Bleeding brakes on a completely dry 356B brake system

[Paul Giganti]

The next stage on my full 4-wheel brake job is bleeding a completely dry brake system. Since I replace all the brake cylinders AND rebuilt the master cylinder, pretty much all the brake fluid drained out during the process. Today I tried using my vacuum brake bleeder starting on the rear right drum. I pumped mostly air for twenty minutes—never even pumped enough fluid out to fill the small reservoir bottle. I checked all the fittings for air leaks—seems everything is air tight. Closed up the bleed screw and tried the brake peddle—nothing—all the way down to the floor with no pressure at all. I thought maybe I'd try bleeding the left rear to see if that made a difference. Same result. I could see fluid bubbling out of the bleed screw, but it also never stopped pumping air.

Question: Is that a symptom of something I did wrong in the rebuild, something wrong with how I'm bleeding the brakes—or am I just not being patient enough with the process? Should I go all the way around, and around, and around?

[Geoff Fleming]

The first step in bleeding a completely dry system, is to fill all of the lines with brake fluid.
Fill the reservoir and then open one of the rear valves. Use a short length of clear plastic tubing fitted over the end of the valve and into a container in order to catch the over-flow. Now manually pump the pedal until you actually see fluid emerging through the clear line. Close that valve and move to the other side. Repeat the procedure on all four wheels. Push the pedal to the floor each time and after about ten pumps, re-fill the reservoir. Important to keep it full, not pumping air. In this way, you will have fluid in all the lines and slave cylinders. Of course, there are two slaves per front wheel, so now you repeat the procedure on each of the valves, using the clear tubing.
Only when there is enough fluid in the system, will you be able to use the vacuum bleeder, which really is used only to get rid of the residual air bubbles.
Be sure the brake shoes are cinched up and the rod from the brake pedal to the master cylinder should only have about 1/8" of clearance before it contacts the master cyl. piston, otherwise you will not be maximizing the effectiveness of the brakes.

[Edwin Ek]

Paul,

Your post is timely! I visited my mechanic today, and he had just rebuilt the brake system. The system was dry, and we had exactly the same symptoms! I was the unskilled labor working the brake pedal and my mechanic was working the bleeder screws.

We got a firm pedal after 15 minutes or so. We were talking about what took so long, and then we got distracted talking about something else. I will ask him tomorrow what the scoop was.

[Ronald Sieber]

My mechanic friend Toomy and I found that by elevating the rear of the car, we were finally able to bleed the brakes. Until we did that, it was very frustrating. I hope that this solution woorks for you.
=rds

[Thomas Sottile]

If you use a vacuum pump you will save all that pumping and the master cylinder.

[Al Zim]

I always had some luck (a long time ago) of filling the master cylinder reservoir, opening all the bleader's and slightly depressing the brake pedal. Mr. Gravity did the rest, sometimes. Now we use a pressure bleeder. al zim

[Olivier Auvray]

I always had some luck (a long time ago) of filling the master cylinder reservoir, opening all the bleader's and slightly depressing the brake pedal. Mr. Gravity did the rest, sometimes. Now we use a pressure bleeder. al zim

+1!

[John Brooks]

I use a elastmear flask and tube like the serving manual, but I put a small check valve in line so it can't back flow. Also I invert a full pint can of fluid in the MC reservoir quickly. It will fill the MC until the fluid level reaches the spout, then stop until the level drops again. I always pump the pedal. The pint can can be removed quickly without spilling and leaves the reservoir about 20mm below the cap.

A cheap Aquarium air check valve that works, I found some spring loaded ones that takes 10psi of pressure to open and bleed. These worked much better than the cheap ones from WM. But when done with them just discard since the fluid is hard on the internal seals on both types.

This eliminated the additional advice and spousal complaining. Farthest wheel first