Who's in the "I broke a 7.25" club?

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MRGTX

MRGTX

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Nearly everyone who comes to this section of the forum who has a 7.25" is either running a collector/survivor/restoration car, planning on swapping it out or has yet to discover how fragile they are. :D

Ok...so I know we've heard stories of folks who have drag raced with them and even finished the 1/4 mile with them in tact but these are almost always with very mild small block motors and with the limited slip version of the 7.25" which seems to be extremely rare...and maybe someone can verify this; quite a bit stronger if you can find one.

So what's your story? Was it catastrophic?

When I was about 20 (half a lifetime ago...though my tastes and habits haven't changed much :D ), I finally found the extra cash to get some relatively sticky tires on 15" wheels to replace the hilariously skinny 14" rollers. Well, it wasn't long after that that the stock 318/904 proved to be too much. Evidentially, my normal driving shenanigans resulted in a cracked carrier after laying a minor strip of rubber, while showing off to my buddies. Honestly, it didn't seem to take much though it probably let go after lots of fatigue over years of being driven by a kid with a heavy food...but still, a 150rwp engine on all season radials was enough to do the trick!
 
I sheared the spider gear pin on the original 7 1/4 in my car leaving a stop light one night. Decently built 318 with 70 series radials. Lined up against a 68 Camaro at the light, when it turned I took off and halfway through the intersection it let go.
 
Funny this thread popped up today.
Over the last month or so, I have been stockpiling 7.25 rears and parts with the intent of deliberately blowing them up to find the common failure points and hopefully producing some upgrade bits to give the little suckers a chance.
Just last night, I was thinking to myself that I really need to get on this project
 
I grenaded one behind a mild 318. It only took two good burnouts and it came apart. It had chewed up everything to the point it was like gravel on the inside.
 
I can "help!""
I'm thinking of a you kind of set them up and I knock them down kind of thing LOL
Have "lead foot" will travel.... :thumbsup:


whitepunkonnitro said:
Funny this thread popped up today.
Over the last month or so, I have been stockpiling 7.25 rears and parts with the intent of deliberately blowing them up to find the common failure points and hopefully producing some upgrade bits to give the little suckers a chance.
Just last night, I was thinking to myself that I really need to get on this project
Click to expand...
 
I'm in the "woulda if I'd kept one!!"

This winter I replaced a "modern" 8 1/4 in a 98 Dakota some kid broke, spinning one wheel stuck in ice and snow. He broke the spider shaft IN THREE PIECES, and then those all bound up in such a way that he DROVE IT 30 MILES on "one" axle, meanwhile, the other axle was wandering in and out of the housing because it had no C clip!!!

Bought a used one out of a 4x4 which has the spring pads on the wrong side, bought new pads and welded em on. Just left the old ones on there!!
 
Oh yeah and I broke one in my first Duster and didn't even waste time with the one in my second Duster. I took that out before I ever drove it.
 
Never. I've owned many cars with 7.25 rear ends, and never lost a one. No, I didn't put a 350 hp motor in front of them.
  • In fact, I have a 7.25 rear in my '74 Duster right now. 318 4bbl, home ported heads, mild cam and dual exhaust. Have a few runs at the drag way (high 14's) and many runs out of town. No issues.
  • no, this doesn't mean I think they are tough. But I do think they are better than most give credit for....
 
Yep. I too bave broken one.....3.23 open 7 1/4. Small 14" tires in my 69 318 904 barracuda. The spider gears let go.....
 
I destroyed 4 in my daily driver when I was 16 , car was a 1978 aspen with the super six!!! tore up the spider gears when ever I turned the corners to fast.lol could never blow up the little six tho, just the rearends, guess they didn't like spinning the tires .
 
Decided to sell my 65 Barracuda so I took out the 8 3/4 to keep and put in a 7 1/4. I think it lasted about 2 weeks. Went to lunch one day, launched at a light and bam! By the time I got back, it was locking, binding and hopping. Broke the spider gear and crossshaft. Had to swap the 8 3/4 back in.
 
:BangHead: Knockin on wood here. The 9" isn't ready yet for the swap. Of course it did survive my 16 year old daughter for 2 years and me for the 12 years since then.
 
