Which is the better fluid to use if you have a choice between 80w90 and Dexron? I guess I am trying to figure out which one offers more protection and lasts longer.
Also, this is not for my Ford truck, this is the fluid going into the manual transmission of my 1991 Mazda 626. Thanks for any input!

 

http://forums.mazdaworld.org/102-626...il-type-2.html

Looks like the Dexron is the best bet. I remember my one F150 with the five speed (mazda tranny) had the fluid and not gear oil.

 

^^ Thanks for the link, I have been having a hard time finding a decent Mazda forum. I put 80W90 in the trans per the owners manual (it said either was ok) but I believe I will switch it out with Dexron. The reason is because now it grinds 2nd gear ever so slightly when the car is cold. Dexron is what came out,(cause it was red) and I think it was a little low to begin with.

In conclusion, old,dirty, not enough Dexron= no grinding.
Fresh correct quantity 80w90= 2nd gear grinding

Plus, the leftover Dexron can be used to drain and refill the powersteering reservior.

 

Super slippery synthetic lubes will aggravate a worn synchro blocker ring condition and cause gear clash. You might be better off with Dexron III and a friction modifier.....probably a cut-and-try procedure to see what combination works best.

 

I was going to drain the gear oil and try the Dexron.
What brand and how much friction modifier do you recommend? BTW, the trans capacity is 3.5 quarts.

 

A little research turned up this stuff recommended for synchro boxes in 75W85 GL4: Redline MTL or Castrol Syntorq LT. (Amsoil makes an MTL as well, but it's probably expensive as he*l.)
These lubes are designed for manual trannies and each has the proper friction modifier built into its additive package.
http://www.redlineoil.com/product.aspx?pid=140&pcid=7