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Discussion Starter · #1 ·
First of all I want to state that I'm no engineer and the observations here are from personal experience and 40+ years as a auto and bike repair shop owner/mechanic. In the last 30 years I've built well over 1000 automatics for every application from stock to all out race applications in 1000+hp race cars and monster trucks.

For those of you (including myself) that use ATF in the primary here's some facts that I have verified over the years.
There are approximately 25 types of ATF but I'll cover the 5 most common as the other twenty are either obsolete or very vehicle specific.

Type F or (Ford) fluid was developed for and used in Ford automatic transmissions back when the clutch discs were made of sintered bronze or asbestos and there were no bearings used. All parts were supported by bronze bushings and thrust washers. It is essentially 20wt hydraulic oil (pure mineral oil) with a red dye and that's it. It is commonly sold as Racing ATF under brands such as B&M Trick Shift because it provides the quickest lockup of the clutch packs (Hardest shift). It has no place in 99.9 percent of modern applications unless you're just looking for neck snapping shifts (or in the case of motorcycles used for drag racing where quick and harsh clutch engagement is the primary goal and you're gonna change it very often.

Dexron II and III are the most commonly used fluids with the only difference being additives in Dexron III to make it more compatible with the electronics used in modern transmissions.
They both have an additive package that includes friction modifiers for smoother cluch engagement, oxidation control, viscosity stabilizers, corrosion inhibitors and proper lubrication of bearings and bushings of all types. Since the advent of gerotor pumps and better friction materials such as Kevlar and Aramid, Dexron II or III has even replaced the use of Type F for racing use by most transmission builders.
Dexron III is commonly used in many automotive manual tranmissions and is probably used in more transfer cases of 4WD vehicles than any other fluid.

ATF+3 uses higher quality base oils with the highest content of friction modifiers to prevent torque converter shudder. It lubricates a bit better than Dexron III but can also cause slow clutch engagment (slipping). If you ride easy and your primary goal is smooth clutch engagment then this is the fluid to use in your primary if you're gonna run ATF.

Synthetic ATF comes in many formulations but the most common is Dexron III. It has the same properties of clutch engagement as Dexron III with some advantages.
The main advantage of synthetic fluid is it's ability to resist thermal breakdown. If you ride in extreme heat or just want to extend your primary fluid change intervals then this is probably your fluid.

You may want to think about this too. Although the primary doesn't generate much heat in and of itself that's not the only concern when choosing a fluid.
The primary on your motorcycle is not a seperate entity. It is attached to the engine and it acts as a giant heatsink for that engine. The temps seen on a long hard run are probably within 20-40 degress of the engine oil temp.
Mineral based ATF starts to break down at around 220 degrees and is almost useless as a lubricant at 250 degrees.
On most Harley's the rear exhaust is in close proximity to the primary case and that adds heat too.

I have measured the temp on my primary after a hard run and have never seen temps above 180 degrees but that doesn't mean it doesn't happen. If you ride loaded, two up, in heavy traffic, the desert, or alot of hard pulls in the mountains then you'll probably see temps over 200 degrees.

Most people notice that shifting is immediately improved when they change over to ATF in the primary. This is because ATF is designed for wet clutches. When you pull the clutch in it releases cleaner than with motor oil. You'll also notice that finding neutral is no longer a chore.

Personally I use any major brand of regular Dexron III and change it out every 5000 miles but if I did alot of the riding described above I would probably use synthetic (although I am a cheap old bastard).

I'm not promoting the use of ATF in the primary!
But!
ATF has proven itself in hundreds of millions of auto applications and tens of millions of manual tranmissions and transfer cases.
You almost never see a 4wd transfer case failure anymore and I've personally seen 4wd trucks with a quarter million miles on a manual transmission and transfer case using Dexron III and still going strong.

I feel comfortable using it in my primary and I love not hearing the rattle when I snick it into first. But what I really love is not fussing with trying to find neutral on a cold day. And the over 300,000 miles I've put on primary's with ATF without a single lube related failure doesn't hurt either.

