8.25 vs. 8.75?

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413barracuda

413barracuda

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Hey Folks,
I am new to the site and have a opinion question for y'all. I have a 68 barracuda with a 413 wedge,727, purple cam,750 holley,and headers. It has a 8.25 now I think, but inherited a 8.75 with 2.76 ratio,new axles,11" drums when I bought the car. Should I change to the 8.75 or run the 8.25 as long as it lasts?
 
What gears are in the 8 1/4 and is it an automatic if it's an auto and you don't go pounding the crap out of it it'll probably last. Also which 8 3/4 is it, 741,742 or 489. Look for the casting number on the bottom of the nose (just below the yoke) last 3 digits. If you do switch to the 8 3/4 you'll have to have the drive shaft shortened.
 
Some times less is more, 8 1/4 gives you HP and takes less HP to use it...
8 3/4 :burnout: is stronger :glasses7: If it's not needed, why change :happy1:
 
Yeah it's a 727 from TCI. The casting on the 8 3/4 is 489. I was told the 8 1/4 that is in it has 3.73 gears. It runs good now with no noise, except the driveshaft I think is too short now. There is a little sound from it at the tranny tail shaft.Thanks for the feedback!
 
Just don't beat the 8 1/4 to much. Have the 8 3/4 ready for when the
little axle go's south.
I've seen 8 1/4 last along time behind a stout small block.
 
memike said:
Some times less is more, 8 1/4 gives you HP and takes less HP to use it...
8 3/4 :burnout: is stronger :glasses7: If it's not needed, why change :happy1:
Click to expand...

This is generaly incorrect. The amount of power difference to turn the larger rear is less than 1 HP. The bennifit of the smaller rear is an ever so slight weight difference and sometime the cost of the ring and pinion/set up parts. That is it.

The draw back is a lower HP/Torque ceiling in power handling terms.

The 8-3/4 can withstand 600 plus HP all day long. It served my buddy well in his all steel 69 Dart into the 9's for years. 500 cube roller camed, Indy headed monster.

tractorfix said:
I've done EVIL things to 8.25's. They can take a lot.
Click to expand...

I agree. The 8-1/4 can take a good amount of power. But the question is how much power are you putting out. Honestly, I do not know the ceiling of it's limits. But I do know it'll take a Duster w/a 400 into the 11's for a long time.

I would yeild at around the 500 HP mark.
 
I would say they are pretty close performance wise, but my question would be regarding the bolt pattern. All 8 1/4" are large bolt pattern, so is your front assembly large bolt also? That would explain why the 8 1/4" is in there instead of the 8 3/4". If the front is small bolt and the 8 3/4" is small bolt also, I would change to all the same to avoid having to carry 2 spare's. If the 8 3/4" is large bolt, then the axles have been either redrilled, resized or are aftermarket unless it is an early B body rear. A little more info would be helpful to determine the best combination for your set-up, but all things equal, the 8 3/4" is a superior rearend for a couple different reasons. First, the center section is easily interchangeable, and the larger ring gear is stronger as is the pinion shaft from the 742 and 489, and the variety of different centers and gears and they're availability is to me more desireable!! JMO, Geof
 
I wished I put my money in to an 8 3/4 axle years ago. I went with 3.91's in my 8 1/4 alxe and took the axle out and they cleaned , painted it. Cost $750 over 10 years ago. Now I'm stuck with the 3.91's, if I had an 8 3/4 I could easily remove the center and have different gears. Now I either have to drive the car 50 mins to my trans shop or worst yet remove the whole axle and lug it up there in a POS car.

So if you going to change axles why not get the better-easier to work on 8 3/4 ?
 
I have beat my 8 3/4 with a big block and a four spd for almost 30 years. My motors has always been kinda mildly built 383's probably around 400 hp or less but I have never had a problem.
 
The other draw back of the 8-3/4 is the price of the whole rear ham/center section.
That is why I stay with the 8-1/4. Gears and parts are 1/3 the price of an entire 8-3/4 center section.

Of course, the 8-3/4 in my Cuda will never leave....unles a DANA is in order.
 
couple thoughts here if your just running street tires you will probably never break that 8.25 even thought the motor is large and has a huge power potential if it cant hook up there is not a lot of pounding especially with a 727 trans. the 8.75 rear is a brutally strong piece. is this rear(8.75) a a body rear if it is its a direct bolt in accept the drive shaft. then you have to deal with the small a body bolt pattern. you can buy axles to get the bigger pattern but then again if your not running slicks its not going to be a issue also the wheels you now have wont fit .witch brings me back to the 8.25,why change it if your not going to run slicks.even if you run slicks it would be hard to break the 8.25 in my opinion.back to the 8.75, to give a idea of how strong these rears are when rick hendrick started racing his shevys with geoff bodine driving and even when K shrader raced for him they used a chry 8.75 rear with only oiling mods rick said the ford type cost money to modify to get to the level of the chry rear. nascar made a rule that all manufactures must use a 9 inch ford type rear.(they claimed after modification they were safer ahhhhh ok).i agree with rumble here the pricing of the parts, the power loss on the 8.75 is very minimal
 
I've always like to play things a little safer. When I built my 71 Swinger, (started out as a /6-904-7.25 combo, I went to a crate 360-727-dana 60. It was over kill for the power train, but I feel that I never taxed the rear.

More importantly, I salvaged the Dana from a Roadrunner that was wrecked at about 42,000 miles, and it was free!
Having the Dana narrowed and having the spring perches and shock mounts relocated was still less costly than either purchasing a new 8.75 or rebuilding one. I never considered the 8.25 back then, but I suppose it would have still been more costly than modifying the Dana (I think).

For the 72 Swinger, (originally a 318 car) I did use an 8.25 to back up the mildly built 318/727 combination. Back then I was a little hesitant about it, but it's proved to be an excellent piece.

I did have an 8.75 Sure Grip in my 73 Fury III wagon, behind a 400/727 combo when I lived in Jersey. it was an excellent snow mobile, and I could always rely on it to get me from Clifton to Secaucus for my job during snow storms.

Now that I live in Georgia, I found out that "snow" is a four letter word, here. If the word "snow" pops up in the weather forecast, you will not be able to buy milk bread, eggs, or bottled water, schools will be closed, and so will most places of employment!
It doesn't have to snow, mind you. They just have to say it might. lol
 
The 8.25 is not a bad rear, it just is what it is. I like to overbuild things so upgrades are never an issue. It's hard to argue with bulletproof.
 
I've seen chevy guys run Chrysler 8-3/4 rears before.
(2 even ran the 727)
 
I believe the axle shafts on the 8-3/4 are stronger, and the bearings don't ride directly on the axle in that rear. The 8-1/4 is a c-clip rear end that the bearings ride on the axle shafts if i'm not mistaken. On the plus side of the 8-1/4, a lot of light duty trucks used them.
Since you have it, I would certainly switch to the 8-3/4 and be done with it. Are you sure the rear you have isn't the 7-1/4 under there now ? The covers on the back are very different looking.
 
:burnout:Thanks for all the input. As of right now I am going to keep the 8.25 in and build the 8.75 to have in case I trash the 8.25. I don't know the H.P. of my engine and am only going to run street tires for now. Who knows if I'll ever run it on slicks. Thanks again!:blob:
 
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