Sportster Transmission Oil
Thread Starter
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Seasoned HDF Member
Joined: Aug 2007
Posts: 8,196
Likes: 3,085
From: NW AR
Sportster Transmission Oil
Any suggestions on an oil for a Sportster transmission/primary?
I need something that won't make the clutch drag and yet provides good lubrication for the transmission. I've been thinking of trying a quality ATF, like Mobil 1 or Toyota. Many automotive manual boxes use ATF, so it should hold up to the shear loads and still be good for the clutch plates. I've seen that someone used MT90 successfully, as well as another Redline gear oil. Maybe the same Mobil SHC630 I've been using in my bike. It doesn't have any friction modifiers, so it should be OK for the clutch.
I'm just not happy with Forumula + and they don't make Sport Trans anymore (and I finally used up all I had).
I need something that won't make the clutch drag and yet provides good lubrication for the transmission. I've been thinking of trying a quality ATF, like Mobil 1 or Toyota. Many automotive manual boxes use ATF, so it should hold up to the shear loads and still be good for the clutch plates. I've seen that someone used MT90 successfully, as well as another Redline gear oil. Maybe the same Mobil SHC630 I've been using in my bike. It doesn't have any friction modifiers, so it should be OK for the clutch.
I'm just not happy with Forumula + and they don't make Sport Trans anymore (and I finally used up all I had).
Ultimate HDF Member
Joined: Sep 2005
Posts: 8,641
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From: Ozark Country
Myself and most that I know with Sportsters (including a couple of Harley dealership mechanics) run nothing but Mobil 1 synthetic 75W90 Gear Lube in the combination primary/tranny.
It has a API GL-5 rating, for heavy duty use in gears and differentials, and the moly ppm count is low enough that it won't cause any possible problems with the wet clutch.
No one I know has had any problems, and one Sportster (owned by a Harley mechanic) has been running the Mobil 1 75W90 for over 85,000 miles.
If you want to run a 'engine oil' in your transmission it's your choice, but I run gear lube, not engine oil in the manual transmissions on my cars and trucks, as well as the manual transmissions on my bikes.
And before anyone mentions 75W90 gear lube being 'too thick' you need to know that the viscosity (thickness) of engine oils and gear lubes are measured differently.
75W90 gear lube has about the same viscosity, or thickness, as 20W50 engine oil..
It has a API GL-5 rating, for heavy duty use in gears and differentials, and the moly ppm count is low enough that it won't cause any possible problems with the wet clutch.
No one I know has had any problems, and one Sportster (owned by a Harley mechanic) has been running the Mobil 1 75W90 for over 85,000 miles.
If you want to run a 'engine oil' in your transmission it's your choice, but I run gear lube, not engine oil in the manual transmissions on my cars and trucks, as well as the manual transmissions on my bikes.
And before anyone mentions 75W90 gear lube being 'too thick' you need to know that the viscosity (thickness) of engine oils and gear lubes are measured differently.
75W90 gear lube has about the same viscosity, or thickness, as 20W50 engine oil..
Thread Starter
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Seasoned HDF Member
Joined: Aug 2007
Posts: 8,196
Likes: 3,085
From: NW AR
Thanks, guys. I'll pick up some M1 75W90. We have over 50K miles on the bike now, all but about 1K put on by my wife, and I just put a new clutch and primary chain in it. I won't go through the details, but let's just say I want to be extra careful with the clutch. I also am not comfortable putting engine oil in the transmission. I think the SHC 630 is a little too slipery for the clutch plates, but it works well in my 5 speed.
Stage I
Joined: Apr 2010
Posts: 1
Likes: 0
CAN I use 75/90 if i put 20 /50 in the engine?
im not sure if i can mix them or if i should stick with one kind, i put 20/50 in the engine and wondering which to use in the tranny
any suggestions
any suggestions
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Stage IV
Joined: Jan 2022
Posts: 4
Likes: 0
From: Surrey
Red line Vtwin Primary case gear oil
[QUOTE=OldFenderGuy;5502499]Myself and most that I know with Sportsters (including a couple of Harley dealership mechanics) run nothing but Mobil 1 synthetic 75W90 Gear Lube in the combination primary/tranny.
It has a API GL-5 rating, for heavy duty use in gears and differentials, and the moly ppm count is low enough that it won't cause any possible problems with the wet clutch.
No one I know has had any problems, and one Sportster (owned by a Harley mechanic) has been running the Mobil 1 75W90 for over 85,000 miles.
If you want to run a 'engine oil' in your transmission it's your choice, but I run gear lube, not engine oil in the manual transmissions on my cars and trucks, as well as the manual transmissions on my bikes.
And before anyone mentions 75W90 gear lube being 'too thick' you need to know that the viscosity (thickness) of engine oils and gear lubes are measured differently.
75W90 gear lube has about the same viscosity, or thickness, as 20W50 engine oil..
For my 1996 1200 sporster I have used Red line 75W80 Primary cse gear oil. The specs on it is API Service Class GL-4 SAE Viscosity Grade (Gear Oil) 75W80 SAE Viscosity Grade (Motor Oil) 5W30. Fully Synthetic.
It has a API GL-5 rating, for heavy duty use in gears and differentials, and the moly ppm count is low enough that it won't cause any possible problems with the wet clutch.
No one I know has had any problems, and one Sportster (owned by a Harley mechanic) has been running the Mobil 1 75W90 for over 85,000 miles.
If you want to run a 'engine oil' in your transmission it's your choice, but I run gear lube, not engine oil in the manual transmissions on my cars and trucks, as well as the manual transmissions on my bikes.
And before anyone mentions 75W90 gear lube being 'too thick' you need to know that the viscosity (thickness) of engine oils and gear lubes are measured differently.
75W90 gear lube has about the same viscosity, or thickness, as 20W50 engine oil..
For my 1996 1200 sporster I have used Red line 75W80 Primary cse gear oil. The specs on it is API Service Class GL-4 SAE Viscosity Grade (Gear Oil) 75W80 SAE Viscosity Grade (Motor Oil) 5W30. Fully Synthetic.
Last edited by FXWG1980; Feb 11, 2023 at 02:52 PM. Reason: added text to previous memeber post
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Stage IV
Joined: Jan 2022
Posts: 4
Likes: 0
From: Surrey
For my 1996 1200 sportster primary/trans fluids I have used Red line 75W80 Primary case gear oil. The specs on it is API Service Class GL-4 SAE Viscosity Grade (Gear Oil) 75W80 SAE Viscosity Grade (Motor Oil) 5W30. Fully Synthetic.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,052
Likes: 993
oil type is determined by gear cut, not all oils will perform well if used outside the intended lube specification.
hd sport oil is in the class of mobile one syn gear oils. if does make a diff between the weights, i use the heavier oil.
you did not mention the year, earlier sportsters used engine oil as they inter-mixed with the engine oil.
hd sport oil is in the class of mobile one syn gear oils. if does make a diff between the weights, i use the heavier oil.
you did not mention the year, earlier sportsters used engine oil as they inter-mixed with the engine oil.