489 Rearend Case

[venom04]

I heard that they were a good rearend case, could someone explain why?  If so.

[resq302]

Its not that the case is the good thing.  The pinion gear is more beefier than the others such as the 741 and 742 housings.  The 489 I think has a 1 7/8" pinion shaft.

[Nacho-RT74]

FOUND THIS... GREEEEAT INFO SOURCE
http://www.autohobbydigest.com/8_75.html

so now a question... if pinion is the difference, when I change axle ratio, I need to be sure the new pinion is 1 7/8" to match with case ?

[Chryco Psycho]

Yes , the gears have to match the carrier to fit , the only exception to this is the 742 gears can be installed in a 489 carrier If you use the correct pinion brg to fit
the crush sleeve is the weak link in the 489 , but there is a spacer to eliminate the crush sleeve makin git as strong as the smaller 742

[Ghoste]

I thought the 742 was bigger but the tapered pinion shaft in the 489 had something to do with making it stronger?

[Nacho-RT74]

the more torque needed on a shaft is when torque change the attack point. On 741 and 742, the torque is suddenly cut where you change from shaft to pinion diameter. So we can say we have a "weak" point there

For a while tapered shaft pinion makes all torque distribution along the lenght of pinion shaft.

we have a simply example... I think every body has broken a bolt or screw head when you tight or loosen it... has you broken someday a tapered screw/bolt head ? Maybe yes but is a little bit harder

[John_Kunkel]

All three of the pinions have the same diameter step where the yoke splines transition to the pinion stem so, from a torsional standpoint, the larger stem is of no advantage.

Where the larger stem has an advantage is in supporting the pinion gear, under high load the pinion gear tends to deflect away from the ring gear which reduces the tooth contact area and can lead to gear tooth failure. The larger diameter stem offers more resistance to deflection.

Because of the basic case design, the larger stem pinion must use a smaller bearing to remain within the confines of the housing; the rear pinion bearing used in the 489 housing has about 15% less thrust load and lateral load capacity than the 742.

[Nacho-RT74]

well I was so close ... I wanted to mean also about deflection, what's in directly relationship with flexibility and torque on that point

[Chatt69chgr]

Great explanation John.  That probably explains why the drag racers preferred the 742. 

[Ghoste]

So why did Direct Connection recommend the 489? (and I guess MP still does, don't they?)

[John_Kunkel]

So why did Direct Connection recommend the 489? (and I guess MP still does, don't they?)

Why did MP chose the 742 configuration for their aluminum third member housing?

After many years of consuming Mopar literature I've come to the conclusion that there is only one thing that's constant and that's..............change.

[Ghoste]

Good question John, good question.