Combining different Primary Fluids?
Seasoned HDF Member
Joined: Sep 2017
Posts: 12,233
Likes: 4,943
From: England
And mostly being the oils meet the same specification they can be mixed else it wouldn't be possible to go from mineral to synthetic.
Road Warrior
Joined: Nov 2022
Posts: 1,538
Likes: 542
From: MN
Mineral and synthetic oils are fully mixable. They are both hydrocarbons - you can google the answers within the oil company websites (I worked at Mobil for 3 years).
My advice is don't worry about draining dry. No different than a car or truck automatic transmission.
My advice is don't worry about draining dry. No different than a car or truck automatic transmission.
Thread Starter
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HDF Community Team
Joined: Oct 2018
Posts: 4,347
Likes: 3,392
From: Seattle
I wont hurt it, but if you really want to get most all of the old fluid out, drain primary. After it stops draining, start engine, depress clutch lever, keep the engine running while depressing lever for 10-15 seconds. Shut down engine. Now watch the primary drain hole, youll see how much more fluid comes out.
Made me think about the way the fluids would mix and how they would perform, because after a few seconds running the miixture would essentially be homogenous. But because it requires you to not drain it completely I got curious about combining mixtures and what could change the way a clutch engages or how hard it is to get into neutral, ect.
And the idea of durability or detrimental effects.
There's some people who run a dirt bike transmission fluid instead of a primary fluid and I found that pretty interesting because I had no idea you could do that, and how someone would come up with that idea.
Since there's always amounts left in the bottle, what if someone was switching to a different product and combined an old bottle with the new full fluid bottle?
Lots of very interesting questions, probably just incredibly obscure and maybe dont have any tested answers yet.
Road Warrior
Joined: May 2007
Posts: 1,434
Likes: 384
From: Arkansastan
Nah the difference in fill is just what made me curious about the mixing of different products.
Made me think about the way the fluids would mix and how they would perform, because after a few seconds running the miixture would essentially be homogenous. But because it requires you to not drain it completely I got curious about combining mixtures and what could change the way a clutch engages or how hard it is to get into neutral, ect.
And the idea of durability or detrimental effects.
There's some people who run a dirt bike transmission fluid instead of a primary fluid and I found that pretty interesting because I had no idea you could do that, and how someone would come up with that idea.
Since there's always amounts left in the bottle, what if someone was switching to a different product and combined an old bottle with the new full fluid bottle?
Lots of very interesting questions, probably just incredibly obscure and maybe dont have any tested answers yet.
Made me think about the way the fluids would mix and how they would perform, because after a few seconds running the miixture would essentially be homogenous. But because it requires you to not drain it completely I got curious about combining mixtures and what could change the way a clutch engages or how hard it is to get into neutral, ect.
And the idea of durability or detrimental effects.
There's some people who run a dirt bike transmission fluid instead of a primary fluid and I found that pretty interesting because I had no idea you could do that, and how someone would come up with that idea.
Since there's always amounts left in the bottle, what if someone was switching to a different product and combined an old bottle with the new full fluid bottle?
Lots of very interesting questions, probably just incredibly obscure and maybe dont have any tested answers yet.
Road Warrior
Joined: Nov 2022
Posts: 1,538
Likes: 542
From: MN
It's kind of a one-way street with 3 oil sumps - in a pinch, you can use engine oil in the trans & primary, but not the other way around. Engine is the only sump oil that supports combustion byproduct blowby contamination (detergent / dispersant additives).
SAE Viscosity Grade range numbers are different between engine and gears, somebody poste the chart above. Since HD gearboxes don't take EP additive oil (GL-5), there's no danger to using engine oil in it. It's just not optimum - has nonrequired additives.
Also why engine oil has to be changed more often, and the only one with a filter - combustion blowby contamination. The other two only get metal wear fines over a long time, and water emulsion from the breather atmosphere air.
SAE Viscosity Grade range numbers are different between engine and gears, somebody poste the chart above. Since HD gearboxes don't take EP additive oil (GL-5), there's no danger to using engine oil in it. It's just not optimum - has nonrequired additives.
Also why engine oil has to be changed more often, and the only one with a filter - combustion blowby contamination. The other two only get metal wear fines over a long time, and water emulsion from the breather atmosphere air.
Seasoned HDF Member
Joined: Jan 2007
Posts: 20,616
Likes: 4,440
From: anacoco, la
nah, no worries. as long as the fluids that you are using are wet clutch compatible.
the biggest reason people say not to use synthetic is a carry over from earlier days. synthetic motor oil has friction modifiers in it which do not play well with the clutch. nowadays, they do make a synthetic primary fluid, so you could mix the syn and mineral and be fine.
the biggest reason people say not to use synthetic is a carry over from earlier days. synthetic motor oil has friction modifiers in it which do not play well with the clutch. nowadays, they do make a synthetic primary fluid, so you could mix the syn and mineral and be fine.
