I would like to change the transmission fluid in my 89 F350 Diesel w/ ZF 5spd. What are the suggestions for best lubricant? The truck has 160,000 miles on it.

Thanks

 

use a mercon synthetic ATF and you will be just fine.

 

I gotta fess-up and say I knew mercon / dexron was the manufacturers suggestion. Without getting into a real long story, here is my dilemma. This truck has probably 100,000 miles pulling a 30' livestock trailer and the transmission makes some noise at highway speed. Nothing ridiculous, but it is annoying. I have tried 85-140 gear lube. It didn't work because I couldn't shift gears. Next I tried 20-50 motor oil and it worked until cold weather and again shifting was hard. Currently it has 5-30 synthetic motor oil. My thinking was thicker lubricant would reduce the noise and it did somewhat. Any suggestions what to try next?
Thanks

 

Redline MTL or Redline Hightemp ATF
Pennzoil Synchromesh
Amsoil MTF
BG Synchroshift
Specialtyformulations MTFglide or Synchroglide
Torco MTL-L or MTF-R

Since you can't use the thicker fluids due to shifting issues, you'll have to live with the noise.

I would risk a thicker gear oil like Redline MT90, SpecialtyFormulations MTL-P or MTL-R, and Amsoil MTG. These fluids are ~90wt, but being a synthetic they should shift when cold unlike the 20w50 ad 85w140 honeys. Or, blend 50:50 with their thinner counterparts, for example Redline MTL/MT90 blend or Amsoil MTF/MTG.

And, try overfilling the tranny by a pint or so. That might provide a little noise insulation. So does coating the transmission with thick paint, rustproofing rubber snot, or other soundproofing. But, those will also increase tranny temp. Insulating sound will also insulate heat.

There are also synthetic motor oils. Look for a 0w40(Esso XD3, Amsoil, Synlube, or Mobil1) or a 0w30(Castrol, Esso, Amsoil, or Mobil1) synthetic motor oil. The '0w' will help with that cold flow and the 30wt should be quieter then a 20wt ATF. The 40wt will be quieter then 30wt.