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For some time Harley-Davidson has had an oil transfer or migration problem on certain touring models and they are still trying to figure it out. Listen in to this entire podcast episode to learn what it's all about and how to diagnose it. In this written article below are just the highlights. I try and keep it fairly basic and easy to understand.
Introduction to the Harley oil transfer problem:
Harley oil transfer is when oil moves over from the transmission into the primary case. This eventually leaves the transmission very low on oil and the primary with too much oil. Of course, a transmission with low or no oil will certainly fail and need to be repaired or completely replaced.
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Understand, there will always be a small amount of Harley oil transfer between the transmission and primary cases (small amounts-2 oz or so). This is normal and it's only when larger amounts are transferring that causes issues.
This has been a frustrating issue for Harley over the years because it doesn't happen to all of their motorcycles.
There are two shafts in the transmission, the main shaft and the countershaft, both having 6 gears. When the gears are turning, air and oil get blended and mixed around covering everything, and pressure is created. To help with the pressure, Harley designed a breathing transmission which is why you'll see the vent hose on the top of your transmission.
The main shaft of the transmission extends all the way over to the primary side (right side). A push rod goes all the way through the hollow main shaft and it engages and disengages the clutch basket. The primary case has the clutch, compensator, primary chain and is an oil bath system. The oil here also gets blended and creates pressure when things are turning. This pressure is supposed to be relieved through the hollow main transmission shaft and back into the transmission and breath through the same transmission breather tube. Clearly this method is not working all the time and there are issues.
2014-2016 Twin Cam:
Harley tried to fix this on the 2014-2016 twin cam models. Engineers resigned the main seal and spacer between the transmission and primary for closer tolerances. This seemed to fix the issue for those bikes that experienced it.
2017 & newer Milwaukee-Eight:
In 2017 Harley released the Milwaukee-Eight motor and it didn't take long for the same issue to arise on select bikes. Harley oil transfer is isolated to touring models and especially those that are ridden long distances, which really blends the oil, builds pressure, and gives the oil much time to slowly transfer over. Those who ride short distances and don't ride often will likely never see the problem as there is not enough time for it to take effect.
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Harley made a kit for the M8 that contains a transmission gasket and oil deflector called a “slinger” to combat the issue. The slinger is installed at the end of the hollow main transmission shaft and is supposed to sling oil away from it so there will be no oil transfer through it.
Then came the 2018 and newer M8 models and the same Harley oil transfer problem existed. Harley made another kit for these models. The kit is basically a breather hose with a plastic shoe. A hole is drilled in the backside of the primary case and the breather hose (vent) is installed. This new breather vent is to prevent the vacuum effect on the transmission, thus stopping the pulling of oil from the transmission by the primary. This kit is only being put on those bikes that actually have the issue.
How to determine whether this is an issue with your bike:
The best way to find out if the Harley oil transfer issue is happening on your Harley is to check your transmission oil level, especially on longer rides. If you see no leaks around your Harley and your transmission oil is getting low then you likely have the issue. Also, your primary case will be overfilled with oil when checked.
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I own a 2020 CVO with a M8 117 engine. No problems until last oil change. About 8 ounces more oil in primary and short that amount in Tranny. The breather tube had been installed at factory. The oil drained from primary was dark and looked like crankcase oil.
Any suggestions?
Oh, boy. Not off the top of my head.
I have same problem with dark, discolored primary oil in my 2018 M8 107 Street Glide, plus obvious transfer of fluid from transmission. Dealer is installing Primary Vent kit today which they think will solve the problem. Fingers crossed that this works.
It worked on my 2017 Road King.
My 2020 flhx came new with the vent kit installed. I’ve been running redline tranny fluid since the 500 mile break in service. Redline for those not familiar looks like strawberry quik. So when it transfers to the primary which is running formula+ It mixes and makes a cloudy grey mess with a slight pink appearance. So 1.) for me the vent wasn’t a complete fix 2.) I keep a close eye on trans fluid level bc it doesn’t take long to get low 3. Switching to formula+ in the trans bc the fluid will def be going into the primary. That way can remove fluid from primary and add top off trans as needed between changes.
Also fwiw, had a 2019 flhx which is when I first encountered the problem. Back then Dealer of course said I was the only one who ever had the issue. Was doing my own 500 mile service at about 400 miles and shit when I discovered trans oil level was not showing on stick. Dealer put kit in, I went on cross country trip and traded for the 2020 shortly after that. Thinking of going to Goldwing now.
I just changed transmission oil in 2014 ultra limited. I put a whole qt of redline in it. It’s on jiffy stand. When I check the oil level it reads add. What’s wrong? Thanks I’m advance.
I have a new-to-me 2020 FLHX, purchased with 6600 miles, and ‘woman’ driven prior to that. Upon my initial check-out of this bike I noted that the main engine oil level was low….WAY low…. like not showing on the dip-stick. I added nearly 2 qts, and then rode the bike about 100 miles prior to doing a 3-hole fluid change. Approaching this first from the Right side of the bike while laying on my back in the driveway, I first drained all the old engine oil (or ‘sludge’ would be more like it). Pretty ugly! Then I drained the trans, and to my delight, it looked clean and clear! I did NOT ‘measure’ the amount of trans fluid being drained, which was probably an error on my part….but I just wanted to get it done. I then went to the left side of the bike and drained the primary. That too came out ugly! A very dark gray in color, and probably 40oz overall. Clearly my 2020 has the oil migration or ‘transfer’ problem!! So, while the motor company may say it’s now ‘fixed’, I would beg to differ! Anyway, I filled the trans with RedLine, as well as the Primary, and I’m going to do a few hundred miles then change the primary again, just to get the ‘crud’ out of it. What concerns me is that I’m about to leave on a 3000 mile trip in about 4 weeks, and I don’t want my trans to shoot craps while I’m on the road. So, I may have to hit a dealership up about half way into the trip just to get this checked. But, I hope SOMEONE can come up with a genuine ‘fix’ for this, as this is NOT how a motor vehicle should operate!!!
My 2017 FLSS is migrating transmission fluis to primary. Had Indy dealer check for the condition and within 200 mikles all the fluid was found in the primary. My question here is is the Primary Vent Kit avasilable to independent dealers and I read that kits are made for M8’s. While my bike is a TC.
Kits can be purchased at any HD dealership. You can have it installed where you want.