Geno:coffee:
 

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Thanks for the write up. The info clears up a lot of questions that I had about ATF . I love oil threads, how do you feel about crankcase oil for these air cooled V twins?
 

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Discussion Starter · #5 ·
Thanks for the write up. The info clears up a lot of questions that I had about ATF . I love oil threads, how do you feel about crankcase oil for these air cooled V twins?
I'll be the first admit that I'm in the dark when it comes to oil.
I use whatever brand name 20w50 is on sale at the time and change it out every 3000
I'm not hard on oil though. 99% of my driving is 100 mile or more trips and most are 300 miles or more. No city driving at all and I almost never drive less than 45 mph so my Road King stays fairly cool.
I mapped my FuelPak a tad on the rich side to insure the oil temp never sees more than 210-220.
If my driving consisted of short trips and heavy traffic or lots of idling I wouldn't hesitate to use Mobil 1 or Amsoil but with the riding I do my oil doesn't look much different when I drain it out as when I poured it in and the inside of the motor looks as clean as the day I drove it off the lot.
I do check my cam tensioners every 10,000 though and they only made 17,000 on Harley Syn3. I used this while it was in warranty because Harley will use every possible tidbit to deny a claim. The last 18,000 on mostly 20w50 Valvoline dino and the tensioners look like new. This could and probably is because the rough edges of the chains got polished off on the first set of tensioners though. I doubt that the oil had anything to do with it.

I think if you use good quality oil and filters that these T/C's will go 100,000 with no major engine work.
I can't say that Synthetic oil isn't better because it surely is but your riding style has more to do with the life of the engine than anything else so you have to weigh the cost difference in service over the life of the engine. If your riding style cooks the oil between changes then you probably would benefit from the use of a quality synthetic or more frequent oil changes.
I do think there is a lot of hype when it comes to oil.
Some guys change their oil every 2500 miles and use $20 filters and $12 buck a quart oil in all three holes. that's $3200 bucks over the life of the engine.
That'll get you a helluva rebuild with choice parts and 90+ hp.

We're all anal about something or other.
Personally I use a torque wrench on even the lowliest screw. It's my obsession.
It's absolutely ridiculous to torque the screws on switch covers but I do it.

I'll tell you this. The only harm you'll do by using the best oils too often is a thin wallet and a lot of used oil.:)

For my money I'll save the difference and build me a hot rod bagger when it's time for a rebuild.

Geno
 

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Discussion Starter · #8 ·
Thanks for the replies.

I'm glad I found this forum.
There's a wealth of info and knowledge to be gleaned from here.

The best thing I've seen here is the lack of bickering and insults that plauge so many forums and make it impossible to wade through the sh*t to get to the good stuff. Kinda like a wife sometimes:hystria:

Geno
 

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I hate to say it but he is right. Oils today (Dino) are soo good, there is absolutely no reason to us synthetic. If your racing at high RPM's (10,000rpm +) then maybe. Using synthetic is just for piece of mind. Everyone would do just fine on 20W50 engine oil from any manufacture and change it every 3000 miles. But even that is overkill. As ING insurance would say "Save Your Money". As for the ATF, I use it and love it. No clutch drag and smooth clutch engagement. One day Harley will realize this and recommend ATF. Hell the industry already knows this, it's just us harley folks that old habits are hard to break.

Change oil every 3000 and filter (any good filter) and for heaven sakes, us ATF in the primary. You will be pleasantly suprised as I was. I am not changin back to motor oil in my primary ever again.
 

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First of all I want to state that I'm no engineer and the observations here are from personal experience and 40+ years as a auto and bike repair shop owner/mechanic. In the last 30 years I've built well over 1000 automatics for every application from stock to all out race applications in 1000+hp race cars and monster trucks.

For those of you (including myself) that use ATF in the primary here's some facts that I have verified over the years.
There are approximately 25 types of ATF but I'll cover the 5 most common as the other twenty are either obsolete or very vehicle specific.

