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Did you know that brake fluid is hygroscopic? In short, this means it literally draws in water from the surrounding environment.This leads to the potential for corrosion in your car's brake system if you leave the brake fluid for too long. It's a good practice to change it every other year.The way to do this is to flush the old fluid out of the system using fresh fluid. When you've finished with the flush the system will be full of new fluid.The process is basically the same for bleeding the system after you perform some work that opens the brake system to air, such as replacing a brake line. The system must be free of air to work properly so you will need to remove it by bleeding the system.Please keep in mind that brake fluid is corrosive to paint so try to keep it from getting on your car's paint. Be sure to rinse it off if any does land on your paint.Also, always remember to wear gloves and glasses and any other protective equipment you feel will help keep you protected when working with automotive fluids as most are toxic or caustic to some degree. In the same vein, always remember to catch the fluid in an appropriate container and to dispose of it properly. Your city, county or other jurisdiction can help identify the best way to dispose of it.

  1. Mercedes W123 Brake Fluid Flush/Bleeding, Preparing the power bleeder: adım 1, 1 resimden 1.
    • Begin by filling your power bleeder with a bottle, or two, of brake fluid.

  2. Mercedes W123 Brake Fluid Flush/Bleeding: adım 2, 1 resimden 1.
    • Secure the top on the power bleeder.

    • Then put the cap on the end of the hose securely on to your brake fluid reservoir opening.

  3. Mercedes W123 Brake Fluid Flush/Bleeding: adım 3, 3 resimden 1. Mercedes W123 Brake Fluid Flush/Bleeding: adım 3, 3 resimden 2. Mercedes W123 Brake Fluid Flush/Bleeding: adım 3, 3 resimden 3.
    • Pump up the power bleeder. It may take a little while, especially if you've drained the system to replace hoses or something similar. Keep an eye on the gauge. It doesn't take a lot of pressure, just 5 to 10 psi.

    • Keep an eye around your brake fluid reservoir for leaks as you pump up the brake bleeder. The reservoir is not usually under pressure during use so leaks may show up where they hadn't before, especially in these two locations:

    • The sensor float caps on top of the reservoir

    • The rubber seals between the reservoir on the master cylinder

    • If you discover a leak you may need to stop the bleeding process to replace these bad seals. Or, alternately, try a method of brake bleeding that does no use a pressure bleeder. You will need to research these methods elsewhere.

  4. Mercedes W123 Brake Fluid Flush/Bleeding, Using the bleeders: adım 4, 2 resimden 1. Mercedes W123 Brake Fluid Flush/Bleeding, Using the bleeders: adım 4, 2 resimden 2.
    • Find the bleed screw and nipple on the first wheel you'll want to bleed.

    • Shown here are the bleed screws from the front, in red, and the rear, in green.

    • When flushing or bleeding your system, always start as far from the front of the car as possible. You should bleed your car in this sequence:

    • Rear passenger side

    • Rear driver's side

    • Front passenger side

    • Front driver's side

  5. Mercedes W123 Brake Fluid Flush/Bleeding: adım 5, 1 resimden 1.
    • While it's possible to bleed your brakes with the wheels on the car, it's easier with the wheels off and it's definitely easier to show the process...

    • The next step is to slip your 9mm wrench over the bleed screw.

    • Then put the open end of your plastic hose on the nipple. The other should be secured inside your catch container. Any type of bottle will work well...

  6. Mercedes W123 Brake Fluid Flush/Bleeding: adım 6, 1 resimden 1.
    • Now open the bleed screw and watch as fluid begins to flow.

    • If you're flushing the system leave the line open until you see fresh fluid coming out. Tip - buy fluid a different color than that currently in your car. Doing so makes it very easy to tell when the fresh fluid reaches the end of the line.

    • If you're bleeding your system you'll want to leave the nipple open until you no longer see any air bubbles at all coming out of the bleed nipple.

    • Repeat steps 5 and 6 on all four wheels using the sequence noted in step 4. It's recommended to go through the entire sequence twice.

    • Be sure to keep an eye on the power bleeder during this process. Do not let it de-pressurize or run dry; either can allow air to enter the system and you'll need to start bleeding all over.

  7. Mercedes W123 Brake Fluid Flush/Bleeding, Correcting the fluid level: adım 7, 2 resimden 1. Mercedes W123 Brake Fluid Flush/Bleeding, Correcting the fluid level: adım 7, 2 resimden 2.
    • Once you've finished bleeding, remove the power bleeder, being careful not to let the hose drip on your car's paint.

    • At this time your brake reservoir will be over-filled with brake fluid. It may actually spill over slightly when you remove the power bleeder. Wipe this up right away with a shop towel or rag.

    • You'll now want to remove the excess fluid with a suction device. A turkey baster can be used, as long as you make sure to never use it in the kitchen again!

    • Before you can insert the suction device, you'll need to lift out the screen in the fill neck of the brake fluid reservoir.

    • Remove just enough fluid to get it down just below the "MAX" line.

  8. Mercedes W123 Brake Fluid Flush/Bleeding: adım 8, 1 resimden 1.
    • Close up the reservoir. Wipe up any brake fluid that dripped. Check all four bleed screws for any leaks and tighten if needed.

    • Take the car for a test drive. Go slowly at first. If the pedal feels soft or the brakes do not respond, stop the test drive, return to your work area and re-bleed.

    • If the test drive goes well, do another check for leaks when you return.

  9. Mercedes W123 Brake Fluid Flush/Bleeding, Success!: adım 9, 1 resimden 1.
    • Don't let that bottle of brake fluid sit around long - in this bottle, it looks pretty refreshing! And there's a convenient straw....


When finished, go for a careful test drive and then check for leaks.

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Nicolas Siemsen

Üyelik tarihi: 06-12-2013

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Hello - I'm going to be flushing/bleeding the brakes on my W123 soon. What is the diameter of the plastic hose that's attached to the wine bottle? Does it have to be a specific diameter to fit over the bleed screws? Thanks!

Sinan - Yanıt

Hi there, I used some spare vinyl hose I had on hand already and I don't quite remember what size it is. However, this type of hose is rather flexible so going for a smaller size rather than larger would be a good idea - it can stretch to fit over the bleed screw. If I had to guess, I'd say a 1/4 inch inner diameter hose would work OK. Also, you don't technically 'need' a hose on the bleed screw - you can instead just let the fluid drain in to a wide mouth container of some kind. The hose just makes it easier to see when all the bubbles are gone and the fluid is running clear. Good luck!

Nicolas Siemsen -

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