Tamiya #42313 Large Shim Set for Gear Differentials

But first, a little background…

Effectively, I haven’t been racing for the past 3 years. Personal circumstances and choices meant I could’t attend club races regularly, and because I wasn’t racing regularly, I felt less inclined to attend the bigger events.

Last year, I tried to race in the Iconic Cup, and for whatever reason I had lots of problems, and didn’t achieve what I felt I should have done.

This winter, I tried again with the CWIC XRS (run by the Chippenham club). Again, lots of problems with the car, combined with being well off the pace.

I would be intrigued to know what is the root cause of the problems – lack of practice, my increasing age, outdated equipment, or simply a lack of motivation. Sadly, I don’t know the answer.

What I do know (and this is what leads me on the the real topic of this post), is that if you under-perform, you end up in races that you shouldn’t be in, where driving etiquette appears optional. And you get battered.


I am still running my Tamiya/Samix TRF418 with the 419 rear diff. It is a car I have struggled with on many occasions. As the winter progressed, I managed to get a degree of consistency out of it on the new-to-me Hudy tyres and ETS carpet. Unfortunately, consistency doesn’t count for much when you get punted repeatedly by lapped traffic.

The rear diff broke – breaking an input gear and coning the shims.

While searching for some replacement parts, I spotted these:


The set includes 2x 0.3mm shims to go behind the input gears, 2x finer 0.1mm shims for the same location, and 4x 0.1mm shims to go behind the spider gears. As these shims are the same size as the gears themselves, loading should be much more even, reducing the tendency for the shims to cone. Also, the large size should make it harder for oil to find it’s way through the seals, reducing leaks. We’ll see if this works out in practice.

In terms of re-assembling the diff, I always shim the input gear so that it rotates smoothly with minimal backlash. Just one 0.3mm shim was enough for this on both sides. I will reappraise the shimming next time I have the diff apart.

I also put a 0.1mm shim behind each of the spider gears, and assembled the diff dry to make sure everything worked smoothly, again with minimal backlash. It did, so I filled the diff with oil (#2000 for now) and put it back in the car.

I have to say that I don’t buy in to any of the diff-building “voodoo” that you may read about elsewhere. Tamiya’s parts are fundamentally good quality. I don’t sand down the gears, I don’t weigh the oil, I don’t use special slime on the seals. I just lube the seals with the normal silicone oil, make sure there is no flash on the gears, and fill the diff until the fluid sits just above the cross shafts.

Plan is to get this on the track again this week and see if it runs properly again. Will be glad to put this winter’s racing behind me!


Samix V2 chassis conversion for the TRF418

I have to confess that I’ve been struggling with the Tamiya TRF418. Although there are a great many things to like about this car, the handling on carpet (for me at least) has not been one of them. I’ve tried all the tricks that have worked with other cars in the past and none of them have made a enough of a difference – the rear of the car has always been extremely edgy and unpredictable.

A radical change was required.

I pondered a complete change of car – the TRF419 is tempting, but after my poor experience with the TRF418 it may well prove to be another failure. The latest Yokomo won the worlds and seems to have the most refined design of any of the traditional 2-belt cars. I could go on. But my decision was made when I noticed that Samix had released an updated version of their chassis conversion. “Buy it now”.

The Samix V2 carbon fibre conversion

Before I go any further let me mention the excellent review of this chassis on kentech’s blog. My conclusions are pretty similar, and my pictures are not as good. But there are a couple of small differences in the V2 chassis that I thought it would be worth sharing.


In the package (just a plastic bag with a header card, the style of the packaging suggests it is made in a Chinese factory somewhere) you get the bits and bobs pictured above. The full conversion includes both a lower and upper deck, a centre-line motor bulkhead, a front steering bridge and some LiPo mounting jaws. You can buy just the chassis plate if you want, and there is also an aluminium chassis option if you like your car to be too heavy and too stiff…


If we take a look at the chassis, compared to the original Tamiya plate (on the left) you can see that it is not as waisted between the suspension mounts and the central area, and has slightly different cut-outs (mainly to accommodate the new motor mount). The chassis is drilled for the original Tamiya motor mount too. At the front, you can see that Samix have included an alternative set of steering post mounting holes, further forward than kit. These will give quite extreme Ackermann and I’m not entirely sure when you would want to use them. There are also holes for the battery mounts and the optional fan mount. The Samix chassis is a couple of mm narrower overall, and pretty much the same thickness at ~2.3mm.

