I will be installing a new master cylinder this weekend. Does anyone have experience replacing one on an R51 Pathfinder? Or any tips in general for installing a master cylinder? I have experience replacing brake pads, rotors, and calipers. I have flared and bent hard brake lines. I have worked on just about every other part of the brake system so I guess it's time to learn about master cylinders. I've looked at the service manual and it seems pretty straightforward. Any suggestions?

is it actually leaking? Or just a spongy brake pedal?

Pretty sure its a simple install. The trick is getting all the air out during the bleeding process.

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Spongy brake pedal. Bleeding the brakes didn't seem to help so the master cylinder appears to be the culprit.

Have a read on this post:

http://www.thenissanpath.com/viewtopic.php?t=7749

I know its different symptoms, but might be worth looking at.

Thanks. That's good to know for future reference.

I installed the new master cylinder this morning. The brakes feel much stronger and more responsive. however there is air in the brake lines that I have not been able to get out. I bench bled the new master cylinder and bled the line fittings on it after it was installed. I then bled all 4 calipers with no improvement. I have a couple of ideas. The brake lines going from the master cylinder to the ABS module are higher than the master cylinder and is the highest point in the system. Is it possible that air could be trapped here? Also do I need a special scan tool to allow the ABS system to be bled? The service manual does not mention that such a tool is needed.

Some pictures from replacing the master cylinder. Replacing the master cylinder itself is a stupid easy job. It's only two bolts. The tricky part comes in bench bleeding the new master cylinder and bleeding air from the brake system after installation. I referenced the service manual during the job but found it to be a bit lacking for the typical shade tree mechanic.

Removal: Disconnect negative battery cable and remove brake fluid pressure and level sensors. Remove brake lines from master cylinder and remove master cylinder from brake booster. Here's where I deviated from the service manual. The manual says to open bleeder valves at each brake caliper and drain brake fluid. I did not. My intent was to avoid bleeding each wheel cylinder if at all possible.





Close up shot




Master cylinder removed




Bench bleeding. There are numerous tutorials on this and the new master cylinder should come with instructions so I won't go into detail on this. It can be a bit messy so be prepared.





New master cylinder installed.