farmall 140 rear axle gear noise

Hi guys, I have a 1968 farmall 140 with a very noisy rear axle/
transmission, prior owner has tried to repair twice. My question to you guys is I have a 1940s farmall A parts tractor. will the back end off the A work on the 140? thanks for any INFO

Before you rip into changing rear ends....try listening to someone elses farmall or maybe change oil/grease in rear end. I have 2 farmall 100s ( see my handle) The gears on those are straight cut and tend to make a lot of noise.

Stand at left rear tire and try to shake the tractor back and forth. I have
replaced final drive axle bearings in a 140 before. Sometimes the nut that
holds the side dresser drive loosens too causing play. A loose, dragging
brake band can make lots of noise too. Having used several offset Farmalls
I can say the gears are very noisy.

Straight gears will not be as quiet as a modern drivetrain, but it shouldn't be grit your teeth noisy, especially if there is a noticeable change in pitch as it goes from "pull" to "coast" (load/no load).

I got a Super A well over a decade ago, and when I mentioned that I thought the tranny was noisy, was told "they're all that way". I checked fluids, changed oil, pulled the shift cover and checked gear teeth (all there and no chips) and top shaft bearings, and all seemed OK. I used it, and used it, and because I had no other tractor to replace it with, kept using it. It kept getting worse. My sister has a 140, and when I heard that one move, it seemed silent in comparison! Finally pulled the shift cover and checked the bottom shaft, and the bearings are not only gone, but apparently had been long before I got it - I couldn't even find parts or pieces, though there is some silver now showing in the oil.

The only thing I can think of is that enough water sat in the tranny to rust the bearings, or even blow them up, but some former owner pulled the pieces when it came apart, added fresh oil and unloaded it on the next unsuspecting sucker, who eventually ended up being me.

Short answer to a long story: if it doesn't sound right, take it apart and figure out why. It's possible you have a bad bearing, or that one of the final drives has been running dry due to a leak that was never fixed or an oil level never checked, or that the dif gears aren't shimmed right; and if everything seems good, you've probably missed something. Least likely of all is that it's just plain worn out, because if oil is kept full and without water (or ice), and if seals and bearings are replaced as needed, most of these old gears last a very, very long time, and are not all that noisy.