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8 3/4 Rear End change - 742 vs. 489? #1003020
05/30/11 03:42 PM
05/30/11 03:42 PM
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Pennsylvania
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moparsenior Offline OP
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I plan to install 4.30 gear in '66 Coronet 8 3/4 rear. Undecided whether to install new ring and pinion in my existing 742 case vs. springing for a complete center section, which would afford me flexibility when swapping betweeb road and strip.
If I go with the complete center section, should I consider a 489 case?

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: moparsenior] #1003021
05/30/11 03:58 PM
05/30/11 03:58 PM
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Rio Linda, CA
John_Kunkel Offline
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The 742 is the preferred case, it has the largest pinion bearing.


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Re: 8 3/4 Rear End change - 742 vs. 489? [Re: John_Kunkel] #1003022
05/30/11 07:01 PM
05/30/11 07:01 PM
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WV,USA
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wvmarv Offline
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Quote:

The 742 is the preferred case, it has the largest pinion bearing.




wrong, the 489 case has the largest diameter pinion shaft at 1 7/8" and is the most sought after. see this link.
http://www.hemmings.com/mus/stories/2004/10/01/hmn_feature21.html

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: wvmarv] #1003023
05/30/11 07:36 PM
05/30/11 07:36 PM
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Posts: 25,618
Rio Linda, CA
John_Kunkel Offline
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This has been talked to death, the 489 might have a larger pinion stem but it necks down to the same size as the others at the yoke. The smaller rear pinion bearing of the 489 makes the pinion more likely to deflect under load.

Note that the factory chose the 742 platform to make their aftermarket aluminum housing.

The Hemmings article claims the 489 is the most sought after.....I would ask "by who"?


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Re: 8 3/4 Rear End change - 742 vs. 489? [Re: John_Kunkel] #1003024
05/30/11 07:50 PM
05/30/11 07:50 PM
Joined: Feb 2004
Posts: 7,194
Harrisburg, Pa.
screamindriver Offline
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tech archives with pics... link

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: John_Kunkel] #1003025
05/30/11 07:52 PM
05/30/11 07:52 PM
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Posts: 3,407
S.E. Florida, USA
rrunner Offline
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742 for me.

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: screamindriver] #1003026
05/30/11 07:57 PM
05/30/11 07:57 PM
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Kirkland, Washington
Pacnorthcuda Offline
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Yes, the 489 uses a larger ID but shorter bearing than the 742. Regardless, this is really splitting hairs, as they both use the same smaller front bearing and the front bearing is far more likely to fail.

As far as deflection, perhaps the 742 case is better supported in this area than the 489. I don't know, but if a person is going to sweat the details of this to ensure the strongest rear--get a Dana

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: Pacnorthcuda] #1003027
05/30/11 09:00 PM
05/30/11 09:00 PM
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Posts: 1,462
Mrytle Beach SC
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johnscudashop Offline
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Well put

6658522-100_2011.jpg (392 downloads)
Re: 8 3/4 Rear End change - 742 vs. 489? [Re: wvmarv] #1003028
05/31/11 10:07 AM
05/31/11 10:07 AM
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U.S.S.A.
JohnRR Offline
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Quote:

Quote:

The 742 is the preferred case, it has the largest pinion bearing.




wrong, the 489 case has the largest diameter pinion shaft at 1 7/8" and is the most sought after. see this link.
http://www.hemmings.com/mus/stories/2004/10/01/hmn_feature21.html




Guess again , as delivered the 742 is by far the stronger of the 2, the biggest problems with the 489 is that POS crush sleeve and the POS cone type sure , even when switching out the to a solid spacer and a clutch type sure grip the 742 still gets the nod with it's dana 60 like inner pinion bearing .
johnscudashop , what is the suregrip in your picture an Auburn ? It's a bigger POS than the original borg warner cone unit ...

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: JohnRR] #1003029
05/31/11 11:09 AM
05/31/11 11:09 AM
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Andrewh Offline
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regardless of strength, I think the crush sleeve on the 489 makes it the worst choice. Espeically if you are going to take it appart to put in new gears. the 742 seems to be easier to put together.

however, met someone at a show saying how hard it was to find gears for the 742 for a highway cruiser.

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: Andrewh] #1003030
05/31/11 12:27 PM
05/31/11 12:27 PM
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Upper Midwest
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MoparforLife Offline
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except for the lack of available gears the 741 is mighty tough to beat too. Have had them and beat the crap out of them.
If using the 489 up grade to the solid space and you will be in fine shape.

Re: 8 3/4 Rear End change - 742 vs. 489? [Re: MoparforLife] #1003031
05/31/11 06:07 PM
05/31/11 06:07 PM
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Posts: 293
CA
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David Lee Offline
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Unless you plan on putting some real serious HP on them anyof the pumpkins will work fine on a street car. I rin 5.38 with a spool on my stocker and have no problem what so ever


Ah...so many pedestrians, so little time...






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