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MiltonFarb

Super Hot Shot - Drive Problem

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My Super HotShot has developed some sort of drive problem that we're struggling to figure out. The car has been running perfectly until recently, however we now have a problem where if we lift the car off the ground all the wheels spin fine but as soon as we put the car down there is some motion, the car starts to screech and then nothing more.

I've taken the gearbox apart and regreased, checked the pinion alignment on the motor and also rebuilt the front of the 4wd mechanism but still get the same problem.

Any ideas much appreciated

 

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Have you checked the grub screw on the pinion? 

That black screw should be on the flat side of the motor axle. 

RKPO23h.jpg

540 motor axle is cut flat on one side. 

If the grub screw is not on that flat side, the shaft will turn, but the pinion won't.  It would screech then. 

This is the most common cause of screeching and halting.  

PPyQq45.jpg

 

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Checked again and it was on the flat side, but unscrewed and refitted - still the same issue. I'm wondering if something is out of alignment between the motor and the first cog so will take the gearbox apart again and see if I can spot something.

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Maybe you have the spacer plates for the pinion incorrectly setup or one has fallen out?

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Take motor out . Push car . If it still locks , check dog bones and see if they are NOT binding up . Check that 

wheels spin on front , grab one wheel and turn it . Then do the same on rear . As this will let you know

if it's front or rear . Just need to find what it is 1st , so you  , know where and what it is so you can fit it .  

Now of course , if motor is out and you can push car without is binding , it's got to do with motor or

pinion . 

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I think I may have found the culprit

This is the gear that attaches to the pinion from the motor - unless I'm mistaken looks like its been ground down on the side that connects to the pinion ?

IMG_0516.jpeg

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Yep - that'll be the culprit! It looks like the pinion hasn't been engaging across all of its width though. The manual will have instructions on how far onto the motor spindle the pinion should go (some give a measurement, some have a plastic tool to set the spacing, and some say to put the cardboard from a screw bag between the motor and the pinion). Whatever method it uses, I think that could be adjusted to give more overlap of the gears. If you're not running a stock tamiya pinion (and you're often best not to, as they're aluminium and wear down really fast - steel ones last longer), then bear in mind that the pinion teeth might be closer to or further away from the motor with a given gap between the round bit of the pinion and the face of the motor.

So I'd get a new one of those gears, and check how far the pinion is on its spindle really carefully when rebuilding it with the new gear.

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Incorrect spacer plate fitment, check the manual very carefully when replacing the spur gear toget the spacer plates correctly fitted.

The above informationfrom AJB123 is correct, but not for a hotshot

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23 hours ago, Snappy1 said:

Incorrect spacer plate fitment, check the manual very carefully when replacing the spur gear toget the spacer plates correctly fitted.

The above informationfrom AJB123 is correct, but not for a hotshot

I agree the space plate fitment needs to be correct, but I'm talking about how far the pinion is pushed onto the motor spindle, and not how tightly the pinion is engaging with the spur gear. That worn plastic gear is only worn across about 1/3 or its width. Incorrect spacer plate fitment could easily cause it to ruin the gear and slip, but it would still wear it across most of its width if the pinion is correctly adjusted onto the motor spindle.

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