Introduction

The brake fluid on your W123 is contained in a reservoir on top of the master cylinder. It's clear plastic to allow you to check the fluid level. It's not as easy as it may seem, however, due to the design of the reservoir. Check out this guide for the tips.

Here you see the clear plastic reservoir for your brake fluid in your W123. Take a look at it to see the level of the fluid and the color. If it is dark, consider flushing it out with new fluid. There is a guide for that on the main W123 device page. Take a close look at the front of the reservoir and you'll see the MAX mark. The fluid should not be above this line. If it is, you can extract a bit of fluid with a plastic syringe that you can get at your local auto store.
  • Here you see the clear plastic reservoir for your brake fluid in your W123. Take a look at it to see the level of the fluid and the color. If it is dark, consider flushing it out with new fluid. There is a guide for that on the main W123 device page.

  • Take a close look at the front of the reservoir and you'll see the MAX mark. The fluid should not be above this line. If it is, you can extract a bit of fluid with a plastic syringe that you can get at your local auto store.

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Here's the trick, though - standing up near the front of the car by the headlights you cannot see the back of the reservoir. The reservoir is designed with two chambers with a baffle between them. The fluid can be low in the rear chamber and you won't be able to see this from the front.
  • Here's the trick, though - standing up near the front of the car by the headlights you cannot see the back of the reservoir. The reservoir is designed with two chambers with a baffle between them. The fluid can be low in the rear chamber and you won't be able to see this from the front.

  • You'll need to stand at the side of the car near the front driver's side wheel

  • See here in this picture that the fluid on this car is almost at the MIN mark in the rear chamber. The chambers are reversed; the rear chamber is for the front brakes, and vice versa.

  • Note that brake systems do not run low on fluid unless there is a leak. A leak in the brake system is a safety issue. If you find that your brake fluid is low, find out why or ask a shop to check, and fix the issue just as soon as possible.

  • In the meantime the fluid can be topped off until it reaches the MAX mark. Use only DOT 3 or DOT 4 fluid to top if off.

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Conclusion

If you need to top the fluid off, be sure to clean around the reservoir cap if it's very dirty before unscrewing it.

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Nicolas Siemsen

Member since: 12/06/2013

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2 Comments

Personally, I never advise people to add brake fluid except in an emergency, and it needs to go to the shop if it needs fluid. Most cars are designed so that when the brake fluid levels drops it indicates worn brake pads or a hydraulic leak. Mercedes Benz recommends flushing the brake fluid every two years, ALL car manufacturers should do the same! Go with DOT 4 fluid too, it has a higher boiling point and better additive packages. Your guides are great BTW!

Bruce B - Reply

Very good point, Bruce! I should have been more clear that if the brake fluid is low, top it off to avoid it running out and letting air in, but be aware that it is NOT normal for brake fluid to drop like it might be normal for engine oil level to drop slightly between oil changes. I will update the guide with that warning.

Thanks for the compliment! They only get better when folks make constructive comments like yours. Thanks!

Nicolas Siemsen -

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