Syringe Bleeding a Master Cylinder
Mark Simpson
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In the past, bench bleeding a master cylinder was often a slow and sometimes messy process that often left you unsure if you actually purged all the air out. The process has become vastly faster and easier with the advent of syringe bleeding. Mark Simpson demonstrates how to syringe bleed a master cylinder using a kit from Master Power Brakes and high-quality DOT3 brake fluid.
When replacing a master cylinder, it's important to, you know, bleed all the air out of the master cylinder before you even bolt it up to your car. What you don't want to do is, is, you know, just throw it on the car, fill it full of fluid, and start pumping away on your brakes and hoping to get all the air out of the system because air can become trapped inside the master cylinder itself and work against you in actually getting the system purged of all the air. So what we do is bench bleed the master cylinder. And it's just a process of, you know, forcing fluid into it and making sure that we've got the air out. In the past, the way to do these, most guys would just fill the reservoirs, they'd go down to the NAPA, or the local auto parts store and they'd have, they'd sell a kit that would bring a couple of tubes up into the master cylinder reservoirs.
And then you would take a screwdriver and pump in and out on the piston and let the fluid pass through the, the system that way. You know, it works, it's not necessarily the best nowadays. Nowadays, a lot of shops prefer doing what they call the syringe method. The syringe method is basically a way of forcing fluid through the port and back into the reservoir. And we'll start by actually putting fluid in both the reservoirs.
We have a syringe, we got this one through Master Power Brakes. We'll put that in the reservoir and suck up some of this fluid. We'll then pull the plug. And force this fluid, and you can kind of see the bubbles as it's forcing the air out of the master cylinder. Now it's important to have eye protection on when you're doing this, and you will get fluid, you gotta have your plugs ready.
It'll be a little fluid that will come through. Now, if you notice, when I was actually pressing on the syringe, I was holding it up at a little bit of an angle to keep this air bubble that's in there. You can force that out by simply raising the tip of the syringe, forcing that out, still a little bit, but you can work, watch for that. And you wanna slowly introduce the fluid until you're getting a good, solid, consistent, smooth stream with no air coming through. Then once you have a good stream, put the plug in and move to the other side.
Once again, you can see the air getting purged out of the system, there go a stream of bubbles. Again, push slowly. You know, it will come shooting out of there, if you push too fast. Mount, put the plug back in. You're ready to seal this up and we'll get her back on the car.
Not fully explained. The brake lines sitting aside will not introduce air when hooked up? I went from feeling confident about install to having more questions.
Why not get 2 short lengths of brake line and attach a check valve (like the ones used to bleed wheel cylinders) and a fitting to fit the master cylinder port. You could then avoid all the plugging and unplugging and the associated mess you get from spilled brake fluid.