hello! i just picked up a 1991 f 150. i recently replaced the clutch and i am looking for the correct transmision fluid to put in. it has the 5.0 engine with the 5 speed manual transmission. i am getting lots of mixed suggestions for transmission fluid. some say to use Mercon V some say any gear oil will work. another is saying Mercon has a specific gear oil for the the manual transmission. i'm lost as to what i should use. i dont want to have to replace the transmission by using the wrong fluid.
Thanks

 

If it’s a 5 speed it’s supposed to have automatic transmission fluid 🤔 but because there’s no gasket where the transmission case splits for repairs lots of people have found out the hard way that automatic transmission fluid will find the smallest imperfection & over time will leak out, that’s probably why some people are putting gear oil in them, I would just check where the case bolts together and if it’s not leaking & you drain auto fluid out I’d put it back, because even the thinnest gear oil will make one harder to shift in really cold weather, ask me how I know, lol, I had a friend who literally melted some of the parts in his because it had a little leak in the case, it’s kinda something we take for granted unless you park on a paved driveway, I have no clue why Ford or Mitsubishi or whoever made the 5 speeds in the 90s didn’t put a gasket there because especially if it’s a 4+4 over time the transmission is going to be torqued back and forth & every once in a while one will start to drip, now as far as I know the 4 speeds took gear oil, or at least the one in my 89 did,

 

Hi there, welcome to the forum!

 

Welcome.

 

Welcome to the forum!