Hi All-
I've got a 1965 F100 4x4 300 4 speed and I seem to be having an odd transmission or drivetrain noise.

When Im driving down the highway between 40 and 55 and let off the gas it sounds like the drive shaft from the transmission to the transfer case is going crazy as if the universal joint is going bad but there is no play in it at all. It sounds like a bad joint and I can only replicate the sound when I start to slow down but as I slow down the noise also disappears. The sound seems like it's coming from the passenger side of the transmission tunnel which is right above the divorced driveshaft.

Before all of this started I also broke the u bolts that hold the rear driveshaft to the transmission when my foot slipped of the clutch in a parking lot. I replaced both of the ujoints on the rear driveshaft while I had it out and now this mystery noise is progressively getting worse. Im at the point now that I would rather detonate what ever is making this noise so I know what to fix.

Thanks in advance everyone!

 

Know anyone with a Go-Pro camera you can clamp on underneath aimed at the driveshaft, then go for a drive? Other choice is get it up on a chassis lift and spin it up to speed with the tires off the ground. Assuming you have already verified that the driveshaft didn't get bent, and there was no damage to the rear differential or transfer case.

Had a 70 Challenger that did basically the same thing, turned out to be a bad brand new U-joint.

 

Your rear driveline should come off of the transfer case in the 65 if it is still factory 65 4x4. There is a short drive line between trans and TC. I get a loud noise or somewhat loud noise in my truck that has been constant since I started driving it a few years ago. It is only when the drive line is no longer under pressure from accelerating or maintaining speed. I believe but am not sure that it is the TC grommets worn out and letting metal to metal with the mounts of the TC occur. It has never become worse but just seems to maintain one constant sound. I will soon be ordering grommets for the TC to see if that will quite the noise. Maybe you have changed the alignments on your rear drive shaft causing the same condition. Good luck with your problem.

 

Can you describe the noise? Is it a clunk, a whine, rattling like baseball cards in bicycle spokes as you slow down (only older guys will get that one). Always go back to the beginning. If you had no noise before you dropped your foot off the clutch, as Buzz44 says, you could have an alignment issue due to broken transfer case mounts. I just purchased those mounts - all 4 upper and lower for $29.00 made out of poly instead of the all rubber ones. Get underneath with a pry bar and see how much you can jack the TC around / up and down. Attached pic is mounts we are taking about. Top right is where your trans to t/case shaft goes. Good luck. Check all your fluids while your at it...