8 1/4 vs 8 3/4???

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KramerSwinger70

KramerSwinger70

70 Dart Swinger360
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so some of you told me for my daily driver project i should go with an 8 1/4 suregrip for my 360 dart (when it comes haha) anway ive seen a lot of people doin 8 3/4 suregrips with the same engine. what differences would i see as far as performance, mileage, ect if i went with a 8 1/4 or 8 3/4? i need sbp so is 1 easier to find in sbp that the other. thanks!
 
They didn't build 8 1/4 sbp rear diffs, so you have only one choice and that's to go with the 8 3/4. The 8 3/4 is stronger and also a lot more expensive to buy. Good luck.
 
From the factory, '72 and earlier, 8 3/4 SBP. '73 and later, 8 1/4 BBP. Mileage and performance would be a function of the gearing. I doubt there would be a significant difference for any other reason.
 
You could have the axles redrilled and the center hub turned down if you find an 8 1/4 and want to keep the car sbp. Would probably be cheaper than a 8 3/4
 
They did have small bolt pattern 8-1/4 rearend in older lower perf. V8 A-bodies. I remember seeing one in a 68 Dart that was a 273 car. I'm not positive but I think it wasn't until 73 when they went to BBP so any pre 73 8-1/4 will work.

Using a 8-1/4 will probably be a little bit faster and get a little better fuel mileage but it will be a minor difference They will take alot of abuse, especially in a light A-body, but they are not as strong as a 8-3/4. Depends on the power level you have whether or not you need a 8-3/4. I generally figure if it's 400 hp or more it needs a 8-3/4. JMO
 
im gonna run 270 max, prolly. cars a streeter and a weekend warrior essencially. run it at the drags wen i can but itll b a school, work, fun driver
 
Dartnut said:
They didn't build 8 1/4 sbp rear diffs, so you have only one choice and that's to go with the 8 3/4. The 8 3/4 is stronger and also a lot more expensive to buy. Good luck.
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They did have small bolt pattern available with 8.25 in '73 and up cars, a car could still get small bolt pattern if it had drums all the way around.
 
thanson_mopar said:
They did have small bolt pattern available with 8.25 in '73 and up cars, a car could still get small bolt pattern if it had drums all the way around.
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I think you are mistaken. Are you sure that it was a 8 1/4 not a 7 1/4?
They were typically 7 1/4 sbp. slant 6 cars. (9" brakes) non power brakes.
I've never seen a factory 8 1/4 sbp.
If a '73 and up was ordered with power brakes, it automatically got the bbp discs and a bbp rear diff. (regardless of engine)
If a '73 and up was a small block it automatically had bbp discs and rear diff.
I personally own 3 a-bodies '73 and up with 7 1/4 bbp rear diffs.
One is a slant 6 '74 dart sport hang 10 bbp power brakes 7 1/4 bbp.
Two is a '73 scamp 318 manual disc brake bbp and a bbp 7 1/4.
Three is a '74 dart 4 door 318 manual disc brake bbp and a bbp 7 1/4.
All are automatics.
I have 5 '73 and up slant 6 a bodies manual brake cars and all are 9" drum cars with sbp 7 1/4 diffs.
I have seen many more that coincide with this option. (or lack thereof)
All cars are factory equipped and unaltered.
Do you (or anyone else) have any pics or other documentation to the contrary?
I'd like to see it and then i would eat my words.
Chrysler also didn't make a body 8 3/4 rear diffs after the '72 model year and definitely not in bbp either.
Thanks,
Tom.
 
My 69 came with a 7.25 SBP behind a 318 and 904, and ten inch drums. All replaced with 360, TKO and an 8.75.
 
