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2 months ago

July 2013

  • Text
  • Motor
  • Racing
  • Chassis
  • Suspension
  • Transmission
  • Tires
  • Features
  • Buggy
  • Apex
  • Brushless
RC Car Action - July 2013

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Tech Center SPONSORED BY WHY IS MY TRUCK GRINDING WHEN I ACCELERATE? Q I was running my 4WD SCT with a belt drive system the other day and it was fine until I hit a wall and destroyed my sensored brushless motor as well as some suspension components. I replaced the broken parts and the motor and it still doesn’t run correctly. When I accelerate, the truck makes a grinding sound. If I accelerate slowly, it does not make the sound, but driving the car in any normal way makes the noise come back. Can I run the truck like this or am I hurting it? A If it’s making a noise under normal load, I wouldn’t recommend running it. You could be causing more damage to the drivetrain and you should take the time to fix it now. Whenever there is a noise coming from the drivetrain that is not the normal “whoosh” of the bearings and gears, it is an audible hint that there is something wrong, and it’s just a matter of time before a small problem gets bad enough to do some real damage. When you take a hard hit, there are usually some obvious broken parts, but there can be other damaged parts that do not show themselves until later, especially if the hit was hard enough to damage the motor. When diagnosing drivetrain issues, start with the easy things first. Since the motor was replaced in this instance, there are some issues that could have cropped up as a result of its installation. An incorrect gear mesh is an easy mistake and can cause lots of drivetrain noise, so check that first. The sensor wire can get damaged or severed in a big wreck and it can cause the motor to run strangely and make some extra noises that may sound like grinding, so it is a good idea to check it or test it with a new one. If the new motor isn’t the issue, then it could be a me- chanical issue in the drivetrain. Again, start with the simple things first. Give the wheels a spin with your hand to make

sure the noise is not coming from a bad knuckle bearing or a loose wheel. While the wheels are spinning, watch the outdrives and make sure they are running true. If they wobble, they need to be replaced. If your truck is a belt drive, it is a good idea to check for excessive wear and check the tension on the belts, as skipping belt teeth can create excess noise. Also check for slop in the outdrives and make sure there is no debris impeding the motion of the axles. If the problem persists, you will have to dig a little deeper into the drivetrain. The differentials have a lot of moving parts, so they should be inspected for damage and rebuilt if necessary. The input shafts of the differentials run at high speeds and these bearings are some of the first to fail, so inspect them closely. A damaged or broken bearing can cause excessive drivetrain noise by itself or it could be allowing gears to float and get out of mesh, which could also be the cause of the noise. Sometimes bearing failure creates a heat buildup that can warp the diff case, so inspect the diff case to make sure the bearing seats are not being misshapen. Make sure the diff gears are all intact and that the teeth have a smooth crown and are not pointed. If the gears are pointed, they are worn out and need to be replaced. When you hear a drivetrain noise, find the cause and get it fixed before it fails mid-run. Check the simple things first, and if necessary, rebuild the drivetrain until the culprit is found.

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July 2013
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