Thought I had a line on an A body 8.25 rear for my wagon but that fell through so I'm wondering if the 7.25 open diff would be strong enough for my use. Engine is a a mild Slant 6, but I'm going to upgrade sometime in the future to 10:1, hotter cam, and dual Webers on an Offy intake. Also I do kind of tend to drive agressively (or as my wife says, "stupidly") sometimes. I'm ordering a front disc brake kit next week and need to decide on 4 or 4.5" lug pattern. If the 7.25 is strong enough I'll go with the 4" to match the rear, but if I'm going to need the 8.25 (or 8.75) might as well get 4.5 since that's what the eventual rear will have. Thanks.
Is a 7.25 rear strong enough?
- Thread starter glockr
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Professor Fate
Push the button, Max...
Wait on the disc conversion until you get your rear.
A 7.25 will hold up for a bit, but not indefinitely. Especially a pegleg rear, and extra especially if you're going to beat on it.
An A body 8.75 will still be 4" BC, unless it's been converted.
An A body 8.25 will be 4.5" BC.
A 7.25 will hold up for a bit, but not indefinitely. Especially a pegleg rear, and extra especially if you're going to beat on it.
An A body 8.75 will still be 4" BC, unless it's been converted.
An A body 8.25 will be 4.5" BC.
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Mine has withstood some mild abuse in Vixen so far. Her current engine sounds similar to what you have planned.
I used to abuse the hell out of 7.25 rears and never had one break. They clunk and whined but never wanted to give up. Run what you have and hope she gives you some warning before giving up.
The ‘73 and up 7-1/4 with 4-1/2 inch bolt circle and 10 bolt cover is a little stronger than the earlier version. One with a sure grip (if you found one!) would last pretty well indefinitely behind an automatic.
I absolutely destroyed the original 7 1/4 in my 1970 Dart Custom in 1976, with a stock 318 2bbl. Broke the spiders and pieces went everywhere!!! Swapped in an 8 3/4 that is still in the car and doing fine, thank you very much. The car has had a 340 in it since 1978 and the 8 3/4 has over 150,000 miles on it...
If you decide to change to an 8 1/4" axle, ask around. Surely someone nearby has one for sale.
I might would try the sure grip later 7-1/4 behind a stock 318, but that would be about the limit. Not a V8 rear by any stretch of the imagination, even though the factory did their best to prove otherwise…
Does anyone make one of those mini locker type of differentials for the 7 1/4" axle?
Also....Is there any differences between the years that would prevent one from swapping axle shafts to change a 4" bolt circle axle to a 4 1/2"?
You know, like a 73-76 V8 front disc car axle as a parts donor?
I've always just defaulted to the 8 1/4" or 8 3/4" axle but with those can get costly.
Also....Is there any differences between the years that would prevent one from swapping axle shafts to change a 4" bolt circle axle to a 4 1/2"?
You know, like a 73-76 V8 front disc car axle as a parts donor?
I've always just defaulted to the 8 1/4" or 8 3/4" axle but with those can get costly.
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Nope.
Professor Fate
Push the button, Max...
Ask, and ye shall receive...
Mopar Axle Pkg 7 1/4" A-Body 5X4 1/2" Bolt Pattern (pair)
And no, there's enough differences between the early and late 7.25s that the axles will not interchange.
junkyardhero
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it'll be just strong enough until it isn't.
personally i'd upgrade to an 8.25, 8.8 or 8.75
going with 4" bolt pattern limits your wheel and tire choices.
personally i'd upgrade to an 8.25, 8.8 or 8.75
going with 4" bolt pattern limits your wheel and tire choices.
I guess if you're really in LOVE with the 7 1/4" axle then those Dr Diff shafts are worth the money but then you're still limited by the weak differential.
An 8 1/4" axle can be found for that money.
An 8 1/4" axle can be found for that money.
Correct, but no lockers or limited slips available new.
Right. It's just not something I'd consider doing until I absolutely had to. So far, mine has held well and I've ripped it around some. The key is it has 13" tires on it which won't hook up.
junkyardhero
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i'm of the thought that if you're not doing neutral drops or one wheel peels fifty mile an hour up a down way street it should be fine.
but i'd still be on the look or building one for the inevitable demise i know to be looming.
Yup. Spend money on stuff you actually need to.
junkyardhero
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like hookers and black jack. or poor life choices like the 4dr dart in yucca valley that's cheap and just screaming for an LS because i need another project like i need a hole in my head. but i digress...
i'm sure somebody here has one priced right, and within striking distance. if not spring fling is coming up and that's not too bad of a haul from NV
I'm not in love with it. It's what I have. The Ford 9" ain't quite finished yet. So I've serviced the 7 1/4, drained it, cleaned it out put fresh oil in it. I may even replace the axle bearings and seals if it stays under it much longer, even though they're not leaking or making noise. I don't drive it like a dumbass, so I'm not worried about it breaking. I have no doubt it would last indefinitely if I chose to leave it under the car. It's what's there, so I'm taking care of it.
7 1/4 came stock behind 273 2bbl.
Mine has 322,000 miles on it.
It will hold up just fine
Mine has 322,000 miles on it.
It will hold up just fine
It may have been on this forum where I read that what kills these units is extended one wheel peel burnouts. In this case, the spider gears are under great strain as opposed to two wheel burnouts where the spider gears are somewhat stationary.
Sure Grips for 7 1/4" axles are rare.
The Roadkill guys had a mid 70s A body project where they welded the differential and did a series of drag races with it. Eventually, it started making some bad noises.
Sure Grips for 7 1/4" axles are rare.
The Roadkill guys had a mid 70s A body project where they welded the differential and did a series of drag races with it. Eventually, it started making some bad noises.
doogievlg
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I ran one behind a worn out 360 for a few years. Even took it to a drag strip and turned a 14 with it. I was 18-23 at the time so it saw a healthy amount of burn outs and abuse.
Correct. The spiders spin so fast when one wheel is spinning that they over heat and weld themselves to the cross shaft and then spin the entire shaft in the case and destroy the entire case.
And if you overwhelm one outright on an “all weather roadway surface” (it’s a thing they use on around here on the backroads that is similar to the finish on a concrete bridge because the plow trucks have to maintain primary highways first) by both tires spinning and then catching traction, you’ll split the spider gears clean in half. They make some impressive noises (even while in neutral!) when being pulled onto a rollback after doing that.
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FYI...
I was checking my rear brakes today and as I was spinning the drum heard and felt click click click. Not a sound or feeling I had ever felt.
I checked the level in the 7 1/4 and ended up adding 6 oz shy of a quart.
The last time it was serviced was 2010 and 20,000 miles ago.
The car sat for 4 years and the pan under the diff had maybe a few tablespoons on it, and in the 5+ years I have had it maybe another 2 tablespoons.
There was nothing to suggest the oil was leaking out as it was driven.
One tough rear end!
I was checking my rear brakes today and as I was spinning the drum heard and felt click click click. Not a sound or feeling I had ever felt.
I checked the level in the 7 1/4 and ended up adding 6 oz shy of a quart.
The last time it was serviced was 2010 and 20,000 miles ago.
The car sat for 4 years and the pan under the diff had maybe a few tablespoons on it, and in the 5+ years I have had it maybe another 2 tablespoons.
There was nothing to suggest the oil was leaking out as it was driven.
One tough rear end!
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