so....is a 7 1/4 really all that bad

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Princess Valiant

Princess Valiant

A.K.A. Rainy Day Auto
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I am cleaning up my mopar stable and area and I can count 6 7 1/4 rear ends that I have been holding on to......simply to be a packrat.

Well I am starting to think that since I am using a slant six car as a daily commuter, why not just leave use up the 7 1/4s and as they go out or break, simply replace until the stock is depleted then upgrade to something bigger.

Most people act like 7 1/4s are some kind of disease but behind a s slant six with a one barrel....would it be so bad to use them up.
 
Unlike popular belief, I've been doing huge one tire fire burnouts with my duster (slant six and 7.25) since I've gotten it on the road two years ago. It hasn't given me any grief or blown out. But of course this is behind a pretty much stock slant so not a big torque monster lol
 
Ran one for years behind a small block 4-speed in a Duster.
I did have an extra one for a spare but never needed it.

Run what you have, with 6 or 7 of them, you will wear the car out before you go thru that many rear ends.
 
Run them till they break then worry about it.
 
Make darn sure it has fluid in it. Daily driver, easy stuff they are perfect.

Can't count the number of 7.25's I've taken apart from running cars that were bone dry.
 
I would say sell them but it's hard to even give them away. Hold into a few but I doubt you will ever have an issue behind a slant six car. I ran one behind a mild small block for three years. I even took it to the drag strip a few times. Never once had an issue. I think they are underrated.
 
RaniDart70 said:
I am cleaning up my mopar stable and area and I can count 6 7 1/4 rear ends that I have been holding on to......simply to be a packrat.

Well I am starting to think that since I am using a slant six car as a daily commuter, why not just leave use up the 7 1/4s and as they go out or break, simply replace until the stock is depleted then upgrade to something bigger.

Most people act like 7 1/4s are some kind of disease but behind a s slant six with a one barrel....would it be so bad to use them up.
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They are fine for your intended usage. Replace the wheel bearings every 100K and keep good fluid topped off. If any are Sure Grips they are worth a lot on e-bay, I've seen the Sure Grip carrier go for as high as $400.
 
66fs said:
They are fine for your intended usage. Replace the wheel bearings every 100K and keep good fluid topped off. If any are Sure Grips they are worth a lot on e-bay, I've seen the Sure Grip carrier go for as high as $400.
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I wish .....no sure grips. I don't even have sure grips in the other car which I have an 8 3/4 in. :???:
 
crackedback said:
Make darn sure it has fluid in it. Daily driver, easy stuff they are perfect.

Can't count the number of 7.25's I've taken apart from running cars that were bone dry.
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do they have a problem with leaking or was it just 40+ years of no one checking it and not taking care of stuff.
 
Some people seem to want the biggest, heaviest of everything. Then wonder why their car is slow and gets bad mileage. Everything is a trade-off. Big brakes = more sprung weight. When I run across an early A 7.25" locally, I'll grab it for the future. You'll be long passed away before you run our of 7.25" rears, so upgrading can be an issue for your heirs. As long as there are straight axle pickups, there will be rear-ends they can use.
 
RaniDart70 said:
I wish .....no sure grips. I don't even have sure grips in the other car which I have an 8 3/4 in. :???:
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A Sure grip is easy to add to an 8 3/4, you swap the carrier and set the backlash.
The 7 1/4 never seemed to leak much fluid either.
 
They are good for a slant or V-8 at 318 2 bbl or less. Anything more and chernobyl...

I went through three 7 1/4 rear axles on my 68 Barracuda 318 daily driver.

Nothing special, just a 318 with the cam from my brother's Lil Red Express (stock 340 auto cam), Rhoades lifters, 9.2 compression, 360 heads, 69 340 intake, Holley 600 vac secondaries with stock exhaust manifolds and 2 1/4" dual exhaust with h-pipe.

It wouldn't spin the tires, but performed well, idled at 22.5" Hg and got 17.75 MPG on the highway. I went through three 7 1/4" axles in 4 years...

The last time it happened, was the last straw for the 7 1/4 for me. I was going down the highway at 70 MPH and heard noise coming from the rear. I slowed down to 55 - 60 MPH and within a couple of miles I see my driver's side tire and axle shaft pass me on the shoulder....

I was able to slow the car down so I could go fetch my tire and axle that had finally come to rest along a farmer's fence.... Then I see that the gear lube that is leaking out of the axle is on fire.... So I put that out with a shop rag that I had in my car and went to find my tire.... Luckily I had super stock leaf springs and Mancini Racing U bolts that were very long, and they saved my quarter panel from any damage...


