7 1/4 rear strength

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valiant1966

valiant1966

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Given the growing scarcity(and cost) of 8 3/4 rear ends for A bodies, does anyone have an idea of how much horsepower the 7 1/4 can take and is the Sure-Grip any stronger than the one legger? Maybe share with us what broke yours or whatever?
Everyone talks about how weak and puny they are but just how weak and puny are they? I think a lot of people who may be stuck with no other choices would like to know. Thanks.
 
To give you and some members an idea on this subject my 1970 318 2 barrel equipped with an automatic trans Barracuda came with a 7 1/4 sure grip.... at 140.000 miles my spider gear retainer broke after I beat the chit out of it for 3 years.
I think a standard trans is harder on them.. plus these cars was lite and was not meant to carry 4 people. If these 7 1/4's was rebuilt correctly new bearings (inner and outer and pinion) a stock 318 210 hp and not abused will indead hold up.. I will be going 8 1/4 when and if mine goes away.
 
On my first car, a '63 Valiant 3-on-tree. 170 /6 I went through at least three diff's.

I think to the scrap yards an 8 1/4 rear was worth more in cash than slow moving merchandise during high scrap prices and those diffs are becoming scarce also..
 
This subject has come up a few times in the past. So here again is my take on this... There is no doubt the 7.25 is the weakest of the rear ends in our beloved Mopars, but I am in the group that does NOT believe they are total junk. I had a 7.25 sure grip, 276 gears in my Dart (which started out /6)... kept it in when I upgraded to a 360... Drove it for 2 years that way... and i wasnt always kind to it.. lol.. There was plenty of spirited driving.. took it on a 300 mile trip to the Mopar Nats (twice!), and it was still doing its job when I finally pulled it in favor of an 8.75... While I may be the exception to the rule as far as how well they hold up (especially during spirited driving) I would have to say that as long as you dont have some monster high horse motor in your car and your just driving it as you would drive any other car (and not beating the snot out of it) the 7.25 should hold up... I got a great deal on an 8.75 and couldnt pass it up.. and I always planned to put more pony's under the hood.. so the upgrade was needed.. hope this helps some
 
A 7-1/4 will last if you don't hot rod the car at all and don't happen to turn a corner where one wheel breaks traction and grabs again like on ice and snow. I've got a collection of seven of the things which have spider gears ripped out from either spinning one wheel due to a fast take off or turning a corner on ice with a basically stock 273. I even busted one with a 225 in a 63 Valiant. I have one 7-1/4 that has lasted quite well behind a 273 and now a 360.(driven mildly) It is a sure grip so I believe there is a huge difference between the open and sure grips 7-1/4s for durability. There were thousands of cars with 7-1/4 rears that never broke when driven like the family car they were but as soon as you get one wheel to spin the spider gears tend to rip right out!
 
A 7.25 has no place in any kind of performance build. They were only adequate behind a slant and were beyond their limit behind a base v8.
 
Wow!! Interesting to see all the different opinions and varying amounts of success with the 7 1/4. And yes, the 8 1/4 are getting almost as scarce and pricey, at least in my area.
I like to "drive' my cars but try not to abuse them. At least not too much. lol Great thoughts though. Thanks.
 
I've obliterated 3 of them ( all open rears ) 2 in slant cars, one in a 318. IMHO it's when and how bad it will fail. The spider gears went in all of them.

Now that being said, I've daily driven a 7 1/4 rear for 6 years, 3 of those years with a manual, and 2 years with a turbo installed on the slant and it held up. Have I learned how to drive better as to not kill the rear end? Have I "settled down" and drive like a grandma to save the rear? NOPE, I drive like a wild moron :D Well not exactly but you get the point. Some last, some don't.
Do you have a good lasting 7 1/4 in your car? Beat on it and find out :lol: Just make sure you have a backup or that you can stand it being down for a while...I don't think they are all that bad per se, after all they are 35-40 years old at this point...

Seriously, bigger rears are getting pricey, but keep your eyes open and be ready to jump on a good deal when you find one, they're out there. If you're not a purist look at the phord 8.8 rear swap...I just did one, it's pretty easy, you get disc brakes and a limited slip rear in the process if you buy the right one. I think I paid $200 for the whole conversion, I couldn't resist the benefits vs cost calculation for the 8 3/4 vs the 8.8 but then again, my car is no show car.
ok, my rambling is over ;)
 
First car part I ever broke - in my dad's /6 '64 Dart wagon.
 
Still have mine in and working great! 91 360 with 727 only been a year but it pulls hard and did some great burnouts. Just changed the rear oil and everything looks fine.
 
If you like to gamble the 7 1/4 is the perfect rear end.