The biggest difference is the amount of flex. The Samix chassis is significantly softer than the Tamiya one.


The top decks are very similar. Same thickness (~2mm) and similar amounts of flex – the main difference being the extra hole at the front of the Samix deck to fit the steering bridge if using the alternative Ackermann setting.


The other big change with the Samix conversion is the centreline motor bulkhead. This is another step closer to equal left and right flex. Samix have chosen to use a floating layshaft and supply some different flanged bearings to allow it to work with the Tamiya pulleys. The final assembly is pretty solid – just take care that you build it with the right screws in the right places as there are no instructions! The motor is now only held in with two screws at the bottom. I’m not a fan of this design but a lot of cars have been using it recently and I don’t recall seeing any damage because of it. A feature that I do like is the way that the bulkhead post is completely removable – so if you choose to run without the top centre screw, you can remove the part that touches the top deck as well. I’m running mine with the screw to start with.

The quality of these parts is pretty good and although the anodising is not 100% consistent, the colour is very close to Tamiya’s own and you don’t notice anything when they are in the car. For some reason my spur and pulleys would only spin freely when fitted in a particular direction, so keep an eye out for that.


Staying on the topic of quality, there was only one part that needed a little extra work, and that was the top deck. The leading edge is just a fraction of a mm too long and binds against the bulkheads. A few minutes with an emery board solved this – you want the top deck to drop easily into place to prevent tweak. There is no problem at all with the position of the drilled holes – the chassis builds up as straight as the original. This was something that kentech noticed in his build, so obviously there hasn’t been a change to the top deck dimensions in the V2 kit.


I also treated myself to Samix’s 40mm fan mount. This is nicely made from aluminium, and as you can see it has a small channel at the side to guide the fan wire. They also offer a 30mm mount. Naturally the chassis comes pre-drilled for this accessory and it fits neatly just behind the motor. I use a 40mm x 15mm fan and I have to say that it is held in place very solidly by a couple of M3x20mm screws – much stronger than servo tape.


Once completed, the Samix TRF418 looks something like this. It takes a little time to swap over the parts, but as I mentioned before the quality is good and everything fits in place.

I’ll briefly mention the LiPo mounts – the jaws are a good size for the standard race LiPo’s, and have a small range of adjustment. More importantly, the tape slots are in a slightly different place and grip the LiPo a lot better. It’s a small change but one that really gives you a lot more confidence in the battery mounting. I won’t shed a tear for the misaligned servo mounts that Tamiya expected me to use in the original kit!

The final thing I want to mention about the build is the flex (again). Once the bulkheads are bolted on, the extra flex of the lower deck is somewhat reduced. However you can still feel the difference in your hands.

The first race

Of course a car that looks good on the bench is one thing but what really matters is how it goes on the track.


My debut with the Samix TRF418 was at the second meeting of the CWIC series earlier today. This is a popular carpet series on a 30x20m track with a competitive field of over 50 entries in 17.5 Blinky. The first meeting with the standard TRF418 was a real struggle, I just couldn’t get any consistency out of the car and ended up well off the pace.

The performance of the Samix TRF418 seems to be a solid step forward.

If I could characterise the original 418, it was a car that started the day undriveable, and ended the day tricky. The Samix started the day tricky, and ended the day driveable. I’m OK with that – the track is always low on grip in the first round, and I would rather have a car that is lively when the grip is low than one that understeers when the grip is high. The balance of the Samix throughout the rest of the day was good – neutral, with a nice flow through the corners. It would slide the rear end a little if you were aggressive with the throttle or steering, but this can help get the car into the corners. The original 418 was so inconsistent that you could never tell which direction the rear end would go next!

