Regular readers will recall that we reviewed Pro-Line’s eye-popping Ultra Reservoir Shocks for scale trucks back in the April 2017 issue, and found the reservoir tech to be as functional as it is stylish. Since then, the Pro-Line CNC machines haven’t slowed down, and now there’s a second member of the Ultra Reservoir family: the super-sized cans you see here, for the Traxxas X-Maxx. Unlike the Ultra Reservoir Shocks we reviewed back in April, which are complete dampers with springs, the Ultra Reservoirs for X-Maxx include only the caps and reservoirs; the bodies, springs, rod ends, spring perches, and preload collars are carried over from your X-Maxx’s stock shocks. Here’s how everything goes together, and what to expect when you hit the dirt.
Pro-Line dry-fits the reservoirs to the caps for packaging, but you’ll need to disassemble them to install the O-rings and reservoir internals. If you fill the shocks the way Pro-Line recommends in the YouTube video detailing the assembly, you’ll also need to remove the X-Maxx shocks’ seal cartridges. You can reuse the oil in the X-Maxx shocks if it’s still fresh, but you’ll need to add more oil to fill the reservoirs. For the best build, I recommend using all-new oil. I also suggest lubricating the O-rings on the caps, reservoir pistons, and bleed screws with seal grease such as Pro-Tek R/C Premium Blue for the best performance. The machined parts fit as precisely as you’d expect, and between the printed instructions and Pro-Line’s assembly video, you should be able to breeze through building and filling the shocks. Depending on the position of the reservoir piston, the shocks can be assembled for maximum reservoir capacity or minimum internal pressure. Reduced internal pressure is easier on the shock seals, so that’s how I built my shocks. The final step is reinstalling the shocks on the truck. Pro-Line supplies machined Delrin pivot balls and washers to fit the caps, and the reservoir-equipped shocks simply bolt into place like the stockers.
I’ve put a few hours on the shocks since installing the caps, with no leaking or weeping to report or any degradation in performance—they still feel freshly built. Without the luxury of side-by-side testing with stock and reservoir-equipped shocks, the X-Maxx suspension didn’t feel significantly different after installing the reservoir caps. Nor was a change expected since I didn’t alter the shocks’ damping or spring rate. The plush, mile-deep suspension feel the X-Maxx is known for is unaltered by the reservoirs, which is a good thing. The reservoirs did seem to come into play on big hits that use up all the suspension travel. Under these conditions, the reservoir-equipped X-Maxx seemed to rebound less, which helped keep the truck under control. The benefit of the reservoirs is that the X-Maxx’s excellent shock performance should last longer with the reservoir caps since there’s more oil in the shocks to do the work of absorbing the big hits an X-Maxx takes. More oil also means less oil heating, and reduced internal pressure means the seals are worked less hard, all of which results in more wheel time between refills or rebuilds.
Pro-Line’s Ultra Reservoir Shock Caps are beautiful, functional additions to the X-Maxx. The parts are precisely made, nicely finished, and assemble easily (although you should be prepared to get oily anytime you’re working on shocks). They’re not inexpensive at $90–$110 per pair, but you’re getting precision equipment made with premium materials—and since these are X-Maxx parts, they aren’t small. For the money, the Pro-Line caps deliver the technical wow factor of functional reservoir shocks, greater life between rebuilds, and improved big-hit performance. And the Ultra Reservoirs look super-cool, which, for a lot of X-Maxx fans, will be reason enough to buy a set.