1997 B3000 manual tranny making noise in 3rd and 5th (O/D) need help to diagnose!

[ThermonuclearWarrior]

I have a 1997 Mazda B-3000. The transmission makes a strange sound in 3rd and 5th (Overdrive.) It makes it in the other gears too, but it's quieter. Also seems to make a noise when it's in neutral if the truck is moving. I'm told it's the transmission itself. Need some help diagnosing the issue. Also could use a transmission and some help putting it in! Thanks!

 

[Shran]

Is the fluid full and the right type (ATF or engine oil?)

Lots of things it could be, but these transmissions develop leaks out of the rubber shift rail plugs on the top of the trans and slowly become low on fluid, which damages the bearings and causes anywhere from a mild whine to catastrophic failure. If it's just making a little noise, fix the leak and run it... they will last quite a while. Typically you'll have a whine in every gear except 4th if this is the case.

Could also be related to the pilot bearing, throwout bearing, transfer case, axles, etc.

 

[ThermonuclearWarrior]

I'll look at it today or tomorrow and see if I can get you a good answer. I've never touched the fluid, but I had a shop replace the output shaft seal, because it had a slow leak. Might have something to do with it. Thanks for the info!