Q: Brakes not pumping up.

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Brakes will not bleed or even pump up. Brake fluid is not going into the master cylinder. Already installed new master cylinder and made sure the booster was working to push the cylinder in.

My car has 104000 miles.
My car has an automatic transmission.

The best thing to do with a new master cylinder is to bench bleed it. Here’s how:

  1. You use a vice to grab the nubs of the master cylinder and mount it up about waist high. If you don’t have a vice, there is usually another way to hold the master cylinder.

  2. Most master cylinders come with a couple of hoses and some threaded fittings. You attach the fitting to where the brake lines go, attach the hoses to the fitting and place the ends of the hoses into the master cylinder reservoir.

  3. Use a large Phillips head screwdriver to push the piston of the master cylinder in. Be careful not to push it in to the end of its travel. It could damage the inner seals and you don’t have to use a Phillips head screwdriver, just something like it.

  4. Keep pushing it in and out until the lines you have placed in the reservoir are no longer pushing air into the reservoir.

  5. Keep the lines in the reservoir and mount the master cylinder to the car.

  6. Remove the bleeder lines and attach the brake lines.

  7. Begin at the right rear wheel and bleed all four wheels until you don’t see any air coming out. Remember you will need to move the the air bubble from the master cylinder to the wheel you are bleeding at. This means to keep in mind how much fluid that is that will need to be moved through the line.

It is often hard to get fluid moving through a master cylinder on the car. If you don’t want to remove the master cylinder from the car, remove the brake lines and follow the bleeding procedure as if the master cylinder were mounted in a vise. Sometimes you have to use slow short strokes to get the bleeding started.

If you should need assistance with this, I recommend enlisting a certified technician, such as one from YourMechanic who can flush the brake system at your own convenience.

Good luck!

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