Mercedes W123 Brake Reservoir Rubber Seals Replacement Repair Guide

Difficulty

Moderate

Steps

Time Required

                          30 minutes

Sections

Brake Reservoir Rubber Seals
13 steps

Flags

BackMercedes W123
Full Screen
Options
History
Save to Favorites
Download PDF
Edit
Translate
Get Shareable Link
Embed This Guide
Notify Me of Changes
Stop Notifications

Introduction

What you need

Step 1

              Brake Reservoir Rubber Seals

There are a total of four rubber seals that help to keep brake fluid inside of your reservoir during use. When the rubber ages, it can crack, and harden leading to the potential for leaks.
The first pair of seals cover the brake fluid sensor floats. They can be easily seen on top of the reservoir. These are very visibly cracked.
The second set of seals, also called plugs, seal the area where the reservoir enters the master cylinder.
The reservoir is not under pressure when using the brakes so these seals can be in pretty rough shape and still work OK. However, if you bleed your brakes using a pressure bleeder you may find fluid shooting out! That will hint at a good time to change them…

There are a total of four rubber seals that help to keep brake fluid inside of your reservoir during use. When the rubber ages, it can crack, and harden leading to the potential for leaks.

The first pair of seals cover the brake fluid sensor floats. They can be easily seen on top of the reservoir. These are very visibly cracked.

The second set of seals, also called plugs, seal the area where the reservoir enters the master cylinder.

The reservoir is not under pressure when using the brakes so these seals can be in pretty rough shape and still work OK. However, if you bleed your brakes using a pressure bleeder you may find fluid shooting out! That will hint at a good time to change them…

1024

Step 2

Begin by draining the brake fluid from the system.
You will need to jack up the car, and remove the wheels. See the W123 guide page for help with both of these topics.
Now you can open the bleeder on each caliper to let the fluid drain in to an appropriate drip pan. It will take a while as it will drain slowly. Let it drain until it is barely dripping and the reservoir is empty.

Begin by draining the brake fluid from the system.

You will need to jack up the car, and remove the wheels. See the W123 guide page for help with both of these topics.

Now you can open the bleeder on each caliper to let the fluid drain in to an appropriate drip pan. It will take a while as it will drain slowly. Let it drain until it is barely dripping and the reservoir is empty.

Step 3

Now you can proceed to remove the reservoir. Start by unplugging the two sensor wires from each of the two floats.

Now you can proceed to remove the reservoir. Start by unplugging the two sensor wires from each of the two floats.

Step 4

With the sensor plugs disconnected you can simply pull the reservoir out of the master cylinder. Pull straight up. It may take some force. You will have a bit of brake fluid drip and splash at this point - have a bit of water ready to rinse it off the painted surfaces underneath.

With the sensor plugs disconnected you can simply pull the reservoir out of the master cylinder. Pull straight up. It may take some force. You will have a bit of brake fluid drip and splash at this point - have a bit of water ready to rinse it off the painted surfaces underneath.

Step 5

With the reservoir free you can pull the seals off the sensor floats. They should pull off with just some prying with your fingers.
See the second and third picture to get a good view of the condition of these seals once pulled. You can see for yourself why these were leaking!

With the reservoir free you can pull the seals off the sensor floats. They should pull off with just some prying with your fingers.

See the second and third picture to get a good view of the condition of these seals once pulled. You can see for yourself why these were leaking!

Step 6

Lightly coat the new seals with some brake cylinder grease (not brake pad grease!!) or some clean brake fluid.
Push the new seals on over the floats until they seat firmly in place.

Lightly coat the new seals with some brake cylinder grease (not brake pad grease!!) or some clean brake fluid.

Push the new seals on over the floats until they seat firmly in place.

Step 7

Now it’s time to replace the plugs on the master cylinder. You can get an idea here of their condition - they are pretty rough.
These seals should also simply pull out by hand.

Now it’s time to replace the plugs on the master cylinder. You can get an idea here of their condition - they are pretty rough.

These seals should also simply pull out by hand.

Step 8

In this picture the front plug has been removed. Proceed to carefully clean around this area with a shop towel. Do not allow dirt to enter the master cylinder - clean so that the dirt goes out, not in.

In this picture the front plug has been removed. Proceed to carefully clean around this area with a shop towel. Do not allow dirt to enter the master cylinder - clean so that the dirt goes out, not in.

Step 9

Coat these plugs with some brake cylinder grease, or brake fluid, and push them in. A wide flat blade screw driver used gently can help push the seals in.
You can see in this picture both new plugs installed.

Coat these plugs with some brake cylinder grease, or brake fluid, and push them in. A wide flat blade screw driver used gently can help push the seals in.

You can see in this picture both new plugs installed.

Step 10

Now you can push the brake reservoir in to the front plug opening. Do this with the reservoir at an angle from the master cylinder.

Now you can push the brake reservoir in to the front plug opening. Do this with the reservoir at an angle from the master cylinder.

Step 11

Once the front of the reservoir is inserted you can rotate the rear end in to place and push it in to the plug.

Once the front of the reservoir is inserted you can rotate the rear end in to place and push it in to the plug.

Step 12

Your brake fluid reservoir is now ready to go, except for the plug connections. Re-install them.

Your brake fluid reservoir is now ready to go, except for the plug connections. Re-install them.

Step 13

Re-fill your brake reservoir with clean DOT4 brake fluid.
Then, proceed to bleed your brakes using the pressure bleed method. You can click here for a guide on this process.

Re-fill your brake reservoir with clean DOT4 brake fluid.

Then, proceed to bleed your brakes using the pressure bleed method. You can click here for a guide on this process.

After your first drive check for leaks.

Cancel: I did not complete this guide.

                                                                                      9 other people completed this guide.

Author

                                      with 3 other contributors

                    Nicolas Siemsen

Member since: 12/06/2013

38,128 Reputation

                                      79 Guides authored                  



                       Badges:
                       30







                                                        +27 more badges

Team

                       Master Techs                        

                                                  Member of Master Techs 



                    Community                     


                                            310 Members                     


                                            1,168 Guides authored

Introduction#

What you need#

Team#

Introduction

What you need

Team