Ok I am not sure what is wrong.  I bleed the rear brake multiple times already but it still feel mushy to me.  I have SS line running so I know that is not the issue.  I get plenty of rear stopping power since it can easily lock up the rear tire, but because it is mushy its hard for me to gauge the amount of pressure I should apply.  The bike is a 91 with 6K miles. 

Can it be something wrong with the rear master cylinder or is the rear brake just mushy?

Thank!

How many revolutions does your rear wheel make when you get the bike on the centre stand and give it a good spin?

I don't know.  Why you ask?  That said I was cleaning the chain the other day and I noticed when I was rotating the wheel there seem to be tight spot.

When I was having trouble with the rear on my Ducati recently I went ahead and bled every fitting.  Bled the banjo on the master, the banjo on the caliper, and finally the bleeder screw.
There may be a small pocket of air somewhere that just won't get out.

Unlike the front the rear brake mechanism has several pivots, clevises and pins.

I would check the mechanism and and all linkages carefully for wear, any significant play in these parts could give rise to the condition you describe.

Lube everything with grease while it's apart.

How much free play should there be on the rear pedal before the brake is engaged?

Thanks

EK to ER =47mms
ES to EY =55mms
K1 and on =55mms

Measured between the top of the foot rest and the top of the rubber sleeve on the brake pedal.


Courtesy of Haynes.