I took my 1994 F150 4x4, 5 speed into the dealer because the clutch failed one cold morning. They found that the slave cylinder needed replacing. I asked them to go ahead and replace the clutch while they had the transmission off because it had 55-60% wear on it. The repair took 10 days and once I was told that the transmission had to be dropped again because there was a vibration when the truck was started.
Now when I take the the truck on the interstate and put it into overdrive, after 5-8 minutes a high pitched hum can be heard. The stick shift is vibrating and the noise corresponds with the vibration. Letting off
the excelerator stops the noise as does dropping it into 4th.
I took it back to the dealer and they put friction modifier in it. The noise
continues.
Any help would be welcome, thanks.

 

I wish I could help, but the fact of the matter is the last time I worked on a stick shift I was 16 years old and the transmission only lasted a few days after that. I work on E4OD/4R100s only, sorry.

G