This is an optional Traxxas "Spiral Cut" Rear Machined Ring and Pinion Gear. These gears are machined for the ultimate precision and feature a spiral cut on the teeth, creating slightly larger surface area and increased durability.
These gears cannot be used with the older TRA6879 gears!
NOTE: These gears are for use in the rear gearbox only!
This product was added to our catalog on February 21, 2018
I have installed this spiral-cut ring and pinion gear set in both the front and rear differentials on my Traxxas 4-Tek Supra GT4 car (with a Castle Creations 1410 3850 Kv motor and a Copperhead 10 ESC using an S3 lipo battery), and have run numerous tests hitting 60-MPH, but here’s the thing…
First off, I used a highly sticky gear grease on the spiral-cut ring and pinion, and after testing for several hours, the wear pattern on the gear teeth of both gears was immaculate; I couldn’t have asked for better - the actual wear was immeasurable - perfect swipe on the teeth.
The ring gear is mounted on the differential housing as the stationary gear (it’s not adjustable), and the pinion gear is adjusted using shims between the pinion gear and its support bearing. I setup the gear lash as best as could be done - trust me on this one.
Problem #1: the pinion gear slides on the driveshaft it’s attached to (and the bearing it sits inside of), and in that, the gear lash goes from full tooth-surface contact when the pinion is slid towards the ring gear, and then when the pinion gear is slid away from the ring gear, the actual gear lash you’ve created using the shims comes into play.
The biggest problem is that the pinion gear needs something to seat the thing in place and to stop it from sliding into the ring gear. Which leads us to…
Problem #2: because these gears are spiral cut (cut on an angle), when torque is applied to the pinion gear, the pinion is going to be forced to move in the direction of the gear’s teeth angle, so turning one direction, the ring and pinion gears will bind slightly from digging into each other, while going the other direction makes the gears push apart from one another (because of the gear’s cut angle). Sorry if I’ve lost you.
Problem #2 is the real problem because the ring and pinion at one end of the car are pushing themselves apart, while the ring and pinion at the other end are pulling themselves together. This can also lead to the center driveshaft being forced slightly in one direction or the other. This problem becomes apparent when the car is coasting and motor braking (the gears get noisy). It can also create uneven wear on the main spur and motor pinion gears.
BOTTOM LINE: these gears are incredible strong and resilient, but there’s a flaw in the system, and until there’s a better way to adjust and secure the pinion gear in place, YOU WILL PAY A PRICE IN PERFORMANCE! The stock Traxxas straight-cut ring and pinion turn effortlessly, the spiral cut gears just flat don’t, and the cost is loss in power. Full stop.
These gears may be better suited for the crawlers.
Additionally (note to Traxxas engineering), a spiral-cut ring and pinion gear assembly should have the pinion gear placed below the centerline of the differential by about 15° for spiral cut gears to even make a difference in performance, and that would also quiet these noisy buggers down considerably.
Side note: yes, I know that the Traxxas write-up says this ring and pinion are for the rear differential only, but it makes no sense to have spiral-cut gears in the rear and straight-cut gears in the front. The front gears that are recommend has a different pinion type and does not connect to the driveshaft of the 4-Tec 2.0/3.0 system.
Thank you for your time on this matter.