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Open 8.75 shaft pin sheered

Doorkicker

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This is more of a curiosity type of question and potentially a very obvious answer.

Going down the road - nothing special, 45 mph, cruising - and suddenly a very loud grinding noise came from the rear. It stopped and then did it again. Was only a mile from home. Pulled apart to find the shaft retaining roll pin was sheered and the shaft had drifted into the pinion gear. The pinion gear actually faired well. Not only did I find a shattered roll pin, but even the remains of someone's tool used to put the pin in.

The rear is a 742, 3:23, and the car is well into the 650 hp range (I'm building a new 489 3:55 sure-trac II, hence not worried about this rear). I haven't beat on it. Still letting the engine break-in and getting into its rhythm.

So, the question is: What would cause the roll pin to just sheer inside like that? I would think it would require serious rotational forces placed on the shaft, but how would that occur? The spiders rotate around the shaft, so did one lock onto it? The spiders turn freely on the shaft currently. What am I missing? Or, is it just one of those things that happen sometimes... Drop some of that killer Mopar knowledge on me.

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shaft.jpg
 
Had pretty much the same thing happen with a rear end in my pickup (9 1/4?) years ago but there wasn't any little tool that someone left behind. Too many one wheel peels? Mine got lots of that over the years and raised cane going through a tunnel in the middle of the night on the way home from work. It made me wonder if it was going to lock up before I could get out of that hole. My fix was to shove an 8 3/4 under the truck. Take it apart and see if there's an signs of the spiders trying to seize up on the shaft....
 
@Cranky I think that may be it... one-leggers. I have lit it up a few times, mostly unintentionally... LOL
The spiders are ok and spin on the shaft all good. I'm thinking - now that you mention it... the thrust block probably just captured the shaft (?) during one of those "slips" :) and the pin was already crapola, so it gave out. I'm going to toss a new pin in it and see what happens. I was just curious what folks thought. It's Monday and I don't feel like working... just calling it like i see it...mondays suuuuuccckkkk.
 
Non sure grip cases will do that. If the car is pounded on. The rear suspension is set so it spins both tires. Been there. sounds like s machine gun. Then locks up.
Doug
 
Non sure grip cases will do that. If the car is pounded on. The rear suspension is set so it spins both tires. Been there. sounds like s machine gun. Then locks up.
Doug
EGGZATLY! It sounded horrible. LOL Great point about the suspension... never thought about that.
 
Nothing wrong with a 742 case and I prefer them over the 489 crush collar setup as long as a SG is used and the collar eliminator. Both are tough units. My 68 R/R has a 741 open and 2.76s built for MPH not smoke shows.
 
Nothing wrong with a 742 case and I prefer them over the 489 crush collar setup as long as a SG is used and the collar eliminator. Both are tough units. My 68 R/R has a 741 open and 2.76s built for MPH not smoke shows.
Yeah... This is actually my third rear of four. I have a 741 with a 2:94 (highway, running great), 742 with 3:23 (this one, which is more of my beater), and the 489 with 3:55 I'm building now for more serious stuff. I have one more 741 case that I may use for something really low. Until this episode, they've been rock solid.
 
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