Milwaukee 8 Engine Problems
Seasoned HDF Member
Joined: Feb 2016
Posts: 8,001
Likes: 6,901
From: NC
I have a 2019 FLHTP with 21,000 miles. I bought it with 1120 miles on it in 2021. I had an issue with the tranny fluid migrating to the primary. I installed the Harley vent and have not had that issue since. I frequently ride 150-180 miles at 78 mph on the interstate. Refuel then do it again. I've done several 500+ mile days.
Seasoned HDF Member
Joined: Mar 2021
Posts: 18,252
Likes: 3,679
From: backwoods
I have a 2019 FLHTP with 21,000 miles. I bought it with 1120 miles on it in 2021. I had an issue with the tranny fluid migrating to the primary. I installed the Harley vent and have not had that issue since. I frequently ride 150-180 miles at 78 mph on the interstate. Refuel then do it again. I've done several 500+ mile days.
About the so called "oil transfer issue" : This can be considered as history 
This issue only occured in M8 engines which were equipped with the hydraulic clutches.
Due to the shape of the gasket between the trapdoor and the inner side cover , which closes only the outer side of the transmission case , and NOT the space where the rubber cap of the actuator is situated
What happened , was that the actuator also worked like a kind of "balloon pump" by sucking transmission oil through the tiny openings what the gasket did not cover., and press that collected oil through the hollow shaft into the primary , due to these two compartments shared the same closed inner atmosphere.
By making that closed atmosphere leak ( by installing that rubber vent ) , the unwanted "balloon pump" effect had been abolished..
It maybe sounds all a little confusing , but when you ( f.i.) should look up the picture at page 7 - 7 , fig. 4.6b of the Clymer M8 manual , it all will be clear.
This issue only occured in M8 engines which were equipped with the hydraulic clutches.
Due to the shape of the gasket between the trapdoor and the inner side cover , which closes only the outer side of the transmission case , and NOT the space where the rubber cap of the actuator is situated
What happened , was that the actuator also worked like a kind of "balloon pump" by sucking transmission oil through the tiny openings what the gasket did not cover., and press that collected oil through the hollow shaft into the primary , due to these two compartments shared the same closed inner atmosphere.
By making that closed atmosphere leak ( by installing that rubber vent ) , the unwanted "balloon pump" effect had been abolished..
It maybe sounds all a little confusing , but when you ( f.i.) should look up the picture at page 7 - 7 , fig. 4.6b of the Clymer M8 manual , it all will be clear.
103 TC had hydraullic clutch, no vent, and no venting through starter. Which isn't a lot but some.
I have heard there was some issues before M8. I wouldn't be surprised there was, and most people who change it every 5k don't notice it, if just a little. Fluid levels have changed in the 6 speed tranny before the M8s too. I wonder why.
Cruiser
Joined: Mar 2007
Posts: 163
Likes: 32
From: Amsterdam , The Netherlands
The CVO Ultra Glide TC110ci , with hydraulic clutch has a so called "3 piece pushrod" which has the inner diameter of the hollow shaft in the gearbox .
Replacing the stock thin M8 pushrod by such a "3 piece pushrod" was the first solution to prevent oil transfer into the primary
Replacing the stock thin M8 pushrod by such a "3 piece pushrod" was the first solution to prevent oil transfer into the primary
Last edited by sjoko; Sep 8, 2023 at 06:26 PM.
Seasoned HDF Member
Joined: May 2008
Posts: 21,132
Likes: 12,693
From: South Carolina
Road Master
Joined: Apr 2018
Posts: 986
Likes: 442
From: Sivier County Tennessee
Hi everyone, I am well aware that the early M8 engines from 2018 - 2020 had their fair share of mechanical issues. Am in right in thinking that the problems have been ironed out in the 2023 models? I currently have a 2015 twin cam and am think of upgrading to a new fatboy but I keep hearing things like stick with your twin cam
new M8s are nothing but trouble
Are they right? I am interested to hear from anyone that has one and whether theyve had a good or bad experience with it
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
Whatever. Nobody said they did not make a mistake with the prior pumps. I am saying there is now verifiable proof that the latest version is in fact solid.
We can compare the mod list all day, if you want. My 128 with all that and more has 20K miles on the latest version HD oil pump so far, without an issue.
My point was, you should not be telling new guys that are asking for advice that the sky is falling with the latest oil pump version.
We can compare the mod list all day, if you want. My 128 with all that and more has 20K miles on the latest version HD oil pump so far, without an issue.
My point was, you should not be telling new guys that are asking for advice that the sky is falling with the latest oil pump version.
Maybe you shouldn't assume what you know nothing about.
https://www.cvoharley.com/smf/index.php?topic=118283.0
Club Member
Joined: Apr 2016
Posts: 11,541
Likes: 8,375
From: Inland NW
Why don't you try telling this to Steve @ Fulsac.
Maybe you shouldn't assume what you know nothing about.
https://www.cvoharley.com/smf/index.php?topic=118283.0
Maybe you shouldn't assume what you know nothing about.
https://www.cvoharley.com/smf/index.php?topic=118283.0
As usual, you are trolling the M8 threads, trying to show your superior intellect as a mechanic. Stop. You can't even review threads correctly, and put dates together.
That post CLEARLY dates the previous version(s) of the pump, and not the newest 8 lobe introduced in the May 26, 2019.
You are bouncing around this site trying to be all-knowing for some reason, and you are nothing but a piece of ****.
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Road Warrior
Joined: Sep 2016
Posts: 1,887
Likes: 1,059
From: SE Washington
Why don't you try telling this to Steve @ Fulsac.
Maybe you shouldn't assume what you know nothing about.
https://www.cvoharley.com/smf/index.php?topic=118283.0
Maybe you shouldn't assume what you know nothing about.
https://www.cvoharley.com/smf/index.php?topic=118283.0
Good job
