Non A-body mopar question

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1968 Dart 270

1968 Dart 270

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I just looked at a 67 Coronet 440 that's low mile. Has 318 with torqueflite. I was doing some research online and a couple folks claimed their 67 or 66 coronet came with a 7 1/4" rear end. My question is what determined which cars got the weak rear end? One person stated that all 318 cars got the 8 3/4" but then a couple guys wjth 318 cars claimed.theirs also had 7 1/4" reads. Given that many here say the 7 1/4" was even too weak for the smaller dart with 273,Why would Chrysler put that weaker rear in the larger bodied coronet with 318?
 
Well I wouldn't want one. I've had f bodies (Aspen/volare) with that rear and my first Dakota with a non magnum 3.9 had one and I blew it to smithereens not even being hard on it.
I replaced it with an 8-1/4.
If the car is otherwise nice, and the price isn't crazy id buy it even if it had a 7-1/4 but would looking for a better rear end constantly until I found one, whether I blew the 7-1/4 or not.
 
O.p., did you look to see (or ask the owner) what rear it had?
Real easy (REAL easy) to tell a 7 1/4 from an 8 3/4. Smooth round backside, 8 3/4, cover on the back with bolts, 7 1/4.
Unless you are planning an engine swap, a 7 1/4 could be fine. Of course an 8 3/4 is preferred.
 
We all have experienced or heard of car guys scattering a 7 1/4. I wonder what the rate of 7 1/4 failures was when they were newer, 3-10 years old?
A friend of mine has a 66 Coronet, originally a 225/7 1/4 car.
 
33IMP said:
O.p., did you look to see (or ask the owner) what rear it had?
Real easy (REAL easy) to tell a 7 1/4 from an 8 3/4. Smooth round backside, 8 3/4, cover on the back with bolts, 7 1/4.
Unless you are planning an engine swap, a 7 1/4 could be fine. Of course an 8 3/4 is preferred.
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Yes,it's a 7 1/4". Very easy to identify.
 
Did they stop using the 7 1/4" rears in B Body cars like the coronet and satellite I'm 1968? I think in 1969 that the 318 cars had 8 1/4" rears or the beefier 8 3/4" depending on engine,right?
 
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Is what rear end in the car going to make or break you buying the car? Sure the 7 1/4 is the weakest of the three rear ends mentioned in this thread so far. And yeah peeps love to chime in saying how their 7 1/4 didn’t last long. Who knows how long that 7 1/4 has been in the car? If it rolled off the assembly line with it then it’s lasted 57 years already! Prolly good for another few years. Maybe it was put in 45 years ago? No one here can definitively say what came in that car nor claim when/how that rear end will crater.
 
1968 Dart 270 said:
I just looked at a 67 Coronet 440 that's low mile. Has 318 with torqueflite. I was doing some research online and a couple folks claimed their 67 or 66 coronet came with a 7 1/4" rear end. My question is what determined which cars got the weak rear end? One person stated that all 318 cars got the 8 3/4" but then a couple guys wjth 318 cars claimed.theirs also had 7 1/4" reads. Given that many here say the 7 1/4" was even too weak for the smaller dart with 273,Why would Chrysler put that weaker rear in the larger bodied coronet with 318?
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Because it was fine behind a 318, most people that bought a 318 car were using them as family trucksters.. if i was just making a car to drive and not beat on i would change the oil in it and use it. it probably made it 100k already without breaking..
 
BTW.. '67 coronet was my very first car... slant 6.. got it for free and put in a $11 timing chain and drove the piss outa it :)
 
In my 55 years of street driving, I've had quite a few cars with 7.25s/and autos and have never even hurt one of them. One of them even had a high-pressure, 340-2bbl with headers.
Now transmissions, those I have blown up.
 
Icetech said:
Because it was fine behind a 318, most people that bought a 318 car were using them as family trucksters.. if i was just making a car to drive and not beat on i would change the oil in it and use it. it probably made it 100k already without breaking..
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In my opinion, this ^^^^ is the correct answer to your question. For a driver you can enjoy.


Now, if you're planning a swap to a high-suds 340/408/440/500 a swap is certainly in order.
There are many upgrades possible/available. 8 1/4, 8 3/4, 8.8, 9 1/4,Dana 60. Other than the 8.8, and the 9 1/4, direct bolt-in can be found.

Personal preference? For an inexpensive, high strength rear with great parts availability, an 8.8 is hard to beat.
 
My question was what determined why some 66-67 coronets with a 318 and torqueflite got a 7 1/4" rear and why others with the exact same engine and trans got an 8 3/4" rear.
 
Murray said:
7 1/4' not too weak for a 318.
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According to many here it is too weak for even the 273. My 68 Darts rear end just failed and it's a 273 with auto and I never beat on the car even once. It just failed being driven normally down the street to work. I'm sure many of the rears did hold up though because many of these cars have 200k miles on them.
 
1968 Dart 270 said:
My question was what determined why some 66-67 coronets with a 318 and torqueflite got a 7 1/4" rear and why others with the exact same engine and trans got an 8 3/4" rear.
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Very likely based on ‘owners desire’. Back then you could pretty well custode your car with any option. Sometimes the type of rear end was included in an option package if ‘heavy duty cooling’ or ‘towing package’ or ‘heavy duty suspension’. Or if you wanted a certain ratio rear end you had to get a different type of rear end. These days cars can’t be customized nearly as much without a package including dozens of items. And perhaps it was a dealer/fleet/promo order vehicle?

Point is you’re not going to know the answer 57 years later unless you know who checked off the boxes of the order sheet for that car.

Will it rain on September 28, 2356?
 
