Sure grip 7 1/4 strenght?

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Hipo65

Hipo65

Yeah I'm "That Guy"
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Hello again my fello A-body poeple. ive been doen alot of work to the ol 65 gt & she is runnen real good (rebuilding front end as i type this) I had an honest qustion of the guys who have delt with the ol 7 1/4. Honestly will it live very long behind my hi-po 273? i just swaped in an isky e-4 cam & direct lube lifters (That has gotta be the best cam for this little motor fyi!) helped "alot" in the power dept. now as i get ready to open up the tranny & ive got a custom built 2500rpm stall (ish) corse spline converter for it & gonna drop in a set of 2.76:1 wide raito planetry gears while im overhauling the trans. the rear currently works great! its a 3.23:1 clutch style sure grip. I know thease little guys are kinda hard to find soo do i run it until it blows? or sell it now while it works fine & look for an 8 3/4? i wanna keep the small bolt pattern is why im not looken @ running a 8 1/4 (i have one in the shed) just dont want bbp. Thanks for advice:burnout:
 
they are considerably stronger that an open 7 1/4 but for your engine combo you might want something stronger. I would try to find an 8 1/4 or 8 3/4 for it. your 7 1/4 should live till you find one. you can probably sell the smaller SG and recover much of the cost of a bigger rear.
 
it will live a very long time behind a driver
but if you race it, or do hole shots / burnouts, it will not last so long
 
I am in the process of pulling out my 7 1/4 today. It made it threw 4 years of driving with me behind the wheel and a 360 that has some goodies. I had it at the track twice and went three two sets of tires. I am not trying to contradict these guys but from my experience as long as you are not hooking up then it will be fine.
 
65Valiant, i sure will the only thin id keep is the 10 inch drums unless i find an 8 3/4 thats got all the small bolt hard where already. Powerwagonpaul i have a complete 8 1/4 abody rearend out of a 74 dart but i want to keep the small bolt pattern i have now is the only problom.
 
Had the same,3.23 SG in a 67 Dart 100,000 + miles still in it when I sold the car. The car was a automatic. A 4 speed,,, It may break parts. CharlieS drag races his .
 
What is it that makes 7-1/4 rears weak? Do the gears themselves not hold up, or do the axle shafts snap? All of that? Whats the deal?
 
Just to piggyback this thread:
I've never really messed with a rear end.And I've never built anything with high torque. I have a 7.25 rear in my swinger. That should do just fine as a DD if I just restore and clean up the /6 right? For a DD, would it even be worth it to swap to an 8.25?
 
i have one behind the 349/904 in my dart.it seems to be doing just fine.however i think if i had a 4 speed or some fatter tires it would go bye-bye with enough abuse.
 
I want to keep the set of really nice small bolt ralley wheels that are on it. plus its got the bigger 10 inch drums all around. I wondered about it hooking up it has 235 60 14 on the rear & itll turn em for a little bit then hooks rite up. I think the higher stall & lower tranny gear set will really be pushen it. Im not maken it a drag car or anything just squeezen every last drop out of my combo. Its how i roll!
 
Darter6 said:
Had the same,3.23 SG in a 67 Dart 100,000 + miles still in it when I sold the car. The car was a automatic. A 4 speed,,, It may break parts. CharlieS drag races his .
Click to expand...

X2
I ran 235/60/14 on my last Duster, the tires would spin, not hook.
The rear end never gave me any issues.
It had about every engine combo in it.
6 / 904 stock 70K miles.
Ex wife locked the 225 engine up on a 120 mph run.
Put a 318/727 in it, she ran that motor until it smoked bad.
Dumped in another 69 318 and a 3-speed standard trans, clutches became an issue.
Put a serious high reving 318 .060 over 4-speed in it.
I got the car back in a divorce, she held the throttle wide open on the motor trying to blow it.
The rear end still worked after 10 years of abuse. I had a spare just in case but did not need it.
The key was it spun the tires not hooked up.
 
Without the stall convertor it would be ok. With the stall it is like dropping the clutch on a 4 speed she wont live long.
 
I ran a 3.91 SG 7 1/4 rear in my drag car for many, many years. Just took it out last fall. Did not break it. The SG clutches finally started slipping. The weak part of the 7 1/4 is usually the spider gears. There are only two of them in a "open" rear, and the cone type SG. The Clutch type SG has 4 spider gears. IF the 7 1/4 was the clutch type SG I would not have a problem using it with an auto trans. I would not consider a 7 1/4 with a stick trans. Shocking the rear will kill it.

