So I almost have a rebuilt Mitsubishi (FM 146) installed and wonder what folks use for gear oil? The supplier recommended 10W40 engine oil....seems very thin? Manual call for 75-85 gear oil? Older ranger, 1989.

andy

 

Yes, use gear oil in FM146, many like results of Red Line MT-90, synthetic 75/90 gear oil, say it shifts smoother and runs quieter

 

Actually, 10W-40 motor oil is about the same viscosity as 75-85 gear oil. Motor oil has additives that are best for engines and gear oil has additives that are best for transmission that require gear oil. Motor oil will work in a transmission, but is not optimum for it. It is best to stick with gear oil in an FM-146.
Many people think the FM-146 is not a good transmission. I always liked the one in my 4WD 89 STX. I drove it almost 200K miles before selling it to a work mate and it never gave me any problems other than over heating when towing in 5th gear one time. I always thought it shifted smooth and could be shifted quicker than the Mazda M50D. I don't recall it being noisy.
I towed my race car all over the country (in 4th gear) and did a lot of off-road trips with it. It was also my daily driver and I was pretty hard on it. It held up well. As I recall, I used Valvoline 75-85 (maybe 75-90 eventually) synthetic gear lube.

 

Thanks for input. I wore out the original transmission because I used the ranger to pull a 16 ft double axle trailer loaded with 20ft logs off mountain roads In 4wd. This was years ago. Had a rebuilt put in in 2002 and then that rear tailshaft case cracked...forget circumstances. Now this second rebuilt is almost ready to test. All I have left is to attach transfer case, driveshafts, speedo, shift linkages, and add oil. I will likely go with that 75-90 weight synthetic. Thanks on input!

Doing all the work on the floor of garage....throwback to my teen years!