Part 0 - Lock the Diffs 

“What fool put a center diff in this thing?” 

I call this part 0 rather than part 1 because a monster truck or rock crawler with three open differentials is just plain silly. It’s not like it has electronic traction control or “gerotor” couplings.

 Locking the center diff is easy.  Don’t put in the diff balls and use JB weld to seal it shut.  Do this first, so that it will be dry by the time you finish building the kit.  If you’re a fan of perfection, you can shim it to keep it steady, or JB weld it with the balls in place (without the balls it’s a little thinner).  There is no reason to ever undo this.

 Don’t have JB weld?  No problem.  Use a pair of screws to screw the two halves together…you might have to drill a couple of holes.  I found it easier to go to the hardware store and pick up JB Weld.  In case you like the screw idea, here is a picture:

The axle diffs are a little more tricky. If you look online, you’ll see a lot of different answers about some kind of goo that you can put in there to lock them.   Some of these can even be undone.   Well, forget about all that.  There is a much better way that is easy to undo. 

When it comes time to build the axle differentials, you will be given three small bevel gears and a little “Y” on which to mount them (all illustrated clearly in the instruction manual).  These little bevel gears rest between the two large bevel gears that connect to the output shafts, or “half shafts”.  Instead of mounting all three of them on the little Y, mount only two.  Then take the third and wedge it between them, making sure they sit flush (they sit perfectly flush when properly positioned).  This will make it impossible for the large bevel gears to rotate at different speeds, locking the diff up tight.   

Look carefully at the picture below…see the third bevel gear wedged between the other two?  It’s a perfect fit and a perfect diff lock.

  
(These first two images appear courtesy of rc-whirlybird, who saved me the trouble
of disassembling my truck - thanks!)

When you want to unlock the diff, just take the third one out from between the other two and mount it on the “Y”.

Keep in mind, though, that locking both axle diffs is only for dedicated crawlers.   People who like to drive around their house should leave both open or just lock the rear, as locking one axle diff will hurt your turn radius, locking both will make it hard to turn around in an empty parking lot.   Also, if you lock an axle diff, you will need to put a high torque servo on that axle.  With an open axle diff, a regular servo is sufficient.

Part 1- All Stock Mods 

"Tamiya instruction designers hate you... "

 There is really no other way to explain why the assembly instructions contain all the steps you need to build a really bad truck with under an inch of ground clearance.   Nevertheless, I followed them to the letter, and wound up with exactly what I thought I’d get when I first looked at the kit…a neat truck with a ridiculously high disposition and a ground clearance that would make it hard to crawl over a salt shaker.

 Before I could even stand to look at it, the body had to come down.  Sitting as high as it was, it looked like some absurd child’s toy designed by a madman with a crack habit.  

 Since I had the MaxClimber kit, that was simple enough.   All it took was lowering the little rubber tubing that determines where the body rests, maneuvering the body as low as it would go.   The outer fenders required a little trimming for wheel clearance, but all in all, it looked great.   That, of course, brought up the first question.   Why does Tamiya have you build it to look, well, dumb…when you can build it to look better with the same parts?

Once the absurd body problem was taken care of, the next major issue had to be addressed…ground clearance.   Like a lot of people, my first choice was to run out and get 2.2” stadium truck wheels and some stadium truck tires.  That helped with ground clearance, going from about an inch to just under an inch and a half, but I just didn’t like the look.   The tires were too big and the truck tended to roll over more than it had without them, so I put the stock tires back on.

It was time for plan B.   

I took a good long look a the chassis, and decided that the cantilever links, the links that connect the cantilevers to the axle, control the ground clearance.   So I made them longer by unscrewing the rod ends.  Measuring between the ends of the rod ends (the metal parts only), I extended them to 14mm.   You can use the gold wrench that came with the kit as a guide…the end of the wrench with two openings should just be able to squeeze between the plastic parts.  I put the wheels back on and put the truck on the table, only to discover that there was very little difference.   After a moment of frustration, I realized that the shocks needed to be adjusted.  Using the thicker shock clip in the kit (an unused part) remedied the situation.

The result was nothing short of amazing.   Almost 1.5 inches of ground clearance with the stock tires, just as much as was gained by switching to the ungainly stadium truck wheels!

However, as most mods do, this one affected something else.  There was now a slight clicking coming from the drivetrain…the stock dogbones were binding.

Once again, this called for a long hard look at the chassis.   There are three links that connect the axles to the chassis:  the cantilever links, the upper links, and the lower links.   The lower links control the distance of the axle from the chassis, and together with the upper links, they control the angle of the axle relative to the chassis.  In essence, making the lower links longer (while keeping the upper links the same) rotates the axle down, so that the outdrive points at the ground.  Decreasing their length relative to the upper links rotates the axle up.   The opposite is true of the upper links.

After some tinkering, I increased the length of all the links to the following measurements (once again, measure the metal part of the rod between the rod ends only):

  lower links: 45mm 
upper links: 34mm 
(cantilever shock links stay at 14mm)

However (there it goes again), the dog bone is not long enough and falls out immediately.   There are two ways to remedy this: find a slightly longer dog bone, or be stubborn and refuse to give up on the idea that this kit could be built better out of the box.

Now, I called this section “all stock”, but you will need something not found in the kit…foam.  Just about any foam will do.  Cut out some small pieces and stick them in the outdrives, both axle and center diff.

