7 1/4 weakness

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motorpirate

serial mopar owner
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I'm sure this will get everyone's plack flowing but here goes.
I have heard and read forever here and elswere how pitifully weak the 7 1/4 spicer rear end is.no doubt the 8 3/4 and 8 1/4 are both bigger and stronger,but.who has broken one and how did it break?
I have owned no fewer than ten cars with 7 1/4's,most with slants,three with V8's,two that were drag raced all through my college years.never with slicks but as sticky of street tires as I could find(with liberal use of "track bite")
counting these from my own abusive ownership(they were all driven as hard as possible,My Hyper Pac '65 valiant would get 2nd gear rubber with its 904 so it did at almost every gear change!!)And counting the many that came thru my familys shop all thru the 60's 70's and 80's I only saw three fail.and they were all spider/side gear related.Ihave noticed many members here running 904's in some pretty high power applications(due to shortage of 727's?)
I just wondered if anyone could shed some light on how else they fail,and if there was any interest in trying to make one "live"
 
The axles are fairly weak, so don't break the tires loose going around the corner, especially with an open rear setup.

I just put an 8 1/4 in my Duster to replace the 7 1/4 that was behind a very warm 318 for the two years I have had it. It held up nicely and can be used again if I need to. The will last a while if they are taken care of and one is aware of its weak points.
 
I ran a 7.25 behind a mild 360 on street tires for about 6 months in my '69 Barracuda. It wasn't "abused", but I sure as hell didn't take it easy on it, either. After a while it developed a loud "clang" that was audible whenever I'd drive it, but I didn't bother to inspect it because I didn't care about it. I think I finally killed it doing donuts in a dirt field about two years ago. It makes a hideous grinding noise whenever it's rolled, go figure. That rear end is still under the car to this date (for sake of moving it around), but the car hasn't been driven since then.
 
spider gears went in my 79 apsen with 318 after getting stuck in the snow. never did quit working just very loud on the turns.
 
I had a stock 273 2bbl 4 speed with dual exhausts added with a little over 80,000 miles on it. F60 14 bias ply tires on the rear with an open diff 7 1/4" rear. I made a hard shift into 2nd & broke some (don't remember for sure how many, but I think it was 2) teeth of of at least one of the spider gears. The car was still driveable but the rear made a lot of clunking noises. My dad wanted me to just replace the spider gears. I told him it would just break again & bought an 8 3/4" rear instead. Never regretted it.

I should add that this car had a VERY noticeable gear whine from the 7 1/4" rear axle on acceleration when I bought it, so I imagine somebody had been into the rear for some reason before I bought the car.
 
I started off with a Slant 6 in my 69 Barracuda and it had a 7 1/4 rear. After two years, I swapped in a 318 my dad and I built to stock specs except for boring the block out to make the cylinders straight - I believe it was to 20 thousands. The 7 1/4 rear lasted for quite a number of years behind the 318 - I'd have to guess about 5 or so before the spider gears let go. At that point I swapped in a 8 1/4 from a local junk yard. Being a teenager, i wasn't exactly easy on it, but it did last for a while!
 
My 7 1/4 went bang and alot of crunch crunch. One of the spider gears didn't like it's home anymore so it left the housing. In a big hurry, luckily enough there was enough carnage to bind up everything enough to putt home. I think it had somthin to do with the 1 mile 1 legger burnouts. But i'm not sure.
 
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