7 1/4 rearend longevity

[furz4444]

I have a 7 1/4 rearend in my dart running 2.76 gears. Mild built 318 and 904 trans. Engine has duals, no headers, mild cam, 600 holley on a old streetmaster intake. Heads are small port standard 318. Car runs realy good as is and I am able to get ove 18 mpg, think I could get 20 with headers and better carb. I am working on narrowing an 8 3/4 for this car and hope to be done later this summer. What I am wondering is how long will this little rear end live with street driving, I do drive the car alot during the summer, sometimes 3 or 4 hours from home and I don't want to end up stranded somewhere. Once and a while I do run it pretty hard but it will never see any regular racing. Was wondering what other experences people had using this rearend as I have seen spider gears go out on these behind slant sixs on occasion. It has made it 80k in the car as a standard 318 2BBL already. Anybody care to speculate how much of a chance I take to continue to use this.

[ehostler]

Stay away from hard launches and you should be fine.

[dodger1]

I agree with Ed.My 7 1/4 lived behind the mild 360 (carb, cam, headers) in my Mirada for 2 years and was in the car for 120,000 kms before that. Of course it had 2.26 gears but I still think you're OK till the 8 3/4 is done.

[it's all dodge]

My 7 1/4 made it to about 160,000 miles, then broke 150 miles into a 600 mile trip. It was behind a stock 225 /6 with three on the tree. I didn't do a bunch of tire spinning either. But the week before it went bad, I could here it making more noise, I knew something was up

[Jack_440 Savoy]

Years ago I had a 64 Valiant 273 4 speed that I raced a Lot and it "Took It" right up until 8# psi with M+H RaceMasters. I was Lucky it lasted as long as it did. But, With a "auto" I wouldn't worry about it unless it's your daily driver.

[MrChemist]

I had a 7 ¼ a long time ago when my car had a mild 318. Just days after breaking in the motor I turned a corner, mashed the loud peddle and completely destroyed the rear end. The car has had an 8 ¾ rear end ever since. Be mindful of the throttle and you should be ok until the 8 ¾ is bui

[360duster74]

So it would be a good idea for me to get a 8 3/4 rear end in my cammed 360 duster that is backed by a 7 1/4? How much do the 8 3/4 rear ends go for?

[1973Swinger]

Dont count the 8 1/4 out if you cant find a 8 3/4 for a decent price. With some upgrades the 8 1/4 can hold up pretty well to a smallblock. As far as a 7 1/4 goes, I have one in my 318 2bbl Swinger, which has about 80k on it and its seen some abuse. Even though it doesnt make any noise or anything, I wouldnt trust it as far as I could throw it though and have a built 8 1/4 waiting to go in.

[dodger1]

One of the mags (sorry, can't be more precise) had a write-up on the Dakota 8 1/4's which actually have a slightly larger ring gear and beefier axles, etc. Apparently they are pretty strong units and the width suits A bodies as well as FJM's. I replaced my 7 1/4 with a cop 8 1/4 and a new Auburn plus bearings. No probs in 4 years, but I don't race with it - just a driver.

[360duster74]

I was reading on the 8 3/4 rear end thread in the Tech Archive and it said the 8 3/4 was made up until '74. I didnt see them mention anything about any A body 8 3/4 rear ends for 73 or 74's, all the applications for A bodies were only mentioned up until '72. If that is true, am I safe having my 7 1/4 behind my 360 in my '74 duster or do I need to upgrade ASAP?

[360duster74]

Anyone have this problem or are the 7 1/4 rear ends from 74 and on more reliable?

[Challenger72360]

If this is repeat knowledge, sorry, I thought '73'74 Dart/Duster came w/8 1/4 behind V-8s. I have found my 8 3/4 cases in '72 down A bodies with small bolt patterns, and have had C body axels cut down to fit the case. I had Mosier cut my axles, I would order thier axels though(they know exactly what you need), I twisted the end of one of mine, hardness is gone because of cutting, I keep it to use to mock-up A body 8 3/4 builds.

[Challenger72360]

360duster74, I had a '74 7 1/4 fail in about 6 months(4000 mi.)behind a very mild 318.

[Challenger72360]

360duster74, I had a '74 7 1/4 fail in about 6 months(4000 mi.)behind a very mild 318.

[360duster74]

Well Challenger, the car originally came with a 225 /6. So thats my reason for asking. Sorry I didnt add that info.

[rumblefish360]

Originally Posted by 360duster74

So it would be a good idea for me to get a 8 3/4 rear end in my cammed 360 duster that is backed by a 7 1/4? How much do the 8 3/4 rear ends go for?

360duster74 Anyone have this problem or are the 7 1/4 rear ends from 74 and on more reliable?

360duster74 I was reading on the 8 3/4 rear end thread in the Tech Archive and it said the 8 3/4 was made up until '74. I didnt see them mention anything about any A body 8 3/4 rear ends for 73 or 74's, all the applications for A bodies were only mentioned up until '72. If that is true, am I safe having my 7 1/4 behind my 360 in my '74 duster or do I need to upgrade ASAP?

It would be a great idea to get a 8-3/4. Expensive, but worth it. Like said above, do not count out the 8-1/4. It is a fine rear. Also, yes on the Dak's slightly larger ring gear. I think I read 8-3/8's.

7-1/4's did not change in strength from year to year.

The 8-1/4 replaced the 8-3/4. It was a cost effective move. The 8-1/4 has proven itself worthy for what the factory does with it for many many years now.

If I was in your socks, I would drive the 360 easy until I find a suitable replacement. It's not "If it brakes" but really the case is "How soon it will brake."

