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Old February 13th, 2022, 12:06 PM
Prowbar Prowbar is offline
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Join Date: Dec 2020
Location: Friesland, the Netherlands
Truck: 1965 GMC 1500, 305E, SM420
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Default Re: Drivetrain noise

Quote:
Originally Posted by AZKen View Post
Humming/grinding noise does not do it for me as a description. It's very hard to tell which of the noises I hear is the one you are asking about. I hear a low pitch rumble and a higher pitch "whine". First sounds like exhaust. Second sounds like normal gear mesh noise. Sounds like many old trucks I've had. But noise from a video/cell phone is very difficult.

All I can say is experiment with the clutch pedal. Push clutch pedal in when the noise starts and see if it goes away. What noises are there when down shifting. Do some coasting with clutch pedal in to see what noises you hear at different coast speeds. Try to run on different era paved roads. Do you have cruise/car style tread tires? or snow/mud..... or radical tread design? Bias, radial....

Do you feel any vibration frequency that matches the sound frequency/pitch/tone?
What viscosity lube in trans? Synthetic lube. "GL" number?

What outside temp do you have now?
To clarify, the noise appears at 11 seconds into the video and lasts until 17 seconds into the video. It sounds like something is grinding, or a low pitch rumble as you said Ken.

It could be exhaust but I've switched mufflers and it is still there.

This happens when the RPMs drop (after shifting). The usual SM420 gear whine is apparent in the video but not what I'm talking about. In 4th gear there should be barely any tranny noise because it is a 1:1 and the gears are not subjected to a load.

What noises are there when downshifting? No noise like this, just the gear whine when shifting to lower gears.

It happens in all types of roads. The tires are Toyo open country 235/85 R16 radials, new tires. Not a off road type by any means, no radical threads.

Do you feel any vibration frequency that matches the sound frequency/pitch/tone? No, nothing is felt other than hearing that noise.

What viscosity lube in trans? Synthetic lube. "GL" number? straight 90W GL4 mineral lube.

What outside temp do you have now? About 43 degrees Fahrenheit.

Will do some testing with the clutch pedal.
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