Dartnut said:
I think you are mistaken. Are you sure that it was a 8 1/4 not a 7 1/4?
They were typically 7 1/4 sbp. slant 6 cars. (9" brakes) non power brakes.
I've never seen a factory 8 1/4 sbp.
If a '73 and up was ordered with power brakes, it automatically got the bbp discs and a bbp rear diff. (regardless of engine)
If a '73 and up was a small block it automatically had bbp discs and rear diff.
I personally own 3 a-bodies '73 and up with 7 1/4 bbp rear diffs.
One is a slant 6 '74 dart sport hang 10 bbp power brakes 7 1/4 bbp.
Two is a '73 scamp 318 manual disc brake bbp and a bbp 7 1/4.
Three is a '74 dart 4 door 318 manual disc brake bbp and a bbp 7 1/4.
All are automatics.
I have 5 '73 and up slant 6 a bodies manual brake cars and all are 9" drum cars with sbp 7 1/4 diffs.
I have seen many more that coincide with this option. (or lack thereof)
All cars are factory equipped and unaltered.
Do you (or anyone else) have any pics or other documentation to the contrary?
I'd like to see it and then i would eat my words.
Chrysler also didn't make a body 8 3/4 rear diffs after the '72 model year and definitely not in bbp either.
Thanks,
Tom.
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I have seen a few factory slant six cars with manual 10 inch drum brakes....not 9 inch.....with 8.25 and sbp. And they were for sure 8.25 not 7.25, I know the difference. Chrysler did some weird stuff, it is also said like you mentioned before that they stopped production on the 8.75 in 72, however some earlier 73 cars have been seen with the SBP 8.75's that were left over from the 72 model year but still put in the cars from the factory.
 
73charger said:
would some1 b really cool and fiind me an 8 1/4 sbp? sounds like thatd b easier to swap in than an 8 3/4sbp
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swapping in a 8.25 wouldn't be any easier than swapping in a 8.75, its just the cost involved. 8.75 parts are more expensive and finding the rear end itself is more expensive.
 
thanson_mopar said:
swapping in a 8.25 wouldn't be any easier than swapping in a 8.75, its just the cost involved. 8.75 parts are more expensive and finding the rear end itself is more expensive.
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if i can get an 8 1/4 id be better off. the sure grip differential is like $300 for 8 1/4, $700 for 8 3/4
 
Dartnut said:
I've never seen a factory 8 1/4 sbp.
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Tom I have. I know right now where the Dart sets that has one in it. I have seen many others also that are definitely a 8-1/4 with sbp. They were all pre 72 cars I saw. From your description what your seeing is 73 and up cars.

Also Thanson is right about there being a few 8-3/4's used in 73 cars. They were extremely rare. You'll most likely never find it in the books anywhere that they used a 8-3/4 in a 73 car but Ma Mopar wasn't going to throw away new 8-3/4 rearends left over from the 72 model year so they used them up in early 73's. Again their wasn't many at all, but you can possibly see one. In the nearly 30 yrs. of being into Mopars I've seen 1 that I know for a fact was an all original 73 340 Duster and it had a 8-3/4. That's the only only one I've seen but I have read posts from reliable guys that say they've seen 1 or 2 also.
 
ok, how di know what I have? i looked at it when i was under thecar to remove the tank. did notmeasure it though. 1970 swinger mnual brakes, 318/904..........what is the visual diff between 7 1/4 and 8 1/4? I belive the 8 3/4 kinda looks like a ford 9 inch with the thrid member installing from the front of the axle and a solid housing.........right????? can someone post a picture on here for me???? please
 
mrnurse said:
ok, how di know what I have? i looked at it when i was under thecar to remove the tank. did notmeasure it though. 1970 swinger mnual brakes, 318/904..........what is the visual diff between 7 1/4 and 8 1/4? I belive the 8 3/4 kinda looks like a ford 9 inch with the thrid member installing from the front of the axle and a solid housing.........right????? can someone post a picture on here for me???? please
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you are correct about the 8 3/4....it does look look similar to a ford nine inch with ahe third member removed from the front.

7.25 is easy to tell from the 8.25, just count the number of bolts on the rear cover. If it has 9 bolts then it is a 7.25, an 8.25 has 10 bolts and also has an oval shaped rear cover.
 
mrnurse said:
ok, how di know what I have? i looked at it when i was under thecar to remove the tank. did notmeasure it though. 1970 swinger mnual brakes, 318/904..........what is the visual diff between 7 1/4 and 8 1/4? I belive the 8 3/4 kinda looks like a ford 9 inch with the thrid member installing from the front of the axle and a solid housing.........right????? can someone post a picture on here for me???? please
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Your wish is my command:-D

epnn9d.jpg
 
thanks........now i have to go back and look again but i thinki got the little one....
 
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