7 1/4 Rear Differential ~ Experiences

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Prine

Prine

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I did a Search....and could not find what I wanted to know so here I am starting this thread.

I want to know:

YOUR experiences with the Good, Old, Tried and True 7 1/4 Differential.

I will start with one of my own Experiences.

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One day I was sitting at a Stop sign and turned Left, in my 1974 Dodge Dart Sport (of unknown Actual Mileage) and accelerated Kinda Heavy with a stock 360/904....and heard/felt
a LOUD CLunk/POp....didnt know if ran over a piece of pipe in the road or what so I drove up to the next red light and motioned to turn left and held short till it was clear and slowly accelerated and it did it again Clunk/POp....I knew it broke something in the diff but I wasnt sure what.

I eased it the 1 mile back to the house and jacked it up and popped the cover off.....sure enough it got the Spider Gears.

Wasnt in a position to do a 8.75 swap so ordered the Spider Gear set from Yukon and rebuilt the carrier myself in the garage in -15* Oregon weather with basic hand tools.

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Anybody ever EXPLODE one?
 
My personal experience with a 7-1/4. Mine was a sure-grip. I beat the living **** outta that rear behind a stock 273, a mild 318 & later a warmed over 360. Damn thing never failed. Not a peep!

My best friend's 7-1/4- not so much luck. '70 Duster, 225 /6 3sp manual. Again we beat the **** outta the car & it worked fine until 1 day when he went to Burger King to get lunch for the guys at work, right in the middle of the lunch rush hour, just as he let the clutch out to pull away from the drive in window..POW!! BANG!! The spider gear pin blew right through the rear cover & locked the whole rear up! Right in front of the drive-in wiondow! At the peak of the lunch time rush! Oh man the line of cars honking & people cursing at him as he tried to push it away! Uh-Uhh! No way was this thing moving! About an hour & 1/2 later the tow truck was able to clear it out of the way. The Burger King manager was pissed! Not to mention when we got back to work with everybody's cold lunch how much **** he took for it!
 
Mine howls between 60 and 70 mph. Never beat on it, and the granny that owned the car before me didn't either, far as I can tell. Drained it and put in fresh lube - no difference. Has less than 80K on it - original miles slant 6 75 A body - big bolt pattern. Changed one outer axle bearing, seemed to quiet a little but never really went away. Must be the gears (?) Funky sealed bearing, round ball bearings, not the typical tapered roller bearing. I have an 8 1/4 waiting in the wings if/when it goes or I get around to it.
 
I beat on mine for 7 years. 5 of those was behind a 360. I took it to the drag strip a few times even. Pulled it out last summer and gave it away. Never a single issue after 3 sets of tires!
 
Prine said:
I did a Search....and could not find what I wanted to know so here I am starting this thread.

I want to know:

YOUR experiences with the Good, Old, Tried and True 7 1/4 Differential.

I will start with one of my own Experiences.

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Anybody ever EXPLODE one?
Click to expand...



Does catching one on fire count??? While the axle shaft passed me with the tire still bolted to it....


I had a mild 318 with 9.2 compression, 360 heads, 4 bbl, dual exhaust in my trusty old 68 Barracuda. (along with MP super stock springs)


Was driving down the highway doing 70 and heard noises coming from the rear end. So I slowed down to 55 trying to figure out what was happening. Then I see my left alxe shaft with the tire still bolted to it pass me on the right shoulder of the road, then finally come to a stop. When I got out to look, my tire and axle had come out of the alxe housing, and the gear lube was on fire. I was able to beat the fire out with a handy shop towel from inside my car. Luckily the arch of the super stock leaf springs and the long Mancini u-bolts kept the quarter panel from getting any damage. Then went to fetch my tire and axle while I waited for a tow truck.


That was the 3rd 7 1/4 axle that I blew up with that engine, so I went to 8 3/4" and didn't ever blow another axle again in that car.
 
7.25 rear diff's have Bolt In axles....and are not C-Clipped like the 8.25

I have given every 7.25 equipped car, I have owned, all kinds of Hell.....burnouts....135mph top speed runs....corner turning Single Tire Frier rips.....water puddle Tire Drying burnouts....donuts in pea gravel,....and never truely broken one like we all like to think is so easy....never had a Big Block to stress one...but everything from Mild 318's to Mild 360's.