Type F or (Ford) fluid was developed for and used in Ford automatic transmissions back when the clutch discs were made of sintered bronze or asbestos and there were no bearings used. All parts were supported by bronze bushings and thrust washers. It is essentially 20wt hydraulic oil (pure mineral oil) with a red dye and that's it. It is commonly sold as Racing ATF under brands such as B&M Trick Shift because it provides the quickest lockup of the clutch packs (Hardest shift). It has no place in 99.9 percent of modern applications unless you're just looking for neck snapping shifts (or in the case of motorcycles used for drag racing where quick and harsh clutch engagement is the primary goal and you're gonna change it very often.

Dexron II and III are the most commonly used fluids with the only difference being additives in Dexron III to make it more compatible with the electronics used in modern transmissions.
They both have an additive package that includes friction modifiers for smoother cluch engagement, oxidation control, viscosity stabilizers, corrosion inhibitors and proper lubrication of bearings and bushings of all types. Since the advent of gerotor pumps and better friction materials such as Kevlar and Aramid, Dexron II or III has even replaced the use of Type F for racing use by most transmission builders.
Dexron III is commonly used in many automotive manual tranmissions and is probably used in more transfer cases of 4WD vehicles than any other fluid.

ATF+3 uses higher quality base oils with the highest content of friction modifiers to prevent torque converter shudder. It lubricates a bit better than Dexron III but can also cause slow clutch engagment (slipping). If you ride easy and your primary goal is smooth clutch engagment then this is the fluid to use in your primary if you're gonna run ATF.

Synthetic ATF comes in many formulations but the most common is Dexron III. It has the same properties of clutch engagement as Dexron III with some advantages.
The main advantage of synthetic fluid is it's ability to resist thermal breakdown. If you ride in extreme heat or just want to extend your primary fluid change intervals then this is probably your fluid.

You may want to think about this too. Although the primary doesn't generate much heat in and of itself that's not the only concern when choosing a fluid.
The primary on your motorcycle is not a seperate entity. It is attached to the engine and it acts as a giant heatsink for that engine. The temps seen on a long hard run are probably within 20-40 degress of the engine oil temp.
Mineral based ATF starts to break down at around 220 degrees and is almost useless as a lubricant at 250 degrees.
On most Harley's the rear exhaust is in close proximity to the primary case and that adds heat too.

I have measured the temp on my primary after a hard run and have never seen temps above 180 degrees but that doesn't mean it doesn't happen. If you ride loaded, two up, in heavy traffic, the desert, or alot of hard pulls in the mountains then you'll probably see temps over 200 degrees.

Most people notice that shifting is immediately improved when they change over to ATF in the primary. This is because ATF is designed for wet clutches. When you pull the clutch in it releases cleaner than with motor oil. You'll also notice that finding neutral is no longer a chore.

Personally I use any major brand of regular Dexron III and change it out every 5000 miles but if I did alot of the riding described above I would probably use synthetic (although I am a cheap old bastard).

I'm not promoting the use of ATF in the primary!
But!
ATF has proven itself in hundreds of millions of auto applications and tens of millions of manual tranmissions and transfer cases.
You almost never see a 4wd transfer case failure anymore and I've personally seen 4wd trucks with a quarter million miles on a manual transmission and transfer case using Dexron III and still going strong.

I feel comfortable using it in my primary and I love not hearing the rattle when I snick it into first. But what I really love is not fussing with trying to find neutral on a cold day. And the over 300,000 miles I've put on primary's with ATF without a single lube related failure doesn't hurt either.

Geno:coffee:
Geno,
Great post. I couldn't find anything with it that I would disagree with.
george
 

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all of the ATF bottles have dire warnings about using the correct fluid for your application, are there any major concerns about mixing the diffrent ATF's (for use in a primary, not concerned about automotive application)

is a simple drain and fill sufficeinet when changing to a diffrent ATF, or is a flush of some type warented?
 

