08 Heritage - Have not dug into the brake issue yet but here is what happened.

Front brakes don't feel right. Seems as if there is no brake no brake then brake. Pads look okay. I noticed the paint around the master cylinder shows sign of brake fluid leak. The old fluid looked nasty as well. I completely flushed the front brake system with new dot 4 fluid and bled the brakes. Still feels the same as it did before.

Rear brake completely failed on me while riding a few days ago. I had no issues with it for a few hundred miles then went to use it and it went straight down with no braking. I see no visible leaks or anything. Odd it worked so well then a short time later it was gone.

I plan to replace the master cylinder rubber seal on the top. Not sure if something else in the system needs rebuilt or has failed and needs replaced. What is your thoughts?

 

Sounds like you may need a master cylinder rebuild or replace. The cups can/do eventually fail..

 

I thought that too.

What do you mean "cups"?

 

The cups attach to the piston in the master cylinder. They seal off against the bore and are what builds fluid pressure when you apply the brakes. If they are leaking by, that explains the loss of brakes. I've not personally been into an HD master cylinder, but they are all pretty much the same internally..

Edit: Seems Harley sells the kits. The cup is shown in the second picture on. Seems to have only one.

http://www.docshd.com/drag-specialti...ductid=7751499