7 1/4 as bad as they say

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young gun

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i just bought a 76 duster with a 7 1/4 rear end and the guy i bought it from said that even if i do a small burn out that the rear end would defiantly break. is this true are they really that weak. (i know burnouts are good for a stock rear end )
 
i don't think they are that weak, but i know they aren't the strongest, and for a young gun like you and me, i would definatley swap out for something bigger, possibly the 8 3/4
 
could they with stand occasional burnout.i want to get a 8 3/4 but i do not have the money.
 
Es definayely. If you have a stick dropping the clutch at high rpm's is going to cause alot of problems. My Demon used to have a 7 1/4 in it and with an automatic tranny I did at least 30 brake stands and never even had a problem with it.


Jeff
 
young gun said:
could they with stand occasional burnout.i want to get a 8 3/4 but i do not have the money.
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Not unless it is a sure grip (posi).

I had one grenade on me when I pulled out into traffic (no burn out) after I swapped the stock 2bbl for a 4bbl on a 318.
 
Nothing wrong with a 7&1/4 rear. There were even some 7&1/4 posi units produced. I dont know what horsepower you're throwing at it. If its the original rear its 34 years old and aint broke yet. If it was so easy to break the previous owner would have broke it. I've got one under a 73 V8 car with over 300,000 miles on it, including burnouts, towing, etc..
 
young gun said:
could they with stand occasional burnout.i want to get a 8 3/4 but i do not have the money.
Click to expand...

You could find an 8.25 rear out of a later a body. It would be cheaper than an 8.75 and stronger than the 7.25.
 
The original rear in my cuda was a 7.25. I built the \6 with more compression, a cam, 4bbl, headers and dual exhaust. I drove it that way for about 20K miles and did not hesitate burn rubber and it held up fine. I did swap in an 8.25 in preparation for a hot 360 but if I hadn't gotten the 8.25 for free I would have waited for the 7.25 to break before swapping it out.

I was given a 73 Dart by a co-worker that he purchased new, it had a 318 and a 7.25. This car had over 300,000 miles on it when I got it and still had the original 7.25 and according the the co-worker he never had any axle problems.

Mopar continued to use the 7.25 in the last years of the rear wheel drive cars and 2wd 4cyl/v6 Dakotas through 96. If it was such a poor design it wouldn't have had such a long run. Any axle will break if you exceed it's design limits and the 7.25 is certainly not a performance axle but it's fine in \6 and 318 applications that are not pushing major power increases over stock.
 
7 1/4s are actually pretty strong if the rear gear is a 3.23 or numerically higher (3.55,3.73,3.91,etc.). The only ones I have managed to break were in the 2.76-2.96 range and they usually split the carrier. Add a Suregrip and the strength improves dramatically. I am currently running a 3.55 7 1/4" in my '66 Valiant with no problems so far.
 
I agree that there's nothing inherently wrong with the 7¼ rear. Mopar put 'em behind 273 HP with Torqueflites. I had one in a HP '66 Dart with over 300k on it with no problems. I had another on the back of my '73 that ate a bearing last summer with 87k on it. (In fairness to the axle, I think it had been submerged in water.)

As part of converting the Dart to BBP, I'm replacing the SBP 7¼ with a BBP 7¼. I can't get in to measure without taking it apart, but the BBP axle shafts appear to be larger diameter than the SBP shafts. If that's the case, it could account for the disparity of experiences with the axle.
 
my cuda has one and it's held up to burnouts and drag racing, but thats with out slicks.\\my gear is 3.55 and i run 85/140 lucas gear oil.
don't do any donuts or burn the tires in a corner.
Thats how you break them or any rear end for that matter.
 
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