This takes some patience, as you may or may not get it right the first time.  What you want is a dogbone that stays in the cups (on both ends) throughout the entire articulation range.  Too much foam on one end or too little on the other will push that end out too much and the dog bone will drop.   I got one of them right the first time, but dropped the other one during testing.   A little more foam on one end and all was good.

The end result is a truck with a ton of articulation and a respectable ground clearance, using all stock parts (and some foam).   It really makes you wonder how much money Tamiya lost in sales by marketing the truck with the limited clearance and articulation.   I came very close to not buying it for those reasons, I’m sure many decided not to.

Part 2 - Not So Stock Mods

“Never throw anything away…”

At least in RC.  If you follow this tenet in your daily life you will be featured on a Discovery channel show about crazy people.

The items that I’m glad I didn’t throw away are the cheap plastic shocks from the Losi Mini-T.   Most people buy the aluminum shocks right away and toss the old plastic ones away (hopefully not in the trash).  Some people sell the old ones on EBay for a couple of dollars (usually about $3.00).  I happen to own a Mini-T with aluminum shocks, and had the plastic ones lying around somewhere.   If you have multiple sets, use the back (longer shocks).  If you only have one set, buy another set on EBay.  Until then, you can use the shorter ones on one side (I put them on the front…my other set is in the mail)…just don’t mix them up. 

When attaching the shocks, do not remove the ball ends on the cantilevers, even though they look like they’re too big.  The shocks are made of soft plastic that will easily stretch its way on there.  Just use a pair of pliers to force them on, then push them past the center of the ball and they will move freely.

The extra articulation comes from the fact that the cantilever links (the Mini-T shocks) can expand or contract as needed.   When a wheel is lifted, its cantilever connector can contract, and the opposite wheel’s connector can expand, allowing the axle to articulate outside the boundaries of its suspension geometry.  In other words,  it can move more than the length of the suspension links allow.

The only problem with using the Mini-T shocks was that the truck became very “tweaky”.  When driving, even slowly, the chassis would move left and right a lot, twisting or tweaking as the truck moved.  This is present to some small extent in the stock configuration as well, but the truck almost immediately rights itself.  Not so with the Mini-T shocks.

Quickly annoyed at this, I realized that while I wanted the extra articulation of a flexible cantilever link, using an extra shock and getting all sorts of freaky tweaky action was uncalled for.  So, off came the springs, solving all my problems.  When driving flat, the TLT rested on the fully closed Mini-T shocks and drove like stock.  When articulating, the opposing link expanded as necessary, greatly increasing the motion.

Some ground clearance is lost when removing the springs (as that reduces the length of the cantilever link), but a couple of zip ties used as spacers remedies this.  Raise the spring-less shock and wrap zip tie around the metal shaft, pulling it tight and clipping off the excess.  I used two zip ties with the bottom one wrapped around a small block of foam (because I was in the mood to cushion the shafts). 

Using zip ties is the quickest way to shim the shock…feel free to come up with a more elegant solution.

Part 3  - Center of Gravity

“He who puts battery on top of chassis will roll down hill…”

All of these mods did nothing to improve the truck’s performance.  That’s right…nothing.  All they did was give me some online bragging rights. 

“Look at my awesome TLT!  Behold the articulation in its stock form!  That’s more that you have and you stretched it by five feet!  I’m better than you!  Muhahahahahaha!”

Ahem.  What I did not post was that this silly truck flipped over every time I tried to climb anything.  Raising the ground clearance raised the center of gravity, and extra articulation made it easier for the top of the chassis to pivot to rollover position every time I crossed an obstacle.

I was ready to cry.  All that work, for nothing.   Instead of crying, however, I decided to do something about it.   The first step was to go from six cells to four.  That helped.  It did cut down on top end (oh no, you mean I can’t race my rock crawler??) and a little run time, but it was nothing to write home about.  I mean the gains, as well as the losses.  The truck still rolled over.

I realized that the batteries had to come down, but the chassis is so small there isn’t much room.   I looked at putting them on the axles as some crawling enthusiasts suggest, but that would mean I’d have to run 2 cells.  Not good.  

Here is the pack:

And here is how it’s mounted:

I had to cut away a part of the plastic gear cover to make the batteries sit flush.

Part 4 - Conclusion

“Ah, how it all comes together…”

What a difference!  The low center of gravity allowed the extra ground clearance and articulation to work in the truck's favor.  I could now climb things that previously were unapproachable.  In short, I had a real rock crawler that from a distance looked like a stock TLT-1 MaxClimber.   I have an E-Maxx tire worth of articulation (that’s 1.2 soda cans for those who need precise measurements), 1.2 540 motors worth of ground clearance, a center of gravity so low I can climb on the ceiling (but only when I’m sleeping), and the only non-stock parts are a pair of three dollar Mini-T shocks.

Why didn’t the engineers in Tamiya do this to begin with?  I don’t know.  Maybe because they are evil and want us to suffer.  Or, maybe because it feels so much better to do it yourself, and this is, after all, a hobby.

Good luck with your own TLT, and I hope you enjoy these mods as much as I do.  There’s no limit to where you go from here; stretches, custom chassis, etc.  Just remember that you bought the TLT because you liked the size, and that a bigger crawler isn’t necessarily better, it’s just bigger (rocks come in all sizes).  Enjoy.