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Some of these cars are pushing 60 years old. Even with regular maintenance how long are wearable parts expected to last? I had same car, 67 Coronet 440 318 car that was swapped to 383. Can't remember what rear was in it, but never had a diff issue.
 
1968 Dart 270 said:
According to many here it is too weak for even the 273. My 68 Darts rear end just failed and it's a 273 with auto and I never beat on the car even once. It just failed being driven normally down the street to work. I'm sure many of the rears did hold up though because many of these cars have 200k miles on them.
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Sometimes mechanical things just fail. Did you put all 200k miles on your 68 Dart? If so and there was no one event you recall that would have severely stressed it over the last 57 years then chalk it up to metal flaw.
 
Shoot, one teenage burnout 50 years ago could put a diff on the die list decades later.

As far as 7.25’s go, I did multiple 100 yard burnouts for 5 years behind a 318 and then 1 or 2 years with a bit over stock 5.9 Magnum and the 7.25 never blew up.
(Yea I felt pretty lucky)

I thought 7.25’s didn’t come in Coronets at all. Hmm
But I’m not a Mopar historian either, so there’s that.
 
TrailBeast said:
Shoot, one teenage burnout 50 years ago could put a diff on the die list decades later.

As far as 7.25’s go, I did multiple 100 yard burnouts for 5 years behind a 318 and then 1 or 2 years with a bit over stock 5.9 Magnum and the 7.25 never blew up.
(Yea I felt pretty lucky)
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same here, i've done miles of one wheel peels in clapped out 318 cars with 7.25's and never had a problem. but those were all with like 195/70-14's that were hard as rocks.

same situation knocked on a set of 215/60's and scattered the thing goosing it on a RH turn.

lost an axle on another at speed while on the freeway. was a crazy lo-miles grandma grocery getter that never saw a lick of abuse.

but precisely to your note, nobody knows the full history. some innocuous event decades ago could've started it on the path that intersects with you JDA on a nice sunny day and the thing having a spontaneous disassembly event.

i said in another thread, these parts were never intended to last this long. they were basic transportation pieces designed to work within a specific set of parameters and we've long since exceeded that. roll on a 7.25 like you roll dice man, at your own risk.
 
H22A4 said:
Sometimes mechanical things just fail. Did you put all 200k miles on your 68 Dart? If so and there was no one event you recall that would have severely stressed it over the last 57 years then chalk it up to metal flaw.
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Nope, 71k Original miles car. Engine ans trans still in fantastic shape. Bought it off the original owner. Guess it's just one of those things
 
TrailBeast said:
Shoot, one teenage burnout 50 years ago could put a diff on the die list decades later.

As far as 7.25’s go, I did multiple 100 yard burnouts for 5 years behind a 318 and then 1 or 2 years with a bit over stock 5.9 Magnum and the 7.25 never blew up.
(Yea I felt pretty lucky)

I thought 7.25’s didn’t come in Coronets at all. Hmm
But I’m not a Mopar historian either, so there’s that.
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Yep,that's true. I have no idea what the previous owners driving habits were before I bought my car.
 
junkyardhero said:
same here, i've done miles of one wheel peels in clapped out 318 cars with 7.25's and never had a problem. but those were all with like 195/70-14's that were hard as rocks.

same situation knocked on a set of 215/60's and scattered the thing goosing it on a RH turn.

lost an axle on another at speed while on the freeway. was a crazy lo-miles grandma grocery getter that never saw a lick of abuse.

but precisely to your note, nobody knows the full history. some innocuous event decades ago could've started it on the path that intersects with you JDA on a nice sunny day and the thing having a spontaneous disassembly event.

i said in another thread, these parts were never intended to last this long. they were basic transportation pieces designed to work within a specific set of parameters and we've long since exceeded that. roll on a 7.25 like you roll dice man, at your own risk.
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All very valid points. You're right. I have no idea what the previous owner drove like. Just that I've tried to be gentle on it since I've owned it. I understand too that they weren't expecting people to still be driving them 50 some years later or that many would have 200k plus miles on them. It's just a shame because the weak link on these a bodies is the rear ends. Everything else is pretty much bullet proof if not abused
 
1968 Dart 270 said:
All very valid points. You're right. I have no idea what the previous owner drove like. Just that I've tried to be gentle on it since I've owned it. I understand too that they weren't expecting people to still be driving them 50 some years later or that many would have 200k plus miles on them. It's just a shame because the weak link on these a bodies is the rear ends. Everything else is pretty much bullet proof if not abused
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The short answer is the 7.25" would've been std. equipment for Slantys & 'teeners, You could always option up in those days, so finding an 8.75" behind them is surely possible as well. 8.25" rears didn't appear 'til '72-'73, so there's -0- chance that was an option in Your prospective ride.
FWIW, I beat the crap out of My '69 Dart Custom w/the Slanty including multiple neutral-drops for over 3yrs, then dropped a cammed 'teener in it & proceeded to burn the piss out of the pass tire with that bootleg 7.25" rear. I left clouds of tire smoke drifting over the cornfields on the ridge, for about a year(w/an auto) I pounded that thing, then I pulled up in front of some other friends of My Bud riding shotgun(BIG guy)...I blocked it up ready to put on a show & 'POP'!!! LOL........later it got a 4spd & 8.75"......but when I pulled the cover..there was almost no gear oil in it...duh...no signs of leakage ever but, who knows if it had been full of lube???
 
If it's as nice as you say, that rear wouldn't stop me from buying it. The 7.25 weakest link was the spider gears when free spinning from water/ice and then grabbing hard. The sure grip axles were stronger then most think, but were rare and good ones are almost non existent these days.
 
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