for the tail housing loosened over time causing the shaft to bind and weld to a gear.

The happened in a 2.8L V6 Firebird so there wasn't a lot of power going to the wheels. This was cause by the mechanic who repaired it a year or so prior improperly torquing the bolts.
 

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Yeah I'm genuinely worried about snapping this one now, I was so surprised that it happened because i've heard of 600 horsepower challengers launching on a slick at the track and not breaking their transmissions & I grenade mine on a simple street pass?

I'm praying it doesn't happen again as 2 times will be hard to explain to the dealer. Thank God it was covered.


I typically dont launch the car much and when I do its nothing too harsh & I rarely if ever track it. All it is is mainly hard 1-2 and 2-3 shifts this definitely shouldn't have happened from that!
I can appriciate that you worry about the dealer's reaction to a second broken transmission......but really the reason I posted was try to relieve your worry on this one.

What happened to you was crazy unusual. You'd TRULY be beating the odds in a BIG WAY to break a second trasmission main-shaft. Far more likely something else in there breaks. Main-shafts really are TOUGH pieces. Tougher than most everything else inside the case.

If this one breaks......it's stil more likely to be something OTHER than the main-shaft that goes.

Enjoy your car.....this isn't gonna happen again. You'd have a better shot at winning the State lottery than you have at busting two main-shafts without slicks, a steady diet of drag racing and stupid big RPM Clutch dumps at the starting line.
 
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