Monster Truck Madness: Building a JConcepts Reactor Monster Truck Part 1

Hey everyone! It’s time to resurrect Monster Truck Madness for a few weeks, as I’ve officially started building a JConcepts Reactor Retro Truck—and let me tell you, I have a lot to say about this truck.

A few weeks back, I wrote about my plans for the Reactor build—think of that as a “Part 0” prequel. You can find a link to that right here. In that post, I went over my reasoning for choosing the 13” wheelbase kit over the short wheelbase version, as well as the general early-’90s hybrid monster truck vibe I’m aiming for.

There is one change to that plan, though.

Originally, I was going to run a Chevy Snoop Nose body. Instead, I’ve decided to go with the JConcepts Chevy S10 body.

Why the change?

For starters, I’ve actually had the S10 sitting around since it was released and have never used it. It’s time. But more importantly, I think it’s going to fit the spirit of this build really well. This isn’t going to be a clean, perfect, “by the book” body mount. Some trimming and tweaking will be required to get it to sit right—and honestly, that’s part of the charm.

It fits that early ’90s feel, where teams were still figuring out how to make those fiberglass bodies work on these evolving chassis. There’s a bit of trial and error baked into the look, and I want to capture that.

Plus, it gives off some serious Equalizer #1 vibes, which is arguably one of the first true hybrid suspension monster trucks out there. That alone sold me on it.

Alright—on to the build.

Now, let me set expectations here. I’m not going to do a step-by-step instruction manual walkthrough. There are plenty of great video resources out there for that. That’s not really what I’m interested in doing.

What I am interested in is giving you my general impressions of the build, along with some specific tips and observations that might help you if you’re planning to build one of these—or maybe even help you decide if you want to.

Sound good? Let’s get into it.

First off, the presentation and packaging are top notch. This project is clearly a labor of love for JConcepts, and it shows right away. In addition to the standard instruction manual, you get a laminated history booklet on the Reactor, along with a really nice 8×10 hero card. It’s just cool stuff that adds to the experience.

The kit itself is broken down into lettered bags, each containing the parts needed for a specific step. Everything is well organized and easy to follow.

Before diving into specific components, I want to point out one important tip: pay close attention to your hardware.

Take the time when you open each bag to use the 1:1 hardware diagram at the front of the manual. Lay out your screws and identify them before you start assembling.

There are some kits where being off by a millimeter here or there isn’t a big deal. This is not one of those kits. Using a screw that’s just a little too long or too short in the wrong spot can cause issues later. Take your time here, and you’ll save yourself headaches down the road.

Now, let’s talk about the diffs.

The first differential was, without question, the trickiest part of the build for me so far. Specifically, dealing with the tiny washers during assembly.

Do yourself a favor and build these in a clean, controlled workspace. If one of those washers drops into carpet… yeah, good luck.

Getting both sides of the diff assembled without those washers slipping out of place took a bit of patience. What worked for me was using a small dab of the included blue grease to hold them in place. Once I did that, everything went together much more smoothly.

From there, the rest of the axles and drivetrain came together fairly well, though I will say the exploded diagrams in the manual took a bit of studying at first. The side-view illustrations were extremely helpful in figuring out what went where, and once I got through the first axle, the second one went together much faster.

As someone who has built enough Clod Busters to practically assemble the axles without looking at a manual, working on the Reactor is… a bit of a trip.

Yes, it’s still a motor-on-axle design—but that’s about where the similarities end.

The Reactor’s transaxles are light years ahead.

Even setting aside the machined components and the overall higher-quality materials, the sheer amount of adjustability is what really stands out.

With a Clod, you’re dealing with open diffs, fixed geometry, and very limited gearing options without aftermarket parts. Everything is pretty much locked in.

With the Reactor? It’s a completely different story.

You’ve got oil-filled differentials, adjustable motor mounts that make changing pinion sizes easy (I’m running the included 25T pinions with 27T JConcepts Silent Speed motors), configurable axle angles via clockable knuckles… and yes, slipper clutches.

Now, I know some of you coming from the 1/10 off-road world might be thinking, “Okay… and?”

But for those of us in the retro monster truck scene, this level of adjustability is huge. We’ve been used to working with very limited options for a long time. Having this kind of flexibility built right into the platform is honestly pretty incredible.

Alright, this post is getting a bit long, so I’ll wrap things up here for Part 1.

Next up, we’ll be diving into the chassis, leaf springs, and shocks.

I’ll update this post with a link to Part 2 once it goes live.

Until then, keep it on all four’s!