HarleyTechTalk

Rebuilding the master cylinder on my Sportster with twin discs that uses the 11/16" bore master cylinder.
I managed to make a bit (a lot!) of a mess of the outer seal that goes over the piston cap.
HD don't sell that seal separately... Vexing given the cost of the rebuild kit!
Does anybody know what it is?
I doubt it is a special HD design part.

item #4

I'd just go to a bearing seal place with the old and new parts to see what they had

OEM rebuild kit may be a bit expensive. But aftermarket is cheaper, e.g. there is a 11/16" kit by Drag Specialties DS-195045 for cheaper. Whether it fits your application and/or quality is ok, I don't know.

My Sportster has a pair of proper Brembo Goldline racing 4 piston calipers on it, fitted by the first owner in 2000. Steve Harris of Harris Performance in the UK. Yes, HIM if you know of him!
Brembos want DOT 4, master cylinder wants DOT 5. Bike has been off the road for 2 years and I can't remember what was in there!
DOT 4 in the master cylinder is turning out to be a very bad idea. I don't think the seals like it.
DOT 5 being silicone is effectively inert so the Brembo seals shouldn't be concerned about it at all.
Note I am NOT mixing fluids! The nice clean system has never had DOT 4 or DOT 5 in it.

The DOT 4 works on the bench when making sure the master cylinder is primed and working.
Put it on the bike a few days later and nothing! It won't even squirt out of the master cylinder never mind down the lines to the calipers.

The seal ID is 9mm. The OD is probably 21mm, exact thickness unknown. 4mm or so?
It is almost certainly made of EPDM.

I put Dual HD Brembos on my 03 Fatty over a decade ago, the system has had DOT5 in it from day one,

it hasn't missed a beat   

can you post some pix ?