7-1/4 Rears....How Strong?

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pastortom1

pastortom1

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Since we got some input on 8-1/4's, I thought I'd ask about the 7-1/4 rears on A-Bodies.......... I've seen quite a few of these on cars at shows and cruises, and the chrome covers are hard to miss from the back........

Some guys have told me about their Posi's and gears they've put in, and how they really like them for street use..........How about chiming in on these rear ends so we can be a little more educated on the matter.........

Not everyone can afford to change out the rear on their car, sometimes just due to labor costs these days........if they have a 7-1/4, what are their options today? How much Horse Power are these rears capable of handling? What about axles and splines?

Is there any hope for the 7-1/4 crowd?? If you guys have one (or more), I'd like to hear some opinions.......and from some pro's as well.......It's a subject I can't find much info. on here..........

I have one in my '67 Barracuda survivor, and to be frank, I'd like to beef it a little instead of just taking it out.....it's a survivor, and it's important to me to leave it that way.

Come on guys............Let's hear something constructive about these rears.

:read2:
 
I am running a 3.91 SG 7 1/4 rear in my 66 Valiant drag car. These rears will take more abuse then they are given credit for. However they must be in good condition ( remember most of these rears have many, many miles on them). The factory had gears available from, in the 2.0's to 3.91, also sure grip units. The old "direct connection" program had "racing gears" available, in 4.10, 4.56, 4.88, and 5.13 ratios. The sure grips were available in the clutch type and the cone type. The clutch type is the most desireable as they can be rebuilt (if you can find the parts), and they have four spider gears, as compared to 2 spider gears for the open and cone type units.
 
All I can say on the 7's is that you find them often under slant cars and also some v8's that were considered a light duty application. I have a '71 slant car that came with one and had a '73 parts car with a 2bl 318 that had one. The rear does work, but generally has a reputation for issues with any sort of power. Well, having said that, I did read somewhere recently that they had a reputation for going out even under stock slant cars. Think I saw that in an old issue of Mopar Action or something.

There were various gears available for the rears and you might even find a posi for one. In general it seems that if you do have one that goes out you can get another from a fellow Moparite for little or no money just to get it out of their yard as it were. I've seen them for sale here for $25 complete and a chap down the road just got one given to him to replace the one he had howling away.

As far as aftermarket gear and axle availablity you'd have to look at places like Randy's Ring and Pinion perhaps. Axles you could see what strange and mosier have. Generally I am guessing that most will say why bother spending that money unless you are doing a stockish resto when the 8.25 can be had for so little and is strong enough in stock form to take quite a bit of power? You don't have to swap to the later Dakota splined axles. Just depends what you want to build.

Cost wise though don't underestimate your skills on install etc. I picked up a good 8.25 complete rear out of a '73 scamp in the local U pull (self serve yard). Got the complete thing for $100 with the Ubolts and spring plates. Swap is simple with just basic hand tools. Air tools make it faster, but not needed. I did pull the cover off ours, clean it and inspect it, painted the thing, put new lube in and redid the brakes on it. Standard stuff for any rear you are dealing with.

Do a search on the board and you will find my swap write up and others. The only thing I had to do was swap the emergency brake cables from my old rear to the new one as they were a different style and kick myself for not taking the time to unbolt the brake hose off the donor car to the rear instead of cutting it. Hose was a bit pricey at $40 or so (going off memory).

Really a very, very simple swap.

Only other thing you have to do is have your driveshaft sortened by a shop. This cost me $80 to $100. Don't remember now and don't remember how much I had it shortened, but I know I posted it before in the swap write up.


Well, hope that helps at least a bit.
 
I had a 7 1/4 behind my 65 Cuda 340 4 sp car. I had a lot of pass's down the track with it. It was never rebuilt, but checked out with fresh oil. It finally broke when I went to a slick.
 
That's what I'm talking about.............. Naturally, a good slick is gonna do some damage to a light duty...........BUT, a lot of guys have had some good results, and lasting results, from the 7-1/4's............

How much horsepower do you suppose your 340 was putting to that rear?.........and how about that first response to the thread.......How many horses do you suppose you were cranking?

AND.............In my Demo with the 8-3/4, we had to use a double shot of the Mopar lube (with the whale oil or whatever is in there....) to quiet it down a bit and really lube up well................What do you think of the same on a 7-1/4?..........Overkill?........Better safe than sorry?

:read2:
 
pastortom, it was an all stock bottom end 10 : 1 motor with a solid lift sig erson (I think about .5 lift) headers, and a torker II with a 780 vac holley. The 7 1/4 had no posi but I had slapper bars with one side set up real tight so it made the first tire to spin plant hard. The slicks were not very big they did bite hard.
I think if I would of had an auto car the 7 1/4 would of survived the slicks, but I was young (back in 86 or so) and stupid so I never thought just take it easy off the line then get into the gas.

There is no such thing as overkill for a 7 1/4.
 
So all things considered, what would be the maximum horsepower recommended to a good clean 7-1/4 posi?

Does Mopar have a recommendation anywhere in it's records?........What would YOU say.........250? 275, 300? :read2:
 
Burnouts are the enemy of 7 1/4 rears. Especially with 4 spd. cars. The sure grips are stronger but would not recommend repeated burnouts, they are just to weak to handle that stress. Even if you go to the track every so often if you stage without a burnout & baby it off the line you should be fine. My 65 Valiant with original 7 1/4 sure grip & 3.23 has about 225 rear wheel horsepower and I have tempted fate with a few burnouts on the street with no prob. You could probably go up to 275/300 rwhp horsepower as long as your carefull with it. All depends on what you want. My Valiant is a cruiser so I'm fine with the 7 1/4. If I wanted to romp on her everytime I take her out I would want to upgrade to at least & 8 1/4.

Oldschoolcuda
 
I am putting a 71 340 in my 67 Barracuda and am going to give the 7 a whirl. I will be pushing in the neighborhood of 300 HP I hope. I think it has 3.23 gears and did real good with my 273 4bbl. but It only had about 210 hp. I will see how long it will last.
 
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