Gear Oil Question 2003 FLSTC
Thread Starter
|
Advanced
Joined: Oct 2022
Posts: 80
Likes: 27
From: SW Missouri
Gear Oil Question 2003 FLSTC
Something I was thinking about while buying my oil today.
I have been using Royal Purple 75w-140 for a long time in my transmission, and was wondering what others use in their transmissions, and why do you use it?
I started using the RP in all of my 4-speed transmissions in 1999 in my Big Block Chevelles and was always impressed with the way it performed. I am hardcore about using gear oil in a manual transmission in my bike, and I'm very satisfied with the way it works in my Harley, but haven't thought about using anything else, so, what gear oils are others using and how come, because everyone has a favorite, and who know, there might be something better.
Thanks
Rocky
I have been using Royal Purple 75w-140 for a long time in my transmission, and was wondering what others use in their transmissions, and why do you use it?
I started using the RP in all of my 4-speed transmissions in 1999 in my Big Block Chevelles and was always impressed with the way it performed. I am hardcore about using gear oil in a manual transmission in my bike, and I'm very satisfied with the way it works in my Harley, but haven't thought about using anything else, so, what gear oils are others using and how come, because everyone has a favorite, and who know, there might be something better.
Thanks
Rocky
Last edited by Rocky Hill; Jan 11, 2026 at 12:32 PM.
Club Member
Joined: Apr 2016
Posts: 11,593
Likes: 8,420
From: Inland NW
Brand wars aside, I have always used synthetic 75w140 in Harley transmissions.
Hell, now they even sell it for use in the primary, so I do that, too.
I am not a Royal Purple fan, for my own reasons, I run the Lucas product
Hell, now they even sell it for use in the primary, so I do that, too.
I am not a Royal Purple fan, for my own reasons, I run the Lucas product
Seasoned HDF Member
Joined: Oct 2012
Posts: 13,105
Likes: 13,049
From: Texas, USA
If you are "very satisfied" with the way Royal Purple works in your Harley why would you switch? What would make a different one better? Because another product works well in someone else's bike? Because someone says so on the internet?
For the record, I use Mobil-1 75w140.
For the record, I use Mobil-1 75w140.
Thread Starter
|
Advanced
Joined: Oct 2022
Posts: 80
Likes: 27
From: SW Missouri
If you are "very satisfied" with the way Royal Purple works in your Harley why would you switch? What would make a different one better? Because another product works well in someone else's bike? Because someone says so on the internet?
For the record, I use Mobil-1 75w140.
For the record, I use Mobil-1 75w140.
Last edited by Rocky Hill; Jan 11, 2026 at 03:22 PM.
Cruiser
Joined: Feb 2007
Posts: 144
Likes: 131
From: West Michigan
I used Mobil 1 75w-140 for years and switched to Redline heavy shockproof. If you do any research on gear oil additives vs motor oil additives one would never run motor oil in their transmission.
That being said I think the HD transmission is a pretty robust unit and can take an awfully lot of abuse. I once ran one with no oil for 80+ miles (don't ask) and the only thing that had any damage was the trap door ball bearings. The gears and roller bearings looked like new.
Just think of the quality of the gear lubes and oil in the 1940s, scarry.
That being said I think the HD transmission is a pretty robust unit and can take an awfully lot of abuse. I once ran one with no oil for 80+ miles (don't ask) and the only thing that had any damage was the trap door ball bearings. The gears and roller bearings looked like new.
Just think of the quality of the gear lubes and oil in the 1940s, scarry.
Trending Topics
Seasoned HDF Member
Joined: May 2019
Posts: 5,900
Likes: 11,342
From: NE Ohio
75/140
Not sure what brand. Valvoline maybe?
Hell, might even be Walmart SuperTech?
Noting extraordinary about my riding conditions, so I don't figure I need expensive oils enhanced with UUA*
because a manual trans is a gear box
So I figure gear oil ought to do it
*Unicorn Urine Additive
KTF
Not sure what brand. Valvoline maybe?
Hell, might even be Walmart SuperTech?
Noting extraordinary about my riding conditions, so I don't figure I need expensive oils enhanced with UUA*
and how come,
So I figure gear oil ought to do it
*Unicorn Urine Additive
KTF
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
