G1 - Something humming at high speed

[yamy]

Hi everyone. I have an '82 G1 that runs great except that it has a weird humming noise at high speed - I can get it up to about 26 mph now, thanks to the help of this forum, although I haven't made any major changes to it.

Anyway, this noise sounds like it’s coming from the drive train, maybe the gearbox. The sound is a low-to-high hum that oscillates once every second, which is weird since everything rotating in the drive train rotates at a much high speed that the noise. The rear gearbox has oil up to the filler plug. Not sure what else to check, but as I’m typing this I just had a thought – may I could jack up the rear and run it high speed to help pinpoint the source of the noise. (Just got to make sure the cart doesn’t come off the jack stands, like in Ferris Buhler ).

Thanks ahead.

[TheNewGuy]

Yep, jack up the rear and run it. Hopefully you can locate the source of the noise.

[sho305]

Every one I ever ran hummed at high speed, soon as the clutch is shifted all the way out, then it hums with engine speed. This is caused by the inside grooves of the drive belt bottoming on the sheaves as best I can tell you. I had a lot of sleds that did the same thing. If the noise is not that, please try to describe it. The belt hum only happens when the clutch shifts all the way out, top gear so to speak.