PS: Hypo65, You cannot put the wide ratio planitary gear set in a 65 down 904.
I'm not sure about a 66 or 67 trans, yes on a 68 up 904. I think on a 66 or 67, you need to change the output shaft also to use the wide ratio gears. That is why you can't do it on the 65 down, the later output shaft can't be installed in the early case. You will also need a fine spline converter to use the wide ration gear set. Then if you have a 64-67 273 the converter needs the small dia pilot to fit the crank.
 
4spdcuda66 said:
What is it that makes 7-1/4 rears weak? Do the gears themselves not hold up, or do the axle shafts snap? All of that? Whats the deal?
Click to expand...

with a small 7 1/4" ring gear, you have a very small pinion gear, and teeny tiny little end gears (the ones that the axles fit into, and the ones that rotate inside the carrier) the smaller the gear, the weaker it is
 
caferacerx said:
with a small 7 1/4" ring gear, you have a very small pinion gear, and teeny tiny little end gears (the ones that the axles fit into, and the ones that rotate inside the carrier) the smaller the gear, the weaker it is
Click to expand...

Gotcha. Thanks.:thumblef:
 
In short, yall play around with your little 7.25s. I'll be wavin at you when I drive by in something with an 8.750, or 8.25.

I'm not backin off my opinion. Yall do what you want, but the FACT is that stock slant six cars BROKE 7.25 rear ends. They are weak, sure grip or not and I don't give a rat's *** who tells you some who shot john about how long they ran one behind ten thousand horse power for 150 years, the FACT is if you run a 7.25 behind pretty much anything with any semblance of power, you may end up walking. "I" am not going to ever stand up and tell somebody on here or anywhere else how "good" a 7.25 is or that they should run one. Because they SUCK.

Some may say something REALLY stupid like "the rear tires break loose so the rear end will hold up". Lemmie clue you in on something. Ever heard of spider gears? Got any idea how fast they turn? The answer is REAL FAST. And here's a little physics lesson for you. The smaller the diameter of a gear, the faster it's spinnin. Get me? Here's some more physics for you. Even if it's a sure grip, the axles CAN spin independently of each other. Got any idea how fast ONE SIDE axle and spider gears turn? That's right, follow along with me. There are two axles so that means if only one is spinning, it's spinning TWICE as fast as both together. Yeah. It's COOKIN. And on that TINY LITTLE cross shaft that the spider gears ride on building up all that heat.

The 7.25 is the smallest most fragile rear end from Mopar. They will tear up if you sneeze on them good. Just because some few got lucky doesn't mean it will always happen. But believe what you want and good luck with that. lol

I'll put it like this. If ALL I had was a 7.25 under my car, I would wait until I swapped it out before I drove the thing. Simply because I don't like walkin.
 
caferacerx said:
with a small 7 1/4" ring gear, you have a very small pinion gear, and teeny tiny little end gears (the ones that the axles fit into, and the ones that rotate inside the carrier) the smaller the gear, the weaker it is
Click to expand...

We have a winner. Not only the weaker, but the FASTER those little weenie gears spin and the more heat they build up.
 
Charrlie, We did the gear swap in a "67" 904 case and yes you have to change the front pump/input from a 68 up. Can't say about a 66 case for sure.
 
I had it behind my 273 Commando for one summer. It held up. I was an open 2.76 ratio. I had 255/60 14 tires. Since I already had an 8 3/4 waiting to go in I drove that 7 1/4 very hard and had no problems at all. Had it at the track etc. Anyway, I do feel al lot safer with the 8 3/4 that I know can take any abuse. But surprisingly that little 7 1/4 held up.

Good luck!
 
Hipo65, the only way you can still use your SBP wheels on an 8 1/4, would be to redrill the axles and drums, but im not even sure that would work as I have never tried it or know anyone who has.
 
CharrlieS yer rite on the no-go gear swap, the splines on the output shaft are diffrent 'bummer' but i do have a small pilot 2500 corse spline converter built ready to go after i overhaul trans. Guess ill shelf the gears for now. But here once it starts throwen snow i probbly will pull the diff & put er up for sale & keep my eye out for 8 3/4 diff.
 
I would just add my 2cents, switched my 65 formula s from a 7 1/4 to a 8 1/4 rear for the reality of being able to put 14 inch rally wheels and better grip! I drag raced hard back many years ago with a 66 cuda 318 motor ran high 12's finally blew my 7 1/4 rear away! It was the weak link for sure! I had a 8 3/4 rear built for it and it became the strong part of the car! My current 65 runs strong and also 318 not quite so fast yet as it is just a road car, fun in the sun! However, we went to the better rear for a good reason as safety and potential speed down the line was our ideology when building this big boy toy! Also the bigger rears have more parts to play with!!

65Cudalover
 
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