Yep, a T-5 W/C is a needle bearing tranny and so needs thin fluid. Ford spec calls for "Mercon" (NOT Mercon V) f.e. '95 Mustang GT. If your parts shop only offers GM spec oils "Dexron II" will do the job as well as Mercon.
Roughly two liters go into the filler plug, using a squeeze bottle.
Only the old trannies like f.e. Top-Loader use the thick 80-weight oil because there are no needle bearings.
I posted on this topic earlier this year after extensive consultations with various reputable T5 rebuilders. The issue was synthetic versus non-synthetic. All but one of the rebuilders I consulted advised not to use synthetic. In layman's terms, it can be too slippery for the synchro's to work as intended. When I changed from redline back to non-sythetic, most of my "can not get it into first gear" problems went away. One source advised that in his company's poll of race car drivers and their crew chiefs, all but one avoided synthetics in a T5. One driver said that trying to shift was like hitting a wall. In the C4, I like either redline or royal purple. In my mind, this is still an open question, but at least for my own application, I avoid the synthetics in a T5. If I recall correctly from G-Force website, they will not warrant their G-Force T5 trans unless their own brand of ATF is used inside the case.
Fill after the driveshafr is hooked up!!
I found a cheap fluid pump at Harbor Freight ($4.00) that works great for filling underneath. I didn't cut all the clearances for the shifter so removing it would have been difficult.
It is just little cheap plastic pump, but I bought several.
Ken, I have synthetic in mine, and will agree with the "hitting the wall" comment. Mine shifts fine, but you can't force it to shift fast with the synthetic. Since I never rush the shifts anyway, I don't mind this little feature. The synthetic should help longevity, just don't assume maximum shifting performance, in my experience.
Thanks for the comment - one more for my mental file cabinet on this topic. I guess when the day comes to have the "awesome" stang, I simply moot out the question and go with a 6 speed automatic. :lol:
I wondered about using synthetic ATF. Transmission shops carry an additive they call "friction modifier" for transmissions. Among its uses is to be added when a low friction ATF like Dexron is used to refill an auto trans that is supposed to use older type fluid. I have personally used this stuff just for that purpose and it cured a car of "shuddering" in reverse.
It seems to me some of this stuff might be just the trick to enable use of synthetic ATF in a T5. Put some in and fill the rest of the way with your choice of synthetic. If I had one of my T5's anywhere near being useful in a running vehicle I'd try it myself.
If anyone cares to experiment, I'm afraid I don't recall the name of the particular stuff I used. It was in a very small bottle though, about 6 to 7 ounces. I know there are also rather higher priced additives specifically for Hondas and Toyotas, but this stuff is more generic. If pressed I can call the shop tomorrow and find out exactly what they gave me that worked so well.