I am also wondering......what is the Power Limit of the 7.25?

Has anyone ever gone faster than say 12.xx's in a 1/4 with one?

I have personally taken my 1974 Dodge Dart Sport...360/904/7.25 to the drag strip and made a couple of 1/8 mile passes.....2.0 60' ft....10.05 @ 80 being the best.....and driven the car from New Mexico to Oregon....then Oregon to Texas.....and logged over 30,000 miles with NO PROBLEMS.
 
I had a wheel bearing go out on one. It was in a '72 duster 198 slant 6 3 spd standard on the floor.
I never abused it to cause this, i just swapped the axle and all out of the left side from another one i had laying around in a parts car and drove it for another 10,000 miles before i sold the car.
All the other ones i had didn't give me any problems at all, but i never abused them either.
One was in a '69 Coronet 4 door with a 318 auto that i drove for years.......
 
Sorry to say but I have not had much luck with the 7.25. My first Dart was a stock 318 2bbl and broke the rear at least three times back in the late 70's early 80's. I tortured and abused that car so I cant say it was the fault of the rearend. The only rear Ive used since then is the 8.75 and have not had any problems, using various big and small blocks and beating the piss out of it every chance I had.
 
Dartnut said:
I had a wheel bearing go out on one. It was in a '72 duster 198 slant 6 3 spd standard on the floor.
I never abused it to cause this, i just swapped the axle and all out of the left side from another one i had laying around in a parts car and drove it for another 10,000 miles before i sold the car.
All the other ones i had didn't give me any problems at all, but i never abused them either.
One was in a '69 Coronet 4 door with a 318 auto that i drove for years.......
Click to expand...
'69 Coronet would have had an 8-3/4 in it.
 
My dart had a 318 and a 7 1/4. I've done lots of burnouts with it, no issues so far, but that was a 150hp 318 with skinny tires. I'm taking bets on how long it'll last with a 400+hp 360 and 255 rear tires! :burnout:
 
DartVadar said:
My dart had a 318 and a 7 1/4. I've done lots of burnouts with it, no issues so far, but that was a 150hp 318 with skinny tires. I'm taking bets on how long it'll last with a 400+hp 360 and 255 rear tires! :burnout:
Click to expand...

Do the burnout in front of your house. That way when the rear blows up you can push right into the driveway to swap it for 8.25/8.75/Dana 60 (pick your poison).
 
I kept the 7.25 in my 65 Valiant. The rear was the last thing I swapped out. Should have done it the other way, but I didn't. It had a zero deck 360 with KB 107s, heads milled to 62CCs and ported much as they would flow, .021 MP head gaskets, 508 Mopar cam, LD340 Dougs headers, MP ignition. Real HOT 904 with 3500 converter and manual reverse valve body. It had 15x9.5 Center Line Auto Drags on the rear with MT 28/11.5/15 ET Streets. After cam break in, I pulled it into the street and yammed on the gas HARD. We pushed it back in the driveway. I put an 8.75 in it the next weekend. It stripped the spider gears down to nubs.
 
1970Duster said:
Do the burnout in front of your house. That way when the rear blows up you can push right into the driveway to swap it for 8.25/8.75/Dana 60 (pick your poison).
Click to expand...

Good point! Don't want to be far from home when it goes.

I have an a body 8 3/4 so i'll be ready when it goes. LOL
 
Lonewolf3165 said:
'69 Coronet would have had an 8-3/4 in it.
Click to expand...

The car has a B-Body 7 1/4 in it from the factory, it is a '69 Coronet Deluxe 4 door 318 column auto.
I still have the car for that matter.
I also have a '69 Coronet 440 4 door 318 column auto with a B-Body 8 1/4 rear end in it.
(The first year for the 8 1/4.)
 
I was worried about the 7-1/4 in my 64 (360 4 barrel with 904 auto). Tuned it with a friend of mine who knows all of the ins and outs of Mopars, he did a pretty good burnout with it and it didn't break (thankfully). After seeing this I am going to drive it like an old lady until I have upgrade parts on hand.
 
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