Rear end/transmission noise/slack
 

My 1990 f150 302 automatic had some driveline slack and noise. Mechanic checked it and thought it was the rear end. Bought a good used differential and had it installed. Took care of most of the slack, but continued to have high pitched noise in lower gears. Noise improves as you upshift, but is still there in higher gears. Mechanic that installed the differential said that all transmissions like this have that noise and would have to live with it. Find that hard to believe. Any thoughts?

I don't think so. I don't seem to remember my '91 having any noise like that. You might want to try a tranny shop and see what they say. Just my 02. :)

Tried a transmission shop and they somewhat agree w/mechanic, 1990ish f150 transmission does have more noise in lower gears. My truck is very low mileage, but sat, unmoved, in a backyard for two years. Transmission guy says truck sitting still for two years and upper part of the planetary gear exposed above fluid may have allowed gear to pick up rust. This would definitely cause the noise I'm hearing. Going to try changing fluid and filter first. If that doesn't work, looks like a rebuild to me. Seeking input. Thanks

Fair enough, my '91 was pretty high mileage and saw lots of back roads so definately no rust on any of the gears. :)

I had gone to aamco.very honest and understanding.would refer them to others.