Im trying to bleed my brakes, why do i need the brake fluid in the bottle?

Do not drive vehicle without bleeding brakes first. You can switch brake pads or change rotors without bleeding but never when changing a caliper.

Mighty Mac makes a vacuum tool with a small brake adapter for catching fluid from the brake system. Imitators use similar designs. Then there is gravity bleeding which you can look up on the Web. There is a one-way valve which can be connected on one caliper at a time or finally some put out 4 bottles filled with brake fluid and hoses from each brake bleeder. The bleeders are opened and the owner pumps the brakes himself until pressure is good on pedal. The owner then tightens each bleeder before removing brake hoses to auxillary bottles.

The last method is shaky because the hoses can pop off if not secure to brake bleeder and then system can vent air and you would need to redo.

First of all, I hope you got a new master cylinder with your disc brake kit. A new master cylinder should be bled before connecting the brake lines and then never allowed to pull in air during the rest of the bleeding process. A couple of fittings ans hoses should have come with the new master cylinder [see the kit listed for a picture]. If the master cylinder has an air bubble, you won't be able to properly bleed the rest of the system.
For the rest of the system you can make up a small catch bottle like the one pictured in the one man brake bleed kit; make sure the hose goes tot he bottom of the catch bottle. You have to cap the master cylinder reservoir before pumping the brakes or fluid will squirt out and all over; brake fluid is a like paint remover. Then start with the brake farthest from the master cylinder and bleed fluid out by having a buddy pump the brakes while you hold the catch bottle above the bleeder port so no air gets back in. [hint, put some pipe teflon tape on the outer threads only, not the inner end of the bleeder screws to seal the threads]. Check the master cylinder level often! If the brakes still are spongy after the first round of bleeding, have a buddy pump up the brake pedal with the bleeder screw closed and hold pressure on the pedal; you then open the bleed port until the pedal goes to the floor; have your buddy hold down the pedal until you close the port. Repeat on all brakes until the pedal is firm.

Supplies you will need:

bottle of brake fluid

small clear container

18" length of 1/4 inch I.D. clear tubing

wrench that fits your bleed screw

another person

Open hood,loosen lid to brake reservoir to be able to monitor fluid level. Removing the tires makes it easier to access bleed screws but not necessary on all vehicles. Start at the caliper farthest from the reservoir, attach tubing onto bleed screw so it is tight fitted on bleed nipple.Put enough brake fluid into clear container and put open end of tubing into fluid, ensure tube stays in fluid throughout entire process as to not suck air into system. Have your assistant sit in car and pump brake pedal three times and hold to floor, then loosen bleed screw just enough to relieve pressure in brake line, the brake pedal will sink right to the floor..this is normal. DO NOT RELEASE BRAKE PEDAL UNTIL BLEED SCREW IS TIGHTENED AGAIN. Repeat this process until clear tube is full of brake fluid and no bubbles come out of caliper. Repeat steps for all calipers. Hope this helps

Most cars are done the same way:
1: Farthest brake from the master cylinder (rear)2: Opposite side from the first brake.3: Farthest from the master cylinder on the front.4: Remaining brake.
BTW: I would advice using the traditional method of using a clear bottle with some fluid in the bottom and a clear hose running out of the fluid, through the bottle top and which can connect to the bleed nipple. When bleeding fluid, make sure the fluid in both the master cylinder and to the bottle is clean before closing off the bleed nipple. Then pump the brake after bleeding each brake and feel for any softness. If you feel softness after bleeding any particular brake, then you will know that you just introduced air into that brake line, and will need to bleed again.NEVER allow your master cylinder to become totally empty whilst bleeding as this will mean you have to bleed all air out of the total system and start again from scratch. This can be a huge pain!

You will need a friend to help. Pick up an extra bottle of brake fluid that your vehicle manufacturer recommends. Open the bleed valve on the closest brake first. Have your friend gently push the brake pedal until fluid comes out bleed valve. Tighten bleed valve. Check your brake fluid tank and top up as needed. Work your way around the vehicle repeating this procedure.

For left hand drive vehicles: (If the car does not have ABS system you do not need any diagnostic equipment!)

IMPORTANT NOTE: You need using diagnostic equipment connected to the data link connector of the car in order to bleed the ABS block. Follow instructions by scantool equipment for bleeding the ABS block.

1. This bleeding procedure requires two people. Remove the brake system reservoir cap, and fill up with new brake fluid until "MAX" level is reached.
2. Lift the car, or use a channel for access under vehicle.
3. Put the gearbox in "N" - Neutral position, or in "P" - Parking position for automatic transmission.
4. Start the engine and push the brake pedal firmly for 4 - 5 times to the floor, and maintain the brake pedal pushed to the floor.
5. Begin with the rear right wheel. Another person remove the dust cap and loose the brake caliper bleeding screw until the brake pedal goes to the floor. At this moment maintain the brake pedal pushed to the floor, engine idling, and tight the brake caliper bleeding screw. Use a plastic hose: one end connected to the brake caliper bleeding screw, and another end inside a recovery bottle for used brake fluid.
6. Repeat steps no.#4 and no.#5 until no air flows through the brake caliper bleeding screw. Tight the brake caliper bleeding screw, and put the dust cap in their place.

IMPORTANT NOTE: All the time check the brake fluid level in the brake system reservoir, and fill up if necessary!

7. Push the brake pedal firmly for 4 - 5 times to the floor, and maintain the brake pedal pushed to the floor, engine idling.
8. Continue with the rear left wheel. Another person remove the dust cap and loose the brake caliper bleeding screw until the brake pedal goes to the floor. At this moment maintain the brake pedal pushed to the floor, engine idling, and tight the brake caliper bleeding screw. Use a plastic hose: one end connected to the brake caliper bleeding screw, and another end inside a recovery bottle for used brake fluid.
9. Repeat steps no.#7 and no.#8 until no air flows through the brake caliper bleeding screw. Tight the brake caliper bleeding screw, and put the dust cap in their place.

