I have an 07 dyna street bob. I had some trouble with the brakes not returning fully and couldn't figure out the problem. I rebuild the master cylinder and still same problem. My brakes have been feeling funny in many different ways sometimes to tight sometimes to loose, so I thought it was the pistons but I cleaned them well and pushed them back into bores repeatedly....same problem. I bought a mity vac and tried bleeding the brakes with it to get the air out which I decided it must be as I could here the new m/c seals squeeking. It won't pull fluid its like the bleeder was clogged...so I checked bleeder it was fine. Opened up the brake line at the caliper, no problem there the mity vac will suck vacuum. Then I opened line at m/c I thought it might be a collapsed line...nope thats not it. I do see in the m/c there was basically no fluid in the piston and it takes FOREVER for it to drip and bubbles to appear under the cap. And yes I had the cap off while I was using the mityvac.

Is it that my m/c holes are clogged that are in between resovore and piston in the m/c? The mity vac should suck it through no problem right? Also are these just holes or is there a valve of some kind?

 

I tried sticking a very small wire into the 2 holes side by side at bottom or reservoir. Do these go straight down or do they turn before going into cylinder bore? I can stick wire a little ways down but stops. Looks like it's clean and in great shape. I guess I'm going to just have to take it apart and blow air through it.

 

I would make sure that the hose hasn't collapsed/kinked internally between the MC and the caliper before I suspected the MC.

 

Maybe make sure the...not sure what they are called, technically, the bolts that go thru the both sides of the caliper are not seized up or sticking. Anti-seize on these parts works wonders. If it's an older bike, or not, moisture in the brake fluid will cause pitting after time on the piston and cause problems. Just a shot in the dark here. Is this a up and coming problem or all of a sudden.

 

on my ironhead they go straight down. I dunno about the newer ones i never had to take one apart. Assume it to be the same. I had the little tiny hole clogged in the mc on the ironhead and it threw me for a loop for awhile.

 

Does it feel like the brakes are still applied after you let loose from the lever or pedal?

 

Since you tried just about everything else...

Simple and cheap, you should just do a full caliper rebuild. Pop it off and clean it out with brake cleaner, scrub off the pistons, and replace the dust seals/wipers and o-rings and put it all back together with new fluid. It make a world of a difference.

 

Agree, Brake lines are lined on the ID, that lining can go bad and break loose, just a little flap inside that line can drive you crazy. Id drain the Master cylinder, take banjo bolts out of the MC and caliper and make sure both of those are clear, then while the brake line is loose id pull it off and drain, try to blow through it once its empty in both directions.

 

Check the brake hose, like DDuess and Jeff W suggest. I was an auto mechanic for years and the flex hose on the front brakes often would fail on the inside lining. You can’t tell by the feel of it, it just wouldn’t let the brakes retract. Sound similar?

 

I bet that is the problem. The holes in the master cylinder are not clogged but now I need a new high e guitar string...only wire small enough to stick in there. I thought I ruled out brake lines by unscrewing from m/c and being able to suck out the fluid no problem. But when I hook up to m/c it won't pull any vacuum. I was thinking however and I bet it is because the holes in the m/c are so tiny it creates enough vacuum to collapse a flap inside of the hose to clog it up...when I unscrew the hose from the m/c there isn't enough vacuum because of basically no resistance and it can pull fluid through. These are stainless braided lines so I didn't think they would be at fault but I don't know HOW CHEAP these stainless lines are as I didn't put them on the previous owner did.