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TollyRC

Racing Fighter Gearbox/Diff issues

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Hi Guys, Have just finished building a Racing Fighter with my son. It’s run for about 1.5 hours but has now developed an annoying clicking noise from the gearbox. It does it when driving forwards and backward but its worse when going backwards. It has no effect on the speed that the car moves at though. 

Also, the rear wheels only spin in opposite directions intermittently when being turned manually. The rest of the time only one wheel spins and the other doesn’t move at all. To be honest I didn’t check the diff was working properly when I first built it so don’t know if it’s always been like this or has developed this problem at the same time as the clicking noise.

Ive stripped and rebuilt the diff and box 3 times now and can’t cure either problem. 

Any ideas or tips would be appreciated as my son is rapidly losing interest! Thank you. 

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Does it do it when the wheels are off the ground? If so, take the drive shafts out and try again. If it still does it you'll know for sure it's something inside. Is there anything floating around inside the spur gear cover?

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Hi, thank you for replying. yes it does it with the driveshafts removed, it’s definitely diff related! There’s no sign of anything inside the cover either. 

Its as if the gears in the diff aren’t meshing properly all of the time. It does feel very notchy when you turn it by hand, but I’m not sure if this is just how they are supposed to feel..... I never had this problem with my good old Falcon back in the day ! 

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Hmmm. I can't see what else it could be. I guess you're running bearings rather than bushes? If so, could be a dodgy bearing. 

10 hours ago, TollyRC said:

Also, the rear wheels only spin in opposite directions intermittently when being turned manually. The rest of the time only one wheel spins and the other doesn’t move at all. 

 

This doesn't sound right either. It definitely point to something with in the the diff unit itself. Maybe open it up a 4th time. Are there any burrs on any of the idler gears?

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And when you open it up, perhaps take some photos and upload them here? Maybe one of the old hands will spot something?

Also perhaps check the pinion lateral alignment with the spur. Is the grub screw clear of the spur and are the teeth in good nick?

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Thanks for the advice guys. Cleaned the diff and reassembled it again and the diff now works properly!

Still got the clicking sound though and no obvious reason I can see. Have got some bearings on order to replace the std bushes to see if that cures it. After that it’ll be on to replacing all the gearbox internals in turn I guess! 

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On 6/2/2020 at 1:15 PM, TollyRC said:

Thanks for the advice guys. Cleaned the diff and reassembled it again and the diff now works properly!

Still got the clicking sound though and no obvious reason I can see. Have got some bearings on order to replace the std bushes to see if that cures it. After that it’ll be on to replacing all the gearbox internals in turn I guess! 

Check the motor mount. My son's racing fighter developed some serious clicking and it turns out the screws to the motor backed out just slightly which made the motor slightly loose and move around which did two things.  First it created bad clicking as the pinion was no longer always properly in sync with the spur gear, and it ruined the integrity of the screw holes in the plastic motor mount to the point I had to replace it. 

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