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Vacuum Brake Booster Removal
 
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Pelican Technical Article:

Vacuum Brake Booster Removal

Tom Morr

Time:

2 hours2 hrs

Tab:

$400

Talent:

**

Tools:

Line wrenches, sockets, pliers, screwdriver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Replacement brake booster

Hot Tip:

Disconnect the brake pedal's return spring to safely remove and install the booster

Performance Gain:

Better braking

Complementary Modification:

Flush fluid in conjunction with bleeding

Brake problems are often messy. When brake lines are undone, corrosive brake fluid often seeps out and must be contained before it eats paint. Even brake pad changes are dusty and unfriendly to lungs, skin and eyes.

Knowing these brake facts, a blown vacuum booster might sound like a pain to replace. However, the ancillary operations are more involved than removing the booster itself. Please refer to the master cylinder removal article for details about the primary preliminary operation.

Also, the lower dash panel will have to be removed to access the pin that connects the booster to the brake pedal. I removed both the main knee-area lower panel piece and the flexible black one that covers the pedals for better photos (please see the dash-panel article for step-by-step details). Depending on your size and bodily flexibility, the pedal pin might be accessible by only removing the flexible rear panel piece.

Play it safe and gently pump the brake pedal with the engine off to help depressurize the booster. This will minimize the chance of the travel sensor sealing ring getting sucked into the booster.

Then disconnect the booster's wires and lines in the engine compartment. Pry out or unscrew the vacuum line. Also, a circlip/snap ring needs to be pried off in order to remove the diaphragm travel sensor. Circlip sizes can vary between Lucas and ITT/Ate boosters. Replacing the circlip is always recommended. Verify that the new circlip is the same size as the old one.

The wires can vary depending on optional equipment: specifically Brake Assist System (BAS) and Electronic Stability Program (ESP). In general, follow the wires coming out of the booster and unplug them at the BAS module or fuse box. New wiring pigtails should be attached to the replacement booster. If equipped, the BAS module bracket has nuts to the master cylinder mounting studs on the booster. Sliding the BAS off the bracket allows it to be moved out of the way. This makes the booster easier to lift out of the engine compartment.

Working under the dash, the booster needs to be disconnected from the brake pedal. Access is improved by removing the brake travel sensor (please see the dedicated article for details). Also, consider removing the pedal return spring. (I didn't and was rewarded with a black eye when the pedal sprung forward.) Pulling the retaining clip allows the pin to be removed, disconnecting the pedal's arm from the booster's fork. Two nuts secure the booster to the firewall. They're located at approximately 5:00 and 11:00, looking at the firewall from the interior.

The booster can then be carefully shimmied out. The brake lines at the ABS manifold might need to be flexed slightly to get the booster out. Replacement reverses the removal steps. The master cylinder should be bled after reassembly (please refer to our article on that process). The lines will also need to be bled at the calipers.

The torque spec for the brake booster mounting nuts is 20 Nm.

With the master cylinder removed and the brake lines plugged to keep out dirt, use a small flatblade screwdriver to pry off the circlip/snap ring (arrow) that secures the brake travel sensor to the booster.
Figure 1

With the master cylinder removed and the brake lines plugged to keep out dirt, use a small flatblade screwdriver to pry off the circlip/snap ring (arrow) that secures the brake travel sensor to the booster. Then the sensor can be slid out of the booster and set off to the side.

The vacuum line is disconnected.
Figure 2

The vacuum line is disconnected. If equipped with a BAS module (arrow), take it off the mounting bracket and disconnect its plug that leads to the booster. Then move the BAS module out of the way.

With the lower dash panel(s) removed, the booster can be disconnected from the brake pedal's arm.
Figure 3

With the lower dash panel(s) removed, the booster can be disconnected from the brake pedal's arm. Twisting the pedal sensor out of its mount (red arrow) creates better access to the lock clip (yellow arrow), which can be pulled with pliers. Unhooking the return spring (blue arrow) helps prevent facial assaults by the pedal. Pulling the pin (purple arrow) disconnects the booster from the pedal. Two nuts hold the booster on the firewall. One is at about 5:00 (green arrow). The other is at about 11:00 (not visible in this image).

The booster can be angled up and out of the engine compartment, being careful to not damage its boot as it passes through the hole in the firewall.
Figure 4

The booster can be angled up and out of the engine compartment, being careful to not damage its boot as it passes through the hole in the firewall.

Lucas and ITT/Ate are the two primary OE booster suppliers.
Figure 5

Lucas and ITT/Ate are the two primary OE booster suppliers. Port and plug configurations can vary depending on the car's options. The part number is normally visible from the engine compartment, making the proper replacement easy to identify.

The booster connects to the brake pedal with a pin, secured by a lock clip.
Figure 6

The booster connects to the brake pedal with a pin, secured by a lock clip. A rubber boot protects the booster between the pedal and firewall. A gasket (arrow) seals the booster against the firewall on the engine compartment side. Replacement is the reverse of the removal steps.

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Comments and Suggestions:
shark Comments: its tough getting under the dash board thanks for the help how much time does it take to remove brake booster do you need to remove switch under the dash i have 4 bolts brake booster mounting thanks again
August 26, 2015
  Followup from the Pelican Staff: Should take about two hours. You will have the remove the electrical components near the pedals or booster. Follow the steps in the article.- Nick at Pelican Parts  
shark Comments: tricks to remove...pin on brake booster
August 20, 2015
  Followup from the Pelican Staff: Did you remove the wire retainer on the left side? Once removed, wiggle the pedal to free the pin as you slide it out. - Nick at Pelican Parts  

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