741,742,489 ??????????

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swifter

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Ok--I'M IN NEED OF HELP BOY'S--My car a 70 Duster with 8-3/4 now has 741 case with 3:91--I'm going to be upping the hp quite a bit and I'm confused with the center section and what to do--Complete street car,Maybe,Maybe once to the track to see what she'll do.I have been told the 489 case is bullet proof but what are the limiting factors on the 741??? If the 489 is the bullet proof case then why do all the aftermarket company's use the 742 case as the basis for replacement cases and center sections??? Has anyone broken a 741??? I know it's the pinion shaft and bearing that are bigger in the 489 but is that true for the 742 case also???? Do I have a concern for my 741 if I'm NEVER going to be putting slicks on it??? I guess I need to know if I should be looking at a different case and center section for security reasons?? Hp right now is 380 to the rear tire and after my motor build i should be seeing 500 hp to the wheels--Once again I need your help and thank you guy's for the teaching--Steve
 
489 and 742 are both stronger than a 741 due to larger diameter pinion shafts and bearings. 489 has the largest diameter and is a straight (non taper) shaft. It's biggest con is it uses a crush sleeve set up (one time use) to set pinion depth. There is a crush sleeve elimination set up but I have no experience with it. 742 uses a tapered pinion shaft which is just slightly smaller in diameter than the 489. It however uses standard shim technology to set pinion depth. You would be pressing your luck with the 741 if you ever caught traction with that much power applied. Either 489 or 742 are much better options at that power level. I had a 742 that survived over a decade with no troubles behind a high torque 440 w/ slicks in a ladder barred 72 Demon street/strip car.
 
I like to tell all the phord 9" guys that Mopar made 3 different 8 3/4 rears yada yada yada, and the smallest/weakest 741 has a pinion width larger than theirs (1.375" vs 1.313"). I'm no expert, but I've never even seen a broken 741.
 
I saw the pinion splined end snapped off of a 741 years ago but he was pounding on her pretty good with a 4 speed and slicks.
 
THANKS guy's I'm sorry the car is a 4 speed but will never have slicks on it--So i take it either everyone has switched to the 742 and no one with a street car has busted a 741---Steve
 
demon seed said:
Sorry Rapom but you got your 742 and 489 flip flopped. The 489 has the tapered shaft.:glasses7:
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Frick I must be gettin senile. Your absolutely correct. And the crush sleeve sets preload not depth. Although... it has been about 10 years since I messed with any pumkin work. Sorry for the miss information.
 
All I ever hear is rthe 741 is weakest.....but after 30 plus years messin with um the only broken ones I ever saw were the 742 and 489.
 
rapom65 said:
Frick I must be gettin senile. Your absolutely correct. And the crush sleeve sets preload not depth. Although... it has been about 10 years since I messed with any pumkin work. Sorry for the miss information.
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Ah I get em mixed up on occasion to. :D
 
swifter said:
THANKS guy's I'm sorry the car is a 4 speed but will never have slicks on it--So i take it either everyone has switched to the 742 and no one with a street car has busted a 741---Steve
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Ain't broke my 741 with a BB in front of it, the bananaskins break loose long before. [-o< Had a heavier 69 Runner years ago with a 383 4 speed and a 741 and couldn't hurt it either.
 
Pinion bearing diameters are not where any 8.75 has an issue. Another of the "someone wrote it so it must be true" scenarios. That's a myth that really needs to go away IMO.

The 741 will work fine in that car along with any other of the cases. I sure wouldn't waste any money buying a 489/742 because of the assumed strength issue.
 
casting year body pinion
741 64-74 ABCE 1 3/8
742 59-68 BCD 1 3/4
489 69-74 ABCE 1 7/8
Now if you do some math and figure the years of some of the big HP cars out there,you can see that they used the 741&742 castings and the dana,s.If you can get a 489 case,yes do it,but a 741 &742 case,s are behind big heavy cars and big motors too.If a 489 case is behind a stock and modified hemi automatic car,any of the cases are good for street use.Now you remember the cars came with,413,426 wedge,hemi,s 383/440 and they used these case,s, so there is know need to worry,mrmopartech
 
How bout the 68 Roadrunner I parted out a couple years ago....................4 speed, HD suspension, 11" drums.................... 741 case open rearend!!! It'll take a lickin' and keep on tickin'!! No worries, Geof
 
i have a 741 carnage.... pictures somewhere too..

cant remember what i figured was the issue, but i know it was a 741.. will have to do some picture digging
 
Thanks guy's--I feel like I'm at school again!!!!!! U never stop learning --Steve
 
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