Slot Car Tech Tips
One of the most frustrating things about new slot cars is that, maybe two times in 10, they’ll run properly straight out of the box. Which also makes it one of my favourite things about buying new slot cars: eight times out of 10, I have to mess with them. I’m never happier than when I’m disappearing to my downstairs workshop, ripping the wrapper off a new acquisition like the fat German kid with the gold Wonka ticket, hell-bent on glueing and screwing and Dremeling some unsuspecting slot-car to performance nirvana.
In future articles here on Slotmeister’s Tech Tips page, we’ll have guest slotheads spill the beans on topics like:
- Running-in motors … underwater!
- Tuning your cars for non-magnet racing
- The light and the truth: lightening and truing
- Better braking and cornering techniques
- Simple tips to improve and maintain your home track
Right up front, though, let’s look at how to get your new, and allegedly ‘ready-to-run’ car really ready and running.
Hurts the masculine ego to admit it, but a 1/32-scale slot-car is basically a mass-produced plastic toy. On the other hand, your average 1/32 slot-car is capable of a scale speed of more than 600km/h. It’s a real, high-performance machine.
Before you even threaten your car with so much as a screwdriver, look carefully around the wheel-arches. It’s not unusual to find ‘flash’ – the seeping of plastic during the body’s injection-moulding process – on the inner lip of wheel-arches. Other times, bodywork just sits too close to a tyre.
Checking the rear wheel-arches is straightforward; if there’s less than, say, half a millimetre of clearance around the tyre, you’ll want to trim the offending bodywork. At the front, where several cars allow axle travel, hold the car upside-down and lightly push each wheel up into the wheel-arch. If the tyre can’t rotate on full compression, you’ll be trimming the front arches, too.
Trimming wheel-arches is easy. Having made a note of each high-spot, unscrew the body from the chassis. Wrap a small square of fine wet-and-dry paper (400’s good) around a finger. A minute or so of finger-twisting, concentrating on the high spot in each arch, takes away the excess material while maintaining the arch’s smooth shape.
Thick or stubborn wheel-arches, or bigger modification jobs, call for a Dremel rotary-tool with a deburring or sanding attachment.
One thing that separates expensive, boutique slot-cars and parts from the more mainstream brands, is their manufacturing tolerances. Fractions of a millimetre’s disparity in the axle, wheel centre and tyre add up to fractions of seconds out of contact with the track surface.
A car’s downforce magnet tends to mask these deficiencies, making totally-true running more of an issue for drivers who prefer non-magnet. But a simple, five-minute tyre truing can make a big difference to the cornering adhesion of your ready-to-run car.
Remove the body. Slide the tyres off the wheels. Look for little moulding bumps (called sprues) around the wheel, where the tyre seats. If you find any, slice or sand them flat. Slide the tyre back on, using a dab of adhesive. Leave it to dry for, uhh, okay, a lot more than five minutes.
Now look in the chassis for the magnet and, if possible, remove it temporarily from the chassis (I just find it easier to do this without a magnet). Place the chassis, facing in the wrong direction, on your track. We want the wheels to spin in reverse, see. Slide a sheet of 400-grade (or more coarse) sandpaper under the car from the rear, butting it up against the guide.
Now go for it. Give that puppy full throttle – for no more than 60 seconds, mind (the tyres can overheat) – encouraging the rear of the car to slip over the paper, sanding off the high spots on the rear tyres.
Do this a couple of times. You can usually see on the tyre’s tread that, not only is it running more round, but more of the tyre’s width is now in contact with the track, too.
Slot-car motors are generally held in place by shaped clips moulded into the chassis. This is great for fast motor changes, but less than ideal in terms of holding the motor fast, period. The motor’s torque reaction in the chassis will rob you of efficiency and wear out gears.
Likewise, ill-fitting rear axle bushes can spin in their chassis clips.
On cars with motors exposed on the underside of the chassis, some drivers like to strap down the motor with packaging tape. With the car’s body removed, a motor’s-width strip of tape is fed, upside-down, over the top of the motor. Each end of the tape is then stuck firmly to the underside of the chassis, pulling the motor down.
Plenty more drivers use hot-glue, simply bleeding it around the base of the motor. Easier still, run hot-glue over the top of each motor clip (being careful not to melt the motor’s plastic bell-housing).
