Published on May 20th, 2024 | by Joe

Honda 400EX Affordable Trail Quad Project Test

With the Yamaha YFZ450R and Raptor 700R retailing for over $10,000, a new sport ATV is a bit out of reach for many of us. With that in mind, we purchased a good running, used Honda TRX400EX at fair market value, and set out to fix any issues and add the necessary parts to ensure durability out on the trail making upgrades where they made sense.  This video will give you a rundown on our parts’ selections, put our project build to the test on the trail, and give you a final breakdown on what it all cost. If you want to watch the build step-by-step, check out the entire build series.


Our Used Sport ATV Choice


The 400EX was produced from 1999-2014 so while some new OEM parts are becoming hard to come by, there are lots of good used parts out there accompanied by pretty robust aftermarket support.  Possessing light, nimble handling that’s nearly on par with the legendary TRX250R accompanied by an efficient, high-torque, four-stroke engine, Honda’s TRX400EX was nearly the perfect sport ATV for the trail right off the showroom floor.  With a well-cared for, or lower hours engine with proper maintenance, it should outlast most any machine in the 450cc class.

Our 2001 TRX400EX was purchased around a year ago on Facebook Marketplace for $3,000.  Overall, the machine was in relatively good condition with the main components, the engine and frame, in great shape. The engine  sounded velvety with a quiet valve train. The frame showed no signs of stress and the lower frame rails had no flat spots with a majority of the factory paint intact. Overall, this ATV seemed to have enjoyed a pretty gentle life although it certainly needed some repairs to restore its OEM Performance.

For the money, we felt pretty good about our purchase. We’d rather spend a little more and start with an engine and frame in good condition than some clapped out big-bore dripping in parts that has 5,000 miles on it with smoke on startup and slop throughout; or even worse, some box of mystery parts.


Like New Performance


To begin the project, we started by replacing anything that was worn or tweaked. We knew before receiving the machine the subframe was bent. We ordered a used, take-off subframe from ATV salvage juggernaut Power Sports Nation. It arrived quickly, but was actually tweaked a bit too.  PSN immediately swapped it out with another one. There was some scarring on the grab bar from wheelies, but it was straight and that was completely acceptable to us for the money. We sanded it and gave it a fresh coat of primer and paint from the factory color matching experts at Color Rite.


With a small bend in the stock stem, we decided to upgrade it with a much stronger, tig-welded 4130 chromoly anti-vibe steering stem from Teixeira Tech. Their products are manufactured in the United States of U.S. sourced materials. Teixeira Tech sells their larger diameter TRX450R steering stem for the 400EX adding additional strength, requiring the use of two TRX450R steering stem clamps and one bushing to work with the EX. Unique to Teixeira Tech stem, the area of the stem that’s surrounded by the clamps is precision ground and heat treated for precise fitment for increased resistance to wear. The steering flag is lowered  to reduce bump steer and gusseted for added strength. They can be ordered in +1 or +2” lengths; we opted for +1 and they can be powder coated in a number of colors.

Sold separately from their stem, Teixeira Tech’s adjustable handlebar clamp and anti-vibe bar mount kit allow four different handlebar mounting positions in ¼” increments moving the bars closer or further away. They’re constructed of CNC’d billet aluminum and feature a black anodized finish. Teixeira also sells an adapter that will let you run their adjustable bar clamp with your stock stem for more adjustment at a lower price.

Switching from the stock 7/8” diameter bar clamp to Teixeira Tech’s 1 1/8” adjustable bar clamps required a new handlebar. We could have used something less expensive, but Fasst Company’s, Flexx Handlebars help reduce fatigue on long rides. Their hanged design allows them to absorb impacts with different elastomers allowing for a firmer or softer feeling on compression and rebound. Preload screws allow you to fine tune their firmness and upsweep. With different heights and sweeps available, no other handlebar company on the market is better at customer service before or after the sale. For this test, we rocked ours with the stock red elastomers providing a relatively firm feeling unless the suspension starts to find its limits.

To restore OEM braking feel and improve power, after a good brake bleeding, the brake pads were replaced with new pads from Braking. Developed for off-road racing Braking’s pads are more centered than the OEM pads for improved heat dissipation and bite.  The rear brake return spring wasn’t original to the machine, so we replaced it with a new OEM one.  To finish making the hand controls smoother and ensure reliability, a fresh clutch and throttle cable were installed from Motion Pro. Fortunately, the stock clutch still feels fresh with the feeling of a groove free basket through the lever.  We wrapped up the controls with a new set of OEM bolts and washers on the heel guards, replacing the zip ties that were holding them on when we purchased the quad.

Tightening up the chassis, we destroyed our stock bearing carrier trying to remove the stock bearings without a proper press. We swapped out the stock carrier with a new Tusk axle bearing carrier from Rocky Mountain ATV. Test rider, Evan Hartzel, has used the Tusk carrier for an entire season in his personal race quad, so it’s already proven to be an acceptable, long lasting, and affordable replacement, costing less than having your local dealer swap out the bearings in the stock carrier.

