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8 3/4 case? #3146980
05/26/23 07:23 PM
05/26/23 07:23 PM
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ar.
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bobs69 Offline OP
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Which one do you like? Street use 741 - 742 - 489. Big block 4 speed car probably going to be hard on it. Thanks

Re: 8 3/4 case? [Re: bobs69] #3146990
05/26/23 08:16 PM
05/26/23 08:16 PM
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Kirkland, Washington
Pacnorthcuda Offline
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742 hands down, no contest. Now if you take a 489 and use a crush sleeve eliminater that’s fine too.

Re: 8 3/4 case? [Re: bobs69] #3146991
05/26/23 08:23 PM
05/26/23 08:23 PM
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Keizer, Oregon U.S.A.
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elmor353 Offline
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I have used all of those cases without a problem. Even the 741, with the supposedly "small" pinion gear is bigger than a Ford nine inch. The factory used them behind some nasty engines and they held up just fine. Unless you're building a 500 horsepower or stronger motor you should be ok. All of the pinion gears are pretty much the same size where the pinion nut sits.

Re: 8 3/4 case? [Re: elmor353] #3147000
05/26/23 09:39 PM
05/26/23 09:39 PM
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Omaha Ne
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TJP Offline
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Being a street car all would likely be fine unless you have your suspension really dialed in with sticky back tires. I would then lean towards the 742 or 489 case twocents beer

Re: 8 3/4 case? [Re: TJP] #3147023
05/27/23 06:56 AM
05/27/23 06:56 AM
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Minn
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SportF Offline
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Wouldn't a pinon break at its smallest-weakest point? AND, aren't all the yokes the same.......so what's wrong with a 741? This has been a mystery to me as much as DOT5 Good luck.

Re: 8 3/4 case? [Re: SportF] #3147056
05/27/23 11:49 AM
05/27/23 11:49 AM
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Posts: 19,151
north of coder
moparx Online content
"Butt Crack Bob"
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i have beat hard on all of the above cases, but since i can's shift a 4 speed for $hit, i'm a wimpy automatic guy. biggrin
beer

Re: 8 3/4 case? [Re: SportF] #3147070
05/27/23 01:35 PM
05/27/23 01:35 PM
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Rio Linda, CA
John_Kunkel Online content
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Originally Posted by SportF
Wouldn't a pinon break at its smallest-weakest point? AND, aren't all the yokes the same.......so what's wrong with a 741? This has been a mystery to me as much as DOT5 Good luck.


Yes, the pinion stem ends are pretty much the same but most failures occur because of pinion deflection...IOW, under load, the pinion gear tries to deflect from the ring gear and tooth contact is lost leading to tooth failure. A larger pinion stem and bearing resist this deflection...the 742 (on the right below) has the best combination of stem size and bearing size to resist deflection.

Pinion stems.jpg

The INTERNET, the MISinformation superhighway
Re: 8 3/4 case? [Re: elmor353] #3147091
05/27/23 02:59 PM
05/27/23 02:59 PM
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Sniper Offline
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Originally Posted by elmor353
I have used all of those cases without a problem. Even the 741, with the supposedly "small" pinion gear is bigger than a Ford nine inch. The factory used them behind some nasty engines and they held up just fine. Unless you're building a 500 horsepower or stronger motor you should be ok. All of the pinion gears are pretty much the same size where the pinion nut sits.


There is a reason the factory went with a Dana behind a stick with a "nasty engine".

That said, the 742 survived just fine behind the warm 413/stick combo in my 64 300 with N50's.

Re: 8 3/4 case? [Re: John_Kunkel] #3147121
05/27/23 06:10 PM
05/27/23 06:10 PM
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Bend,OR USA
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Cab_Burge Offline
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Bend,OR USA
Originally Posted by John_Kunkel
[quote=SportF]Wouldn't a pinon break at its smallest-weakest point? AND, aren't all the yokes the same.......so what's wrong with a 741? ...the 742 (on the right below) has the best combination of stem size and bearing size to resist deflection.
iagree
I've crack, (and had some teeth break off) the outer edge of the ring gear teeth on all three rear ends with a 727 and nine inch slicks whiney down shruggy
Not so on a Dana 60, yet luck


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 8 3/4 case? [Re: John_Kunkel] #3147165
05/28/23 06:59 AM
05/28/23 06:59 AM
Joined: Jan 2008
Posts: 1,201
Minn
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SportF Offline
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Well, I gotta say that picture clears it up for me. Great comparison, thanks for that. Once again Mr. Kunkel's expertise teaches me something.

Last edited by SportF; 05/28/23 07:00 AM.
Re: 8 3/4 case? [Re: SportF] #3147217
05/28/23 11:15 AM
05/28/23 11:15 AM
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northwest USA
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NANKET Offline
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Originally Posted by SportF
Well, I gotta say that picture clears it up for me. Great comparison, thanks for that. Once again Mr. Kunkel's expertise teaches me something.


The credit goes to Dr Diff, the photo was pirated from this article in the tech archives.
There is more to the story also.

Go to the tech archives sometime and start reading. That’s where these guys get lots of this stuff from.

http://www.moparts.org/Tech/Archive/axle/1.html

Last edited by NANKET; 05/28/23 11:16 AM.
Re: 8 3/4 case? [Re: SportF] #3147225
05/28/23 11:42 AM
05/28/23 11:42 AM
Joined: Jan 2003
Posts: 29,639
Hamtramck, PA
Alaskan_TA Offline
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Hamtramck, PA
Originally Posted by SportF
Well, I gotta say that picture clears it up for me. Great comparison, thanks for that. Once again Mr. Kunkel's expertise teaches me something.


FIXED VERSION;

Quote
Well, I gotta say that picture clears it up for me. Great comparison, thanks for that. Once again Dr. Diff's expertise teaches me something.
beer

Re: 8 3/4 case? [Re: Alaskan_TA] #3147789
05/31/23 10:41 AM
05/31/23 10:41 AM
Joined: Oct 2004
Posts: 2,784
Connecticut
FurryStump Offline
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A serious issue with the 741 is the lack of new gear sets in many different ratios. I have beat on a 741 for years, but if starting from scratch would go 742. Which I eventually did when I went to 4:10


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