Need some help here please guys !
My 2013 Harley Davidson Fat Bob has transmission fluid migrating from the gearbox into the primary drive case at the rate of 100ml every 100 miles ! I've just drained the primary and collected 2600ml of transmission fluid ! The transmission fluid in the gearbox barely made it onto the dipstick !
My questions are :-
• Could running the bike with nearly 3 times the recommended amount of fluid , have done any damage ? ( The transmission and clutch have always worked and felt fine with the eexcess oil included ! )
• What is the most likely route that this fluid is taking between the two ?
Due to the rate at which this fluid is moving from one chamber to the other , I was wondering about the possibility that one of the flange bolts ( with 'O' ring) which holds the primary case to the gearbox , is the culprit. These bolts would have been removed when the dealership replaced the bearing oil seal in the primary 4 years ago.
I don't think a weeping seal would allow fluid past this quickly , but if the culprit DOES turns out to be an oil seal , how involved a job is it to do at home ?
I've posted about this problem on here before but I stated that the primary fluid had not risen. At the time it didn't look as if it had , mainly due to me not being to see the level clearly !
Many thanks in anticipation.

 

The job can be done at home. It isn't complicated but it is time consuming. The following video was a great help to me when I did mine. I was a little intimidated going in but now I'm not the least bit afraid to tackle such a job.

 

And btw, I didn't have any leaks. My shift lever was worn out but the procedure for both jobs is the same. You have to remove the inner and outer primary and you always replace the seals when you put it back together. The above video shows you how to do that.

 

Thanks for your help !

 

Am I missing something?

The OP seems to think that transmission lube is somehow making it into the primary drive...

A leaking oil seal will not allow transmission oil to leak into the primary drive.

If a seal leaks, the oil will be dripping off the bike onto the ground.

OP: Are you sure you didn`t overfill the primary, and underfill the transmission?

Bike knocked over in the garage and the kids didn`t tell you??

The only path for oil to go from the transmission to the primary is through the hollow main shaft, but the pushrod passes through there, leaving very little room for oil to pass.

When the transmission is filled to the proper level, that level is lower than the opening in the mainshaft.

Make sure the transmission vent hose is not blocked.

 

The fluid is definitely getting in the primary from the transmission. The fact that I'm losing fluid from the transmission and at the same time gaining it in the primary is too much of a coincidence !
It's physically impossible to pour 2600ml of fluid into the primary since the fluid would simply leak out of the derby cover hole all over the floor !
I've only ever needed to add fluid to the primary once , and that was after a fluid change and I measured the correct 950 ml into a jug in order to get the exact amount in there.
My bike is garaged all the time I'm not on it. It has never been knocked over. The LCD in the speedo would tell me anyway.
My bike is always stored in an upright position and rarely on the jiffy stand but I don't think that would make a difference. Some bikes are stored on a lift over winter with no ill effects.

 

Forgot to mention that the breather was replaced a couple of weeks ago ! ��

 

While there is some discussion on the M8 side about tranny fluid getting into the primary, they mention one possible cause that would be more possible for a fatbob.. That is a leaking motor shaft seal. It's creating a vacuum in the primary and pulling oil from the tranny.. Not sure that the M8 has the same issue tho.. There are a number of M8s doing it and it appears to be at higher RPMs.

 

yea this ! or your trans vent is blocked and forcing it in the primary though the mainshaft.

 

Blocked vent is probably the better bet..