After that, I took in my spare 8 3/4 with 3.23 sure grip to my trans guy and had him go through it.... Never broke that one in 5 years of daily driving and over 200k on that axle....


I call them the weak-suck axle now....
 
I had one in my V8 74 dart parts car. The 10x 2.50" drum setup bolted right to my 8&3/4 , then i got finned 77 cordoba severe duty kelsey hayes drums for the setup.

Reason im saying this, is if your gonna pitch em for scrap metal, the brakes off em if they are a bigger drum setup will likely cross over to an 8.25, or 8.75 rear . You may want to save the bigger brakes from the backing plate out, and chuck the rest.

The 7.25 under the V8 granny green 4 door worked fine for its owner 70,000 plus miles. But a mid 70s 318 is a low compression , weak cam , small valve total dog in stock form.

Hope this helps.
Matt
 
krazykuda said:
They are good for a slant or V-8 at 318 2 bbl or less. Anything more and chernobyl...

I went through three 7 1/4 rear axles on my 68 Barracuda 318 daily driver.

Nothing special, just a 318 with the cam from my brother's Lil Red Express (stock 340 auto cam), Rhoades lifters, 9.2 compression, 360 heads, 69 340 intake, Holley 600 vac secondaries with stock exhaust manifolds and 2 1/4" dual exhaust with h-pipe.

It wouldn't spin the tires, but performed well, idled at 22.5" Hg and got 17.75 MPG on the highway. I went through three 7 1/4" axles in 4 years...
Click to expand...


Well of course, you pretty much had a "73" 340.
 
My friend back in Highschool had a 74 Dart with a mild 318 (4 barrel, 340 cam, headers) and he went through several 7.25s, but he abused them pretty bad. Blew up the spider gears almost everytime. He eventually went to a 8.25 and never had another issue.
 
BillGrissom said:
Some people seem to want the biggest, heaviest of everything. Then wonder why their car is slow and gets bad mileage. Everything is a trade-off. Big brakes = more sprung weight. When I run across an early A 7.25" locally, I'll grab it for the future. You'll be long passed away before you run our of 7.25" rears, so upgrading can be an issue for your heirs. As long as there are straight axle pickups, there will be rear-ends they can use.
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ehhh....brakes are unsprung weight there, Beavis. But your other points are certainly spot on.
 
i also have a 7 1/4 behind my slant. the slant has a offy 4 barrell intake with a holley 390 4 barrell carb and a set of hooker headers , a mild bore with a mild cam. talk about a decent burnout and we also have tons of fun driving and showing the car.
 

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My Barracuda still has the the 7 1/4 in it. As long as you keep them fairly stock, it will do fine. If you start adding power, just wait until it lets go and then upgrade.
 
Had one in my 67 Barracuda when I got the car with a 273 2 bar and automatic

Put the 273 hipo that was in my sisters Formula S after dad put a 318 in it

Well the little 7 1/4 broke the spiders clean off, was young and dumb, went to junk yard and $10 had another 7 1/4 and it lasted about 2 weeks. This time just cracked the spiders and it made a lot of noise going home very carefully.

Pulled the 8 3/4 sure grip out of sisters Formula S and put a junk yard 7 1/4 under it and I got the 8 3/4 LOL

If I would have been smart would have gotten the 8 3/4 out of the junk yard along with a drive shaft and saved a lot of work. It might have cost me $50 back in 1975

But my 70 Duster slant 6 with 3 speed manual did just fine for over 100,000 miles with the 7 1/4

Hang on to a couple for spares but probably the one in there will be fine as long as it is in good condition
 
I like to have spares of stuff. My Demon had a decent 7 1/4, and my '65 had issues with a wheel bearing so I simply swapped them. The Demon's got an 8 3/4 to go into it but it rolls good ont he bad wheel bearing...lol. But I think at 6 you have some scrap money tied up in them...lol
 
I've heard a lot of people say they break even with a slant six, but I have yet to see it.
 
I doubt I will need to add power over stock because my other car is a big block car and they don't all need to be hot rods IMO.

great info here ....this is like a virtual garage chat with a bunch of great mopar minds....thanks
 
Seems like it's pretty split. Some guys have no problems with them after beating on them with v8s and some guys break them just taking it easy.

Keep up with the fluids and crap and take it easy and you should be fine. If I had a slant six I would not think twice about having a 7 1/4.
 
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