Tamiya DF-03 Dark Impact Review
Buildup and review by Sim Tong
1 February 2007.
My very late and on-going review of the DF-03 Dark Impact.
The rear gearbox is a mix of gears and strange bearing sizes including two 1050 bearings, three 950 bearings,
one 830 bearing on the "upper floor" plus the usual two 850 and two 1510 bearings for the ball differential underneath.
In this picture, I actually have an 850 mistaken for a 950 and didn't find out until much later when I was looking
high and low for that last bearing for the front diff.
Internal ratio for this buggy is 55/18 = 3.056
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The kit comes with a 78-tooth spur and a 85-tooth spur. I'm installing the Tamiya slipper set (53925) right from the start.
This slipper set comes with a 82-tooth spur but I installed the kit 85-tooth onto the slipper unit.
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The dogbone pins on most DF03's I've seen eat into the diff cups for some reason. The two shafts on the left are
the stock dogbones. The ones on the right are the Tamiya DF-02 Assembly Universal Shaft set (53791) with the bottom
one inside a TRF415 Swing Shaft Protector (53890). The protectors won't fit the stock dogbones because they have
longer pins but they fit the DF02 universals perfectly. The other interesting thing I noticed was that the stock
dogbones had slightly smaller balls, which meants they probably rattle around inside the diff cups quite a bit.
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Using the protectors presented a few challenges because the slots in the diff cups had to be widened quite
significantly and that meant the diff nut holders needed to be changed to the TRF415 ones as well. The swing
shaft protector set gives 4 protector sleeves but only one diff nut holder, so you will need to buy two sets
(for the front and rear diffs). I'm a little concerned that the diff cups are weakened. We'll see.
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There's a little extra play between all the inner suspension arm hingepins, so the rumour is that Tamiya
is planning to come up with some suspension brace plates to fill these gaps and strengthen the buggy later.
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I wasn't going to wait, so I made my own brace plate out of some scrap aluminium. This is on the front.
Haven't made one for the rear yet but it looks like there might just be enough space for one under the motor.
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I tried a set of aftermarket shocks from 3Racing. They look great but come with some cheesey-looking mounting hardware. I used some M3
stainless steel screws instead of their long black grub screws. The DF-03 manual says to use the innermost mounting hole on the arms for the
front shocks and I've found that the steering rods bind against the shock towers if you use any other hole anyway.
The 3Racing springs turned out to be very stiff and allowed no droop in the front and very little in the rear.
I couldn't seem to find a good set of springs for them (Tamiyas and Associateds were too narrow. Losis were wide but usable but
the fronts were too long hence no droop again).
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To complete my build, I added some Lunsford titanium turnbuckles (Two pairs of 2" and one pair of 1 7/8"),
and a Novak XBR brushless system (10.5 turns).
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The buggy. Stage 1 of it, anyway.
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After some consideration, I decided to swap the regular steering servo with a low profile one. I had an extra Bluebird BMS-706MG
(check out the review here), which didn't seem to fit in my
other cars but turned out to be a very good fit here. I had to cut the rear servo posts on the chassis a little shorter. I
could have done the same with the front servo posts but got lazy and just installed the small plastic servo extension above the
servo ears rather than below them. The ball stud had to go above the servo saver horn. Just when I thought everything was done, the
servo saver binded against part of the chassis, so I grinded down a little of both to get back full steering throw. Quite a bit of work,
but everything sits lower now. I later added a plumbing O-ring around the servo saver which took out a lot of the slop.
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After the maiden run (street bashing in front of the house), I managed to flip the buggy several times but avoided hitting anything
head-on. Nothing broke or popped out but I did notice one screw was missing from the bottom of the chassis. It was one of the four
screws that hold on to the rear gearbox. I later realised I'd been using M3 X 10mm self-tapping screws instead of M3 X 12mm that were
meant to go here.
