How to Replace Your Spool with the 8576 Rear Differential

Like a full-size desert racing truck, the Traxxas Unlimited Desert Racer features a “spool” in place of a rear differential so both rear wheels receive equal power regardless of traction level. This is a good setup for the “loose” conditions of desert racing. When driving on medium- or high-traction surfaces, replacing the spool with the optional 8576 Rear Differential will give the Unlimited Desert Racer more responsive handling and make it easier to drive. Installation is easy, and only takes 20-30 minutes.

8576 UDR rear differential

Traxxas 8712 Tool Kit

To install the differential, you’ll need an 8mm nut driver, 2mm and 2.5mm hex drivers, and Traxxas High Performance Grease. You can use the tools supplied with the Unlimited Desert Racer, but for faster, easier wrenching, we recommend the 8712 7-Piece Metric Hex and Nut Driver Essentials Set. This set includes all the hex- and nut-driver bits required to work on all Traxxas models, plus a convenient carrying and storage pouch. Browse the complete lineup of Traxxas tools here!8012 Tool Kit

The Installation

Use an 8 mm nut driver or the 8 mm wrench supplied with the Unlimited Desert Racer to remove the rear wheels, then turn the model over. From each side of the axle, remove the 4x22 mm screws that secure the trailing arms, the 3x15 mm screws that secure the sway bar arms, and the 3x8 mm screws that secure the limit straps. Next, remove the 4x22 mm screws that secure the suspension links.

Remove the rear wheelsRemove the rear wheels
Remove screwsRemove screws
Unscrew the suspension linksUnscrew the suspension links

Remove the 3x11 mm screw pin that secures the driveshaft to the axle and then remove the axle from the truck. You can set the truck aside for the moment since we'll be working on the axle by itself.

Remove the driveshaft screwRemove the driveshaft screw
Remove the axle from the truckRemove the axle from the truck

The axle shafts must be removed in order to access the spool which will be replaced by the 8576 differential. To access the shafts, remove the 3X12 mm screws that hold the axle cap. Repeat for the other side of the axle. Remove the wheel hex/brake rotor, caliper, axle cap and axle shaft by pulling the assembly straight away from the axle tube. You may need to pull firmly to remove the assembly. Repeat for the other side of the axle.

Remove the axle cap screwsRemove the axle cap screws
Remove the entire axle assemblyRemove the entire axle assembly

Remove the eight 3x12 mm screws that hold the differential carrier to the axle, then remove the carrier.

Remove the 8 differential carrier screwsRemove the 8 differential carrier screws
Pull the carrier away from the axlePull the carrier away from the axle

Remove the 3x12 mm screws that hold the carrier housing together, and split the halves apart.

Remove the carrier housing screwsRemove the carrier housing screws
Separate the carrier housingSeparate the carrier housing

Remove the spool and its bearings. The differential includes new bearings, and simply replaces the spool.

Remove the spool from the housingRemove the spool from the housing
The differential includes the necessary bearingsThe differential includes the necessary bearings

Replace the spool with the differential. The gear side of the differential fits into the half of the housing that has flat reinforcing ribs (see arrows). If you removed the planetary gear assembly or it moved out of position when you opened the housing, make sure the tangs in the metal ring and the 6x13 mm bearing are properly seated in the housing (see arrows).

Install the differential into the carrierInstall the differential into the carrier
Align the planetary assembly properlyAlign the planetary assembly properly

Reassemble the housing and confirm the halves mate fully. There should not be a gap. If you cannot close the housing, the differential is likely flipped. After proper assembly is confirmed, you can reinstall the four 3x12 mm screws into the housing.

Reassemble the housing and check for gapsReassemble the housing and check for gaps
Tighten the housing screwsTighten the housing screws

Apply Traxxas 5041 High Performance Grease to the ring gear, then reinstall the differential carrier into the axle. It will only fit one way; position the axle housing with the suspension link tabs facing up, and insert the differential carrier with the gear on the right, as shown. Reinstall the eight 3x12 mm screws to secure the differential carrier. Now all you have to do is reverse the axle-removal steps to complete the installation.

Grease the ring gearGrease the ring gear
Reinstall the carrierReinstall the carrier
Reinstall the differential screwsReinstall the differential screws

Reinstall the axle shaft assemblies and secure with 3x12 mm screws and then reinstall the suspension links using two 4x22 mm screws

Reinstall axle assemblyReinstall axle assembly
Reinstall the axle capReinstall the axle cap
Reinstall suspension linksReinstall suspension links

Fit the driveshaft back onto the axle’s input shaft, and secure using the 3x11 mm screw pin you removed earlier. Reinstall the 4x22 mm screws that secure the trailing arms, the 3x15 mm screws that hold the sway bar links, and the 3x8 mm screws for the limit straps. Finally, reinstall the wheels, and your Unlimited Desert Racer is ready to hit the dirt with improved high-traction handling!

Reattach the driveshaftReattach the driveshaft
Reattach links and strapsReattach links and straps
Reinstall the wheelsReinstall the wheels
UDR action

Shop All UDR Accessories

For helpful Traxxas how-to videos, be sure visit the Traxxas Support Channel. Subscribe and sign up for notifications to get all the latest Traxxas tech and how-to information. Check out some of our action videos and see for yourself! Click here to go to the channel now.