2015 - Traxxas T-Maxx Classic
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Yes, I got the old version. No, I don't regret it. :)
This is my take on the venerable T-Maxx 2.5. The reasons I didn't go with the newer version are: 1) because I wanted reverse functionality right out of the box, and 2) because the T-Maxx 2.5 is smaller. We all know Traxxas keeps making their vehicles larger while insisting they're still 1:10 scale, and I wanted something that would take up less space than my "1:10 scale" Summit. (seriously, the Summit barely even qualifies as 1:8 scale, it's so large.)
My first two concerns upon receiving this truck were the clutch and the axles. The stock clutch engaged at too low a speed, causing the centrifugal ratchets that engage the forward and reverse gears in the transmission to stall the clutch bell and bog-down the engine over and over -- the net result was a stuttering effect on takeoff. I replaced it with a Buku adjustable clutch, which there is unfortunately no good way to photograph, but it's kinda-sorta slightly visible in the photo above. It allowed me to adjust the clutch engagement point so the clutch shoes would only be lightly dragging against the clutch bell when the centrifugal ratchets in the transmission kicked in, so it doesn't bog-down the engine anymore. The takeoff is much smoother now, though it does still require a momentary burst of almost full-throttle to overcome the truck's inertia and get it moving. That's fine though, because wheelies are fun.
I also replaced the stock slipper clutch with Traxxas' factory upgrade for the T-Maxx 2.5, which uses the newer-style 3-pad sintered clutch design. Why they're not just including this with the T-Maxx Classic nowadays, I have no idea, but at least it works well. Oh, and I replaced the stock 20T clutch bell with an 18T clutch bell to give the little 2.5cc engine more leverage.
As for the second concern, I don't like plastic axles; they always twist eventually (I have to admit the plastic axles on the Summit are impressively strong, though they are definitely an exception), and I prefer pin-and-barrel "CVD" joints vs. universal joints whenever possible, the sole exception being in a RWD vehicle with limited suspension travel. Both are significantly better than dogbones, though; fortunately the T-Maxx at least didn't have any of those. So I went looking for options. There were cheap no-name steel axles available on eBay, but I wanted something better.
For the center axles, what I ended up doing was cobbling together the rear-center sealed axle from a Traxxas upgrade kit for the T-Maxx 3.3, and the front-center sealed axle from the Traxxas upgrade kit for the Revo. The front-center sealed axle from the Revo works perfectly, the only change needed was to install the outdrive cup from the T-Maxx kit onto the front of the transmission. The brass bit that you can see behind the brake hex in the photo above is actually just a used Oilite bushing left over from an experiment with my Axial Wraith; the brake hex isn't firmly fixed onto the end of the center axle, so I needed something to keep it from wobbling, and the 5x11x4mm Oilite bushing just happened to be the perfect size. It was one of those situations where I noticed the problem, grabbed the first thing off my desk that looked like it might work, and indeed it worked so well that I just left it there. (although it occurs to me this might be a good use for the "Black Ice" plastic bushings I bought from LockedUpRC a few months ago, since the plastic won't scratch the surface of the transmission case. Oh well, I'll deal with that later.) I had to grind away a little bit of metal on either side of the front-center axle opening in the chassis, to keep the axle boot from rubbing on the chassis, but that was maybe 5 minutes of work, including test-fitting the transmission and removing it again to grind away more metal.
For the wheel axles, I bought a set of MIP X-CVDs intended for the Revo/Summit/T-Maxx 3.3, and somehow managed to scrape together four stub-axles intended for use with the old MIP C-CVD axles on the T-Maxx 2.5. (those parts are discontinued, of course.) I installed the old stub-axles in the X-CVDs, and voila, I had a set of telescoping steel CVD axles for my T-Maxx 2.5.
The next big problem was the steering. Everyone knows the servo-saver on the T-Maxx 2.5 is garbage, and the steering bellcranks from the T-Maxx 3.3 can be retrofitted onto the T-Maxx 2.5 as long as you can get the transmission-shift servo out of the way. So that's the approach I took, and the new steering works great, but instead of propping the transmission-shift servo up on spacers to get it out of the way, I opted to install a low-profile Hitec HS-8775MG shift servo instead. (they are also useful for touring cars, because they're fast, small, and reasonably high-torque -- and they have 25T splines now, so they can fit Futaba-style servo savers!) With a low-profile shift servo installed at the stock height, I wouldn't have to figure out how to compensate for having the shift linkage operating at a funny angle. While I was at it, I replaced the other servos as well; the steering servo got replaced with a beastly Hitec HS-7955TG, and the throttle/brake servo was replaced with a more reasonable (but still stronger-than-stock) Hitec HS-5645MG.
