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Old February 12th, 2022, 08:21 PM
Prowbar Prowbar is offline
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Join Date: Dec 2020
Location: Friesland, the Netherlands
Truck: 1965 GMC 1500, 478 V6, SM420
Posts: 383
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Default Drivetrain noise

Happen to have this odd drivetrain noise. It is louder than it sounds on the video.

Link to the video: https://www.youtube.com/watch?v=9plCftB58Jg

When the RPMs drop (ex. from 3rd to 4th gear) you can hear the loud humming/grinding noise. It can be duplicated in all gears. Above approx. 1000 rpm it fades away.

This is the 2nd SM420, the previous one had the same sound. I'm suspecting the clutch or the drivetrain, not the gearbox. It sounds like it comes from the transmission.

I'm thinking rattling clutch springs or something like that. Haven't had the clutch apart yet.

I've tried to pinpoint the noise by looking around on youtube but cannot find anything remotely close to it.

FYI: SM420 is in good order. The drivetrain has new u joints and driveshaft support bearing.

Appreciate any input. Thanks.
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