How to bench bleed a master cylinder

Kestas

Staff member
Messages
13,863
Location
The Motor City
I need to replace the brake master cylinder on my 2010 Nissan Murano. I already bought the new unit. The instructions give a choice of bleeding methods. One is to plug the ports and pump the piston until it can't move. The other is to use bleeder tubes that direct the fluid back to the reservoir. What are the pros and cons of each method? I have the plugs for the ports, but I don't have bleeder tubes.
 
Messages
1,528
Location
MN
Either one works. I usually just do the port plug method, then install on the car and have someone pump the pedal while I crack the lines at the master, just like a bleeder screw. Doing it this way I almost never have to bleed at the wheels.
 
Messages
5,887
Location
DFW
Never tried the port plug method. May have to if there's a next time. My 89 Accord used to go through MCs every 100K miles like clockwork. I replaced the unit three times on that car using the small tubes directed into the reservoir. It worked fine, too.
 
Messages
1,479
Location
iowa
Port method is the easiest, and works. You can also mount the MC and use the brake pedal to bench bleed. The problem with either method is when you go to hook up the lines it runs out, and all over. But, if you hold the brake pedal just halfway down or more with a prop rod, or something, then when the pedal is depressed, it blocks the output ports inside the cylinder bore, and then nothing runs out. You can do the same thing when changing calipers, etc. Makes bleeding much easier too, by not letting all the fluid leak out of the master, and lines. It's like holding water in a drinking straw with your finger. You can hold brake fluid for days in the system using that method, but you would probably want to unhook the battery, because your brake lights will be on is all.
 
Messages
17,501
Location
Clovis, CA
All you do is thread in the little plastic adapters where the brake lines normally go. Then you hook the little clear hoses to the adapters and submerge the other end of the hoses below the brake fluid in the master cylinder. Then you take a #3 Phillips screwdriver and push the piston several times. When the bubbles quit coming out of the hoses, you're done.
 

Kestas

Staff member
Thread starter
Messages
13,863
Location
The Motor City
Thanks for the feedback. One bonus with this job is that a brake fluid flush was in the queue. By putting it off I will have only needed to do it once.
 
Messages
2,431
Location
Toronto, Canada
I have always used the tubes to direct the flow back into the mc and the method works extremely well. I don't see how all the air can be purged if the ports are plugged since any bubble that gets trapped has nowhere to go. If the mc is mounted in the vise with the front inclined down, I can see most of the bubbles, but perhaps not all, escaping through the compensating ports when the outlet ports are plugged.
 
Messages
2,431
Location
Toronto, Canada
Originally Posted By: Traction
Port method is the easiest, and works. You can also mount the MC and use the brake pedal to bench bleed. The problem with either method is when you go to hook up the lines it runs out, and all over. But, if you hold the brake pedal just halfway down or more with a prop rod, or something, then when the pedal is depressed, it blocks the output ports inside the cylinder bore, and then nothing runs out. You can do the same thing when changing calipers, etc. Makes bleeding much easier too, by not letting all the fluid leak out of the master, and lines. It's like holding water in a drinking straw with your finger. You can hold brake fluid for days in the system using that method, but you would probably want to unhook the battery, because your brake lights will be on is all.
Holding the pedal halfway down or more does NOT block the output ports. However, holding the pedal down, even if just a bit, blocks the compensating ports and then vacuum will prevent fluid running out. It works well, I can attest to that from experience.
 
Top