Base kit gearbox click

What might we have here? Both of our gear boxes from the base kit are getting this same intermediate click, which is more noticeable at slow speeds but happens with or without load.

Something is quite wrong.

First thing to check is that you’ve got the right size pinions and gears and everything is in the right holes.

Are you driving one motor or both motors in that test?

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That’s with both motors driving on that side. I don’t know that we ever tested it with just one going.

We did rebuild the gearbox, but the only fishy thing we found was a warped e-pin, which we were hoping was going to be the ticket, but apparently it’s something else.

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This is weird. Usually, gearbox noises are cyclical an repeatable, like a beat in a song.

I can’t tell if one of your gear meshes is slipping, as Tom is hinting to above, or you have a bad bearing. I suggest disassembling again and trying to see if each bearing spins freely.

Let me know if you need any parts replaced.

Andy B.


Appreciate it. Bearing checks will be the first thing on the agenda this evening.

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In addition to checking the bearings, was the gearbox actually greased?

Was anything overtightened? Gearboxes are best assembled with hand tools so nothing is over torqued.

Are gears assembled in the correct orientation paying attention to which faces of gears have little “nubs” vs what’s flat?

Were bearings pressed in gently using a soft material like wood? Or were they pressed on directly with a metal press or hammer?

Is the motor mounted correctly?

Lots of grease. I believe they were able to assemble everything by hand or with a rubber mallet. We’ll definitely be paying close attention to orientations when we take it apart again tonight.

@Andy_Baker I haven’t assembled one lately but do tough boxes still require the break in run?

Try running just one motor at a time before disassembling. Remove the breaker for one, run it, swap, run it. See if only one side is presenting an issue, which could be poorly secured motor, or if there is a more general problem.

Our students put together one gearbox with a flipped gear, so the “ridge” was on the wrong side. So complete take apart was required.
In the past, we’ve had one CIM screwed in funky and it caused intermittent clicking sounds.


I asked an AndyMark engineer about it a while ago; they said it’s good practice but not required.

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I agree that it’s not required, but it definitely won’t hurt.

Andy B.


Oooh, do tell us more about this break-in run…

To break in the gearbox you run the gearbox dry for half an hour, disassemble, clean out any metal shavings, and then reassemble with grease.


We’ve done the break-in run on many Toughbox variants and we’ve never heard any of those non-periodic sounds heard in the video before or after. The ridges on the gear sides have to face the bearings adjacent to the gears or the gears rub on things they shouldn’t rub.

I’m looking forward to the new Toughboxes with the symmetrical and pocketed gears!

I’m not sure if this applies to CIM motors, however, I sometimes hear a similar noise if I over tighten some screws on Falcon 500s. You might want to check if there is something similar on these motors. It could also be a bad bearing.

This shaft issue may be a root cause.

Andy B.

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Ok, that sounds exactly like our problem. Pulling everything else off, the shafts are definitely drawing circles.

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In the meantime, might see if local teams have old TBminis they can source older straight shafts from.

Here’s a video we took of the shaft earlier this evening as we were troubleshooting

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We definitely see that same wobble on the middle wheel of our chassis. I will keep following this thread to find out what the best solution is.