The play in the stock ball joints was minimal enough that we left them alone for now. Shure Interlocking makes a replacement front ball joint kit that requires you to cut out the stock ball joints and weld in a new set. This kit is affordable, but will take some mechanical skill to install. If you want to stick to the stock front end long term, we’d recommend it. We’ll be continuing this build with a new front end in the near future, so while we didn’t swap out the stock ball joints, it can be done.

To keep the engine running strong for years to come, we installed a high-quality foam air-filter from Uni. We then gave the 400 a fresh oil change with Maxima Pro Plus oil offering synthetic oil slickness and protection at a reasonable price.

The stock 400EX tires had tread left, but with multiple plugs already, we decided to switch to a full set of GBC tires. GBC XC Master and Ground Buster III tires already have a pro GNCC championship pedigree with Walker Fowler. Like most of their sponsored riders, we opted to run XC Master tires up front due to their taller tread providing greater penetration in muddy conditions. Out back, we opted for the standard GB3s over the Pro models due to their more rounded profile putting a little less rubber on the ground, making the back end a little easier to break loose and slide with our 400cc machine’s more limited power compared to a larger displacement machine. For sizes, we ran 21×7-10” front and 20×11-9” rear.


Improving durability


While the stock wheels were in great shape, in the event of a flat, beadlock wheels allow you to limp back to camp with the tires still fully mounted. We installed GPS Victory Lock, 10” single beadlock wheels front featuring a rolled inner lip for added strength. Out back, 9 “dual beadlock wheels offer added security. The wheels feature a dual bolt pattern working on both Hondas and Yamahas. We carried these over from our last HMF YFZ450R XC build. They’re available with either carbon or aluminum beadlock rings, which we utilized. They’re constructed of specially heat treated 6061 aircraft grade aluminum with a 190 wall thickness on both halves of their beadlock wheels for added durability. This makes the GPS Victory Lock wheels a little heavier, but they should hold up to years of mindless abuse. Mud plugs are available for those who prefer using them.

Next, we installed a four-piece skid plate set from Ricochet Offroad to keep the underside of our A-Arms, frame and swingarm protected. Made in the USA, they’re constructed of 3/16” 5052 H-32 aluminum. The A-Arm guards and frame skids are held in place by clamps with Torx fasteners used on the entire set. Their rounded edges help prevent snagging on obstacles. The swingarm skid plate’s construction is especially gnarly;  a good thing as it will take the most punishment.  They are available in a bare aluminum finish like ours, or you can have them powdercoated a number of colors to match your machine.

A steering stabilizer is a mandatory upgrade for any sport quad to save both man and machine. It reduces fatigue on the rider and the chances of being knocked off line from uneven bumps or obstacles lurking trailside. Legendary for their high-end shock performance, PEP’s stick style steering stabilizer is surprisingly affordable compared to the puck style dampers on the market. . They offer some adjustability and are rebuildable. Racers used them for decades and they still get the job done today.


Updated look


To wrap the build, our machine needed a fresh look. We replaced the dingy stock seat cover with a custom made seat cover from Cosmic Quads. The red vinyl was a perfect match for the Honda’s red bodywork. The styling and placement of the black Fourtrax and Honda logos were on point providing the exact look we were after. If you want a seamless one piece factory look, you can get that, too, but you’ll need to send Cosmic Quads your seat.

Our plastic was completely crack free, but after more than 20 years, it had its share of abrasions. A new graphics kit from FTR Powersports covered nearly all of the plastic. Its fitment was perfection as usual, and FTR’s thick vinyl and strong adhesive keeps their kits looking good for quite a while if you install them properly on clean plastic. We love its appearance and with that, it’s time to hit the trail.


Ride Test


We met up with builder and test rider, Evan Hartzel, at his private cross country practice track in northern Kentucky to put our new used 400EX build to the test. Hitting the trail, the completely stock 400EX engine doesn’t disappoint. Power starts pulling right off idle building smoothly throughout the midrange before signing off on top. The high torque, lower RPM focused power requires minimum effort from the rider to keep the engine in the best part of the power, easily pulling steep hills, and breaking the rear tires loose or slides on demand. The lower RPM operation also means the engine will last longer over time. Leave it alone, do proper maintenance and it should last for years, assuming you are starting with a healthy engine.

The aged stock shocks are still performing pretty admirably. The ride is a little soft as it always was. It does well at gobbling up the smallest of bumps while still offering enough bottoming resistance for spirited riding on the trail. A little firmer ride would be welcomed for race speeds adding more bottoming resistance for g-outs and righting body roll in turns, but that’s another subject for a future video on this ATV.

The Teixeira Tech stem adjustable bar clamp allowed us to put the handlebars perfectly within reach. We love running Fasst Co.’s Flexx handlebars on trail quads, and this machine is no exception. We ran a stiff setting to minimize unwanted geometry changes while allowing the bars to flex enough to take the edge off bigger hits that push the plush stock shocks to their limits. Being comfortable with the controls allowed Evan to push the EX harder with greater confidence.