Me? I use a wonderful, and highly hallucinogenic product called Shoe-Goo, a silicone adhesive for patching running shoes. Trowel on this transparent snot with a screwdriver and allow to cure. If you ever need to remove it, it can be gnawed off with pliers.
Don’t put your glue away just yet: spinning rear axle bushes will rob speed and, in fairly quick time, ruin the chassis. Similarly, front-engined slot-cars are prone to pop their prop-shaft bushings under hard acceleration. Glue them down.
A lot of drivers use CA glue (aka super-glue) for these, but I’ve had chassis clips snap off. Yet again, I prefer Shoe-Goo. So does the six metre-long, psychedelic codfish who’s watching golf on my television.
It was the best of cars, it was the worst of cars … Back when I first got into this hobby, and was regularly trawling the internet for new and interesting cars, I found one that literally had my name on it.
It was a Porsche 996 GT3 from a brand called Pro Slot. There was a fair old variety of liveries, but this black example was emblazoned with “Eschmann Stahl” sponsorship. (Nothing to do with me; Eschmann is a company that makes specialist steel products).
On lifting the car from the box, I was surprised by how light it felt. The body was palpably thinner than those of the more mainstream brands. The red-wrapped Pro Slot Evo3 motor boasted 26,000 rpm and sat in a pod semi-independent of the chassis. Along with sticky rubber tyres, this little black puppy was itching to go.
Except it didn’t.
There were several reasons. Any one of which would have prevented it from going. The white, plastic pinion had split between two of its teeth (this is why better plastic pinions have a reinforcing flange), and the spur gear couldn’t rotate past it.
The rear axle was covered in surface rust. I’ve since learned that the manufacturer had resorted to using nails. The hard, red motor wires were prone to popping out of the guide. The magnet wouldn’t hold a note to the fridge. And the wheels were among the wobbliest I’ve seen. But y’know, I’ve started most of my romantic relationships on a lot less promise than this.
Great Body, Underlying Issues
The Pro Slot brand is still attached to serious, 1/24-scale racing weaponry out of the US, stuff like 47,000rpm motors that win world championships. But at some time in the 1990s, it seems, Pro Slot had several 1/32 models – Porsche GT2 and GT3, Ferrari 355, Alfa Romeo 156, Ferrari F1 – produced at a factory in Romania, in an apparent tie-up with the venerable Italian brand PoliStil.
In areas like the body’s detailing and finer aspects of finish, along with the abovementioned running gear issues, the Pro Slot cars’ quality was well off the punishing pace already being set by Chinese manufacturers.
But non-magnet racers discovered the freakishly fast fundamentals: the chassis’ stable, yet responsive ‘footprint’; low centre of gravity; independent front axles; deep and slippy guide; torquey and torrential Ev03 motor; the grippy and predictable tyres.
Get a Pro Slot car running right, and it’s probably the sweetest non-magnet car you’ll ever drive.
Obviously, that means buying the car and immediately junking half of it.
First you’ll have to find one, and this is becoming increasingly difficult for two reasons:
- They stopped making them five or eight or 10 years ago
- I keep buying them all
Have a look around the internet and you can still find them, usually on auction sites or at a handful of European on-line retailers.
My area of speciality is the 911 GT3, which gets the Evo3 motor. The Porsche GT2 has a lower-revving (21,500 rpm), gold-wrapped Evo2 motor, but with the GT2’s wider track, a well-driven example will hang onto a GT3 on most tracks. That is, after you’ve rebuilt it.
The Pro Slot body is attached to the chassis by just two screws, on the centreline of the car. Even this is a great thing; running them one turn loose lets the body ‘roll’ in cornering.
To facilitate this even better, I take my darling Dremel and its plastic-cutting wheel and trim one millimetre from the entire circumference of the chassis. This lets the body move free of the chassis edges.
Turning to the mounting pylons on the underside of the body, I place reinforcing sleeves of PVC pipe over them, to provide a broader seat against the mounting points on the chassis. These sleeves also let you tweak body height to ensure that the wheel arches remain clear of the tyres when the body rolls.
These Pro Slot chassis come with independent front axles, which is a great thing: it reduces drag when one or both front tyres touch down in cornering or braking.
If you want to be a real nerd, you can v-e-r-y carefully (by hand) run a 3.5mm drill bit through the plastic axle hanger, and sleeve it with 1/8” brass rod. Needless to say, I do.
