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Discussion Starter #1
Looking for input about my brother in law's 69 coupe. It's got an open differential 8" rear end how much abuse can one of these rear ends handle? Thinking about sticking some 3.55-3.73 gears, and a posi unit if some kind, and of course all new bearings. This is a 99.9% street car, built 393 windsor, tremec TKO.
 

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I had a '67 coupe with a mild 351, C4, and 8" with 3.25 gears in my late teens/early twenties. It was 99.9% street but I drove it hard all time. Probably grenaded half a dozen rear ends in that thing and that was on skinny, stock sized white walls all the way around. They were all open and a posi would have certainly helped but I don't have a lot of confidence in the 8" rear end. It was the only thing that broke on that car besides the stock pressed in rocker studs. Only good thing about the 8" rear end is that they are almost free.
 
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It's built just like a 9" but everything's smaller. They're stronger than most people give them credit for. Not indestructible, but pretty tough. Slicks and a manual transmission with any sort of power, it'll bust-guaranteed. Automatic without a transbrake, it'll last a while.

Myself, my dad and my brother all ran 8" stuff for many, MANY years. I went 6-teen's with one until I put a 9" in, but the car was pretty light (2710). All automatics, C4 at first and Powerglide later on. Mini-spool nonethless, and 28 spline axles. They'd begin to get noisy, pull apart and usually the pinion was failing; but never broke a case.

Similar to 7.5" rears that don't get enough credit....
 

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Discussion Starter #5
I seem to remember reading about the 8" and it not getting the due credit in a hot rod magazine almost 15 yrs ago.
 

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There is not much in the way of support with aftermarkets parts for the 8 inch and they cost more than the 9 inch stuff . my 2 1/2 cents, if you are going to use a "good" street tire or slick you will find the 8 inch's weakest leak soon. you only need to build the 9 inch one time. ideally...
 

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Rear end

You can get a 9-inch differential 28 spline that will fit with your axles that's what I did with my Maverick they had no problem with it A Running 3:49 3000 tci c4. Been in there 8 years.
 

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I grew up in the 60's. I've owned probably 15-20 cars with 8 inch rear ends. Most of them 6 cylinders on stock tires.

I probably blew three or four 8 inch rear ends out while stuck in snow. That's no traction at all. Just the shock of rocking the car with a 6 cylinder. The ring gear is the least of the worries. The spider gears were the main issues for me.

I suspect Ford also knew that, because the K-code 1966 Mustang GT I had came with a 9 inch. And it was just a 15 second car.
 

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I grew up in the 60's. I've owned probably 15-20 cars with 8 inch rear ends. Most of them 6 cylinders on stock tires.

I probably blew three or four 8 inch rear ends out while stuck in snow. That's no traction at all. Just the shock of rocking the car with a 6 cylinder. The ring gear is the least of the worries. The spider gears were the main issues for me.

I suspect Ford also knew that, because the K-code 1966 Mustang GT I had came with a 9 inch. And it was just a 15 second car.
This.
 
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