The car was reliable all day too – nothing came loose, nothing broke. You might notice from the picture above that the ESC is now a Hobbywing Xtreme Stock – this is because I clumsily damaged my LRP Flow while trying to re-attach the switch the the circuit board. Lead-free factory solder is not an easy thing to remove!

Although I qualified in more or less the same place I qualified last time, I was much closer to the A-final on pace and could have got into it without a couple of mistakes in the last round of qualifying. The added predictability of the Samix conversion made it a much easier car to race with and I left with a 1st and 3rd in the B-final. And a smile on my face as well 🙂


PS I am also racing Mini in the CWIC this year. There is a very tight battle at the head of the grid. My Tamiya M-05 is very well sorted now, and the setup has barely changed for the last couple of years. So far I’m leading the championship but every point matters because there is nothing in it between the top three. Good fun.

CWIC 23/2/14 – Blinky

I’ve been struggling with a lively rear end on the TRF418, this makes it quick when the conditions are right but tricky when they are not. I experienced both traits today.

The car was tricky in the first two rounds (and there was a lot of contact as racers got used to the difficult track), but in the third I got a clean run and ended up third. I added droop for the fourth round and the car was terrible with far too much steering, and a partial return to the round 3 settings in the first final (for which I qualified 5th) wasn’t a success (finishing 7th). Widening the front end, reducing the steering lock and making the expo milder helped to make the car more driveable in the second final, and a tidy start combined with others’ mistakes allowed me to finish 2nd after a really good late race battle. The slim hope of stealing a victory this season lives on!

I’m debating picking up a few of the common tuning parts to try a wider variety of settings on the car to make the tail less happy. Although outdoor season starts soon which has a completely different style of track and surface.

TRF diff a la Dave

I’ve read a lot of articles on how to build a TRF gear diff, and some of the are pretty extreme. My way is a lot simpler and doesn’t require any parts to be modified.

This build guide has come about after I had a few difficulties with my diff over its first few races, I’ve got the balance between smoothness and leaks sorted now.

1. Choose your parts. Mine is a TRF418 diff to which I have added TRF silicone o-rings (#42259) and some 0.1mm thick 5x10mm shims (Core RC #CR458, also in Tamiya #51466). The 418 diff includes the metal cross pins (#54311) and lightweight outdrives (#51535) as standard.

2. Make sure the mould lines are well cleaned from the internal gears but DON’T file them down.

3. Assemble the diff according to the instructions but don’t fill with oil yet – take into account that the optional o-rings are a little fatter than the standard black o-rings and you will need to use the fine shims to get the right setting. I start off by shimming so that there is a tiny (<0.1mm) amount of float in the diff outdrive when the pin is inserted, if the outdrive is tight, remove a fine shim.

4. Lubricate the o-rings and gasket with silicone oil and assemble the diff dry. There is no need to over tighten the screws, they just need to be snug enough for the gasket to do its job. The action should not feel too “geary” nor should it have too much backlash. A simple test is to see if there is any float in the outdrives, if there is a little bit it means the gears are not being forced against each other. Adjust shimming to suit – for reference my diff runs with 0.2mm on the long side and 0.1mm on the short side.

5. Fill the diff with your preferred oil. I’m usually using #1000 or #2000 depending on conditions. There are plenty of nooks and crannies in the diff case for the oil to hide in so I always work the diff to help the oil settle. As usual, fill to just above the cross pins. Assemble and install.

This should give a reliable and consistent diff with no leaks from the outdrives. The Tamiya diff does appear to shed oil from the pulley gasket however I do not believe that is a leak, rather the remnants of the oil that seeped out as the diff was screwed together.


Today’s CWIC

Decent result at the CWIC today, perhaps my best of the series, and a better day with the TRF418.

Ended up qualifying 6th but was a lot closer to the front of the pack, in fact I had a shot a TQ in the last round but made a couple of mistakes with an empty track around me. Finals ended as a 6th and a 4t which was about right, I was pressing for 5th in the first one and defending from 5th in the second but didn’t have the extra something that the top few had today.

