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Brake Booster Replacement
 
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Pelican Technical Article:

Brake Booster Replacement

Steve Vernon

Time:

4 hours4 hrs

Tab:

$325 to $650

Talent:

***

Tools:

19mm, 13mm wrench, 13mm socket and extensions, flat head screwdriver, pliers

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Brake Booster

Hot Tip:

Use paper towels and plastic bags to contain any fluid leaks

Performance Gain:

Better braking

Complementary Modification:

Replace master cylinder

Without a doubt, your brakes are one of the most important systems on the car. While brake boosters do not often fail, when they do, you must replace them as there is no way to repair it. If you have been "topping up" the fluid level in the reservoir and cannot find where the fluid has been going there is a good chance that it has been leaking out the back of the master cylinder and into the brake booster.

Replacing the brake booster on the Mercedes W123 is not difficult, it is just a tight fit. It should take no more than four hours including bleeding the brakes. While you can replace the booster without draining the brake fluid by leaving the master cylinder and reservoir intact, I recommend removing both as there is a gasket on the rear of the master that you must replace. Plus if you are replacing the booster now is a really good time to flush and bleed your brake system. You will also need to remove the kick panels to get access to the pedal box.

If you open the brake lines, when you are finished you will need to completely bleed the brakes. DO NOT drive the car without completely bleeding the brakes

While it is possible to remove the brake booster (red arrow) while leaving the master cylinder and reservoir together (yellow arrow) I recommend splitting them so you can give everything a good inspection and cleaning.
Figure 1

While it is possible to remove the brake booster (red arrow) while leaving the master cylinder and reservoir together (yellow arrow) I recommend splitting them so you can give everything a good inspection and cleaning. Please see our article on master cylinder replacement for additional assistance. In this article I split and remove them this does mean that you will need to bleed the system when you reinstall everything

Whether or not you choose to separate the reservoir and master cylinder you need to replace the O-ring on the rear of the master cylinder (red arrow).
Figure 2

Whether or not you choose to separate the reservoir and master cylinder you need to replace the O-ring on the rear of the master cylinder (red arrow). This O-ring creates the vacuum seal between the master and booster.

To remove master from the booster use a 13mm wrench and remove the two nuts (red arrows) and slide the master forward and off the booster.
Figure 3

To remove master from the booster use a 13mm wrench and remove the two nuts (red arrows) and slide the master forward and off the booster.

Now is a really good time to clean up any spilled fluid, dirt and debris under the booster (red arrow).
Figure 4

Now is a really good time to clean up any spilled fluid, dirt and debris under the booster (red arrow).

Use a 19mm wrench and separate the vacuum line from the booster (red arrow).
Figure 5

Use a 19mm wrench and separate the vacuum line from the booster (red arrow). Use care as the line is plastic and gets brittle over the years.

Move to the interior of the vehicle and remove the under dash panel; please see our article on under dash panel removal for further instruction.
Figure 6

Move to the interior of the vehicle and remove the under dash panel; please see our article on under dash panel removal for further instruction.

Follow the brake pedal up to where it meets the shaft for the booster.
Figure 7

Follow the brake pedal up to where it meets the shaft for the booster. You are going to use a set of pliers or a flathead screwdriver to remove the retaining clip (red arrow). This is a really tight area to work, so you may want to remove the front seat so you can lie on your back while doing this remember to take your time and have some patience. Once the clip is out, push the retaining bolt out from the shaft and separate the shafts.

Remove the four 13mm nuts holding the booster to the firewall.
Figure 8

Remove the four 13mm nuts holding the booster to the firewall. Again, this is a really tight area to work. Get comfortable and use a series of extensions and universals and you will get all four off. Once all four nuts are off move back to the engine compartment and simple remove the booster.

Installation is the reverse of removal.
Figure 9

Installation is the reverse of removal. Make sure to install the gasket between the booster and firewall as well as when reinstalling the master cylinder it must sit over the rod inside the booster (red arrow).

If you have opened any brake lines or separated the reservoir and master cylinder you will need to completely bleed the brakes.
Figure 10

If you have opened any brake lines or separated the reservoir and master cylinder you will need to completely bleed the brakes. DO NOT drive the car without completely bleeding the brakes. Please see our article on brake bleeding including using the Motive Power Bleeder which makes it quick and simple.

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