The Good Gear(s)
Italian brand Slot.it, boutique purveyor of slot-car go-fast parts, makes a conversion kit (SIKK05) that’s ready to drop into your Pro Slot car. It includes a rear axle, bronze bearings (peculiar to Pro Slot), 34-tooth aluminium spur gear and a pair of aluminium wheels.
As is usual with Slot.it, all this stuff runs true as goose grease, which is what you need to race non-magnet.
What the kit doesn’t include is the Slot.it brass 11-tooth pinion (SIPS-11). And the 15.8×8.2mm wheels that come with the kit are too small in diameter, so I use the larger, 17.3×8.2mm ones (SIPA18-Al). On the front, I go for the plastic version (SIPA18-Pl).
Of course, nobody says you have to use Slot.it; I’ve also built GT3 and GT2 racers, tweaked up the wazoo, with ultra-light, hollow axles and drilled-out gears and wheels from both NSR and MB Slot.
Ready to Launch
… Starting with the pod. Much as I love the idea of the Pro Slot’s rubber-cushioned motor pod, the sad fact is it doesn’t work. Before replacing the motor in the pod, press on the new, brass pinion and – while you’re at it – replace the rather brittle, standard motor wires with some soft, silicon-sheathed stuff.
Click the motor very carefully back into the pod and remove the rubber block from the chassis. Drop the pod into place and proceed to glue it there (I use Shoe-Goo). Now, snapping the rear axle and bushes into the chassis will hold the pod in the correct place while the glue cures.
The finishing touches are to replace the standard guide’s little suspension spring with a fixed collar, and to use soft, scrumptious Slot.it racing braids. Oh, and I use hard-compound, zero-grip tyres on the front.
You’ll find that you’ll need only a light truing of the standard Pro Slot rear tyres (see separate Tech Tip) to have a staggeringly fast, smooth and great-handling car.
On Slotmeister’s hard, smooth Slotfire track surface, a Pro Slot Porsche brakes deeper than just about anything, backing beautifully into the turns before the syrupy power of the Evo3 motor rockets it out again.
These puppies are proof that the best things are those for which you’ve had to work hardest.
A differential? In a slot-car? Does it work?
Spanish brand Vanquish-MG figured it was pretty smart when, in 2002, it launched the world’s first slot-cars to feature a real, working differential.
The Vanquish diff, comprising bevel-gears within a crown-geared housing, was shared among a range of 1960s-’70s Can-Am and Lotus 72 F1 cars. These were beautifully modelled, with detailed interiors and V8 motor covers – the usual criticism being their scale, which was closer to 1/28 than 1/32.
The differential certainly works in giving Vanquish cars a unique feel in cornering. This is most evident on tight tracks, where Vanquish cars seem to turn in better and where one can spin the inside rear wheel through the corner.
There again, it doesn’t work, in the sense that inside wheel-spin is exactly what full-sized racing cars try to avoid. Oh, and this bold innovation didn’t do any favours for Vanquish, either: the company went bust in 2007.
I have more than 30 Vanquish cars and I just love ’em. That’s partly because of the models represented – I’ve been nuts about Can-Am since I was a kid – but mainly because they’re technically interesting and they dare to be different.
You can still find new Vanquish cars for sale on the internet. With a few tweaks, they’ll provide you with a unique and lasting slot-driving experience.
Taking the “if” out of the diff
Unfortunately, Vanquish diffs also have a reputation for unreliability. Blokes accustomed to out-of-the-box racing sometimes found their cars grinding terminally to a halt.
An external inspection of the diff would usually reveal the teeth of the crown-wheel splayed out like a hillbilly’s gob. You can see the mashed teeth in the example I’m taking apart on the right.
Vanquish, at some point, began adding Vaseline-like grease as a running production change. (You can do this yourself easily; the three-part diff housing snaps apart in your fingers). But greasing the insides seems only to postpone the problem.
Some suppliers, notably Professor Motor, began offering solid-axle conversion kits. While this necessitates fitting a new motor, it’s still cost-effective, efficient and trouble-free. But where’s the fun in that?
I’ve heard all sorts of theories on why Vanquish diffs fail. These include flex in the diff housing causing poor internal meshing, and the teeth on the crown wheel simply being too thin and weak.
