76 xs500 Yamaha - I need a front brake master cylinder...I can bleed front but fluid not returning from caliper to cylinder.

anual Bleeding
The primary and secondary (front and rear) hydraulic brake systems are individual systems and are bled separately. Bleed the longest line first on the individual system being serviced. During the complete bleeding operation, DO NOT allow the brake master cylinder reservoir (2K478) to run dry. Keep the master cylinder reservoirs filled with High Performance DOT-3 Brake Fluid C6AZ-19542-AA or DOT-3 equivalent meeting Ford specification ESA-M6C25-A. Never reuse brake fluid that has been drained from the hydraulic system or has been allowed to stand in an open container for an extended period of time.
NOTE: Non-ABS vehicles have the brake master cylinder (2140) mounted at an angle to the horizontal, bleeding may be better performed if the vehicle is positioned so that the brake master cylinder is horizontal.

1. To bleed the brake system, position a suitable box wrench on the bleeder fitting on the brake wheel cylinder. Attach a rubber drain tube to the bleeder fitting. The end of the tube should fit snugly around the bleeder fitting.

1. Submerge the free end of the tube in a container partially filled with clean brake fluid, and loosen the bleeder fitting approximately three-quarters of a turn.

1. Have an assistant push the brake pedal (2455) down slowly through its full travel. Close the bleeder fitting, then return the brake pedal to full-release position. Repeat this operation until air bubbles cease to appear at the submerged end of the bleeder tube.

1. When the fluid is completely free of air bubbles, secure the bleeder fitting and remove the bleeder tube.

1. Repeat this procedure at the brake wheel cylinder on the opposite side. Refill the brake master cylinder reservoir after each wheel cylinder is bled, and install the master cylinder cap and gasket. Ensure the diaphragm-type gasket is properly positioned in the master cylinder cap. When the bleeding operation is completed, the fluid level should be at the MAX line to 4.0 mm (0.16 inch) below.

1. If the primary (front brake) system is to be bled, repeat Steps 2 through 5 at the right front brake caliper and ending at the left front brake caliper. Bleed the brake master cylinder at the bleed screw after all calipers are bled.

1. After disc brake service, ensure that the disc brake pistons are returned to their normal positions and the shoe and lining assemblies are properly seated. This is accomplished by depressing the brake pedal several times until normal pedal travel is established.

1. Check pedal feel. If brake pedal feels "spongy" repeat bleed procedure, or use the Vacuum method as outlined in Section 06-09, but bleed both rear calipers first.

You can also pressure bleed it. If the abs module needs to be bleed, that requires a special tool. If you have already tried the procedure posted and it didn't work, I'm not sure what next?

A friend had a similar trouble with a Renault Espace. He had pumped loads of fluid through the system but could not obtain a decent brake pedal. He had made an elementary mistake and fitted each brake caliper to the wrong side of the car so the bleed ******* pointed down instead of up.

Your description of what you did and what is happening is so sparse I can offer only a few suggestions.

If the master cylinder was drained during the repair it can be very difficult to persuade an older master cylinder to begin to pump again and a vacuum bleeder could be needed or even a pressure bleeder.

During normal use the master cylinder spends years travelling only a few millimetres. When the brakes are eventually repaired and an attempt to bleed the brakes is made the master cylinder travels the full length where the seals can encounter a wear ridge, sediment and corrosion. It is not unusual for the master cylinder to fail at that moment.

Other possibilities are binding or maladjusted footbrake linkage, broken or weak return springs - including the master cylinder return spring. It is also possible the machining of one of the calipers wasn't completed and a fluid port has not been fully drilled out.

The brake hose is clogged. When under pressure from applying breaks, the piston is forced tight to the rotor. When released the fluid will not return through the hose because there is no real pressure. Replace the hose.
murf427

I'm going thru the same thing...I blew air in the line with pressure and the caliper worked...open heart surgery master cylinder and caliper and no signs of wear and tear...to me its like if the master cylinder doesn't have enough pressure to push the brake fluid......my conclusion ..faulty master cylinder...

Replace the brake lines !
Yamaha service says lines should be replaced after 4 years, and this is one of the reasons why.
As the inner material of the line deteriorates with age, it is possible for tiny pieces to break away and get lodged in the master cylinders return orifice. This could allow fluid to enter the line to squeeze the brake pads, but block the return, effectively locking up the pads.
Ron, Erie, Pa.

It means there is air in the brake line. If the fluid gets too low in the brake cylinder air gets pumped into the system when the brake is applied. A loose fitting or bad seal is usually why the fluid gets low. Fix the leak then add fluid and bleed the system of air. First bleed the master cylinder at the lever. There should be a bleeder valve on the cylinder. Put a clear rubber hose on the end of the bleeder valve. Run the hose into a container so the brake fluid doesn't get on paint or plastic parts. The fluid can mess up the finish. Now squeeze the brake lever several times in rapid succession then hold the lever in without releasing it. Open the bleeder valve slowly and fluid and air bubbles will come out of the valve. Close the valve BEFORE releasing the lever. Do the same thing multiple times until only fluid comes out of the valve. Do not let the cylinder run out of fluid while bleeding. If it does, you have to start all over again.
Now do the same procedure on the wheel caliper.
Understand that the master cylinder and / or the wheel caliper may need new seals. Please rate my answer. Thanks!

youmust compress centre of caliper piston with C-Clamp vise -grips, or large channel-lock pliers. If this does not work then you must crack open the bleeder screw on the caliper and then squeeze the piston back with pliers. Once your brakes are installed you MUST bleed the brakes, to remove the air from the system. If your only doing the front brakes then bleed furthest wheel from master cylinder, and keep topping up fluid as you bleed...

Just take your old line off and replace it with the new line. Be careful because the brake fluid will damage your paint if it's DOT 4. One you have replaced the brake line, fill the master cylinder with the proper brake fluid. Open the bleeder valve and let gravity do it thing. Usually once the fluid starts to flow out of the bleeder valve, all the air is gone as well.

But if the brake lever still feels spongy or no brake at all, first bleed the master cylinder. Squeeze the hand lever and hold it while you loosen the union bolt on the end of the master cylinder. Once the pressure bleeds off, close the valve and repeat the process until you get no air bubbles. Then, move down to the brake caliper and do the same thing until you get no air and a full brake lever. You must do it in this order exactly. Squeeze the lever, open the valve, close the valve, let go of the lever. Do not allow the master cylinder to run dry during the bleeding process.

Good Luck
Steve

If you bleed the caliper and the wheel locks up after you drive a couple blocks you just need to clean your master cylinder on the handlebar, you will see a large hole that feeds the piston brake fluid. Next to it is a tiny pin hole that allows fluid to return to the reservoir , this is plugged with dirt or rust. If you did not overheat the disc and caliper they should be fine. You can get a new oil seal and dust seal for the caliper and a master cylinder rebuild kit from a Yamaha dealer if you need them. Most of the time you only need to pull the piston out of the master, blow out or push a piece of fine wire through the return pin hole to clear it, bleed the system, and it should work like new.

One easy thing to try is clamp the front brake lever overnight. If there are any air bubbles in the system they should be compressed and in theory work their way to the highest point in the system - the master cylinder. Doesn't always work but the price is right.
My experience has been air enters the calipers more than it does the master cylinder due to miscommunication between the person squeezing the lever and the person opening the bleed screw. They do have bleed kits these days that make it a little easier.