The 7881 is Traxxas's Pro-Built rear differential — a complete, factory-assembled unit for the X-Maxx 8S and XRT, supplied with the pinion gear and bearings needed to install it.

Pro-Built means no rebuild. A differential is one of the more involved jobs on a large-scale truck: the case has to come apart, gears and shims sorted, the housing sealed and refilled with the right weight oil, and any of that done imprecisely will leave the diff noisy or short-lived. This unit arrives assembled to Traxxas's own build spec and bolts straight in.

The differential arrives assembled with the ring gear in place, and the heavy duty 11T pinion gear and three rubber-sealed ball bearings are supplied alongside — so everything the installation needs is in the one packet.

That makes it worth keeping on the shelf as much as buying it as a repair. A stripped diff at the track normally ends the day; a spare in the toolbox turns it into a ten-minute swap.

Features

• Complete, factory-assembled rear differential
• Ring gear fitted to the differential case
• Heavy duty 11T pinion gear supplied
• Three rubber-sealed ball bearings supplied
• Genuine Traxxas Pro-Built part

Fits

• Traxxas X-Maxx (77096-4)
• Traxxas X-Maxx Ultimate (77097-4)
• Traxxas X-Monster Chassis (77036-4)
• Traxxas XRT (78086-4)
• Traxxas XRT Ultimate (78097-4)

Per Traxxas's application guide. Rear differential — the front differential is a separate part.

Includes

1 x Pro-Built Complete Rear Differential, assembled with ring gear
1 x Heavy Duty Rear Differential Pinion Gear 11T (#7791)
1 x 15x24x5mm Ball Bearing (#5106)
2 x 17x26x5mm Ball Bearing (#5107A)