Which differential is strong enough to use in my big, heavy Mopar wagon?
This question is most popular with those who are doing big-block conversions on Mopar wagons, either for “more power!” or for drag wagons. Mopar 8-3/4 units are sturdy stuff, but there are some differences. Mopar 8-3/4 diffs from 1965-1974 were identified by three case numbers…the 489 (part#2881489) with a large ‘9’ on the side, the 742 (part#2070742) with a ‘2’, and the 741 (part#2070741) with an ‘X’. Any of these cases will bolt into any other, all can accept the same Sure-Grip unit, and all have the same axle splines. The 741 case has a 1-3/8 inch diameter pinion shaft that was reinforced with a slide-on collar (which makes it 1-3/4 inches in diameter). The 742 case eliminates the collar found on the 741 and has a stronger, forged 1-3/4 pinion shaft. The 489 has an even beefier shaft, measuring 1-7/8 inches. So which one is stronger? Well, as you see from the specs, the 489 is the strongest, followed by the 742, then the 741. Although many people say the741 is not strong enough fo
