Gears grind after replacing motor
 

I have two Tamiya kits I've built and wanted to slow them down by swapping the stock "torque tuned" 540 motor for a 55-turn RC4WD motor.

My Mercedes Cabrio MF-01X rig took the motor swap with no problem. Slowed it down to a speed that is much more fun for mild trail runs... done!

I did the same thing in my CC-01 FJ Cruiser, taking care to make sure the pinion gear is the exact same position, clearance etc. as the stock motor. But it ran with a grinding noise and when I went from forward to reverse, I could sense the gears were skipping somewhere. So I put it back on the workbench and checked everything, but still got the same result. I have checked and re-checked everything many times over, but get nowhere.

I added the little cardboard motor insulator that came with the kit, still same thing.

I went to a different motor, this time a 35T, still same result.

Through all of this, if I went back to the original "torque tuned" motor, everything was silky smooth again.

Any idea what I'm doing wrong? I figured changing the motor in the CC-01 should be simple like it was in the MF-01X, but somehow I can't get it to accept anything but the motor that came with the kit.

Thanks all!

Re: Gears grind after replacing motor
 

Did you use the same pinion gear? Tamiya uses a metric gear (I think mod .6) not standard 48p. Is the set screw hitting the spur gear?

Re: Gears grind after replacing motor
 

Thanks Chino. Yes exact same pinion gear that came with the kit, same pinion gear that works fine with the stock motor.

I'm beating my head against the wall on this one :x! So frustrating.

Re: Gears grind after replacing motor
 

Did you check the set screw? I've seen them catch the edge of the spur gear and make quite a racket.

Re: Gears grind after replacing motor
 

I did not check the set screw for clearance, I'll try that next. Thanks!

Re: Gears grind after replacing motor
 

This....x2. Makes a clicking sound as the gears turn. Very common mistake, I've done it myself several times.

OR the gear cover is not cinched down all the way. Check the pocket under the motor mount and make sure there's no debris that got under it.

On a side note, I usually replace the tapping screws with machine screws after the gear cover is removed a few times. Much better bite into the plastic.