Scored me an Offy!

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Charrlie_S said:
The 7 1/4 rear is not as weak as most people think. I have been running the same 3.91 SG 7 1/4 since 1974. It has been in 5 different street/strip cars. Now resides in my 66 Valiant that runs mid 13's at 94 mph in the in the 1/4 mile. Has slicks, and does 1.79 60 foot times. Also have a 4.56 SG 7 1/4, and a 5.13 SG 7 1/4.
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could this be because of the shorter gearset having a better carrier??? My 7.25 blew up in normal driving, not even being abused. but it was a tall gear, something like 2.76 i think....this was behind a 360 that was MAYBE pushing 250hp at the time....
-Tim
 
Given the goals you've set the 7¼ should be fine. Mopar put 7¼s on 273 4-bbls with auto trans unless a HD axle was ordered.

One of the advantages of running the smaller axle is lighter weight. This is lighter unsprung weight which translates into better axle control by the springs and shocks. This in turn yields a more controlled ride with less tendency to hop sideways over sharp bumps.

If the 7¼ does fail then consider an 8.75 Mopar unit. The most intriguing alternative I've seen are the 8.8 and 9 inch axles from the first generation Ford Granada, Mercury Monarch, and Lincoln Versailles. Spring perch separation is 43 inches and they are within a fraction of an inch of length of the Mopar units. The Versailles even had disk brakes on the rear. The drawback is that the U-joint on the Ford does not fit the Mopar and vice versa. A good driveshaft shop ought to be able to shorten the driveshaft as well as install the necessary fixtures to allow a viable connection.
 
The 7 1/4 sg are a lot different strength wise then the none sure grip 7 1/4. a /6 can easily blow a non sure grip 7 1/4 but the sure grip equipped ones can take a lot of abuse as it sounds like yo can atest to. I would rather run a sg 7 1/4 then an open 8 1/4. Obiously I prefer the 8 3/4 because of it's banjo style, but the 7 1/4 sg is a lot lighter and better for mpg.





Charrlie_S said:
The 7 1/4 rear is not as weak as most people think. I have been running the same 3.91 SG 7 1/4 since 1974. It has been in 5 different street/strip cars. Now resides in my 66 Valiant that runs mid 13's at 94 mph in the in the 1/4 mile. Has slicks, and does 1.79 60 foot times. Also have a 4.56 SG 7 1/4, and a 5.13 SG 7 1/4.
But I do agree about using a stronger rear, if the money is about the same. On a street type car, I would opt for a 8 1/4. Good deals on "A" body 8 3/4 rears are few and far between. A early Ford Mustang V-8 8 inch rear is a inexpensive and viable swap into an "A" body.
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Whew! Thanks for all the advice on the rear axle. That's a lot to think about. It's a stock 74 4/14 open axle on the back, so I'm sure eventually I'm going to need to at least swap out the gears if not more. I'm pretty sure I'll stick with Ma-Mopar for the rear axle though. So maybe someday I may get an 8 1/4, but I think I might do myself better with a 7/14 SG like Charrlie recommends.
 
Actually, I am not recommending changing to a 7 1/4 SG. The 7 1/4 SG units a few and far between (read pricey), and the early style with the clutches is much better then the later cone type. My statement is if you already have a 7 1/4 SG, or can get one for a relativley cheap price, don't say no. Generally a 8 1/4 or a Ford rear is less expensive, and has more parts available at a reasonale price, and is stronger.
 
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