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Vehicle: 2007 Toyota Tacoma 4WD v6 6 speed

I installed a new master cylinder (the truck is at about 120K mi) but when I reconnected all the plumbing, it seems like it is not filling with fluid. The pedal seems two have two extreme states of being depressed and being released, meaning nothing in between, kind of like a power switch, it is on or off. When depressed, the pedal just stays in, does not go back. I did refill the brake fluid (which also feeds the clutch system) after reconnecting all the lines and hoses.

What could be the cause of this? Could there be a plug inside the cylinder fluid intake valve (kind of like it was inside the line out valve, I assume to prevent dust from coming in) that I should have taken out before installation?

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    Did you bench bleed it before you installed? The video may not be your vehicle, but the principle is the same.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 7, 2015 at 16:39
  • no, i did not...
    – amphibient
    May 7, 2015 at 17:04

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First, see if you can get the process started by loosening the pressure line(s) and pumping the pedal a few times. Once some fluid makes it way out and starts leaking, tighten the line(s) and continue to bleed the air out as normal.

If the process still wont start, remove the master cylinder, bench bleed it, then reinstall.

If the master cylinder won't bench bleed (push out fluid when you push the piston in), the seal around the piston may be deformed/damaged. I have had this happen to me only once in many, many replacements over the years.

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