Search the for sale ads on the rear and search E-bay for the rear.
8-1/4's have a nice end reason to use them. Sure grips (Posi for the GM crowd out there) are about $200 new, parts are made new and are off the shelf near everywhere and axle ratios are wide and varied. Only pennys cheaper than a 8-3/4 at best.

Look through this site and others like it to see whats out there.

Also, the intail expense of the 8-1/4 is alot cheaper. You can get them in J-yards easy and cheap. Not so with the 8-3/4.

Click here; http://www.ringpinion.com/
&
http://www.auburngear.com/

[1973Swinger]

Originally Posted by Challenger72360

If this is repeat knowledge, sorry, I thought '73'74 Dart/Duster came w/8 1/4 behind V-8s. I have found my 8 3/4 cases in '72 down A bodies with small bolt patterns, and have had C body axels cut down to fit the case. I had Mosier cut my axles, I would order thier axels though(they know exactly what you need), I twisted the end of one of mine, hardness is gone because of cutting, I keep it to use to mock-up A body 8 3/4 builds.

I thought the same thing until I looked under my 73 Swinger. It is a factory 318 car but has a 7 1/4 under it with big bolt pattern wheels. Strange, but true. I dont know if its an oddity or if someone stuffed a 7 1/4 under it for some reason at some point. My fender tag should tell me what it came with originally for a rear end right?

[rumblefish360]

I do think it will tell you what it came equiped with. I'm not a numbers guy, but the 7-1/4 did come behind 318's stock.

[BigBlockDude]

My 79 Lebaron with a factory 318 4 barrel had a 7 1/4 and about 140,000 miles when I got it. It broke 3 months after. It was all highway miles before. I then put in an 8 1/4 from a cop car, ran it pretty hard at times and fried the posi, but it never broke.

[Jacksdad]

Okay - why, when I had no time (or money), were there a bunch of Aspen and Volares in the wrecking yards, but none since I started looking for an 8 1/4" for the Duster? What I did see though were a whole lot of Dippys and 5 Avenues with 8 1/4s. Lying on my back trying not to p**s off the black widows, I took some rough measurements (total width from flange to flange, and spring center to spring center) and compared them to the one and only Aspen, which had (of course) a 7 1/4, and a Valiant with the small rear end and found this;

M body 8 1/4 - 60 1/2" flange to flange, 44.5" spring to spring

F body 7 1/4 - 59" flange to flange, 44.5" spring to spring

A body 7 1/4 - 55 1/2" flange to flange, 43" spring to spring

I know the F body will fit the A body with the stock spring perch location if you don't mind spreading the springs a little, but it seems the M body rear has the same spring spacing, but a little more total width, which to be honest I don't mind as the Duster rear is too narrow anyway. My question is, has anybody used an M body rear in an A body without problems?

[pishta]

My stock 65 7 1/4 lasted all summer behind a little over stock 340 auto with 11 inch wide tires. Big burnouts, donuts, throwing it in park at 15 mph, fat chicks..you know, all the normal high school stuff It took a neutral drop rolling backwards in a turn to destroy the ring and pinion gears, spider didnt fail.

[Rug_Trucker]

Ford Explorer rears. I saw one with 3:73 and posi with disc brakes $100 at the bone yard. Or Maverick, Comet, Monarch, or Granada rears. My neighbor has a 75 Maverick 4 door he wants to sell for $100.

Big bolt 7 1/4's are normal in 73's.

[Rug_Trucker]

I have a '66 B body 8 3/4 to put in. Narrower than a regular B body.

[pishta]

Originally Posted by Rug_Trucker

Ford Explorer rears. I saw one with 3:73 and posi with disc brakes $100 at the bone yard. .

That would be slick, what are the perch measurements, total width? Do the Calipers have E-brake provisions?

[Rug_Trucker]

I think it is the same width. Yes I would get the cables and the sway bar! Fab some mounts for the sway bar.

It is also a bolt on cover, so get a chrome or aluminum cover. Lie to everyone and say it is a Dana 60.

[pishta]

Looks to be 58.5 according to another reference with no perches, but the pinion is offset 4 inches to the passenger side, is that more than a stock 8 3/4?

[Stoga]

Originally Posted by pishta

It took a neutral drop rolling backwards in a turn to destroy the ring and pinion gears, spider didnt fail.

Did you have one of the ones with the sure grip? Those are supposed to be tougher.
I know that it took about 2 weekends of use at the strip in my old 72 Duster, 318 with a 4 barrel to break the axle. The replacement 7 1/4 only made a few passes before it did the same.
I broke it by leaving off the brake and stabbing the throttle from about 1400 rpm, no neutral drops or anything severe.

[Rug_Trucker]

Originally Posted by pishta

Looks to be 58.5 according to another reference with no perches, but the pinion is offset 4 inches to the passenger side, is that more than a stock 8 3/4?

Ask me how to rebuild a Thermoquad or BBD. Rearends? No clue. I gotta drop an open 3:91 into the '66 B body rear.

[pishta]

Originally Posted by Stoga

Did you have one of the ones with the sure grip? Those are supposed to be tougher.
I know that it took about 2 weekends of use at the strip in my old 72 Duster, 318 with a 4 barrel to break the axle. The replacement 7 1/4 only made a few passes before it did the same.
I broke it by leaving off the brake and stabbing the throttle from about 1400 rpm, no neutral drops or anything severe.

Yes, it was a sure grip and it had tall gears, like 3.73 or whatever the 7 1/4 came optional with. I replaced it with a 2.76 and it was WAY different.

[5thAve]

My 7 1/4 lasted a while with my 360 but I ended up changing it after the transmission died again. I wouldnt worry too much about using it with the 318 for a while.