Maintenance Tonka Clutch Popper

Maintenance: Fix curving (hook/slice)

It’s pretty common for one of these clutch poppers, particularly well worn in ones, to curve off to one side when going at full speed. Some may do that extremely, some only a little, and some by some miracle go pretty much dead straight. Why they curve at speed is complicated and probably a combination of several things. But the first thing is whether you really need to care much about it at all, if it curves just a bit then just pointing it on a angle from the start can help, but if it’s a bit extreme there are some things you can do to straighten them up. If you are doing this with your kids it can be quite a good little project as there is a bit of physics involved here.

So as to why this curving happens, I think it is a combination of a few things, but almost always is relative to the speed the flywheel is turning, which as you may have noticed is very fast. There is a lot of kinetic energy stored in that flywheel and I think that is part of picture. Another part is surface it is running on, and how flat that is and how much grip the car can get on it (for this you may need an anti-slip grip mat for the first couple of meters where there is maximum torque applied). And another is how much side to side movement there is in the rear wheels which can cause the body to shift slightly on the axis, which at speed magnifies this in a small (or large) direction change.

With all of these, adding weight to the right place more or less addresses the issue. This is because it can:

  • counter the force of flywheel if it is shifting and causing movement
  • push the car more firmly into the ground to counter surface variation and give more grip
  • center its weight more and make it more difficult to move much on it’s axles if there is some decent movement there

Generally you’ll want to add about 20grams of weight (maybe more maybe less, depends) to the opposing side that the car is tending to turn/curve. You could use coins or a lead fishing sinker hammered into the right shape. Add the weight to either the far side tray (between the front and rear wheel), or right up the front by the bumper, I’ve found for some right up by the bumper works best, not entirely sure why! Use blu-tack or similar to hold in place so can easily rejig if needed.

Here’s an example, do the opposite if curving to the right.

Where to add weight to help counter curving

You may still need to use some PVC anti-slip matting for the first meter if running on a very smooth surface – like this stuff:

PVC anti-slip matting

So one thing I have found, I think, is that the more horizontal movement in that rear axle is a pretty good indicator of how much it is going to turn. I think this movement is caused by many repeated big hits on the axles after crashes, which causes the internal brass gear and ring on either side of the axle to push the steel side wall out just a tiny bit each time, resulting in a larger gap and therefore more movement. Thing is I’ve got one that is extremely beat up, and not a huge amount of movement, and one that is not too bad that had quite a lot – and that one spun out like crazy, so its not always about how beat up they are. Pushing the side walls back in a bit to close that gap more or less fixed the bad one – but that was very difficult and I very nearly stuffed it for good (and required drilling the motor out and putting it in a vice).

So I wouldn’t really recommend trying to fix like that, and actually the right amount of weight should still more or less sort out even those bad ones, and I wouldn’t worry too much about small veering off – with kids they can even make a game out it as it can make a challenge to go through a certain gap/ posts/ finish line / bowling pin targeting:)

You could also try putting in an e-clip/circlip in this gap, with some grease (white lithium), if you don’t want to push the frame. I haven’t tried that yet but could be a good solution – just need to make sure it’s not too tight as getting one of those clips out once in could be difficult/near impossible:)

They actually addressed/solved this issue in the single clutch Dune Crawler, by adding brass sleeves to the exterior part of the axle between the wheel and the motor which stops/absorbs any horizontal movement before it is translated into the motor gears. Unfortunately for whatever reason they decided not to add that enhancement to any of the subsequent models which is a shame as is quite difficult to add something like that post assembly.

All in all I think real kudos needs to go to the designers of these things, the fact that they continue to operate at all with the force and speed they crash at, repeatedly over years, is a credit to the design engineers, end to end.

7 replies on “Maintenance: Fix curving (hook/slice)”

Glad to see this article – thanks! I still need to perform some controlled experiments on the hook/slice of my cars. I haven’t sanded the rear wheels yet and I expect uneven grip (as you suggest) could be an important factor along with the slop in the axles. Have you noticed a “puffiness” to the harder, front wheels on any of your vehicles? Some of mine appear to widen towards the inside/open edge and if that were uneven, it might explain a tendency to turn as well.

