How To: Seal A Stock Traxxas Slash Differential

The Traxxas Slash is one of the great Short Course trucks. It’s simple construction and great handling make it one of the best bangs for your buck. Tuning-wise, the Slash does include a few of the more important features to change the handling to your liking.

One of the more important tuning options, the differential, lacks the ability to change the fluid. Because it is not a truely sealed diff, any fluid you pour into it ends up flinging out the first time you pull the trigger. Changing the fluid can drastically affect the handling of the Slash (or any of the Traxxas trucks that use this diff), so you can see why it is such an important tuning aid. CompetitionX shows you how to seal this diff and completely change the way your Slash handles.

Items Needed:

A file or dremel. A small dremel sanding bit is recommended.
Motor cleaner. Try and find some that has the little red straw included.
Medium-sized counter sink bit.
2 small, red O-rings. Grab a pair that you use to rebuild 1:10 scale shocks.
2 small shims. Find 2 that are about the same OD as the red o-rings.
25,000-50,000k diff fluid. Any brand will do.
RTV Silicone. I used DAP 100% Silicone Gasket Sealant.

Step 1:

Start by removing the differential from your truck. Disassemble and, using the motor cleaner, blast out all of the black grease…it shouldn’t be much. Clean all the parts and set them aside.

Step 2:

Take a look at the picture to the right. You will see a black-highlighted shoulder that is on the right diff case. Take a mental picture of how tall that shoulder is. When you’re done daydreaming, take your file or dremel and grind that shoulder off both pieces until it is the same height as the rest of the case. You will see the left piece already has this done.

Step 3:

Using the medium-sized countersink bit, CAREFULLY remove material at the hole. Only remove a little at a time. Test fit the o-ring by dropping it in place. The o-ring should extend OFF the diff case to approximately the same height as the shoulder you initially dremeled off. I’ve highlighted the countersink holes for reference.

Step 4:

Carefully re-assemble the large diff side, placing all the gears back in place. Double-check to make sure all the gears seat correctly and then fill with diff fluid. It should be pretty thick and will flow slowly into the diff case. Stop filling when it is about 2/3 high.

Step 5:

Rotate the diff output shaft (from the bottom of the diff case) to help circulate the fluid throughout the entire diff. Add more fluid (if needed) to reach the 2/3 level. More is ok as it will flow out when the case half is installed.

Step 6:

Before you install the case half, take a bit of RTV and put a bead around the inner lip of the large diff case. Re-assemble the diff and screw together. If needed, place a small bead of RTV around the diff where the case halves meet. Wipe away any excess RTV. Install the o-rings on both output shafts followed by the small shims. The shims help press the o-rings against the differential and seal it at this point. Re-install the bearings and put the transmission back together!

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