Before the meeting I had rebuilt the rear diff with the red Tamiya o-rings. These seem to have a much better seal, but also add a little more friction. The car was a real handful in the first round, a few tweaks to the steering rates improved matters, but the car was still sliding the back around in the second round so I went down to #1000 oil in the rear diff which was a big improvement. #2000 was good with the black rings but too thick for the red.

The first round also resulted in both spool blades breaking, there was no way I could cope with this many failures (averaging more than one every other race), so I begged a fellow racer to let me buy his spare set of Roche blade-free outdrives and these performed faultlessly throughout the day. I’m pretty sure I have a reliable platform for carpet racing now, I just need to focus on the driving.

I made a couple of setup tweaks during the day, fitting a slightly softer rear spring and standing the shocks up. The car was feeling better as the day progressed and attracted plenty of compliments but I suspect the improving track conditions were a significant factor. We’ll see how it goes at the next round.

Final comment is on the Protoform shell. I’ve been running Blitz shells for the last couple of seasons and I have to say that Protoform’s material is much more fragile, the front of the shell is covered in tiny cracks after only two race meetings.


First race meeting with the TRF418

Gave the TRF418 its proper race debut at the CWIC today.

First run was a bit erratic, immediately decided to swap the kit springs for something more conventional (ARC White front and Yellow rear, equivalent to HPI Pink/Silver) and to thicken up the rear diff to #2000. I was disappointed to find that the rear diff was already almost completely empty of fluid from just sitting around. This is a bit of a concern as the ARC diff never leaked once. I’ve orders the red o-rings (#42259) and will have to find a way of making the gasket form a better seal too.

The car was greatly improved straight away in the second round although quite edgy on turn-in, as the tyre came in the car was quite driveable and I was 6th in round (I think) from a field of nearly 50 in 17.5 Blinky.

I tried the warmers for round 3 but it didn’t make much of a difference, and as the track grip came up the rear end became more locked in, perhaps too locked in. I messed about with my steering linkages a couple of times during the day because I wasn’t convinced I was getting even steering both ways.

For rounds 4 and 5 of qualifying the car felt pretty good, but as ever I just lack the ultimate pace of the top drivers in the class so qualified 7th. Before the finals I dropped the front end down to ARC Yellow springs too. Results were a 4th (after a lucky start) and a 9th (after one of the biggest first corner crashes I have been in, which knocked the fan out of the car and dislodged the sensor wire, fortunately a marshal noticed the problem and I carried on, a lap down). The car itself survived the shunt and drove just fine.

Apart from the diff concerns (the #2000 didn’t seem to leak excessively during the day), I also broke one of the blades on the front spool, and also broke a 3Racing replacement. I’m weighing up the benefit of switching to a non-bladed spool outdrive (made by Roche). The Lipo mounts were also a pain, because my decision to trim them meant they were prone to twisting around.

General driving impressions was that the car had a lot of turning ability but with a stable rear once the grip came up. A smoother drive than the ARC which always had an edginess indoors, However I couldn’t say it was any quicker as I qualified where I would normally qualify and finished where I would normally finish! Perhaps more consistent though, managing 0.3s difference between average and best in some runs whereas the ARC was rarely below 0.5s. The full-size LiPo may well have helped to stop some late-race power fade too.


TRF418 – The build completed!

And here it is…

TRF418 completed

I won’t go into too much detail about my build – there are already a lot of very good build blogs on the internet from more experienced TRF owners than me – kentech‘s blog is a great example which. But I will list a few of the things that stood out for me as I put the car together.

Good points:

  • Quality
  • Pinned bulkheads
  • Free running transmission
  • Low weight
  • All the fashionable parts as standard (DCJ’s, floating servo mount etc.)
  • Easy to work on
  • Generous “Bonus Parts” in first batch
  • Quality again

So-so points:

  • LiPo mounting system is rudimentary
  • Anti-roll bar mounts fiddly
  • Fussy about spur gears
  • New springs not what I had hoped
  • Steering linkage may need a little work if your radio doesn’t have large EPA adjustments
  • Not many parts or options available yet

Let’s look at a few things in more detail:


TRF 418 body off

The most obvious change is the Yokomo-style top deck. This style of deck has really taken the TC world by storm and everyone has rushed out their own version of it. Tamiya give you lots of options for connecting the motor mount; there is the single post at the front which the motor mount can be either attached to or left to “float” with the use of a supplied grub screw (not an option that is mentioned in the manual, but one I gleaned from kentech’s blog); and there are screw holes in the top of the layshaft mounts as well, which can be connected with the addition of a 0.5mm shim under the top deck. The motor mount also has four slots to give plenty of options for fitting the motor and avoiding the spur gear – very easy to work on.

