Trying ATF in Harley primary

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As I do maintenance on my '00 RK I like to experiment to see what works or doesn't work, and maybe other folks can benefit. Although I definitely follow the mfr recommendations as a starting point, I do admit I'm more willing than most to experiment a little, and with all the wildly varying opinions of the internet I like to see for myself. I'm not trying to outsmart the engineers, but I do recognize that the mfr's interests are not always aligned with the user's interests (to put it kindly). Anyhow, I was due for a primary oil change, I had Valvoline Premium Blue 15w40 in there and it felt fine for the most part but after researching ATF in the primary I decided to give it a whirl. Lots of folks say ATF was like a night and day improvement in shifting and finding neutral, I was skeptical about that mainly because my bike already does that great, not sure how much better it could get but what the heck, let's see. I installed Valvoline Dex/Merc ATF, and although I don't have a lot of miles on it yet it feels about the same as before with shifting and finding neutral, which is to say pretty darn good. I was happy before, I'm happy now. Where I did notice an improvement was in the clutch action, with both Rotella and Valv Prem Blue I'd feel some minor coarseness right in the engagement zone, and with the ATF it was smooth all the way through. I don't know if it's the additives or the lower viscosity, but it's definitely smooth as silk (not that it was a problem before). I didn't notice any increase in primary chain noise, or any other problems. I have no way of knowing if it runs hotter or not. I'm going to run it 4-5k and see what the fluid and magnetic drain plug looks like. With the HDEO in there my drain plug had very little debris and the oil was pretty clean looking, so that's a decent baseline I think. At this point I think I could go either way with the ATF vs something like an HDEO oil from a feel perspective although the ATF for sure is a bit better. Anyway, maybe this helps some of you experimenters. One thing I'll say is if your bike is banging into gear or you can't ever find neutral you have a clutch adjustment problem more than a primary oil problem. But I do love me some Redline SPH in the tranny.
 
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Any thinner oil should be an improvement over the Primary+ or whatever 20W-50 HD puts in there nowadays. Those primaries excel with an SAE 30 or equivalent trans oil. I'm not surprised ATF feels good in comparison. Report back on the drain plug and fluid results at the end of your 5K. I'd be interested to hear if the ATF protects as well as some other fluids.
 
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I did the same thing some years ago. It ended up working out great for me. Gone are the days of starting a cold bike and having it clunk into gear. I will never use anything else in a Harley primary. Much better clutch feel too. I think it was about 2006 when I started doing this. I must have 85-90k miles on two different bikes using ATF.
 
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You'll notice more improvements with the transmission fluid change than the primary fluid. The primary fluid doesn't lubricate your gears and you can almost run anything in the primary and not know the difference.
 

MoreCowbellAz

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I'll definitely report back at 5k. Short of there bunch of debris on the plug magnet or loads of clutch material in the drain I'm not sure I see the downside from using ATF, given the noticeably smoother clutch action. I'm sure I would be happy continuing with the HDEO, but more smoother is more better right? As I said before, I don't see nor did I expect to see any improvement in shifting since my bike already shifted great, so I agree that the tranny fluid has more bearing there. But I'm loving the extra smoothness the ATF provides as you feather out the clutch when in gear. Also, I'm no engineer but logic would make me guess there's nothing going on in a Harley primary in the way of plates, bearings, gears, etc. that you don't see in cars/trucks that use ATF for many times the OCI a Harley would see. I could be wrong there, but it seems the fluid would be up to the task in Harley primary if it can go 50k in an offroad 4x4 or street rod. I will gladly eat my words if I get stranded with a toasted compensator or exploded clutch plates. But I'm betting not.
 
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I'm switching my light truck transfer case fluids from ATF to THF. These fluids may work in your application. www.chevronlubricants.com >>products>>industrial and off-road transmission fluids>> 1000 thf & synthetic all-weather thf 1000 THF 40C 58.4 100C 9.5 VI 145 flash 235C pour -42C SYN THF 40C 44.7 100C 9.5 VI 204 flash 242C pour -45C
 
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MoreCowbellAz

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I don't know the chemistry, but viscosity wise it looks like a slightly heavier version of ATF, like a 30. I know the Valvoline Dex/Merc I put in is a 20. First time I've heard someone mention THF, interesting.
 
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Originally Posted By: MoreCowbellAz
I don't know the chemistry, but viscosity wise it looks like a slightly heavier version of ATF, like a 30. I know the Valvoline Dex/Merc I put in is a 20. First time I've heard someone mention THF, interesting.
You could pop in Type F, which tends to be a bit thicker than the Dex/Merc ATF's if I recall.
 
