Tamiya TRF 419 Project

Page 2: Assembling the Chassis

While writing about this build, I am going to concentrate on the differences between this and the last chassis in the TRF line I built (the TRF 418). I also built a TRF 419X several years ago and wrote about it extensively but without comparison to any other model. The photos and details are still useful.

Can you spot the differences between the TRF 418 (left) and the TRF 419 (right)? It's highly unlikely because they are so externally similar. Not only is the layout the same, many of the parts are the same including most of the suspension. There are subtle differences scattered throughout though. Possibly the only difference a trained eye might spot in the above images is that the pulleys are now black instead of white.

If we compare the TRF 418 lower chassis plate (red) and the one from the 419 (blue), certain changes can be discerned. The biggest important difference is that the motor has moved slightly aft. The holes for the bulkheads have also moved slightly further apart (more on that later), and the cutouts for the pulleys have become smaller. The previous "relief cuts" which had been added to the TRF 418 as a stated improvement have now been removed, also stated as an improvement.

What about the upper deck? It also gets very slight, almost imperceptible changes which can only be seen by overlaying the parts. Overall shape and length are unchanged, but the holes for the bulkheads have been moved slightly apart. The holes for attachment to the motor mount, which were optional on the TRF 418, have now been removed entirely.

Here are some more slight changes. The lower bulkheads have been slightly strengthened at the sides with a thicker profile and smaller lower cutout. The rest of the dimensions appear identical suggesting that these would probably be interchangeable between models, so don't get them mixed up in your parts box or you'll never straighten it out again. The story is similar with the upper bulkheads which have had slightly more material removed making them a bit lighter and weaker. It's interesting that the lower bulkheads got stronger while the upper got weaker. This probably cancels out any weight change.

The shock towers have identical outer dimensions and shock attachment positions, but the bulkhead mounting holes have moved very slightly further apart. In this case they would not easily fit on the TRF 418 without forcing them. The dampers themselves have even changed by a sneaky amount. The TRF 418 (and prior models) used an o-ring (BD8), a shaft guide (BD5), and a rod guide (BD4). Now the TRF 419 eliminates the shaft guide and uses a longer rod guide (BD4) instead. The rod cap, cylinder cap, and spring retainers stay the same, but the cylinder is slightly changed to accommodate the new sealing system. Much less obvious is the fact that the internal diameter of the cylinder has increased by 0.5mm increasing the fluid volume by about 10%. The only external change (which can be seen by looking closely at the picture) is the addition of knurling to the outer rim of the cylinder which makes it possible to visually distinguish the versions. More about this when I build the dampers below. Note that the TRF 419X moved to an even bigger bore for the dampers (+1.2mm) which means that these intermediate diameter dampers seem to have only been used for a single model (although they were available separately as 42287 and are still available [with strengthened V-parts] as 42354).

The build begins with the rear bulkheads, center bulkheads, and motor mount. As previously discussed, the rear bulkheads are extremely similar to those from the TRF 418 but very slightly strengthened. The extremely complex 2-piece motor mount serves to also support the center shaft and will now only accommodates brushless motors with 6 mounting holes (more on that later). This was replaced with a more complex to assemble, but simpler to manufacture 3-piece motor mount on the TRF 419X and an even simpler version on the XR. The split suspension mounts from the TRF 418 have been updated to a "corner" style. Whereas the previous versions were reversible resulting in two spacing options with a single set of parts, these are unique and must be replaced for different spacing. This model uses blocks 1X for the rear suspension. Those little trident looking parts are spacers that go under the suspension mounts to change the roll center.

This aft view on the left was intended to show the new split suspension blocks but they are difficult to see. The bottom view on the right shows that there are 3 mounting holes at each end of the motor mount. By default only the outer 2 are used, but the inner hole can be used instead to reduce chassis stiffness. To maximize stiffness, all 3 can be filled (which is what I ended up doing after this photo was taken).

The front bulkheads are exactly the same as those in the rear. The front suspension blocks work the same as those in the rear but they are 1C instead of 1X (narrower width). The steering posts are unchanged from the TRF 418.