That brings me to the next problem; the throttle obviously didn't need more torque to operate properly, but the brakes do, and yet the stock brakes on the T-Maxx 2.5 *also* suck. The disc is made of rough-cut fiberglass coated with friction material, and the "pads" (not really pads because they have no friction material on them) are thin sheet-metal that don't clamp against the disc so much as bend the moment pressure is applied to them. Unfortunately there aren't really any better brake options for the T-Maxx 2.5, but I did see a handy tip on the Traxxas forum that the stock metal "pads" could be doubled-up for extra strength. I decided to give this a try, with my own personal twist: I sanded-down one side of each metal "pad", then I superglued them together and clamped them together overnight. Then I sanded the side of each "double-pad" that would touch the disc, because if there's one thing I've learned about RC car brake parts, it's that they are *never, ever, ever* flat like they ought to be. Turns out, that simple trick worked great; the brakes went from almost-useless to strong enough to pull stoppies if I wasn't careful.
Also, while I was shopping around for brake parts for the T-Maxx 2.5, I discovered what might be the only *good* option for an upgraded brake disc: a sintered disc made by GPM. It looks and feels remarkably like the stuff the brake pads on my mountain bikes are made of, which is a big improvement over a chintzy piece of fiberglass. I'd still rather have a metal disc and real pads with friction material on them, but I have no complaints about the performance of this setup. (there is actually a metal-disc/fiberglass-pad brake available from GPM as well, but the metal disc is so thin I'm sure it would gouge the aluminum hex the disc rides on. This sintered disc is much thicker and therefore distributes the braking force over a larger area of the hex, reducing possible damage over time.)
Having sorted-out the drivetrain, steering, and braking deficiencies, I started to look at the design of the chassis, and I realized one of the reasons the stock bulkheads break is because they're cantilevered off the end of the chassis plate (this is common knowledge) and the only thing reinforcing them is the chassis brace on the underside. Well then, the next step was to get stiffer chassis braces. Traxxas conveniently makes aluminum chassis braces, and RPM makes a center skidplate that ties the chassis braces together to give them a super-solid feel. (and also keep gunk away from the drivetrain, but I mostly bought it as structural reinforcement.) I did also replace the stock bulkheads with RPM bulkheads, but I saw no reason why I shouldn't reinforce the chassis both ways at once. I also replaced the stock grey skidplates with optional black skidplates so everything would match.
At this point the truck was nearing completion; the only other problem I had was the stock plastic shocks, which I disliked for two reasons: 1) the shafts weren't hardened, and I managed to bend 3 of them to varying degrees (get it? it's a geometry pun!) just by driving around and "jumping" mounds of mulch surrounding garden bushes; and 2) they're plastic. I just don't like plastic shocks; I haven't found a set yet that work properly, because shocks have to be made to very fine tolerances to actually provide consistent damping, and injection-molded plastic isn't accurate enough. I'd had great luck with STRC's aluminum shock bodies and Traxxas' optional TiN-coated hardened-steel shafts on my Telluride and 4Pede, so I didn't have to think very hard about what to use on my T-Maxx. (rebuilding 8 shocks at once was kind of a chore, though.) I don't know how STRC does it, but they manage to reduce stiction to almost nothing, without allowing the shock seals to leak. (I suspect Traxxas' X-ring seals help play a role in this.) Since this is a nitro truck, I had to deal with exhaust spray, and I had the bright idea to equip the two shocks immediately behind the exhaust pipe with RPM brush-guards (also used on my Telluride for different reasons) to keep half-burned castor oil from working its way up the shock shafts, past the seals, and into the shock oil. I added small O-rings around the front edges of the pivot-balls in the lower eyelets, to keep the lower eyelets from being able to tilt side-to-side, so the guards are kept facing straight-forward at all times. As you can see in the picture above, they do a good job of catching spray before it can get onto the shock shafts.
One last little mechanical deficiency that needed to be addressed was reinforcing the rear toe-links. They are each attached to separate, disconnected halves of the rear bulkhead, and I noticed that Traxxas made a little fiberglass-reinforced-plastic tie-bar designed to connect the two links together. When I saw that, a little black plastic bit installed in an inconspicuous location, I realized there was no way Traxxas made that just for bling-value, so I installed one to fend off whatever failure the tie-bar is supposed to prevent. Seems like cheap insurance to me.
