Drag Slash Tuning Pt 3: Differential Setup
Part 3: Tuning the Sealed Differential
The Drag Slash’s new Pro Series Magnum 272R transmission features a sealed, silicone-filled differential for long-lasting performance and enhanced tuning capability. The factory differential setup is the result of extensive testing and will be ideal for the majority of competition scenarios, but altering the diff’s action via fluid viscosity may help you achieve an even more refined setup for your track or the type of driving you prefer to enjoy with your Drag Slash. In Part 3 of our tuning guide, we’ll cover removing and refilling the differential, and what to consider when selecting your diff fluid.
From the factory, the Drag Slash’s differential is filled with very thick 500K differential fluid to optimize performance for drag racing. You may wish to experiment with lower-viscosity fluid for bumpy tracks, or for better road handling if you’re enjoying your Drag Slash as an all-around street car. The Pro Series transmission is designed for easy differential access with no need to split the gearbox halves, so experimenting with diff fluid viscosity doesn’t require a lengthy bench session. Just follow these steps:
From the factory, the Drag Slash’s differential is filled with very thick 500K differential fluid to optimize performance for drag racing. You may wish to experiment with lower-viscosity fluid for bumpy tracks, or for better road handling if you’re enjoying your Drag Slash as an all-around street car. The Pro Series transmission is designed for easy differential access with no need to split the gearbox halves, so experimenting with diff fluid viscosity doesn’t require a lengthy bench session. Just follow these steps:
1. Remove the wire hold-down and disconnect the motor wires.
2. Remove the two screws from the front of the shock tower. The screws behind the tower can remain in place, we’re going to remove the entire rear suspension as a module.
3. Flip the chassis over and remove the six screws that secure the transmission. The entire rear suspension and transmission can now be removed from the chassis.
4. Remove the male driveshaft halves by taking out the screw pins and sliding the universal joints off the differential outputs.
5. Turn the transmission over and remove the four screws that secure the differential cover.
6. Push up on the differential outputs to raise the differential and cover out of the transmission. Remove the bearings from the diff so they don’t fall off and roll under your bench. Wipe any grease off the diff to keep your hands cleaner in the steps ahead.
7. Remove these four screws to open the differential. You may need to wiggle the cover a bit to free it, it’s a precise fit and the tacky diff fluid inside also has some holding power.
8. Lift the blue silicone gasket off of the housing, remove the spider-gear assembly, and wipe the diff fluid off the gears. For easier cleaning, you can also push the output gears out of the housing halves. Any fluid left on the gears will dilute and mix with the new silicone fluid you add, but if you’d like to have completely clean gears before refilling the differential, you can scrub them with isopropyl alcohol and a toothbrush.
Differential Oil
The Drag Slash’s stock silicone diff fluid is 500K weight (5039). The 5136X diff oil set includes 10K, 30K, and 50K weight fluid, and 5130X 100K fluid is available separately. The lower viscosity numbers mean these fluids are less viscous (“thinner”) than the Drag Slash’s stock 500K fluid, and will allow freer diff action. For even heavier diff action than stock, the diff can be filled with the putty-like 1-million weight fluid used by the Unlimited Desert Racer. If you’re racing on an ultra-high-traction track, the super-thick stuff might be worth a try.
The Drag Slash’s stock silicone diff fluid is 500K weight (5039). The 5136X diff oil set includes 10K, 30K, and 50K weight fluid, and 5130X 100K fluid is available separately. The lower viscosity numbers mean these fluids are less viscous (“thinner”) than the Drag Slash’s stock 500K fluid, and will allow freer diff action. For even heavier diff action than stock, the diff can be filled with the putty-like 1-million weight fluid used by the Unlimited Desert Racer. If you’re racing on an ultra-high-traction track, the super-thick stuff might be worth a try.
9. Fill the differential with your choice of fluid. Even “thin” diff fluids are pretty thick, so give the fluid time to flow and disperse through the differential housing. A rubber band and a pair of pliers makes a useful third hand to hold the diff upright and keep the housing from sliding down the output gear’s shaft as you work.
10. When the diff fluid submerges the spider gears’ cross pins, the diff is full and you can close it back up. Make sure the holes in the rubber gasket and case halves are precisely aligned before installing the screws. The screws only need to be snug. Over-tightening will make diff action notchy and may strip the screw holes, so don’t overdo it.
Put Everything Back Together
Once you've topped off your differential with new fluid, it's time to put everything back together. Reverse steps 1 – 6 to reinstall the differential and attach the rear suspension module to the chassis, then hit the street or strip with your new setup.
Once you've topped off your differential with new fluid, it's time to put everything back together. Reverse steps 1 – 6 to reinstall the differential and attach the rear suspension module to the chassis, then hit the street or strip with your new setup.
That concludes our Drag Slash Tuning Guide. We hope your new insights will help you go faster and have more fun, whether you’re out to win races on the strip or just blasting around the neighborhood. Tell (and show!) us what kind of Drag Slash action you’re into by tagging Traxxas on Facebook, Instagram, Twitter, and YouTube. We’ll be watching for you!
If you missed any steps along the way, be sure to check out Part 1 here, or Part 2 here.
