What can a 7 1/4 rear take???

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Chryslerkid

Chryslerkid

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I know everyone likes to go bigger. I also know that most will tell me to upgrade my rear end. However I do not wish to upgrade.

What are the specs, horse power, and torque ratings for a stock 7 1/4 rear end? Is there anyway to strengthen it without spending too much $$$?
 
i have been running my 70,000 mile 7 1/4 behind my 318 for 2 years now after the /6 swap and it is doing great. if you dont abuse it, it will last. if you are power braking it , doing burnouts and **** , its going to brake. especially when transitioning from dirt to pavement. i am running 225/70/15s up to 275/60/15s. i drive it everyday year round. including snow and ice.
 
are you talking factory specs or real world? real world it's all going to depend on what your doing with it. (my opinion) a stock 318 4-speed car on slicks is going to destroy it. a warmed over 440 auto with a loose converter and street tires and street driven as a cruiser could last forever
 
The weak link is the spider gears.Keep it straight when stomping on it. Do not stomp on it when turning. Run it behind a /6 or stockish 318. Hard starts or dumping the clutch will raise your chances of it not lasting. Run it until it proves you wrong.
 
Oh wow. 70,000 on a 318 7 1/4? That's awesome! What kind of transmission are you running 73Abodee?

Just wondering if there is any useful information out there for 7 1/4 rear ends? I am looking for book specs AND real world experience from people who have gone through these little rear ends in order to learn more about them.
 
71swanger said:
Oh wow. 70,000 on a 318 7 1/4? That's awesome! What kind of transmission are you running 73Abodee?

Just wondering if there is any useful information out there for 7 1/4 rear ends? I am looking for book specs AND real world experience from people who have gone through these little rear ends in order to learn more about them.
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it was a slant 6 3 speed manual car. it now has a 318/727 . all i did was shorten the driveshaft. i havent even changed the gear oil. i had an exploded view of a 7 1/4 , i cant find it now, but its in my FSM. you should get you one . its my bible
 
I had one on a 318 with a 833, just like johnny dart said my first hole shot spider gears blew.
 
Nice! 318/727/7.25 sounds very cool. How easy do you have to take it on the rear? Are you cautiously accellerating every time you drive the car or can you comfortably drive it without worrying?

Are manual transmissions harder on the rear end than automatics?
 
The key to making a 7 1/4" live is a limited slip. It also helps if you are running at least a 3.55 gear. What kills them is carrier deflection which causes the spider gears to **** and bind. When that happens something's gotta give and usually it's the spider gears although I have seen split carriers. numerically higher gearing lessens the side loads placed on the carrier by the ring gear and going with a Sure Grip gives you a stronger carrier. I ran a 3.91 geared Sure Grip for years behind a 318 and couldn't break it. It was a replacement for a 2.76 geared open that grenaded at 21000 in the same car.
 
71swanger said:
Nice! 318/727/7.25 sounds very cool. How easy do you have to take it in the rear? Are you cautiously accellerating everyone you drive the car or can you comfortably drive it without worrying?
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my 727 is super tight and it shifts hard enough from 1-2 nd to bark the tire (lol) on the pavement. like johnny says , i dont turn corners and break the tires loose , thats a recipe for disaster. i drive it normal and i dont power brake or do burnouts. its my daily driver so i treat it that way. i occasionally get after it , but not from a dead stop. im sure if i wanted to , i could break it pretty quick.
 

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Lots if good info everyone! From the specs to the real world experience I can begin to understand more about the 7.25 rears and their breaking points.

How can I tell what kind of 7.25 I have? I can identify the 7.25 rear by looking at the bolt pattern on the back, but can I figure out what kind of gears I have without opening it up?
 
71swanger said:
Lots if good info everyone! From the specs to the real world experience I can begin to understand more about the 7.25 rears and their breaking points.