The tire and wheel package was spot on for our needs although we need a minor setup mistake. Rear end traction strikes a perfect balance between forward and braking traction with a willingness to slide on demand, even with limited horsepower. They were clearly the right tire choice for the 400. The front SC masters offered great braking and directional control, although the front end occasionally pushed a bit, due to the stock rear shock being a little too undersprung or our rider weight. This takes grip off the front end and is zero fault of the XC Master fronts. We’ve used them on other machines with even better results. Making this machine’s front end steer RZR sharp will take a little suspension work for riders in the 200 lb plus club.


We did manage to cut a rear tire on one of the beadlock rings due to running a low tire pressure without a run flat system. With GPS aluminum rings, we would recommend staying above 7 lbs of pressure without a run flat system. If you want to run lower, we’d go with GPS Carbon rings. Their aluminum rings would benefit from a larger radius on the edge. When we did cut a tire, the fact that the tire was held so securely in place by dual beadlocks, we were able to easily ride a mile back to the truck with the tire securely seated in place, exactly what we wanted in case of a flat. Next time, we’ll air up a bit and avoid the issue altogether.

Braking power is exactly what we came to expect from Honda back in the day, offering plenty of power that’s easy to modulate. The Braking brake pads offered stopping power at least as good as the OE pads and that’s saying a lot. You can’t ride hard without good brakes and this quad’s brakes work great.

Throughout our testing, we heard the skid plates take some shots that resulted in a few scratches, but no bends or dents, keeping the underside of the machine perfectly intact. Whether your machine is new or used, these skid plates can easily pay for themselves by protecting the expensive underside of your ATV. That’s why we’ve used their skid plates on so many of our builds through the years with no regrets.

Swapping out the control cables, rear bearing carrier, steering stem bearing and other points of play left us with a 400EX that felt as tight and wobble free as it did when it was new. Riding a machine that’s this tight after 20 years proves what proper maintenance can do for the feel and performance of your ATV. With the fresh seat cover from Cosmic Quads, combined with the FTR graphics, we feel our quad’s looks exceed those of the stock machine, and who doesn’t like turning heads on the trail.


Final Pricing


So what did it all cost? Well, as we’ve mentioned, the 400EX set us back $3,000. Replacing everything missing, bent, significantly worn, installing a name brand air-filter and oil change set us back $1,849.13. We could have ordered a used stem and used the bars that came with the quad and saved around $600 on repairs, but our motto is typically, ”Don’t replace it; upgrade it!”

Improving durability and survivability with beadlock wheels, skid plates, a case saver, and the steering stabilizer added $1360.25 to the build. These are items we would add to any new machine we had purchased early on, so why not add them to a good used one we want to keep around for years?

Finally, we spent $325 on the graphics and seat cover. No, this wasn’t necessary, but we wanted our 400 to look cool.

In the end, our build, quad, parts and all set us back $6,534.38. We could have had a good solid runner for around $5,000, but it wouldn’t last as long  or be as much fun to ride or look at.




In the end, we wound up with a fun to ride, tough, trail ready machine for over $4,000 less than buying a brand new one. If you add skid plates, beadlock wheels, and a steering stabilizer to that new machine, our Affordable Trail Quad Project would cost around $5,000 less! Best of all, this project started for $3,000 and if you shop carefully, you could find a 400 as nice as ours for even less. Buy it; build it up as your budget allows; and have a blast!


Machine Manufacturer Price Count
2001 Honda TRX400EX $3,000
Replacement Parts $1,849.13
Subframe Power Sports Nation, Stock 400EX Take Off $248.99
Subframe Primer Color Rite $22.95
Subframe Paint Color Rite $44.95
Subframe Clear Coat Color Rite $22.95
Steering Stem Teixeira Tech, Anti-Vibe $319.95
Steering Stem Bearing OEM $14.30
Steering Stem Dust Seal OEM $7.56
Steering Stem Bar Clamp Teixeira Tech, +1 $109.95
Handlebars Fasst Co. Flexx Bars $399.99
Clutch Cable Motion Pro $8.99
Throttle Cable Motion Pro $8.99
Rear Brake Return Spring OEM $20.19
Heel Guard Bolts and Washers OEM $26.75
Brake Pads Braking, $124.35 3 Sets
Axle Bearin Carrier Tusk $59.88
Tires Front GBC, XC Master, 21×7-10 $175.78 2 Tires
Rear Tires GBC, Ground Buster III, 20×11-9 $157.68 2 Tires
Air Filter Uni, Foam Filter $42.95
Motor Oil Maxima Pro Plus $31.98 2 Quarts
Upgraded Parts $1,360.25
Wheels Front GPS, Single Beadlock, Alloy Rings $267.00 2 Wheels
Wheels Front GPS, Dual Beadlocks, Alloy Rings $393.30 2 Wheels
Steering Stabilizer PEP $300.00
Skid Plates Ricochet 4-piece Skid Plate Set $381.96
Case Saver Tusk $17.99
Cosmetic Upgrades $325
Seat Cover Cosmic Quads, Custom $125
Graphics FTR Powersports $200
Total Build Price 6,534.38

Tags: , , , , , , , , , , , , , , , , ,

About the Author

Back to Top ↑