I am going to put a new master cylinder in my car tonight. My question is ...Do I have to prime the master cylinder? Even if I'm going to bleed all the lines? Thanks in advance! Terry
Yes, You have to "bench bleed" the cylinder. Run 2 short peices of brake line from the ports and bend tham so they discharge into the top reservoir. Put the cyl in a vice, fill it with fluid, and slowly depress the piston with a big screwdriver a number of times untill no air is coming out of the lines. Put the cap on the reservoir, disconnect the lines, and install the cylinder. Then bleed the brakes as usual.
Short answer, yes. It will keep you from pushing air back and forth in the lines. Just hook up the plastic adapters or a short piece of line with fittings so it curs up into the resevoir and has the end below the fluid level. It's easiest if you can clamp it down in a vise or something. Then just pump it slowly until all the air is out of both cylinders. Mount it on the car and bleed well.
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