Lastly, I replaced the stock wheels and tires with HPI wheels and tires from the HPI Savage, which look larger but are actually almost the exact same size as the stock T-Maxx tires; they're just mounted on 3.2" wheels instead of 3.8" wheels, so they look bigger. The stock tires were fine, but I wanted something with a little more grip and quieter rolling, which is odd since it's a nitro truck, but whatever, I'm allowed to be idiosyncratic if I want to be. And I replaced the stock plastic bumpers with the optional aluminum bumpers, not because I wanted stronger bumpers, but because I wanted bumpers that wouldn't discolor when scratched. Black plastic bumpers would've been fine, but I couldn't find any that didn't look weird. (seriously, what were the guys at RPM smoking when they designed their optional front bumper for the T-Maxx?) As you can see from the picture above, the rear bumper has already been scraped by a couple unplanned wheelies, and they still look fine, whereas the stock bumpers had nasty black gashes in the silver paint.
Also, something you may have noticed looking at all the pictures above: The screws are all hex! Yes, I bought a HexHeads screw kit and replaced every single Phillips fastener on the T-Maxx with hex fasteners, so I can actually tighten them properly without stripping them. It's totally un-glamorous but an absolutely essential mod.
And now the question that I keep getting asked: WHY didn't I upgrade to the 3.3 engine??? Well, two reasons: 1) the 3.3 engine is much louder, and 2) I wanted to give the 2.5 engine a chance. It turns out that with the 30% nitro that I run in all my vehicles, plus the optional larger cooling head, proper shimming for the higher-nitro fuel, and slightly lower gearing, it can make the T-Maxx pop wheelies just fine. Sure, a bigger engine would let it haul faster, but the T-Maxx is a true monster truck -- it doesn't have the handling capabilities to go much faster than it already does without posing a serious risk of losing control if I have to stop or turn suddenly. The Losi 3.4 engine in my HPI Bullet is great fun, but that vehicle is for all intents and purposes a truggy with big tires and no wing, and even with its lower stance, it can still barely handle that much power; all it takes is a sudden turn or a bit too much throttle and it's flipping and tumbling all over the place. I'm content for my T-Maxx to be able to drive off-road without difficulty and to do so at a reasonable speed, and the 2.5 engine answers the mail quite nicely.
The mods I made to this truck are pretty run-of-the-mill, but I think they added up nicely.
Finally got around to replacing the crappy plastic exhaust pipe. I don't know if the aluminum pipe (originally intended for the Pro .15 engine) is actually any better, but at least the exhaust note is cleaner now.
I had to make my own exhaust hanger. Rather than trying to bend piano wire into an eyelet, I opted to use a Dubro 2-56 ball-link with the ball replaced from a 4-40 ball-link, so it would fit a suitably large fastening screw. This also means I could fine-tune the length and tilt of the exhaust hanger by tightening or loosening the ball-link, rather than having to make several hangers until I managed to get one bent to just the right length.
I finally got off my lazy butt and replaced the engine in my T-Maxx. It's something I'd wanted to do for a while, because the TRX2.5R was never quite good enough -- a little weak and very raspy-sounding -- but I knew it was going to be a huge pain to wedge my preferred HPI T3.0 engine in there. I was right.
To start with, I had to modify a T-Maxx engine mount to fit the T-3.0 engine, which involved cutting the two halves apart from each other:
Then I had to cut the crankshaft a little shorter, and grind away the threads on both ends to provide the necessary clearance for the flywheel retaining nut and the clutch bell bearings:
Then I had to make an adapter plate to allow the EZ-Start assembly to fit onto the T3.0's backplate. (well, I guess I didn't *have* to do this, but I wanted to keep the EZ-Start if I possibly could.)
Then I had to modify the heatsink to allow clearance for the EZ-Start motor:
Then, because the motor was absolutely filthy with metal shavings, I had to disassemble it completely, wash every single part, and put it back together before installing it:
It turned out to be worth the effort, though, because the engine is only on its third tank of fuel, still running rich enough to choke if I stomp the throttle after it's been idling for a few seconds, and it's already more powerful than the TRX2.5R was:
So I've got a more powerful engine that is also quieter, and I have fewer spare parts I have to keep on-hand; it's an improvement all-around.