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Another thing I noticed is that small pebbles like to bounce around inside the motor area and scratch up the chassis and
the motor. Not a major problem for me but thought I'd mentioned it.
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The first test track was meant for 1/18th scale trucks. Small, with loose dirt all around, and no jumps.
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I ran the buggy with a Novak XBR brushless ESC coupled to my old SS5800 motor. It was a bit of a handful at first.
The tires in this picture were horrible. The kit tires were a little better but not great neither.
The buggy was not the easiest thing to drive and I spent a good amount of time fish-tailing and counter-steering.
Every now and then, the buggy did slide around the corner almost perfectly, so I think the potential for speed is there
with a better setup and a better driver.
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Dirt everywhere. The inside of the bathtub chassis wasn't too bad even though I had a ventilation hole where the ESC and fan was,
but the rear gearbox was coated with dirt. A bit of grease around the gearbox seams would definitely help to keep things cleaner inside.
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Bad news to report on my diff cup custom mods. After the dirt track test, I noticed one of the front cups are a little bent out of shape.
It's probably caused by some rocks. The buggy still runs okay for now but I foresee it failing at some point. After that, the 3Racing diff halves
are going in. The modded rear cups are holding up very well though.
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Note: I've switched back to the kit shocks with one-hole pistons and Tamiya 400 oil all around, and the
gold (medium) DF-03 upgrade springs (53927)and I'm getting a good amount of dampening now.
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More bad news on the front diff halves. I was practising on a small indoor carpet track and one of the 3Racing output cups
were slightly bent out of shape when a universal shaft popped out. The culprit was a loose camber link ball nut that let
the rest of the assembly down. I didn't want to end my day, so I put the front one-way set in and the buggy drove
very well. The lack of front brakes hardly affect my jumping because I almost never hit the brakes when jumping at that track.
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Then, I hit a side wall (barely) and suffered a broken one-way cup. What do they make these things out of?
I looked high and low and Tamiya does not make replacements for these things. The only way to get them was to buy the whole One-way set.
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Left to right: Tamiya DF-03 one-way cup, TRF416 one-way cup, and TRF415 one-way cup. The 416 and 415 are too short.
I have not tested, but Hotbodies seem to have something that might fit (#61452)
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When I first built the buggy, I was a little obsessed with hex hardware and used some button head M3 X 10mm screws as the lower
steering kingpins. They looked great but after a few runs, one of them fell out. In this pic, I've gone back to using the kit M3 X 12mm Phillips
head countersunk screws. The countersunk screws have less contact with the flange tubes that they fit through, and have a (slightly) smaller
chance of getting undone in a race.
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This is how much the buggy weighs with the Team Orion 3200mah Lipo battery and Novak XBR brushless system.
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This is how much it weighs with an Intellect 4600mah NiMH 6-cell stick pack in place of the lipo.
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It shed a few grams when I swapped in a regular brushed ESC and motor, but was still a very heavy.
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Update 30 March, 2008:
I turned the buggy back to full Tamiya-legal specs and raced it in the first round of the Tamiya Asia Cup qualifiers in Malaysia for 2008.
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Damage report: The rear shock tower mounting piece isn't strong enough for the job and kept breaking apart.
I couldn't get a replacement, so I repaired mine and filled in all the channels with Superglue and talcum powder, to make it more rigid.
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Front shock tower was noticeably warped after a day of racing.
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Brand new Tamiya front diff cups were starting to chip off in places.
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One ball stud ripped right out of the rear upright.
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Update 6 May, 2008:
Here's a picture of the DF-03 (right) and a DB-01 with the rear axles lined up.
It's hard to judge where the centre of gravities are but it is clear here that changes in battery weight grossly affects the
DF-03's weight distribution front to back. With the 445 gram 4600mah stick packs I was running, it was just way too
front heavy to land the big jumps. I sold it off and ran a DB-01 for the rest of the race season.
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Useful link:
Downloadable DF-03 instruction manual in PDF form
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