I imagine that spacer on the inside of the engine is pressed on – I wonder if there would be a procedure to push the spacer outward rather than squeezing the motor case inward? Heat might loosen the spacer, but with plastic in there, heat might be a bad idea. Perhaps an e-clip washer could be inserted to fill the gap in extreme cases?

Hey Brody, no problem been meaning to get around to this one! I did have a play with the front wheels of a couple at one point but not sure it did any good, I’ve got a few that have got pretty well worn front tires like what you describe yet they don’t really turn that much so I figured the shift in direction must be coming from the back, or motor.
With that axle spacer, and the gear, they are well and truly fixed to the axle and don’t budge even a fraction (I tried – with a lot of force:)), but funny you mention the e-clip as that’s exactly what I was thinking this weekend when I was in the local hardware store, spotted some circlips (same kind of thing) and thought that could be the ticket. Also the angled/bent type of circlip pliers would work quite well to tighten them in place, but could also do double duty to push the sidewalls in a couple of spots. I think I may have one I’ll give this a go with and will write up the results. But like you say I think this would be just for extreme cases, I think drilling the motor out is a bit of last resort but I do have one that I think fits the bill – it charges up ok (so the main gear lines are all functioning ok), but is needing way too much weight to stop it spinning out which becomes a bit counter productive, and the rear axle moves a lot from side to side on that one. Good little project for rainy weekend:)

Agreed! That car sounds like a good candidate for an extra axle spacer.

I now have four working clutch poppers, all purchased on eBay over the last 5-6 weeks. My younger brother had the blue Vega and red Monza when we were kids and I somehow got to thinking about them over the summer, wondering what ever happened to them. His were the pre-turbo models and I now have acquired duplicates of those two toys along with one turbo Vega (hard to keep this one under control) and a white Porsche that I didn’t know existed before finding your site! The red one didn’t work at all when I got it, so I drilled out the motor and it magically came back to life after a thorough lubrication. I bolted it back in using the center hole and it’s running pretty straight at this point. I was surprised!

One experiment I did today involved the turbo Vega. I applied a thin layer of rubber cement (cow gum in the UK?) to the rear wheels and the car took off on my hardwood floor without spinning out, despite the fact that I revved it up several times. Unfortunately, the rubber cement was only good for a single run and it immediately spun out on the second run.


Great to hear you’ve got a few going, funny thing is just about every one I have was sold as not working/don’t know how this thing is supposed to work, and all bar one (which was admittedly very badly beat up) run perfectly fine after a bit of routine maintenance:) The Porsche is a nice one, and the Dune Crawler, but the 3 Chevy’s are pretty hard to beat, I think they nailed it there at the start to be honest.
I did think about doing that with the rubber cement actually, but wasn’t sure how well it would stick on there – now I know! If the rear tires are quite shiny I have found that the sanding really does give them some extra grip, and if they’re spinning out in the first couple of meters then the grip mat (pvc type) seems to be sure fire way to stop that happening, also try putting a good bit of weight right up front, that seemed to do the trick for one I have like that. Glad you’ve found some of this helpful, they’re a great toy and a shame they just don’t make em like this anymore!

Hey Brody, I’ve added a little update to this one that may be useful – about flywheel movement. Tried removing that movement (by pushing the far frame wall back in a bit by the flywheel), and it seemed to work on one that had a habit of shooting off to one side mid-flight, so might be worth a go as a first thing to try as is quick and easy! Bit of extra lube like a grease type probably worthwhile there between the flywheel and the frame wall where the gear rod (I think there is a small ring/bushing of some sort there) meets the frame.

Interesting – thanks for the tip. This would be the outer wall closest to the flywheel?

Yep that’s the one, where the pin sticks out the side. Just a little push if there is a lot of movement (left to right) of the flywheel, push too much and you’ll tighten the flywheel (I made that mistake:)). It seemed to sort a bad spin out one I have (even when it was on a mat), so could be worth a go if you have one like that.

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