A couple updates:
I got rid of the T-Maxx 3.3 steering assembly that I had been using, and replaced it with a GPM aluminum steering assembly with a separate servo-saver attached to the servo itself. The servo-saver I used is from the Associated MGT, and is much stiffer than the servo-saver integrated into the T-Maxx 3.3's steering assembly.
I also built a front swaybar using spare links from my 4Pede, swaybar retainer brackets stolen from my Ten-SCBE, and some 1/8" music wire from the hobby shop:
The goal is to reduce the front suspension's tuck-and-roll when coasting into corners without having to change the stock mushy suspension, which I actually like in all other conditions. This swaybar may well be too stiff, but the T-Maxx is a big heavy truck with lots of suspension travel that needs taming, so I'm optimistic about the swaybar's performance.
As you can see, it still has plenty of flex. But if this swaybar does turn out to be too stiff, I can just make a new one out of some 3/32" or 1/16" music wire instead; the hard part of figuring out how to mount it is already done, just cutting and bending some wire is a piece of cake.
I finished another round of mods on this truck. This time I replaced the original fuel tank with one that I know will work better, and I replaced the engine again, this time with a Losi 3.4. Yeah, yeah, I know, you told me so. The thing is, the TRX 2.5 worked fine as long as I wasn't running in grass constantly, and the HPI T3.0 worked fine as long as the grass was matted-down a bit. The problem was, neither of those engines could cope with the drag from thick, well-watered grass, and it just so happens that's all I have to run in at my current residence. So an engine upgrade was needed.
First off, here's the adapter plate I made out of Lexan to hold the new fuel tank:
Here it is with the fuel tank attached. The tank I used is from a HPI MT2, which I chose because I already have a HPI MT2 and I know the tank works well. The rear mount on the fuel tank couldn't be used because a standoff post in the rear would've interfered with the shocks, so instead I glued a second layer onto the adapter plate, with a channel cut-out to allow a zip-tie to pass through and anchor the rear end of the tank.
Here it is installed on the truck:
Here's the new engine, and the THS exhaust I bought to use with it:
I was a little concerned that the orange heatsink would look out-of-place on a chassis full of blue parts, but it works quite nicely with the paint scheme on the body.
Major update: I replaced the transmission on my T-Maxx with the newer transmission from the 3.3.
I really wish I'd known to begin with that the 3.3 transmission is a direct fit for my version of the T-Maxx Classic. The only things I had to change were the output shaft in the transmission, and the length of the front-center CVD. I had been using the rear-center CVD from the T-Maxx 3.3, and the front-center CVD from the E-Revo, but the 3.3 transmission requires both T-Maxx 3.3 center CVDs.
I didn't like the micro shift servo that came with the reverse kit, so I hacked-up a spare throttle linkage to fit the old linear servo-saver that I could use with my standard-size shift servo:
It actually wasn't that much work, but it ended up taking me a couple months to finish. That was partly because of distractions like "my job" and "my pregnant girlfriend" and other nonsense, and also because I took apart all of my Losi 3.4 engines, so I could send the pullstarter backplates to a machinist to have ball-bearings installed:
Because the Losi 3.4 is now well and truly discontinued (just like everything else good in this damned hobby), I wanted to make sure my Losi 3.4s would keep working well for as long as possible, and that meant fixing a fundamental design flaw that exists in all nitro pullstarters -- the pullstart shaft spins inside a bushing that ovalizes over time until it can no longer maintain an airtight seal. My old HPI engines have press-fit bushings that I was able to press out, cut shorter with a Dremel, and reinstall in combination with ball-bearings on my own, but the Losi 3.4's pullstarter bushing is integrated into the backplate so it required professional modification.
So, was it worth replacing the transmission in my T-Maxx Classic? Hell yes. Shifting between forward and reverse is more reliable with the new transmission, and because the new transmission doesn't need to spin-up before it can engage, I was also able to turn-down the engagement RPM of the engine clutch so it doesn' t have to drag so much on startup. That will keep the undersized clutch bell from overheating, which was a recurring problem with the old setup. I suppose having a proper steel brake disc with sintered brake pads is also an improvement, but y'know, the GPM sintered brake discs and steel brake plates I was using with the old transmission never gave me any trouble. I kinda wish I had something to use the spares for. Oh well, I can think about what to do with them while I'm enjoying my freshly-upgraded truck.
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