TRF418 Motor mount

The chassis comes with split suspension mounts, a floating servo mount and pinned bulkheads – a feature that I am surprised hasn’t been seen more often since Losi included them on their JRX-S (which was also the first car to have DCJ’s if I remember correctly, 5 years before anyone else took notice). Basically everything you would expect from a car in 2013/14.


TRF418 Diff

The gear diff comes with plastic gears, metal shafts and black o-rings. These give a very free action but not as good a seal as a silicone o-ring. There does seem to have been a small amount of fluid loss through the outdrive since assembly, I’ll have to keep my eye on that. My gut feeling after the shakedown run is that the kit #900 oil (or the #1000 Fastrax oil I built it with) it too free for any conditions and that the rear wheels may “diff-out” too easily. The spool is nicely made with an alloy hub and steel outdrives, which mate to the steel DCJ’s via a blade. The DCJ’s themselves use smaller pins and narrower bearings than usual – Tamiya clearly made the decision to build a compact DCJ that fits within the existing C-hub moulding rather than moulding a new C-hub for a larger DCJ – we’ll see how reliable they prove to be compared to the very substantial parts on the ARC R10 I was running previously.


TRF418 layshaft

The spur gear fitting is new, and unfortunately Tamiya have designed it for a spur of around 2.5mm thickness at the mounting. This means that my RW and Kawada gears are slightly too thick to be clipped into place. You can compensate with extra shims on the layshaft but even a small deficit of shimming is magnified and the spurs move around from side to side. I’ve ordered some Panaracer spurs (which are not that easy to get hold of) in the hope that they will be more secure.

I have drawn up a TRF418 gear chart for 48dp. The tooth count range is from 104 to 116, and the largest pinion that will slide in from the side is 37T, although larger ones will fit without fouling the top deck or motor mount – I have put a 43T on there and there was still room to spare.

One detail in the drivetrain that really pleases me is the belt tension. Superficially it’s a trivial thing, but both belts have even tension and are very free in the kit settings – this shows that the dimensions have been thoroughly thought out. Good engineering. The ARC suffered from an overly-tight rear belt which you needed to run on almost the loosest setting – a sign perhaps of how much of the car was copied straight from other designs.

Not that I am implying that the TRF418 design is original. It isn’t in the slightest, it’s a copy of a Yokomo BD7, because that’s the car the European team drivers spent the last year trying to beat. But it is a thoroughly Tamiya-ised copy, refined to the limit.


The car has new suspension mouldings. These are basically copies of the Yokomo parts but I welcome the change, mainly because they have eliminated all the mounting holes that we never use. This means a stronger, simpler and seemingly lighter component. The new steering knuckles only have one hole, and the new rear hubs have a single hole that makes the rear link shorter, akin to the HPI hubs. I would have liked to see a better ball mount for the front anti-roll bar, the 4mm connector is a bit tight, although squashing it with pliers is a handy trick to free it up.

The suspension assembly has the only obvious mistake in the manual, Tamiya suggest putting an extra 0.5mm spacer on each suspension shaft and there is no way the car will go together with them fitted. Take them off and the arms will drop freely, if you need to take out a little more free play, Tamiya make 3mm inside diameter shims that are perfect for the job (#53585).

The anti-roll bars have been revised with a top-adjustable drop link, but the plastic mountings leave a little to be desired, they move around too freely when you are trying to tighten and adjust them. The ARC mounts should fit, they have lips on the edge to locate them on the bulkheads. Roche make an aftermarket one-piece mount that I am tempted to try as well.