Plenty of better options out there though. 8.8 is great if you don't care about having a ford part. 8 1/4s came in lots of stuff, so non a body ones are around. If you got something the right width or close it wouldn't cost much to have someone weld the perches on. maybe you could even find one with rear discs.
 
Let's not remake this thread again. Get a ford 8.8 out of an explorer. Top sticky link. Done deal.
 
memike said:
If these 7 1/4's was rebuilt correctly new bearings (inner and outer and pinion) a stock 318 210 hp and not abused will indead hold up...
Click to expand...

Perhaps this is the key? I don't know very much about differentials, but it occurs to me that wear might increase the stress. Mine has some lash and clunks when shifting from Drive to Reverse and back to Drive. I don't feel anything while driving when I go on and off the throttle, but I wonder if this could be doing any damage.

Did 7.25's break a lot when they were new, or do they break more often after 40 years and 200,000+ miles of wear? Is there any preventative maintenance that will prevent them from breaking in the future?
 
I have a 66 dart and I also had a question about 7 1/4 rear ends. I am swapping a 360/727 into it, everyone says the 7 1/4 is garbage. I'm pretty handy with a welder so would welding the diff make it so it was stronger by eliminating the spider gears from breaking or would this just kill the axles and the pin? How hard would it be to put a 8.8 out of an explorer in? How much would it cost to have shortening... And other things don't to make it work.
David
 
David66dart said:
I have a 66 dart and I also had a question about 7 1/4 rear ends. I am swapping a 360/727 into it, everyone says the 7 1/4 is garbage. I'm pretty handy with a welder so would welding the diff make it so it was stronger by eliminating the spider gears from breaking or would this just kill the axles and the pin? How hard would it be to put a 8.8 out of an explorer in? How much would it cost to have shortening... And other things don't to make it work.
David
Click to expand...

If you are a good welder than pull an 8.8. Out and grab an extra passenger side (might be drivers side) axel and take it home. Lop off a few inches from the longer side to make them even. Weld up your spring perches and have st it. 7 1/4 can last a while but it could break that afternoon. I ran around with a 360 in front of my old 7 1/4 and I drag raced on street tires and did countless burnouts. I got super lucky.
 
doogievlg said:
If you are a good welder than pull an 8.8. Out and grab an extra passenger side (might be drivers side) axel and take it home. Lop off a few inches from the longer side to make them even. Weld up your spring perches and have st it. 7 1/4 can last a while but it could break that afternoon. I ran around with a 360 in front of my old 7 1/4 and I drag raced on street tires and did countless burnouts. I got super lucky.
Click to expand...
Alright thank you!
 
Still have one in my '74 Duster with 2.76 gears. It's held up to a mildly hopped up 318 auto. Definitely no real power, but been beating on it for about 2 1/2 years now. Many passes at the drag way, and many times more out of town …. LOL It's held up to 14.9 @ 94 mph type of power. I could lose it tomorrow, and the plan it to go 8 3/4 B-body rear which I already have. But for now, it's held up just fine.
 
8.25 with 3.55 gears from a Grand Cherokee or Liberty.
Only about 4 inches total wider and comes with disc brakes/ some with lockers.
Around here they are about 300 complete.
You can even get some money back for the 50 pounds of brackets you cut off.:D
 
I beat the crap out of mine. In fact it leaked oil so about 5 or 6 years ago I just stopped putting oil in it. I beat that thing hard. I tried to break it on purpose a few times. Behind my drag race 360 it got its *** kicked on a regular basis a never even flinched.

When I pulled it out a few weeks ago I kinda wanted to open it up and see what it looked like but I was just to busy and the scrap guy picked it up before I got around to pulling the cover.

Mine musta been a sure grip tho or it welded the spiders its self cuz it burned both tires.
Dont think it would have lasted out the parking lot with my new slicks tho
..
 
The spiders shatter from shock or the cross pin seizes from peglegging. The latter you can install a SureGrip to avoid.
But as to the shocking, autos are waaaay easier on the spiders,cuz you don't shock them the same as dropping the clutch. And the bigger your tire footprint the harder the hit.And the more side gear lash you have, you're just asking for trouble so NO J-hooks.
I blew one up with slanty,big tires, and a 2800TC. And I have driven hard with a 340 auto, and skinnies, for several years, and destroyed the 904 first.. Lucky me I got to learn 904s.
 
My research found that limited slip will take more punishment.
That being said, limited slip 7-1/4” is hard to find in these parts.
 
Limited slip would be nice for the ‘65. That diff needs a going through though. First i need it to move. Was supposed to be this fall, but my customers arent giving me the breaks i need to spend time on it.
The dart 8-1/4” is good, needs seals. It has limited slip. Parts waiting.
 
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