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489-742 Gear Interchange

727

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I read somewhere that at some point mother mopar installed
489 gears in some 742 cases on 8 3/4" third members.
it looks like the large 489 pinion bearing works in the 742 outer race. The smaller pinion bearing is different. Does anyone know which small pinion bearing I could use to install 489 gears in my 742 case?
Also are the differential bearing different sizes in both case? Anyone know the part #'s if they are different?

727
 
If I remember I think I have used the same posi unit in both the 489 and 742 cases. So the carrier bearings are the same, all I did was change the ring gear, as pinions are different between cases. Someone chime in if I'm mistaken, it has been many years since I have done any diff work.
 
you can't put a '489 pinion in a '742 case. the '489 pinion uses a larger inner pinion bearing and it physically won't fit in a '742 case. use ring and pinions that are specific for your housing.
 
The carrier bearing cups are the same size fit in the case but the cones different between the carrier fits. Years ago a buddy of mine said you can swap pinions between the 41 and the 42 case when using the correct rear bearings but I've never tried it. You could probably swap pinions between the 42 and the 89 if you could fine the right bearings but I have no idea if you could find bearings for doing that. It wouldn't be too hard to check that if I ever get time....
 
as the pinion stem increased in diameter so did the inner pinion bearing and the inner pinion bearing housing bores were enlarged in the housing. it's not possible to interchange these bearings without some kind of machine work to the housing or pinion stem. anyhow, that's my take on it all.
 
I had some ring and pinion sets for 489's and I only have one 489 carrier. I was just interested in setting up a bare spare 742 carrier that I had in my shop. Now I'm going to hunt down that article!

727

- - - Updated - - -

http://www.moparfins.com/Repairs/8-3-4_Rebuilding/Information_on_Mopar_Rears.htm

Ok guys, and maybe gals. This is the link to the article. I had it backwards. According to this article 742 gear sets found there way into 489 housings!

Now we know; I guess!


727
 
I have after much research and trial fitting have successfully managed to install a 489 gears set into a 742 case. Bearings are available, I shimmed the races because there is a difference of .400 in length between the seats and the 489 pinion stem is longer.
 
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