YEARS ago - my first Scamp, 318 AT car - tried to do a J strip... slightly down hill behind me... put it in reverse and lit 'em up for a few feet (well, lit it up - no way was that posi) - let off quick and popped it into drive and laid into the gas pedal... *bang* goes the rear end... *confusion* :wtf: was that... and rolling backwards and rolling backwards... hit the brakes - - fiddled with the shift lever a few times.. nuthin'... - well, park worked:lol: - 45min. later the tow truck showed up. Thankfully there was a Mopar specialized shop locally and I was friendly with the owner... I got my first 8.75 a week later.
 
The rear end was the reason I sold my 65 Barracuda that I bought new. It was all Formula S equipped ( except for the S badge) 4 speed with the Sure Grip 7-1/4 " rear end. Just before the 5 yr, 50,000 mile warranty was due to expire, I heard a noise or whine start up in the rear end.. I sold the car. About two weeks later I saw it broke down on the highway. The rear end had given out. The buyer contacted me, and do you know, he was able to get the rear end replaced under factory warranty. I guess they were designed for a 50,000 mile life.
 
Blew one with a 225, blew another one with a 360. They simply were never designed to, and cannot deal with handling any real power. If the tires stick, and there's some real power applied, they'll break.
 
I'm a multi time member. I've got seven broken ones piled behind my Dad's garage. That is probably half of the ones I've ripped the spider gear shafts out of over the last forty years. Managed to tear 'em up with everything from stock 225s to built 340s.
 
My brothers 73 duster broke a 7 1/4 trying to power brake behind a slant 6 2bbl. This was about 30 years ago. My dad was so mad because he had a come pull him home with a chain.
 
mums the word

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Lost a spider gear in mine. Clunk clunk clunk clunk.... All the way home. Changed it out with an 8 3/4
 
1980 Volare slant 904. spiders broke. Low-mileage.

Funny thing is, in 75 or so I put a 340 in a 65 V100 wagon, with a 64 A904 (converted to non-push button) and left the 7.25 in there. The 340 had a complete 318 top end on it including the cam. I drove it like that for about 2 years, peg-legging it everywhere.
The tranny gave up first.
I gave it to my little brother.Who put a 225 in there. And drove it for a few more years. Then blew the 6 up. That 225 was a take-out from a 69 Barracuda I had bought the year before I got married( so 76), and installed a fresh rebuilt into. Well that FB was pretty snappy, and it didn't go un-noticed by my buddies baby-sitter. So about a year later, the kid rolls his 71 Demon340/727. And he wants my BabyBarracuda. So we struck a deal and made a trade. I got a mountain of Mopar stuff, including the roll-over. I went and bought a 74 DartSport 360 4-gear. Less than a year later, I saw the kid walking............ no....... the rearend was ok................a rod had exited the block. Wait, that's not the end. Some time later, I saw him driving it again. Well I had to know, so I chased him down. It turns out slantys run not bad on 5 cylinders. He had just stuffed the hole with rags and drove on. He said eventually it stopped clanging.
My Sport had an 8.25 in it.
Fast forward to 1999, and a lot of that mountain of stuff went into my current ride.
Along the way I've had many more 7.25s but never blew another one up. I didn't actually blow the one up in the 80 either. I bought that car in 94 with a blown up slanty, for $100. The body was mint. I bought a parts car and had the SS rebuilt, while I freshened the 904. The car had been driving just fine until the day the engine blew. Well, after I got the thing running again, I backed it out of the bay, and then I heard it. That awful grinding noise. Hyup the spiders were piled up. Back to the parts car, I went........
 
I wish I pics of mine. half the 3.55 pinion gear teeth just wiped right off the the ring gear looked like a shark bit it. I didnt even look at the spiders but I wonder if one broke and a piece took out the ring/pinion? I rushed to the wrecker to get a replacement rear as I had to get to school monday and all they had was a 2.76. Car went from 'hero to zero' overnight, but it flew on the freeway! It was behind a 340 and I did a neutral drop backing down a driveway AND it was a SG, so I think it was stronger than a peg leg.
 
grimreaper said:
I'm a multi time member. I've got seven broken ones piled behind my Dad's garage. That is probably half of the ones I've ripped the spider gear shafts out of over the last forty years. Managed to tear 'em up with everything from stock 225s to built 340s.
Click to expand...

What's the weak link in a 7-1/4" ? Pinion? Ring gears? I wonder if anything can be added or changed to strengthen it?
 
Everyone of them that I've ever owned. The pinion seal dries out and you leak enough gear oil until you ruin the carrier bearings and the thing begins to growl which you get used to and ignore until it either begins to howl or you sell it or replace it with an 8.25 or an 8.75. About 6 so far and counting.
 
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