Complete T-Maxx Performance Guide
(Part 3)

The Complete T-Maxx Performance Guide

Part: 3

"Transmission / Drivetrain"



Welcome to the 3rd and final installment of my T-Maxx performance guide. In this segment I will show you ways to get smoother action and better performance out of your drive train. I'll also show you how to choose the correct gear ratio for the track and teach you how to get the best performance out of your 2-speed for improved laptimes. So, let's get to it! For part 1 (Suspension Tuning), and part 2 (Chassis Tricks) of my T-Maxx Performance guide series, click the links below.

Click here for Part 1 of the T-Maxx Performance Guide series

Click here for Part 2 of the T-Maxx Performance Guide series




Gearing Choices

There are quite a few different gear combinations available for the T-Maxx. The chart below will give you a good idea of where to start on a truck equipped with a 2-speed. Remember, these are only suggested gear ratios. The actual track layout, jump specifications, surface conditions, etc. will ultimately dictate what ratio is best for your track.


Gear Choice guide
Clutch Bell
Track Size (length end to end)
50ft to 80ft (small & tight tracks)
80ft to 110ft
110ft to 140ft
140ft to 170ft (typical track size)
170ft to 210ft
210ft+ (large & open tracks)

(Note: A 22t clutch bell is also available for the T-Maxx, but is for extreme top speeds and is not very practical for racing on most tracks.)


Track Size

Gearing the truck properly to match the size of the track is critical for fast lap times. You want to be able to effeciently use all of the power that the engine is capable of producing. Being over-geared will put more load on the engine and clutch causing the engine to run hot with less power out of the corners. The idea is to get the engine to clear out before you get to the next corner. The engine produces its best power when it is burning the best air/fuel mixture. This is normally found in the mid to upper RPM range.


Big off-road tracks, such as Johnny Cool Guy Raceway in Euless, TX (pictured above) is a perfect example of a modern nitro offroad track that Monster trucks are raced on. Choosing the right gear ratio is very important on a track this size.


On larger tracks it is ok to gear a little higher because the truck's cornering speed is usually greater. This keeps the engine in the best RPM ranges as described above. If the truck is geared too low on larger tracks, the engine will spend too much time in the upper RPM range. This will cause the engine to run hot, and of course will affect top speed as well.


Jump Placement

The placement of jumps on the track can also have an impact on your gear choices. A lot of tracks will have a set of jumps coming out of low speed corners, so good bottom-end punch is important to clear the set. What this means is that you may have to gear down to make certain jumps effectively. Your truck may be a tad slower down the straight, but it is now getting from apex to apex much more quickly. This set-up will be more desirable when your truck spends the majority of its time in the infield. Of course, this may change if you're on a more open course, with either smaller jumps or easier jump sets.


1st gear jump set
Here are two good examples of doubles that will need to be negotiated in 1st gear. There is simply not enough room to utilize 2nd gear effeciently. Make sure that your truck is geared low enough in 1st gear to get out of the hole (red arrow) with enough punch to clear the double set (yellow arrows).


Second gear jump set
There should be plenty of room before this jump to hit 2nd gear, which would propel the truck over the third jump. Without 2nd gear, this set would otherwise be a double-single, meaning that you would have to jump the first two jumps as a double, then immediatly take the last one by itself. This will take a bit longer to get through, so tuning the 2-speed along with choosing the right gear ratio to clear the whole triple set would be the way to go.

It's ideal to utilize a gear ratio that works best for the majority of the track. If the track has a long straight, but a tight infield, then gearing up to be the fastest truck on the straight is not necessarily going to be the best move. You'll need to maintain a fast pace through the infield as well. If you are coming up short on doubles, and bogging slightly out of the corners, then you can bet that all of the time lost in the infield will never be made up by the fraction of a second that you stand to gain on the straight. A lot of times a racer will get so excited about how fast their truck is going down the straight that they end up forgetting about the turn at the end of it? SMACK !!!



Changing the shift point for different gear ratios


Two-speed adjustments are necessary when changing the gear ratio between the clutch bell and the spur gear. Changing the gears on the clutch bell to a higher number of teeth, and/or changing your spur gear to a smaller number of teeth will give you a higher top speed. This will also take away a little bit of low end punch. This will affect your shift point by making your two-speed shaft turn at a higher RPM, thus causing the two-speed to shift sooner. If you are going to a clutch bell gear that has a lower number of teeth and/or a spur gear that has a larger number of teeth, then the two-speed will react just the opposite. Turn the adjustment screw clockwise for a later engagement, or turn the adjustment screw counter-clockwise for an earlier engagement depending on the need. Adjust the two-speed in small increments. Never turn the adjustment screw more than 1/8 turn at a time before testing the shift point. This is a fine adjustment, and can get way off base quickly if large adjustments are made.