I’ve only ever had one Vanquish diff completely cack itself, though I’ve caught a couple others starting to go south. Here’s what I’ve done since, that’s really worked.
Grease is a word … Glue is, too
One fix I’ve always done pretty much straight away, has been to re-grease the internals and glue the diff housing together.
First, remove the sub-chassis from the main chassis. Next, to remove the diff from the sub-chassis, use small screwdrivers to lever the plastic bearings out of the chassis clips. Try to get both sides to pop out simultaneously.
Now, prise the diff housing apart. Holding it as close as possible to the centre, gently bend it like a fortune cookie. The flange for the right-side axle, which butts up against the back of the crown gear, will probably separate first. The left side, which joins the diff centre about 2mm opposite the teeth, can be gently helped apart with a fingernail.
Replace the grease (if any) with either white PTFE grease, or Tamiya “ball-diff” grease (used in radio-controlled cars). Don’t pack it solid; it just needs a good smear of grease on each of the bevel gears.
Next, look at the flanges on each side of the diff housing, i.e. the surfaces that mate when you snap the housing back together. Using a pin, put a very small drop of super-glue at four equal points around each perimeter. Then – noting that the right-side axle has the longer “sleeve” – snap the three parts back together.
The idea is that gluing the diff housing together will eliminate flex and maintain proper meshing inside.
With the diff still out of the chassis, slide the outer axle sleeves away from the diff housing and put a couple of drops of light oil there. These plastic “sleeves” are actually the axle bearings.
Push the sleeves back up against the diff housing and prepare to put the diff back in the sub-chassis. As with removing the diff, try to replace it with even pressure on both bearings, so that both sides will snap into the chassis simultaneously.
A few grams of prevention, a tonne of cure
Along with the usual range of fully-detailed models, Vanquish also released a couple of lightweight racing versions. These have a lighter body and replace the detailed interior with a thin Lexan panel.
I bought a handful of the red McLaren Racing M8Cs (Vanquish SA51), to set up a new Slotmeister corporate events class with these distinctive-to-drive cars. Our corporate guests, having sampled our standard V8s, GTs or F1s, are often itching to try non-magnet pro racing with our Slot.it Le Mans and other classes.
I wanted these Vanquish McLarens to give the full, diff-driving experience, but guaranteeing the presentation, quality and reliability that Slotmeister demands.
So I went for the whole ball of wax. Firstly, I greased and glued all the diffs, as above. Next, I replaced the standard, plastic rear wheels, prone to cracking at the hub, with increasingly hard-to-get NSR alloy items from Italy. These were fitted with brilliant, Adelaide-made MJK tyres.
I found that the MJKs sagged into the recess between the NSR’s rim ribs, so I filled these with “wheel weegies”, aka skinny O-rings. It’s shot the wheels’ weight saving to hell, but presents more rubber to the road.
My theory on Vanquish reliability also holds that the diff failures are promoted by flexing in the sub-chassis itself, aft of the motor, and that the motor’s standard brass pinion is simply too aggressive for the plastic crown-wheel gear.
To fix the latter, I bought a packet of Plafit nine-tooth (dark blue) plastic pinions. These had to be shaved down to about half of their original thickness (yay, Dremel!) to fit this tight Vanquish application.
To solve the chassis flex and maintain inward pressure on the diff, I got some 1.25mm wire and fashioned a square, U-shaped support, bridging the motor to the axle towers. It’s glued in place with light dollops of Shoe-Goo.
Does it work (part 2)?
Hell, yes! I can’t say I’ve done a zillion laps with all my revamped Vanquishes, but I’ve done enough to suggest that the back-end bugbear has finally been eradicated.
The modded McLarens were immediately among my favourite cars on the uniquely smooth and solid surface of the Slotmeister track. Without magnets – which is how I like my racing – the MJK tyres give more than enough grip to hook up, while still allowing drifts and the unique feel of the differential drive.
Anyway, in researching my modifications for these voluptuous Vanquish racers, I stumbled onto a happy discovery … Namely, that there’s another, sturdier differential that’s used in 1/32-scale, one with the same gear pitch and roughly similar dimensions.
It’s found in the back of Kyosho Mini-Z AWD radio-controlled cars. And five of them are on standby in my workshop drawer.
My Vanquishes shall not be vanquished!