+1 .. ahahaha, this is quite the old thread but i felt i must 2nd that after thinking the same thing after reading the 1st few postsits like a retard convention in here. Gear oil is for rearend gears, i never saw a post with him saying he needed to change rearend gears. Mercron tranny fluid is what you need or GM syncromesh can be used also. Just drain the damn thing, pop off the shifter and pour directly into the tranny. About 3 quarts. pull the fill plug and stick your finger in there, after 3 quarts you should feel some fluid at your finger then you are good.
Recommended Oil and Fill Capacity
TREMEC engineers have recommended Texaco-Havoline Dexron III/Mercon Non-Synthetic ATF. There has been a significant amount of confusion regarding the proper capacity and proper type of ATF for the TR-3650 which may have a correlation with a rather large number of complaints about notchy shifting, shift "nibbling", noisy synchros, and grinding gears. The 2007 Mustang GT owner's manual specified the use of 3.0 L of non-synthetic Mercon ATF in the 3650, while the 2008 Mustang GT owner's manual now specifies the use of 3.0 L of Mercon-V ATF in the 3650. Dexron III/Mercon Non-Synthetic ATF seems to work best for pre-2005 Mustang GTs. NB: Tremec service manual also specifies Mobil 1 Synthetic ATF ( Tremec specification ET-M-99 ) in addition to Dexron III.
Yeah I looked into it more, penzoil it is.This thread has been bumped more times then a hooker on the vegas strip. From everything I have read on these transmissions most people that run synthetic fluid end up switching it out. One of the most common fluids people run is penzoil synchromesh. I just put it in about two months ago and noticed a huge difference in how it shifted.
Well ****, idk what it had when I got it but I put RP in it and there was no change.