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Alright guys I've been considering doing a 12 bolt swap into the elco recently and want some input. My biggest question here is should I use a truck rear end? I am aware that the car rear end is considered stronger because it has a larger pinion shaft at 1.6 something inches where as the truck rear is 1.4 something. Truck rear ends are much easier to get and much cheaper, however, and all the aftermarket parts are readily available for either. So I guess the real question is, has anyone ever had a pinion shaft fail? I've heard of ring gears breaking and spiders cracking and other things but I don't think I've heard of the pinion shaft failing. I'm not looking at monster horsepower and its not a drag car so what do you guys think?
 

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Consider my initial thoughts with a sufficient amount of salt...

Not knowing the structural differences between truck and car 12 bolts, and only logically considering how/why the collective conscious rule of thumb exists, I arrive at this (super preliminary) conclusion: The "rule of thumb" and most often suggested item is generally quoted from the guys that drag race or build monster performance cars. The great majority of us do not live in that world. I'm sure that .2 something more of pinion shaft certainly makes a big difference when it is called upon to accept the input torque from a 600hp monster. The great majority of us aren't dealing out that kind of punishment. I personally wouldn't blink twice at a 12 bolt posi rear from a truck for $200 versus a similar car unit for $1000 for my 229 V6. The truck will give me the same dual footedness for a $800 savings.

Remember, if we only followed drag racers advice, we'd all be running 4:11s or TH350 trannies. Not practical is it? The 200-4R gets a bad rep in drag circles, but I can't wait to get mine installed.

Of course, your mileage may vary, and I'm sure there will be differing view points. I personally do not see a problem with an obviously strong unit for everyday duty.

The true question back to you is "what are you REALLY going to do with it?"
:dontknow:
 

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Alright guys I've been considering doing a 12 bolt swap into the elco recently and want some input. My biggest question here is should I use a truck rear end? I am aware that the car rear end is considered stronger because it has a larger pinion shaft at 1.6 something inches where as the truck rear is 1.4 something. Truck rear ends are much easier to get and much cheaper, however, and all the aftermarket parts are readily available for either. So I guess the real question is, has anyone ever had a pinion shaft fail? I've heard of ring gears breaking and spiders cracking and other things but I don't think I've heard of the pinion shaft failing. I'm not looking at monster horsepower and its not a drag car so what do you guys think?
If you arent drag racing or putting huge HP through the rear end, why expend your money on a 12 bolt in the first place? . If you are really worried about the 7.5" ( I believe) 10 bolt then I would upgrade to an easier to find and likely cheaper 8.5" 10 bolt.

The 8.5" 10 bolt is very nearly as strong as the 12 bolt, lighter, and should be much more plentiful.
 

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The 200-4R gets a bad rep in drag circles, but I can't wait to get mine installed.

:dontknow:
You will be pleased to know:

700 or 200?

"Honestly its not even a fair fight. The 2004R will handle power that far exceeds that of any 700R4 or 4L60 that can be built at any price. 2004R has a better gear ratio spread, better overdrive ratio, will fit many more applications, lighter, stronger ... I can go on and on. The 700R4 is best left to applications where its the only option such as 4WD or All WD, tow vehicles, Lower HP applications or for folks that are more concerned with budget versis strength and reliability." -- Lonnie Diers, OWNER, EXTREME AUTOMATICS http://www.extremeautomatics.com/
 

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If you arent drag racing or putting huge HP through the rear end, why expend your money on a 12 bolt in the first place? . If you are really worried about the 7.5" ( I believe) 10 bolt then I would upgrade to an easier to find and likely cheaper 8.5" 10 bolt.

The 8.5" 10 bolt is very nearly as strong as the 12 bolt, lighter, and should be much more plentiful.
X 2
 

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Discussion Starter #6
Thanks guys I appreciate the input. Sorry I didn't make it back to this sooner, I've been crazy busy lately. The 8.5 is absolutely lighter I agree. I've found that at least around here truck 12 bolts are more plentiful and cheaper, at least at the buy in. The fab work to make it fit may be another story entirely. I guess in order to get a better answer to this question I should give my exact application. Its going behind a predicted (motors not done yet) 350hp 292 inline 6. The motor puts out a boatload of torque and I'm going be using it to pull a sailboat, occasionally a car trailer, and regular loads of dirt, mulch and gravel. The trucks that motor came in all as far as I could tell came with a 12 bolt at least or larger and I'm just worried it's going to want to make the 10 bolt pop.
 

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What usually pops rear ends is either the launch from a high HP motor with slicks that won't spin or the 1 - 2 shift that really hits hard.
What you have behind your 292 should be fine. Steadily applied torque and fairly smooth shifts will make the tires spin before you can break the rear end. IMO put your money and time to another part of the vehicle.
A friend of mine, and also a member here, has a built 292 (10.1 to 1 comp, large valves, head completely re-worked for flow, ported, humps removed and etc., quadrajet carb and headers) in a 55 chevy that will absolutely nail you in the seat running through the original 55 rear with no problems.
 

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I completely agree with 464Elky...the 292 makes good torque at low rpm's and thats great for towing and hauling loads. It's not a parts killer engine in stock form so spend your money elsewhere....What you have can handle the 292 without working up a sweat. I've run 383 small blocks making in excess of 500 lb/ft of torque through a Monte Carlo SS 7.5 rear end...it lives fine as long as you don't use slicks or super sticky street tires...Thats probably near double the torque of your 292.....Dan
 

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built right and treated right the 7.5/7 5/8 rear will live with over 500 hp.no slicks of course.i have only broke mine one time and that was doing a burnout with slicks at the track with a fresh 500+ hp 406 and a severely hard shifting 700.as hard as it is not to no burn outs around corners.that is real dard on any diff. because you are a lot of load on the spiders.the 12 bolts have notoriously weak spiders.they are suposed to be the most effiecient (power wise) diffs gm made. i would use the 8.5 over the 12 bolt any day.bigger pinion and spiders.90 % of diff failures are spiders
 

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464Elky and old coot get my vote, you arent in any significant danger of hurting your present axle, invest elsewhere.
 

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A friend of mine, and also a member here, has a built 292 (.
...I must be showing my age,when you said "292" the first thing pop to mind was the 292 -stright six..not a 283 punch out,although,those 283 really screems too..:beer:
 

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I was talking about an inline It is a 292 6 cyl with a 250 re worked head on it with LP gas option pistons.
 
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