How can I tell what kind of 7.25 I have? I can identify the 7.25 rear by looking at the bolt pattern on the back, but can I figure out what kind of gears I have without opening it up?
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the gear ratio tag is on one of the cover bolts. sometimes if the cover has been removed they disappear. mine happens to be a 2.91.
 

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There is a formula to do this, mark your drive shaft and wheel, tune the drive shaft and count how many times the drive shaft turn to one complete rotation of your wheel.
Do you have the build sheet to your car ? it will be on it if now one changed the gears out.
A good tec can and will jump in here and tell you what you have once you find out
how many turns it took to do one revolution of your tire.
 
2 3/4 = 2.76
about 3 = 2.91
3 1/4 = 3.23
3 1/2 = 3.55

etc etc

if both wheels spin the same direction when off the ground , its a sure grip
if one wheel spins backwards its a one wheel wonder
 
I recognize the rear end as being a 7.25 but ill check for the rear cover bolt for the gears. If that doesn't pan out then ill do the driveshaft tire rotation technique and get back to you guys for more info.

Are sure grips for a 7.25 rear hard/expensive to come by?
 
i've had them in a few cars and never had a problem. just remember it's there and drive accordingly. since you want to know what gears you have, just change the fluid and find out
 
kursplat said:
i've had them in a few cars and never had a problem. just remember it's there and drive accordingly. since you want to know what gears you have, just change the fluid and find out
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Yes they are I have been looking for one for my 66 sedan's 7 1/4 for a couple years now
 
kursplat said:
i've had them in a few cars and never had a problem. just remember it's there and drive accordingly. since you want to know what gears you have, just change the fluid and find out
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You're talking to someone who knows little to nothing about rear ends. Even if I open up the rear end, I would not know how to figure out what gears I have unless there was a sign in there that said 2.91 lol.

Anyone want to give me a quick lesson on rear end for dummies? Or maybe refer me to a good website for this kind of information...
 
memike said:
There is a formula to do this, mark your drive shaft and wheel, turn the drive shaft and count how many times the drive shaft turn to one complete rotation of your wheel.

.
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73AbodEE said:
2 3/4 = 2.76
about 3 = 2.91
3 1/4 = 3.23
3 1/2 = 3.55

etc etc

if both wheels spin the same direction when off the ground , its a sure grip
if one wheel spins backwards its a one wheel wonder
Click to expand...

71swanger said:
You're talking to someone who knows little to nothing about rear ends. Even if I open up the rear end, I would not know how to figure out what gears I have unless there was a sign in there that said 2.91 lol.

Anyone want to give me a quick lesson on rear end for dummies? Or maybe refer me to a good website for this kind of information...
Click to expand...

right there, Mike explained it
 
Not to barge into this thread but has anybody ever "spooled" their 7.25 and what were the results when you did? I've heard of a lot of off road guys doing this not sure how it would turn out on a street car.
 
I ran the 7 1/4 sure grip with 276 gears behind my 360 in my Dart for a couple of years with no problem.. burnouts and all.. I wasnt exactly kind to it.. but from what I have read and heard over the years, I was apparently lucky.. Though I believe if you just cruise the car and your not out beating the snot out of it everyday it should probably last a good long time.. I only upgraded because I got a good deal on an 8 3/4... LOL ..
 
The ratio is stamped into the ring gear. Remove the cover and rotate the ring gear around until you can read it.
 
I have a 7 1/4 in a 70 Dart with a warmed over 318 and O/D 4 speed. So far it is taking the abuse but I don't dump the clutch. I do spin the tires but by gradually adding more power, not by shocking them free. Had a 67 Dart GT with a 328/904 and 7 1/4. Never babied it and it lasted for years. A sure grip would definitely increase the abuse it will take.
 
I can say this, I had a 1970 Barracuda 318 2 barrel automatic car and it came from the factory/build sheet showed 7 1/4.
with a 7 1/4 and it had over 100.000 miles on it, just like my Valiant 7 1/4 first thing I did was replace the outer bearings and seals.
 
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