742 ? 489

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n8ling

n8ling

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So I've got a question about 8 3/4 rear end. What is the difference between 742 c section and a 489 c section, other than the pinion diam. I have a 489 that I was going to use, and have the opportunity to buy the742 which I will. I was also at the local drags this week end (Thunder in the valley) and saw 3 742 cases with blown out ring gears H.P for sure.
 
Both cases are pretty strong. The 742 has a larger rear pinion bearing than the 489, and doesnt require a crush sleeve (the 489 can use a solid spacer and shims though if needed). Some low cost ring and pinion sets are not made for more than street use, and cannot take as much racing abuse. If you need 100% bullitt-proof, a Dana rear is the way to go.

Here is a good comparison of the pinions in those cases:
http://www.moparts.org/Tech/Archive/axle/1.html
 
street gears dont work well with slicks. believe it or not race gears are a softer alloy so the can take the shock without cracking.
 
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