Stellar HDF Member
Joined: Jul 2020
Posts: 2,297
Likes: 1,811
From: space
And youre concerned? Too much overthinking. Drain when hot and roll on. Like an engine, there are no cases where things went sideways because of the type of oil used. Never (few times it can be said) except for low or none and that still isnt because of type. Thats from stupidity. Dont overthink it, switch to what tickles your fancy. Ride often, ride fast!
Shouldn't the primary be refilled before the "roll on"?😵💫🤪✌️
Sorry, couldn't help myself, it's past my bedtime.
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
Nah the difference in fill is just what made me curious about the mixing of different products.
Made me think about the way the fluids would mix and how they would perform, because after a few seconds running the miixture would essentially be homogenous. But because it requires you to not drain it completely I got curious about combining mixtures and what could change the way a clutch engages or how hard it is to get into neutral, ect.
And the idea of durability or detrimental effects.
There's some people who run a dirt bike transmission fluid instead of a primary fluid and I found that pretty interesting because I had no idea you could do that, and how someone would come up with that idea.
Since there's always amounts left in the bottle, what if someone was switching to a different product and combined an old bottle with the new full fluid bottle?
Lots of very interesting questions, probably just incredibly obscure and maybe dont have any tested answers yet.
Made me think about the way the fluids would mix and how they would perform, because after a few seconds running the miixture would essentially be homogenous. But because it requires you to not drain it completely I got curious about combining mixtures and what could change the way a clutch engages or how hard it is to get into neutral, ect.
And the idea of durability or detrimental effects.
There's some people who run a dirt bike transmission fluid instead of a primary fluid and I found that pretty interesting because I had no idea you could do that, and how someone would come up with that idea.
Since there's always amounts left in the bottle, what if someone was switching to a different product and combined an old bottle with the new full fluid bottle?
Lots of very interesting questions, probably just incredibly obscure and maybe dont have any tested answers yet.
Both Barnett and E1 recommend type F ATF or B&M TrickShift with their Kevlar clutch kits.
I take what what the moco recommends with a grain of salt. Synthetic gear lube?
"This kit consists of 10 friction, 9 steel plates and a 10% stronger than stock diaphragm clutch spring. Plates should be pre-soaked in the same fluid you will be using in the bike for about 10-15 minutes. The type of fluids we recommend are any HD petroleum based, non-synthetic, primary oil, as light weight as possible, or even a good petroleum based motor oil such as 10/40 or 20/50 in weight. You can even use ATF Type F or B&M Trickshift. THE USE OF SYNTHETICS IS NOT RECOMMENDED AS THEY TEND TO CAUSE SLIPPAGE.
Last edited by 60Gunner; May 12, 2023 at 09:06 PM.
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Club Member
Joined: Apr 2016
Posts: 11,539
Likes: 8,375
From: Inland NW
Actually Barnett says https://www.barnettclutches.com/serv....aspx?faq_id=4
"Synthetic oil, by its nature, has extra lubricity. This can be a real advantage for the engine, but a disadvantage for a wet clutch. Synthetic oils can cause a worn clutch to fail. All Barnett wet clutches are designed to be run with synthetic or petroleum based oils. * Remember, the single best insurance you can have for your clutch and bike is to keep clean, good quality oil in it!"
We actually take everything you say with a grain of salt, especially with synthetics.
I have been around bike clutches since I was 7, and a mechanic my entire life, I GET IT, but it is 2023 and synthetics are here to stay. The industry adapted, and nearly everybody but you knows it.
Still waiting for 149 lb/ft to eat up my clutch in my synthetic gear oil, Sparky! Go away.
"Synthetic oil, by its nature, has extra lubricity. This can be a real advantage for the engine, but a disadvantage for a wet clutch. Synthetic oils can cause a worn clutch to fail. All Barnett wet clutches are designed to be run with synthetic or petroleum based oils. * Remember, the single best insurance you can have for your clutch and bike is to keep clean, good quality oil in it!"
We actually take everything you say with a grain of salt, especially with synthetics.
I have been around bike clutches since I was 7, and a mechanic my entire life, I GET IT, but it is 2023 and synthetics are here to stay. The industry adapted, and nearly everybody but you knows it.
Still waiting for 149 lb/ft to eat up my clutch in my synthetic gear oil, Sparky! Go away.
Seasoned HDF Member
Joined: Jan 2008
Posts: 13,652
Likes: 11,421
From: State of Confusion
and BAM, just like that a new nickname is born !!!