drained the 140 + installed the 90...
j o
dunno, I have close to 150K on a K 75 FD using 75/140 full synth.
Under the impression K 1200's & the Open Hole R FD's were most affected by the excess "drag factor" of 140 weight.
Since there is no preload to worry about on the new rear drives (the ones with the big hole in the axle), replacing the ball bearing is far less troublesome than on the previous generation rear drives that had to have their preload set up (using shims) EVERY time a bearing was replaced. I did it on my old K100RS, and it was REAL touchy!
K 1200 FD leak below The newer BMW FD's had numerous failures regardless of what friggin oil was used. Reason BMW re-engineered to a beefier design for the K 1600.
K 1600 FD below, note the difference in the lugs
The two major dealers in Gauteng now change the rear drive unit oil at every major service interval, disregarding BMW SA's instructions. Surprise, surprise... the number of final-drive failures has decreased dramatically!
NO BIG deal either way is my opine. If I resided a colder climate 75/90W makes more sense over 140. (maybe) Viscosity chemistry is wunderbar magicKal stuff.
Mobil 1 Synthetic Gear Lube
LS 75W-140
Designed to meet the requirements of light trucks and SUVs where an
API GL-5 75W-140 gear oil is recommended.
For the record,it's Don Eilenberger JO.