IMPORTANT NOTE: All the time check the brake fluid level in the brake system reservoir, and fill up if necessary!

10. Push the brake pedal firmly for 4 - 5 times to the floor, and maintain the brake pedal pushed to the floor, engine idling.
11. Continue with the front right wheel. Another person remove the dust cap and loose the brake caliper bleeding screw until the brake pedal goes to the floor. At this moment maintain the brake pedal pushed to the floor, engine idling, and tight the brake caliper bleeding screw. Use a plastic hose: one end connected to the brake caliper bleeding screw, and another end inside a recovery bottle for used brake fluid.
12. Repeat steps no.#10 and no.#11 until no air flows through the brake caliper bleeding screw. Tight the brake caliper bleeding screw, and put the dust cap in their place.

IMPORTANT NOTE: All the time check the brake fluid level in the brake system reservoir, and fill up if necessary!

13. Push the brake pedal firmly for 4 - 5 times to the floor, and maintain the brake pedal pushed to the floor, engine idling.
14. Continue with the front left wheel. Another person remove the dust cap and loose the brake caliper bleeding screw until the brake pedal goes to the floor. At this moment maintain the brake pedal pushed to the floor, engine idling, and tight the brake caliper bleeding screw. Use a plastic hose: one end connected to the brake caliper bleeding screw, and another end inside a recovery bottle for used brake fluid.
15. Repeat steps no.#13 and no.#14 until no air flows through the brake caliper bleeding screw. Tight the brake caliper bleeding screw, and put the dust cap in their place.
16. Now the brakes are bleeded. Check the brake fluid level in the reservoir. Fill up with new brake fluid until "MAX" level is reached. Put back the brake reservoir cap.
17. Test the car brake system. The brake pedal movement no more than 1/3 of total stroke until the floor, when brake pedal is applied. Maximum admissible is 1/2 of total stroke.

Brake fluid absorbs moisture, and this can rust the insides of the brake system. The moisture was not that big of deal 10 years ago, but on ABS brake systems of today, the rust and other debris that accumulates in the fluid can do lots of internal damage, and can be very costly. Brake fluid can also break down over time from excess heat that is created from within the brake system.
It is recommend flushing the brake fluid system about every 30,000 miles, or at 30K, 60K and 90k tune up. It cost about $90, but you can do it by yourself. To do this flush, open the brake lines located at each wheel and allow the brake fluid from the brake master cylinder to "bleed by gravity", as continue to feed new fluid to the master cylinder until the fluid runs clear at all wheels.You need two people do do this job. One at master cylinder brake fluid bottle under hood, adding fluid, and the other one under the car tightening up the bleeding nipples as necessary, until the discharge clears up. The discharge has to be collected in 16OZ plastic bottle via clear vinyl hoses from the bleeding nipple to the bottle. It is a good idea to replace all 4 nipples with new one. They are cheap and avoid problems in long run. Make sure to use at least DOT 4 brake fluid. Make sure to use a sealed bottle. The life of brake fluid in an open bottle is one week. If the brake pedal is spongy, then go for bleeding of the brake system, one wheel at a time. You must inspect all breaking system components, from master cylinder, up to calipers, or rear brake cylinder for any leak, or malfunction. check the status of brake lines for rust, and if necessary replace or undercoat them.

Brake fluid absorbs moisture, and this can rust the insides of the brake system. The moisture was not that big of deal 10 years ago, but on ABS brake systems of today, the rust and other debris that accumulates in the fluid can do lots of internal damage, and can be very costly. Brake fluid can also break down over time from excess heat that is created from within the brake system.
Is recommend flushing the brake fluid system about every 30,000 miles, or at 30K, 60K and 90k tune up. It cost about $90, but you can do it by yourself. To do this flush, open the brake lines located at each wheel and allow the brake fluid from the brake master cylinder to "bleed by gravity", as continue to feed new fluid to the master cylinder until the fluid runs clear at all wheels.The discharge has to be collected in 16OZ plastic bottle via a clear vinyl hose from the bleeding nipple to the bottle. It is a good idea to replace all 4 nipples with new one. They are cheap and avoid problems in long run. Make sure to use at least DOT 4 brake fluid. Make sure to use a sealed bottle. The life of brake fluid in an open bottle is one week.

No need to have the car running. That just helps supply the vacuum to make them work better but has nothing to do with the basic brake setup.

It's a fairly quick fun job. Take your time have a buddy and lots of brake fluid and you can do as good a job as any shop. (no matter what they say ;-])

Honestly your guess is as good as mine. But I don't think the master cylinder is NOT bad you still have air in the system. Get a big bottle of brake fluid bleed all four sides until you run out of fluid or your brakes work properly. You should divide the bottle's content in four, then use each quantity in each side. You'll be removing air and contaminated fluid from the system. Get a small hose that fits on the bleeders and an appropriate container. I have a good feeling if you do this your brakes will work just fine. I don't know how you are bleeding the brakes. I'll let you know the proper way just in case. This is a two man job, with the wheel off, have someone start the car. Have them pump the brakes a few times to get pressure. 1With the brake pedal UP open the bleeder, 2then have your assistant press the brake pedal all the way down and leave it completely pressed down. 3Close the bleeder valve, once close and only with the valve closed have'm release the brake. Repeat as necessary, bake depressed, open valve first then press brake. DO NOT depress until valve completly closed. Close valve THEN depress. Good Luck!