Well, it appears your buddy is stuck in the '70s. Type F was the Ford specification for auto trans fluid prior to 1977. Beginning in '77, Ford began specifying Mercon fluid in most transmissions, and in all by '81. (Dexron is the GM auto trans fluid spec. Mercon and Dexron III are considered compatible by virtually all.) Beginning in '97, Ford began specifying Mercon V in some trans.
Some oil manufacturers rate Mercon V fluid as compatible with the Mercon specifications, others swear that they are not compatible, so there is definitely some debate on that part. For Mobil's part, they rate their synthetic atf as being both Mercon/Mercon V. For what its worth, I have Mobil 1 synthetic atf in my M5OD.
The difference in Mercon and Mercon V is in the low temperature performance, the resistance to breakdown at high temperatures, and the slipperyness of the oil, from what I've read.
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From personal experience, FWIW, type F WILL NOT "fix" your sticky shifter. I accidently put Type F in my old M5, it was strongly suggested that I get it out before it did damage, I'm sure someone will be able to tell you why, the bottom line is that the specification is for Mercon, not Type F, I'd give it what it wants!
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Well one of the reasons it suggested to get it out of there is actually false, the original type F fluid actually had grit in it (we are talking back in the 50s here) that allowed to clutches to to not slip and we know that adding sand to a manual tranny is not a good idea. But that was changed fairly quickly, but there is still some issues with the friction modifiers in type F against the seals and the syncros as I understand it.
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Back in the old days (circa 1960), a old hot rod trick was to put Type-F in your GM automatic tranny. Due to the different friction modifiers, Type-F would work in a Hydramatic or Powerglide to improve the firmness of the shifts, sort of like a pour in shift kit. You could not, however, put Dexron in a Ford Auto Transmission or it would slip.
Things have changed now, however. I'd run Mercon (not Mercon-V) in there if I were you. You might try some of the stuff they sell at auto parts stores that is supposted to help free sticky shifts (Lucas comes to mind). But FWIW, I've heard of people on here running 80W-90 in their M5OD for a while without major issues.
Also, a factoid most people don't know is that Ford recommended Type-F in their power steering units up until at least 1995.
ive got the mobil-1 synthetic atf in mine right now, never use gear oil if atf is specified, i did that once with a jeep cj-7 4 speed and it was almost impossible to shift in cold weather and then come spring it was very noisy, if the oil cant flow where it needs to go, damage will happen. if you have some internal mechanical problem i doubt a fluid change will cure it, maybe your plastic bushings in the shifter assy are gone and causing problems. some M5OD's sre better than others, my 1st ranger went over 200k with no trans issues, my '93 lost 2nd gear at 80k and currently the replacement rebuilt unit doesnt like to downshift into 4rth or 2nd. and ive changed trans fluid every 6 months since ive replaced it. its enought to make one consider going auto!
I'm certain the 'sticky' shifter is a clutch issue. It's not slipping. I've only had the truck like a week or so now, haven't had time to go all through it yet. I want to change fluids and bleed the clutch before I decide to tear into it...
In a manual transmission, especially one with brass syncros like a M5OD, you probably won't notice much difference between Mercron and Type F. Once you start dealing with transmissions that use fiber lined syncros, the differences in friction modifiers may become more apparent.
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