Two-Speed Adjustments

The shift point of the two-speed is not only important for optimum performance on the track, but it is very important for long engine life and reliability of the engine as well. If the transmission is shifting too soon, power will be lost, and the engine will over-heat quickly. If the shift point is too late, then the engine will be allowed to rev too high for too long. This condition can cause many problems like accelerated wear between the piston and sleeve, plug damage, poor fuel economy, and can also lead to very hot engine temperatures.


Rotate the spur gear until you see the opening inside the access hole. Hold the gear steady while rotating the black shaft that exits the front of the tranny case. Rotate the shaft until you see the second allen screw. Important: Do not turn the first screw. This screw is used only to secure the 2-speed hub to the 2-speed shaft.

The prime time for the transmission to shift is at the point before the engine is just about to ?wind-out? or ?peak?. You don't want it to actually reach its peak rpm, but you'll want it to get close. This will allow the engine to clear out, and continue to produce good power on through the next gear ratio. Check out this link for what the engine should sound like with a properly set 2-speed.


A well-timed shift point is also important on the track. When the transmission shifts into second gear, there is a noticeable ?instant? boost in speed. This boost can upset your truck's handling before and through the turn. This can cause a greater chance of you over-shooting the corner, which adds seconds onto your lap times. For instance, if you're racing on a medium-sized track that has a long straight, but the rest of the track consists of many turns and switch backs, then there is a good chance that first gear will be able to handle all of the infield duties on its own. There is really no need for the transmission to shift until you're on the straightaway. In a situation like this, allowing the transmission to shift in the infield will more than likely hurt your lap times, by increasing the chance of the shift throwing your truck wide in a corner. If the engine is really revving out in an area or two within the infield, then it is ok to allow your transmission to shift; just use good judgment. You may also benefit from gearing up a couple of teeth on the clutch bell to get the rpm down through the infield portion of the track. This, of course, will depend on the track size and layout.




Slipper Clutch Adjustment

High Bite Tracks


On high bite tracks that offer a lot of grip, a properly adjusted slipper can help prevent the front end from lifting up when accelerating out of a corner. This will keep the front end down preventing a push or understeer.



Low Bite Tracks


On slick tracks or surfaces that do not offer much traction, the slipper can be loosened enough to limit wheel spin to keep the truck stable under acceleration.

A good starting point for the slipper setting on the T-Maxx is to tighten the slipper nut all the way until the spring is stacked solid, then back the nut out 1/8 to 1/4 turn. Experiment with different settings for your track conditions to obtain optimum traction with as little wheel spin as possible. Be careful not to run the slipper too loose. This will cause excessive heat build-up and could result in a melted spur gear.


Differential Tuning

The differentials can be filled with a thick lube to slow down the diff action. This will help prevent the diff from unloading when powering out of the corners. Any of the hobby-class differential lubes out on the market should be fine; the thicker the lube, the slower the diff action. Slowing the diff down will also make the truck's traction more positive on throttle. This will typically reduce steering entering a corner, but will actually increase the steering coming out of the corner. Heavier fluids are also beneficial for higher bite surfaces as well. Loose and bumpy tracks will want lighter oils in the differentials.

Normally, I use 50,000wt in the rear, and 30,000 in the front. The heavier fluid in the back gives me a little more ?on throttle? steering, which is desirable for a 4WD monster truck when you need to get around sharp turns. Experiment with different thicknesses to see what works best for your driving style/conditions.

Note: The stock T-Maxx differential gear housing is not sealed. That is why I recommend using a good oil that is designed especially for differentials. "Differential" oils stay on the gears better under use, where as a typical gear grease will sling off of the gear much more quickly.

Sealing the stock T-Maxx diff is an advanced procedure, and requires the precision of high quality machining equipment to modify the diffs properly. However, sealing the diffs is not absolutely necessary. I've run complete 2-day events on unsealed diffs using a good silicone diff fluid. The diff will "lighten" up a bit towards the end of a race weekend, but performance was still good. Unsealed diffs will just need maintenance more frequently. It's definitely worth performing that extra maintenance before a big race though.




The clutch can be adjusted by shaving material off of the shoes for a later engagement. This can be useful if you are on a high bite surface, because it will allow the engine to get up a little higher into the power band before engaging, giving the truck more punch out of the corners. Make sure that you take the same amount of material off of both shoes. Do not try this if you are having trouble getting the truck hooked up on the track. This will only make things worse.