Springs and shocks

New Tamiya springs

Tamiya have finally released their own “large diameter” springs – these are basically the same size as the long-popular HPI springs with a 14mm inside diameter and 25mm length. They are finished in a snazzy pearlescent black. So far so good. But they are also close to useless. The kit Black spring (in the middle above) is 1.5mm wire diameter by 7.25 coils – 15-20% softer than an HPI Silver, and about the same rate  as the old Tamiya Yellow. The new Red (on the left, and included as a Bonus Part in the first batch of cars) is 1.5mm x 7.75 coils, softer again, and a match for the old Tamiya Red. The new Yellow (on the right) is 1.5mm x 6.50 coils, the same dimensions as a HPI Silver, and it measures up to be about the same rate as the HPI Silver and the old Tamiya Blue. This new Yellow spring might have a place in the pitbox but it is not available as a spare yet so I only have one pair. It will be interesting to see what other spring rates Tamiya release in this new size. It’s also worth mentioning the shocks here, Tamiya endlessly revise the design and the 418 comes with the large diameter lower retainers and also a new spring retainer, as well as clear o-rings and the golden-anodised bodies.

TRF418 Shocks


Like many double-bellcrank cars, it can be a pain to get full throw left and right with my radio (a Futaba which only allows up to 120% EPA). I understand why the double bellcrank is favoured but I am not sure it offers any benefit over the single bellcrank used on my old TOP Scythe and Photon, which were a lot easier to set up due to the lever effect. On the 418, I have just about managed to get full lock both ways by using the outer hole on the Tamiya servo saver (18mm c2c) rather than the suggested inner hole (16.5mm c2c). I intend to build up a slightly shorter steering link to get a right angle between the servo horn and said link. This is the setup at the moment:

TRF418 Steering setup

LiPo mounting

Tamiya expect you to use an old set of servo mounts to guide the LiPo into place. It’s not a very good solution. I don’t mind the light weight and simplicity, but they obstruct the tape slots. It would be nice to see an alternative to hold the LiPo in place, even if it is as simple as an L-shaped piece that avoids the slots. In the meantime I’ve cut the servo mounts a little to clear most of the slot. The front of the LiPo rests against a screw in the side of the servo mount, but there is also nothing to stop the rear of the LiPo from sliding into the belt and motor shaft. I’ve stuck a piece of plasticard onto the chassis for the time being and we’ll see how well that holds up. Apparently the LiPo mounts from earlier cars will fit into the two spare holes in the chassis, which begs the question of why Tamiya didn’t include the parts in the 418.

TRF418 LiPo mounting

Final Setup

Tamiya don’t include a true setup sheet in the kit – so I built it according to my usual basic settings for a touring car. That means standard locations for linkages; 5mm front/ 5.5mm rear ride height; 5.5mm front/4.5mm rear droop; 1.5deg front/ 2.0deg rear camber; and 1deg front toe-out.

I’ve gone for a regular weight Protoform Mazdaspeed 6 shell, the standard choice for carpet racing. Tyres are Sorex 28JB. Electronics are a Team Torke (Intellect) 6500 LiPo at 320gm, Futaba S9550 servo (still going strong after many years), Futaba R603 receiver, LRP Flow ESC (best blinky brakes I’ve tried) and a Vampire 17.5 motor. I have a 40mm fan behind the motor, and with all these components fitted the car is just over 1360gms ready to race – right by the limit without any lightweight parts. The ARC was 50-70gms heavier, which led to me using a shorty LiPO; the Tamiya won’t need one and is a therefore a lot easier to work on. The outdoor tyres are heavier but I should be able to get some weight off with a lightweight shell and maybe a few lightweight screws.

Balance is also very good out of the box, in the region of 49%F/51%R weight distribution and evenly balanced from side to side.

The shakedown

I’ve only ran the car for five minutes on carpet since building. It went straight and went round corners which was about as much as I could expect, although as the grip came in it started to feel quite unpredictable which I think may be a result of the free rear diff and the soft springs. I’ll be trying some heavier oils in the diff and some stiffer springs at it’s next race, the CWIC.

Looks like I didn’t keep the review brief after all…