8 3/4 Rear End Question

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bernieca

bernieca

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New to 8 3/4 rear ends. I have a 741 case now with 391 gears. I can get a 489 case with 323 gears and sure grip. I would like to use the 391 ring gear in the 489 sure grip and put the 323 ring gear into the 741 case. Is this possible and if so any issues or anything to look out for? Thanks!
 
If it were me I would just pop a new R&P in the 489 case, not that hard to do if you have a few simple tools. Even if you could change the ring gear you would be mismatching gear patterns and would likely end up with noise.
 
Badsport said:
If it were me I would just pop a new R&P in the 489 case, not that hard to do if you have a few simple tools. Even if you could change the ring gear you would be mismatching gear patterns and would likely end up with noise.
Click to expand...

Makes sense. Thanks Bruce.
 
You would need a torsional torque wrench, dial indicator, some way to press bearings on/off. If you do rebuild it get the crush sleeve eliminator.

You will also want a spanner and something to hold the yoke when torquing the pinion nut. I made mine.
 

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Just curious what is wrong with the 741 case. I ran a 741 case with 391's in my Challenger behind 440 w/4-spd. putting out about 500HP and never had any problems
with that rear.
 
R4Sedan said:
Just curious what is wrong with the 741 case. I ran a 741 case with 391's in my Challenger behind 440 w/4-spd. putting out about 500HP and never had any problems
with that rear.
Click to expand...

The 741 is not a sure grip. plus I always thought the
489 was much stronger. I do plan on going the stroker route but that's a little farther down the line. Just planning ahead.
 
The 489 is stronger but the 741 isn't a weakling like a lot of guys think they are. You could install the sure grip unit from the 489 case into the 741 case with the 3.91 gears. That'd give you the gears and sure grip you want.

BTW: most of the strength difference between a 741 and 489 is the pinion. The 741 pinion is a much smaller o.d. but here's something to think about. What size is the o.d. of the pinion on a 741 right behind the yoke? Answer: it's exactly the same as a 742 or early 489 pinion. Only the newer fine spline 489 gearset is stronger.
 
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