Use a hobby knife to shave the material off of the clutch shoe. Only shave a small amount at a time, and make sure that each shoe is cut identical to each other. This will level out the wear, and provide better clutch performance.

The T-Maxx clutch shoes (#4146X) are already cut from the factory, but you can experiment with by shaving off a little more material for later engagements. The stock shoes (#4146) are uncut and will engage a little sooner than the cut ones. These can be helpful on a slick track with a lot of loose dirt on top of the surface. Be careful not to remove too much material from the shoes, as this will leave the shoes too ?light?. They will not engage the clutch bell firmly, defeating your purpose of getting more punch out of the truck. Trim a little, then try them out in the truck to see what works better.



Clean Bearings

Cleaning the ball bearings inside your Maxx is a very simple task, yet very effective in improving the performance of the truck. There are different brands of bearing cleaning devices out there, but they all perform the same function; getting the dirt and grime out of your bearings. Your local hobby shop should carry at least one or two types of these inexpensive bearing cleaning tools. The model below is the Bearing Blaster by RPM.


Here's a speed tip for new models: Cleaning the heavy factory grease out of the model's ball bearings and replacing it with a light, thin bearing oil will considerably decrease the drag in your truck's drive train. This will not only increase the speed and power of your Maxx truck, but it will also allow the engine and clutch assembly to run cooler and much more efficiently.


Position the bearing onto the conical adapter inside the tool, then cover with the top. Insert the bearing cleaner straw into the cover, and flush out the bearing. Electric motor spray works very well for cleaning bearings. Caution: Always wear eye protection when using pressurized cleaning solvents. Repeat this step until the bearing spins very freely and all of the gritty feeling of dirt has completely gone away. Once the cleaner has dried away, lubricate the bearings with thin bearing oil. It may take a while to do your whole vehicle, but is well worth it in the end.


When cleaning sealed bearings, the rubber seal must be removed from the bearing for easier cleaning. After the bearing is clean and lubricated, simply press the seal back into the bearing until it snaps in.







SportTraxx Racing Tires?

The SportTraxx racing tire is a hi-performance racing tire that works very well on all sorts of different track conditions. The soft compound rubber combined with an aggressive ?hard edge? block tread design achieves the highest levels of traction, even in undesirable conditions. The two-stage contoured insert fits perfectly inside the tire, and allows the tire to do its job more effectively. I run the SportTraxx tires on the majority of the tracks that I race on. Read more about this killer tire here (SportTraxx Racing Tires).


Tire Tuning


The full size pins work great on most driving surfaces, but a good way to maximize bite and response on hard-packed blue-grooved racetracks is to trim the pins down to about half their original length. This minimizes flex and basically gets more rubber to the hard surface, which increases traction. Stick with the full pins for soft loamy surfaces, and try trimming them down for the many tracks out there that are ?grooved? out.



Engine/Transmission Upgrades


Pull starter (part# 5170) Replacing the EZ-Start® system with a pull starter is an excellent way to shed 3.8oz. of weight from your T-Maxx. The weight of the pull starter also sits a lot lower in the chassis than the EZ-Start® system. The TRX 2.5 pull starter is a very reliable one that should only take a few tugs (once the carburetor is primed) to start your TRX 2.5 racing engine. Remember that when switching to a recoil starting system, it will be necessary to use a glow plug igniter to pre-heat the glow plug prior to starting the engine.



FWD Only gear shaft (part# 4994X) Removing the reverse system is a big step to reduce rotating mass inside the transmission; along with the weight of the extra servo that is used to shift the system. A lightweight single-gear shaft replaces the entire system, and is located where the main output shaft used to be. This set-up eliminates reverse (which is not used during racing anyway), and provides quicker smoother acceleration.





If you race at tracks that allow ? any ? type of monster-style buggy or truck conversion into the monster truck class, then you know winning with a real ?bona fide? monster truck is getting pretty tough these days. However, due to the very heavy weight and more expensive parts, engines, and upgrades for the 1/8-scale buggy-trucks, I've seen many people switch back to the T-Maxx in the Monster truck class. The bottom line is that the T-Maxx ? can ? compete with the big block vehicles. This tuning guide will definitely get your T-Maxx where it needs to be on the track. I believe that the key to beating the latest rush of big block 1/8-scale buggy conversions is to keep your small block ?T? light, smooth, and set-up properly, and oh yes ? get out to the track and PRACTICE !!! See ya !!!

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