Took the hog out today and rear brake was spongy. Check resourviour. And it was full. Brake pads are good too What can be the issue?

09 FLHT

 

There's only a few things that can cause a spongy pedal... Air in the system, severely contaminated fluid, a leak in the system, either external or internal, or a damaged (weakened) hose that's blowing up like a baloon.

There's a few mechanical issues that could theoretically cause a spongy pedal but they are so unlikely (especially if you haven't taken anything apart) it's not even worth speculating there.

Focus on the hydraulics - that's most likely your problem.

 

as 2black1s said -- check those first - and with that said, you don't have ABS do you? as I find those always feel spongy- like a GM product compared to a Ford product brake system

 

Bleed your brakes to replace the fluid, then check again.

 

I looked it over with a fine comb..bleed the brakes..fill and refill the resourviour &nothing changed....what else could it be

09 FLHT

 

If you have new fluid and bled the system then you can eliminate those as the causes, provided the bleeding was done properly and thoroughly. I'm assuming during your flushing and bleeding process you also verified no external leakage. So now, if you look at my previous post that only leaves two more options... a defective hose or an internal leak in the master cylinder. My money is on a leak in the master cylinder (assuming everything else you have stated is accurate).