drone- very slight vibration - not exhaust

[Mondo]

Hi,
I have this weird drone that comes up around 30mph & 60mph (especially when cruising at those speeds). At first I thought it was exhaust/rpm/transmission thing but I've slipped the truck into neutral and the drone is still there as it coasts thru the 30/60mph range.
When I put on the brakes there is no difference. There's no shimmy or anything like that. Just a slight vibration. In fact, if you didn't know the truck before you probably wouldn't notice.
I think it has to do with the brakes/wheels somehow as I've recently had a brake job (new rotors/pads) put on. I have the disc conversion and wonder if they somehow used the wrong year parts (I don't know if they're early '70 or later '71-'72 parts). Or if that's even possible.
any ideas?

[geezer#99]

Driveshaft out of balance or pinion angle incorrect.
Also possibly a bad u-joint.

[Steeveedee]

Do you feel it in your hands (front of truck) or in the seat of your pants (drive line)? Does the inside rear view mirror vibrate (u-joints, diff)? Did it do it before the upgrade? The fact that it does it at 30 and 60 MPH tells me that it is a harmonic vibration (u-joints, diff). Not much help there, at the moment.

[HO455]

I too had noise and vibration issues with my truck. Turned out that changing my carrier bearing and aligning my drive shaft took care of some of it. Then a look inside the differential revealed the other half of the problem. The carrier was failing as well as the spider gears.
I recommend checking with the carrier bearing and the drive shaft wear points to start. Then check the angles on the U-joints especially if the truck has been lowered or lifted.
Hopefully you won't have to go through the whole rear end as I did. The WMB thread below has more information on what I did starting on page 13 post 312 and skipping around for several pages.
Good Luck

[67C10Step]

Definitely sounds like drive line but odd that you just noticed it after a brake job. Could be you were not noticing it until the brake job and (if you are like me) you get hyper sensitive for a while until you feel everything is ok.

Had s similar issue on my son’s Toyota Tacoma that has a carrier bearing as well. Toyota replaces the u joints Uber a recall but the slight vibration as still there. I got a digital angle gage and measured everything from the transmission back to the differential. Ended up shilling the carrier bearing down about 3/16” and it took care of 90% or more of the issue.

[LockDoc]

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One easy thing to check would be the harmonic balancer on the front of the crankshaft. I have seen the rubber dampening strip pop out on the front or back and cause the balancer to wobble slightly.

LockDoc

[Mondo]

Thanks guys.... drive-shaft/differential most likely seeing how the rear-end is stock 67 (narrow rear end) and I did do some work on the driveline for the 5.3 conversion several years ago.

[randy500]

Rear axle shaft bearings