Old transmission

[pflaming]

Mine needs new oil. Do I just replace or do I run a cleaner first? 

[Adam H P15 D30]

I would just replace it. Look for GL1-GL4 oil only, stay away from GL5. 

[kencombs]

I'd pull the shift cover and look inside.  Only if there is some 'junk' in the bottom would I flush or clean.

 

If it needs it, put some diesel in it and let that set for at least 24 hours to loosen the stuff up.  Run engine with trans in neutral for a few minutes to loosen it up.  Drain, repeat.  Fill with new oil.

 

If it looks clean, just drain and refill.

[Eneto-55]

I ran (filtered used) ATF in an engine that had really dirty black oil to clean up the crankcase.  I just let it idle for exactly 3 minutes - with my hand on the key, in case I heard anything unusual.  I know all of that stuff about not getting used oil on your hands, but I also use used ATF to clean grease & grime off of my hands, sometimes when it's just in between messy jobs, to start over with clean hands, or before washing with soap & water.

 

So I'd probably opt for ATF in a transmission to clean it, although if I remember right, I probably used kerosene when I cleaned out mine on my 46 P15.