M8 trans fluid leaking in primary

[rbabos]

Don't think that the diaphragm of the Brembo unit made the difference.

Twincam (-2016)
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M8 (2017 up)
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I would think just the opposite,  the diaphragm looks to decrease the volume of the chamber where the oils accumulates and in the center where it is closest to the main shaft it may even  touch when the clutch is actuated. I can't believe that someone have not simply drilled a drain hole in bottom as indicated in this thread earlier. No accumulated oil, nothing to transfer.

That would be a good first step. This is taking way too long to solve.
Ron

[FSG]

Here's the pre Brembo Slave Cylinder, there may/was/is transfer with the previous slave cylinder BUT the diaphragm in the Brembo Slave has made a world of difference and not for the good.

The problem IMO isn't the Brembo Slave Cylinder, it's the way in which HD have used it.

[1FSTRK]

I would drill the return holes myself but if someone likes testing swap the M-8 slave out for a Twin cam slave and see if the transfer decreases.
With these pictures it becomes more evident that they are trapping liquid oil right at the end of the mainshaft and the path of least resistance is right down the hollow shaft to the primary.
.
As far as the MOCO, they know what is happening with most of these problems. The task is not just to fix the problem, it is to fix it in such a way that you can say it was never a problem. You have to mask it as a manufacturing change or improvement that way you do not pay to fix the old ones.
Think 50,000 bikes at $50.00 a bike and it is a 2.5 million dollar bill

[Durwood]

I just pulled mine apart yesterday, I was going to drill a drain hole, the problem is that the lower portion on the slave chamber will be right at the oil level...

It is still apart, and I am pondering cutting the center out of the diaphragm.

[Durwood]

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[rigidthumper]

Is the solution as easy as removing this material? Make that hole big enough, and no more carryover? IMO, they made it this way to allow slave cylinder changes without losing fluid- I'd rather have to add a few ounces in the odd event of having to replace the slave unit, than have to worry about carry over.
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[FSG]

they made it this way to allow slave cylinder changes without losing fluid

I think I've said the same thing earlier   

Yes cut the center out OR jut the bottom half out, the cover needs relieving as well so both would provide a path for the oil to return to the trannie, without relieving the cover the gasket thickness is the only gap for oil to pass thru.

[1FSTRK]

Pics two and three would be my thought. I would leave all of the top to help shield oil from entering the cavity. In in pic three I would insure to remove material only in areas that had good drainage though the bearing housing into the main trans case.

[Karl H.]

FSG, could you mark (if you know) where the tranny oil level is? Could be important imho.

Karl

[rbabos]

FSG, could you mark (if you know) where the tranny oil level is? Could be important imho.

Karl

Better still, do the function of the helical gears force the oil level higher in that area like a pumping action. If so, might be a fix that won't work.
Ron

[FSG]

FSG, could you mark (if you know) where the tranny oil level is? Could be important imho.

Karl

Sorry, I don't know, I've not seen a M8 other than in the showroom.

Darren has said "I was going to drill a drain hole, the problem is that the lower portion on the slave chamber will be right at the oil level..."   perhaps he could draw a line on a pic.

I'd have the bike on the side stand, even the wheels on 2x4s to get an angle such that the slave could be removed without loosing oil.

[FSG]

Better still, do the function of the helical gears force the oil level higher in that area like a pumping action. If so, might be a fix that won't work.
Ron

I'm sure they do, I've said earlier that the gears main and counter will be acting like a screw compressor and pushing oil to the bearing.

That said if they are pushing oil then the opposite side of the gearset should be sucking.  So I'd suck it and see.

[1FSTRK]

Better still, do the function of the helical gears force the oil level higher in that area like a pumping action. If so, might be a fix that won't work.
Ron

I'm sure they do, I've said earlier that the gears main and counter will be acting like a screw compressor and pushing oil to the bearing.

That said if they are pushing oil then the opposite side of the gearset should be sucking.  So I'd suck it and see.

Cable clutch bikes use the same gears and do not have the problem so it is the trapping of the oil not the gears pushing it. I do not have a bike to look at either but if you leave the side by the gears that may be pumping shrouded and open the opposite side so the oil can flow back it should work as well as a cable cover does.

[Karl H.]

Provided the M8 tranny has about the same (?) oil level as the TC tranny it looked like that:

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[FSG]

....the problem so it is the trapping of the oil not the gears pushing it. ...  if you leave the side by the gears that may be pumping shrouded and open the opposite side so the oil can flow back it should work as well as a cable cover does.

the oil is trapped, yes, but it has to get there and it didn't walk, so IMO it's pushed

maybe I'm overthinking it remembering the days I worked on screw/reciprocating air compressors that put out 800 cfm at 3000 psi, they were driven by 12V149s, noisy baskets

BUT ......  the side cover holding the ramps doesn't seal around the end of the mainshaft like the hyd side cover does so there must be some relief rather than just rely on the gasket thickness

[1FSTRK]

......  if you leave the side by the gears that may be pumping shrouded and open the opposite side so the oil can flow back it should work as well as a cable cover does.

BUT ......  the side cover holding the ramps doesn't seal around the end of the mainshaft like the hyd side cover does so there must be some relief rather than just rely on the gasket thickness

Damn internet 
We are in complete agreement on this and have been. Both covers need to be opened up.
All I was trying to say is the machined relief could be biased toward the lower quarter that would drain back best.

I wish I had a bike local. This is a 1 hour test at Vic's shop.
Post 1 feb 17 2017

[FSG]

K and 1          

[Durwood]

Provided the M8 tranny has about the same (?) oil level as the TC tranny it looked like that:

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Karl, I'd say that's pretty close. I eyeballed the stick location from outside the trans through the passageway in the lower portion of the case.

[To The Max]

Hi guys have been following this thread for a while now and I was wondering if you removed the cover but left the slave cyl attached, and pulled the clutch leaver in would oil be forced out of the gap between the housing and the slave cylinder. Max

[topcat3815]

Maybe HD should go back to a cable operated clutch

[dogger]

I agree with topcat. Many of the riders with hydraulic clutches have had some kind of a problem at one time or another.

[les]

Provided the M8 tranny has about the same (?) oil level as the TC tranny it looked like that:

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Those support ribs on the one on the right look a lot more restrictive than the cable housing on the left.

[borno]

The rubber on that Brembo slave cylinder looks just like a LMI pump diaphragm, no wonder it pumps oil.

[1FSTRK]

One thing to note is the problem is not more prevalent in city traffic when you are using the clutch alot, it shows up at mid to high rpm contant running.

[PoorUB]

I agree with topcat. Many of the riders with hydraulic clutches have had some kind of a problem at one time or another.

Cable clutches are not trouble free either. First off look at all the threads we see on adjusting a cable clutch, plus after a few miles the cable wears, then breaks. I have had both, I like the hydraulic better.