I flushed out my 22 year old brake fluid and all was going fine until I got to the driver side rear. I was getting more air than fluid. The reservoir never got close to empty. I finally shut the bleeder screw and was still getting a little air and fluid while I had a vacuum on it.

Is it possibly a bad bleeder screw?

 

That or your vacuum hose isn't sealing on the bleeder as well as it did on the others. Maybe try using a small zip-tie to clamp the hose on, or find a hose that fits tighter. I've had this happen before and is why I still prefer bleeding brakes the old fashioned way.

 

Maybe some dirt is plugging up the bleeder?

 

spfautsch indicated a vacuum bleeder is being used. Is this the case?

 

Yes.

 

spfautsch did mention about the possibility of a bad seal of the bleeder hose. And that does seem reasonable when the bleeder is closed. It is possible that the bleeder did not seal on the caliper, but not very common. Although after 22 years the system would likely have some crud in it. I am assuming the color of the fluid was dark and the bottom of the reservoir has a film on it. With the bleeder closed, try standing on the pedal to see if it leaks. Take the bleeder out and if you can see any problems with it. If you can, wire brush it. At the same time see how much fluid will come out of the caliper by gravity. May be hard to see inside the cavity for dirt, etc. If there is enough fluid flow, try some aerosol brake clean to clean out the cavity. spfautsch does like the old fashioned way to bleed. And it still works. I assume you are by yourself doing this. Two ways to bleed. Find or make a device, (spring loaded), or something to wedge the pedal against the seat. Open bleeder, this will give you a short amount of fluid. Close quickly. And repeat till necessary. Other way is have one end of your hose on the bleeder, and the other end in a clear receptacle with brake fluid in it to see any bubbles. Open bleeder, stroke pedal till necessary. BE WARNED that stroking the pedal beyond what the car has seen in normal driving may dislodge crud in the master cylinder. And you are still dependent on the (seal) of the bleeder threads and hose. You can put some grease on the threads of the bleeder for a better seal.
What can happen when using this type of bleeder is air entering around the threads of the bleeder or even the caliper piston o-ring. Not to common, but has happened.

 

Fluid was almost as black as used motor oil. Since I was not able to bleed one line the new fluid has gotten dark again, but is much better. The brakes feel fine. Thanks!