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The stuff is inexpensive, you could run it for a couple hundred miles and change it out again.
We run Dextron III in the Taurus SHO 5 speed, with recommended changes @50K...:whistle:
 

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Discussion Starter · #15 ·
No concerns at all.

all of the ATF bottles have dire warnings about using the correct fluid for your application, are there any major concerns about mixing the diffrent ATF's (for use in a primary, not concerned about automotive application)

is a simple drain and fill sufficeinet when changing to a diffrent ATF, or is a flush of some type warented?
All ATF's are either straight 20wt mineral oil or synthetic oil to start with. The additive packages are different to address concerns with the electronic components and different clutch materials.
For example:
If you use DexronIII/Mercon in a Honda it won't harm the transmission but it will cause the converter to shudder when it applies.

For Harley applications the only fluid you need to be concerned with is DexronIII/Mercon. If you want to use a synthetic just make sure it's compatible with Dex/Merc.
If you used oil or so called"primary fluid" before then it will mix just fine with the small amount that's left when you drain it out.

If it concerns anyone then buy a couple quarts of Dex/Merc and drain and refill then drive the bike for 20 miles or so and drain and refill again. This will get rid of the mixed fluid almost completely.
It's cheap too. Any brand name fluid will run about 3 bucks a quart so you could flush the hell out of it for less than a quart of primary fluid.

You can use Type F but you'll notice the clutch engages much quicker or harsher and it's not nearly as good at lubricating metal because it's essentially pure mineral oil with a red dye added. It will allow the clutch to hold better in extreme duty or racing apps though so it still has a place for some riders.

You could also use ATF+3 or 4 and you'll notice the clutch engages much slower or "smoother"

For 95% of the riders the Dex/Merc will work best and give them the same clutch feel as 10w30, 20w50, or primary fluid. The biggest benefit of ATF in the primary is the clutch will release much cleaner and stop or decrease the amount of gear clash when you put it in gear from neutral. It will usually make it much easier to find neutral too.

Geno
 

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wow..can't say i have read a more well written topic than that...wow..really informative....got me wanting to change to atf in my primary..and i probably will...never really thought of it ,but it makes really good sense ...thanks alot.......
 

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Good write up, didn't want it to get lost in the shuffle so I made it a "Sticky"
 

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Thanks BOB! This is a really good one! Way to go Geno!
 

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Synthetic ATF comes in many formulations but the most common is Dexron III. It has the same properties of clutch engagement as Dexron III with some advantages. The main advantage of synthetic fluid is it's ability to resist thermal breakdown. If you ride in extreme heat or just want to extend your primary fluid change intervals then this is probably your fluid. You may want to think about this too. Although the primary doesn't generate much heat in and of itself that's not the only concern when choosing a fluid.The primary on your motorcycle is not a seperate entity. It is attached to the engine and it acts as a giant heatsink for that engine. The temps seen on a long hard run are probably within 20-40 degress of the engine oil temp.Mineral based ATF starts to break down at around 220 degrees and is almost useless as a lubricant at 250 degrees. On most Harley's the rear exhaust is in close proximity to the primary case and that adds heat too.I have measured the temp on my primary after a hard run and have never seen temps above 180 degrees but that doesn't mean it doesn't happen. If you ride loaded, two up, in heavy traffic, the desert, or alot of hard pulls in the mountains then you'll probably see temps over 200 degrees. Personally I use any major brand of regular Dexron III and change it out every 5000 miles but if I did alot of the riding described above I would probably use synthetic (although I am a cheap old bastard).Geno:coffee:
Geno

Your post really hit home after riding my bike today in 34 degree weather I could hardly find neutral and it shifted horrible until it warmed up. What is your opinion of the Mobil 1 synthetic ATF ? When I was drag racing my vette none of the automatic transmission builders would recommend it they either said it was too slippery or did'nt know. So I ignored them and used it anyway with no problems. I have several cases of the Mobil ATF laying around and I was thinking about using it in my 2008 FXDL primary case what are your thoughts on this ? What oils do you run in your transmission and engine ?

Thanks >>>>> Inthered
 
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