Transmission fluids
Tourer
Joined: Feb 2011
Posts: 479
Likes: 1
From: Oregon
I've used 75-90, 75-140, syn+. It's all the same, noticed no difference. My dealer is close, it's easier to buy 5 qts syn+ and filter and do all 3 holes. 90wt gear is roughly the same viscosity as 50wt motor oil anyway.
Road Master
Joined: Mar 2009
Posts: 962
Likes: 0
From: .....
A gear oil is made for the way the gears mesh in our transmissions. Gear oil has a different additive package that is specific for the application.
I use red line shockproof heavy. I have also used royal purple and it worked just as well as the shockproof does.
Gear oil is far superior to using an engine oil in the tranny.
I noticed on both amsoil and mobil's websites they recommend the v-twin oil in the tranny,so I emailed both to ask why when it's obvious that a gear oil is formulated for just this type of application.
I was informed that both amsoil and mobil recommend what is consistent with the manufacturers(Harley) spec.
So because Harley recommends it so will the oil company,however as a footnote amsoil recommends severe gear.
Basically I was told gear oil is formulated for this type of application but because Harley says use syn 3 the oil companies suggest their equivalent,even though gear oil is superior the oil company will not go over Harleys head and recommend gear oil first,only secondarily if the v-twin stuff is unavailable
Interesting tidbit of info
I use red line shockproof heavy. I have also used royal purple and it worked just as well as the shockproof does.
Gear oil is far superior to using an engine oil in the tranny.
I noticed on both amsoil and mobil's websites they recommend the v-twin oil in the tranny,so I emailed both to ask why when it's obvious that a gear oil is formulated for just this type of application.
I was informed that both amsoil and mobil recommend what is consistent with the manufacturers(Harley) spec.
So because Harley recommends it so will the oil company,however as a footnote amsoil recommends severe gear.
Basically I was told gear oil is formulated for this type of application but because Harley says use syn 3 the oil companies suggest their equivalent,even though gear oil is superior the oil company will not go over Harleys head and recommend gear oil first,only secondarily if the v-twin stuff is unavailable
Interesting tidbit of info
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Road Master
Joined: Mar 2009
Posts: 962
Likes: 0
From: .....
A gear oil is made for the way the gears mesh in our transmissions. Gear oil has a different additive package that is specific for the application.
I use red line shockproof heavy. I have also used royal purple and it worked just as well as the shockproof does.
Gear oil is far superior to using an engine oil in the tranny.
I noticed on both amsoil and mobil's websites they recommend the v-twin oil in the tranny,so I emailed both to ask why when it's obvious that a gear oil is formulated for just this type of application.
I was informed that both amsoil and mobil recommend what is consistent with the manufacturers(Harley) spec.
So because Harley recommends it so will the oil company,however as a footnote amsoil recommends severe gear.
Basically I was told gear oil is formulated for this type of application but because Harley says use syn 3 the oil companies suggest their equivalent,even though gear oil is superior the oil company will not go over Harleys head and recommend gear oil first,only secondarily if the v-twin stuff is unavailable
Interesting tidbit of info
I use red line shockproof heavy. I have also used royal purple and it worked just as well as the shockproof does.
Gear oil is far superior to using an engine oil in the tranny.
I noticed on both amsoil and mobil's websites they recommend the v-twin oil in the tranny,so I emailed both to ask why when it's obvious that a gear oil is formulated for just this type of application.
I was informed that both amsoil and mobil recommend what is consistent with the manufacturers(Harley) spec.
So because Harley recommends it so will the oil company,however as a footnote amsoil recommends severe gear.
Basically I was told gear oil is formulated for this type of application but because Harley says use syn 3 the oil companies suggest their equivalent,even though gear oil is superior the oil company will not go over Harleys head and recommend gear oil first,only secondarily if the v-twin stuff is unavailable
Interesting tidbit of info
