Grinding noise when accelerating

[ClassicAmeriGun84]

I have just recently bought a 68 F100, 360 which originally had a three "on the tree" but the previous owner switched it to a regular 4 speed. The truck runs well, is in overall decent shape but when I drove it home it makes an awful high pitched whining or grinding sound akin to the sound of dry gears that gets more and more of s higher pitch the faster the speed. I assume that whoever switched the 4speed over didn't install it correctly. What to do about it? Help!

[Ranchero50]

I'd put it on jack stands and check everything underneath. Then run it up to speed on the stand and see if you can figure out where the noise is coming from. Could be something rubbing the drive shaft or low / wrong oil in the tranny or rear. Really hard to guess without being under there.

[carnuck]

Does the noise happen in 4th gear too? That would imply differential and not transmission.

[logjammin]

Having a similar issue. I have a 1970 F-250 with the 360 and I believe the C6 transmission. From a stop I have a large squeaking and shuddering when I accelerate. Seems to occur with acceleration at any speed but is much less noticeable at higher speeds. Started last week and has gotten worse every day. If I find out from my mechanic what is going on, I'll post an update.

[radioactivelarry]

You may have a problem with the drive shaft that is too long or mismatched from the transmission change. climb under and check that also. Do you have a split drive line? Could be the U-Joint in between. Make sure the starter is correct as it could be hitting the flywheel or just simply dragging.
As Ranchero50 recommends put it up on jack stands and run it. Could also be a bad third member (pumpkin).

[carnuck]

Having a similar issue. I have a 1970 F250 with the 360 and I believe the C6 transmission. From a stop I have a large squeaking and shuddering when I accelerate. Seams to occur with acceleration at any speed but is much less noticeable at higher speeds. Started last week and has gotten worse every day. If I find out from my mechanic what is going on, I'll post an update.

Squeaking could likely be a dry Ujoint, then vibes from the worn joint throwing shaft balance off by not aligning the shaft.

[logjammin]

I have just recently bought a 68 F100, 360 which originally had a three "on the tree" but the previous owner switched it to a regular 4 speed. The truck runs well, is in overall decent shape but when I drove it home it makes an awful high pitched whining or grinding sound akin to the sound of dry gears that gets more and more of s higher pitch the faster the speed. I assume that whoever switched the 4speed over didn't install it correctly. What to do about it? Help!

Just took my 1970 F-250 in to a transmission shop who in return referred me to "Idaho Drive Train" for new u-Joints. They replaced the spindles, the center bearing and the u-joints. Solved my issues and the truck drives more smooth than ever.

[ClassicAmeriGun84]

The dust cover that covers the flywheel was missing, found it along with the original 3 speed under a pile of trash in the bed of the truck. Does this pan hold gear oil? Or is it just a "dust cover"? Did I do major damage by driving it in this condition for 25 miles?

You may have a problem with the drive shaft that is too long or mismatched from the transmission change. climb under and check that also. Do you have a split drive line? Could be the U-Joint in between. Make sure the starter is correct as it could be hitting the flywheel or just simply dragging.
As Ranchero50 recommends put it up on jack stands and run it. Could also be a bad third member (pumpkin).

how will I know if the driveshaft is too long?