The sealed gear differential represents an interesting color inversion. Beginning with the TA-06 (and the TRF 417X), sealed gear differentials used black carbon filled Nylon gears and a white Delrin housing. These white gears (left) are stamped with 42285 which means they are new for the TRF 420. Delrin isn't as strong as carbon filled Nylon but is probably more durable. It's not just the material that has changed, the gear geometry has been reinforced as well. The housing, on the other hand, has changed to black. Apart from the obvious color difference, there are some other changes. The previous gear differentials had no centering support for the drive cups other than the housing itself. Now oilite bushings have been added (right) which should last much longer and provide more sturdy support. Note that the drive cups should only be rotating within the housing when there is differential action (one axle is rotating faster than the other, such as in a tight turn) which is probably why bearings were not used Another hidden change is that there is now a slot inside the housing giving access for installing the pin through the drive cup which makes them much easier to assemble. Finally, there is also more oil volume inside the new housing.

Here's the differential mostly assembled before the #900 weight oil has been added. If you look closely at the picture on the left you can see the extra slot located 45° out of phase with the spider gears which is used for installing the pin. The drive cups are aluminum.

Now the rear differential, belt, and upper bulkheads have been installed. I'm using a tool to hold the belt in place until the center shaft is built and installed.

The TRF 419 uses the same 116T spur gear and 20T center pulleys as the TRF 418. The only difference here is that there are no holes to attach the upper deck directly above the center shaft this time.

Like the rear pulley, the front pulley has changed from white to black. The aluminum locked spool is carried over from the TRF 418, but the steel drive cups have changed to have narrower slots since the axle caps have been (surprisingly) eliminated from the front axles.

The steering cranks, bridge, and turnbuckles are unchanged from the TRF 418 and everything fits just as tightly and works just as smoothly as ever.

Now we can attach the upper deck which incorporates a bearing to tension the front belt. There is an extra hole near the front of the upper deck that leads to nothing. It's not for optional stiffening because there is nothing to connect it to.

The suspension arms, steering knuckles, and rear uprights are all reused from the TRF 418. The suspension arms have changed a lot over the years, so it is actually unusual to see them reused.

The assembly of the rear suspension is almost exactly like the TRF 418 except that the hinge pins now have a low friction titanium coating. The rear suspension mount is now 1F which, in combination with the 1X forward mounts, gives a rear toe angle of 3°. The uprights have 0° of toe.

The front suspension is also a straight duplication of the TRF 418. Even the 1C forward suspension mount and 0.5mm spacer are the same.

The rear uprights, aluminum CVD axles, and camber links are also reused from the TRF 418. Noticing a pattern here?

The double cardan steel axles are also completely reused from the TRF 418 except that the axle caps have been removed.

Finally something that changed! Although both the TRF 418 and TRF 419 use C-hubs with 4° of caster built-in, the new F-parts have a larger opening to make more space for the double cardan axle.

Time to build the sway bars. The TRF 419 uses the same system as the TRF 418, but the 419X updated it slightly and then the 419XR introduced bearing support which carried forward to future models. Both the front and rear stabilizers are medium-soft.

Here are the completed front and rear suspension assemblies. If you compare these to the pictures from the TRF 418 you'd be hard pressed to see any differences other than the color of the pulleys.

The differences to the dampers were discussed previously. While these may look very familiar, the inner diameter has increased from 10mm to 10.5mm. This means a new cylinder and piston, but interestingly the threaded caps and spring retainers stayed the same which implies the outer diameter didn't change and therefore the wall thickness must have gotten thinner. This constant outer diameter makes these dampers compatible with any other chassis that used the old dampers, whereas the even bigger 11.2mm dampers introduced with the TRF 419X required other changes to incorporate them. The spring rate has also softened for the TRF 419. The carbon shock towers are shown on the right. The TRF 419X changed them completely to accommodate the shorter dampers.

Now the front and rear suspension are complete with the dampers installed. I never get tired of looking at (or building) a TRF suspension.

I didn't have a display motor yet when I built this model so I used a TRF Transpeed motor I had available. This is destined for a TRF 201 which will actually be driven, so I'll be swapping it out later. On the right you can see the new motor mounting method which uses two screw holes on the bottom of the motor located 60° apart and therefor precludes the use of traditional brushed motors (even for display).

The cantilevered servo mount is also reused from the TRF 418. Both use a high torque servo saver which sadly does not include an aluminum horn.

These pathetic plastic battery holders are reused from the TRF 418 but oriented slightly differently. In both cases, there is no actual retention and glass tape must be used. The TRF 419X improved this slightly with easier adjustability and the 419XR improved them significantly with lateral support, but both still required glass tape. The front bumper and mount shown on the right are also unchanged.

The addition of the body posts completes the chassis. Like all recent TRF chassis, no wheels or tires are included so I've added standard dish wheels and slick tires.

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