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Pinion Gear Slipping

Pinion Gear Slipping

Old 12-30-2011, 05:46 AM
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Default Pinion Gear Slipping

My pinion gear keeps coming loose and I would like some ideas on how to keep it set. I've tried blue and even red locker on the grub screw but it will still move forward after a bit. Any suggestions? Let me know if any further info is needed. Thanks in advance.
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Old 12-30-2011, 06:54 AM
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Is the flat spot on the motor shaft rounded out?


Have you tried to make it tighter with a quality hex tool, not the L shape tool that comes with most RTR kits?


Is there any unnormal vibration in the motor/trans area that could be loosening the grub screw?
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Old 12-30-2011, 07:58 AM
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Originally Posted by got_nitro
Is the flat spot on the motor shaft rounded out?


Have you tried to make it tighter with a quality hex tool, not the L shape tool that comes with most RTR kits?


Is there any unnormal vibration in the motor/trans area that could be loosening the grub screw?
The flat spot is good on the shaft. The only unnormal vibration I can think of would be hard landings...and I have not tried a quality hex tool. I'll have to see if I can pick some up.

I've read of people putting locker on the motor shaft and the pinion itself to help hold it. Is that a good idea?
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Old 12-30-2011, 10:08 AM
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What kind of surface does the end of the grub screw have? Is it flat, semi-rounded, or pointed?

If it isn't flat, try grinding a flat spot onto the end of it. Or, you could dremel a small dimple in the flat face of the motor shaft.
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Old 12-30-2011, 10:55 AM
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Originally Posted by LaTuFu
What kind of surface does the end of the grub screw have? Is it flat, semi-rounded, or pointed?

If it isn't flat, try grinding a flat spot onto the end of it. Or, you could dremel a small dimple in the flat face of the motor shaft.
The bottom of the grub screw almost looks a bit rounded. I think I'll try to flatten it a bit and then go from there.
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Old 12-30-2011, 12:20 PM
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I'm willing to bet if you get in there with a good hex tool and torque it down your problem will go away.
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Old 12-30-2011, 01:25 PM
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Originally Posted by got_nitro
I'm willing to bet if you get in there with a good hex tool and torque it down your problem will go away.
+1, I have been there and done that.

OP, I had the same exact issues with Blitz when I installed a Tekin system in it. Couldn't finish more than a few laps in a race because the pinion would never hold on.

I was using L-wrenches since 2002. They always worked well enough on nitro for me so I didn't think anything else of it. As it turns out, quality hex tools are finished to much better tolerances that you need in order to get just the right amount of torque on the pinion. Another racer saw my issue, lended me his hex tool, and the problem went away.

..I bought a whole set of hex tools the very next day.

Mine aren't a very high quality, but they get the job done. I bought a set of Dynamite tools. I'm not sure how I got by without this type of tool before. I hardly ever touch L-wrenches anymore.
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Old 12-30-2011, 04:34 PM
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I'm going to pick up a good set of hex tools in the next couple days. In the meantime, I thought about how the grub screw is rounded on the bottom and decided to keep it that way and mill a divot into the motor shaft. This motor is dedicated to this truck so I felt ok doing it. I used my milling bits and my benchtop drill and put a nice little divot in there. The grub screw sits down in there nice and I put on some red locker. I'll see what happens once that's dried.
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Old 12-31-2011, 08:25 AM
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As long as everything was grease and oil free, the red should be the end of your probs even tightening with an l wrench. Remember you'll need to use heat to break the grub screw free of the red when it needs to come off.
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Old 12-31-2011, 08:57 AM
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On all my rigs/cars I use blue loctite. Make sure all surfaces are cleaned beforehand. Also let it cure overnight...even using quality hex drivers be careful not to over tighten the grub screw or else you will strip it easily.
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