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THF can also be used as a hydraulic fluid and therefore compatible with fork and shock seals, if the ISO grade is close to your needs.
 
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Originally Posted By: Robenstein
Originally Posted By: MoreCowbellAz
I don't know the chemistry, but viscosity wise it looks like a slightly heavier version of ATF, like a 30. I know the Valvoline Dex/Merc I put in is a 20. First time I've heard someone mention THF, interesting.
You could pop in Type F, which tends to be a bit thicker than the Dex/Merc ATF's if I recall.
I have tried the type F and it made the clutch grab a little quicker. I liked it.
 
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Originally Posted By: Blkstanger
Originally Posted By: Robenstein
Originally Posted By: MoreCowbellAz
I don't know the chemistry, but viscosity wise it looks like a slightly heavier version of ATF, like a 30. I know the Valvoline Dex/Merc I put in is a 20. First time I've heard someone mention THF, interesting.
You could pop in Type F, which tends to be a bit thicker than the Dex/Merc ATF's if I recall.
I have tried the type F and it made the clutch grab a little quicker. I liked it.
Old timer drag racers noticed this too and you would see them putting type F in GM autos for firmer shifts at the drag track.
 
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Originally Posted By: GMBoy
You'll notice more improvements with the transmission fluid change than the primary fluid. The primary fluid doesn't lubricate your gears and you can almost run anything in the primary and not know the difference.
My experience showed me the opposite. I tried 20w50 Mobil 1, Spectro Platinum 6 speed, and Mobil 1 gear lube in the transmission. There was no difference perceived between the three. I used Rotella T, Mobil 1 20w50, and type F transmission fluid in the primary. I didn't like any of them. I put Spectro Platinum Primary Chaincase fluid in and winner, winner, winner. Smooth shifts, and super easy into neutral every time.
 
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Originally Posted By: Robenstein
Originally Posted By: Blkstanger
Originally Posted By: Robenstein
Originally Posted By: MoreCowbellAz
I don't know the chemistry, but viscosity wise it looks like a slightly heavier version of ATF, like a 30. I know the Valvoline Dex/Merc I put in is a 20. First time I've heard someone mention THF, interesting.
You could pop in Type F, which tends to be a bit thicker than the Dex/Merc ATF's if I recall.
I have tried the type F and it made the clutch grab a little quicker. I liked it.
Old timer drag racers noticed this too and you would see them putting type F in GM autos for firmer shifts at the drag track.
I remember those days, I used to bowl with the transmission shop guys next to where I worked at the time. They told me B&M trick shift was just blue dyed, type F. I tried the type F and it did make a difference in my TH350.
 

MoreCowbellAz

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I've heard occasional complaints about the newer compensators as well, not sure if it's fact or myth tho. Back to the ATF feel, I did a lot of riding over the weekend at full temps (was warm here in Phoenix), and I'm loving the smooth clutch feel, doesn't change a bit even after long ride.
 
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I've never used ATF in my primary's. and don't really plan to. I've heard the "good clutch feel" deteriorates after a short time. And there are hub bearings that I feel need heavier lubrication then What Atf can give it. Plus it's cheaper to change $3 a qt oil, then the gears and chain.I'm pretty sure that if Harley thought it was the better choice of lube for the primary, they would recommend it and sell their own version of ATF for use in there.,,
 
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Exactly. I believe ya could [censored] in there and it would be fine. The oil in the primary is for cooling purposes for the clutch and lube for the primary chain. That's it. Those trans gears are what make the clunk and that is usually related to cold too thick of an oil. I believe since 06 all bikes got the helical cut transmission gears. No need for stew here when soup works better. 50w oil works fine in the primary.
 
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I use 15w40 HDEO in the primary and Redline shockproof heavy in the transmission. Shifts like butta with no false neutrals.
 

MoreCowbellAz

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I'm at 1600 miles on the Valvoline Dex/Merc ATF, so far no change in clutch feel or anything, still super smooth. I'm curious to see if the smoothness tapers off with use, but so far so good. I liked it with the 15w40 in the primary before, but noticeably even better with ATF. I'd go back to the 15w40 if I see anything odd on the drain plug at 5k, but aside from that I'd say ATF and Redline Shockproof Heavy is a winning combo. Each had a noticeable improvement.
 
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