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Pelican Technical Article:

Brake Master Cylinder Replacement

Jared Fenton

Time:

2 hours2 hrs

Tab:

$60

Talent:

****

Tools:

11mm flare nut wrench, 13mm socket, drain cup or glass, needle-nose pliers, brake bleeder, brake fluid

Applicable Models:

VW Jetta GL (1999-05)
VW Jetta GLS (1999-05)
VW Jetta Wolfsburg (1999)

Parts Required:

Master cylinder

Hot Tip:

Have a glass or cup on hand to catch brake fluid draining from the reservoir

Performance Gain:

Working brakes

Complementary Modification:

Flush old brake fluid from system

Without a doubt, your brakes are one of the most important systems on the car. The heart of the brake system is the master cylinder, which controls the hydraulic pressure of the entire system. Unfortunately, over many years, the master cylinder has a tendency to wear out and leak. The leakage can occur internally or externally, resulting in a weakened braking system. If you have any problems with your brakes, and you think that it's related to the master cylinder, you should probably replace it.

Replacing the master cylinder on the Mk4 Jetta is not very difficult and should take no more than two hours. The first step is to remove the air box for access. See our article on Intake Airbox Removal for more information.

You'll also want to try to get as much brake fluid as you can out of the fluid reservoir on top of the master cylinder. Open the cap on the reservoir and remove the strainer. Using a fluid pump or turkey baster, get as much of the old fluid out as you can. This helps prevent excessive spilling of brake fluid inside the engine compartment. It's also helpful to stuff a bunch of old rags or paper towels under the master cylinder to absorb any spills. Additionally, it helps to have a glass or cup directly below the fittings leading to the master cylinder. This helps to catch any remaining fluid.

Once the new master cylinder is installed, fill the master cylinder with new brake fluid and pump the pedal a few times to build up pressure. Do not pump the pedal without fluid in it. You could score and damage the inside of the cylinder bore, rendering it inoperable. The last step is to bleed the braking system of air. You'll have to bleed all of the brake lines at each wheel to get all of the air out of the system. See our article on Bleeding Brakes for more information.

In this article, I'll go over the steps involved with changing the master cylinder in your Mk4 Jetta.
Figure 1

In this article, I'll go over the steps involved with changing the master cylinder in your Mk4 Jetta. Replacement is easy once the intake airbox has been removed. See our article on Intake Airbox Removal for more information.

Press the tab on the electrical connector (green arrow) going to the fluid level sensor and pull the connector off.
Figure 2

Press the tab on the electrical connector (green arrow) going to the fluid level sensor and pull the connector off. At this point, you'll want to try and get as much fluid out of the reservoir as you can using either a fluid pump or turkey baster.

Note the fluid line connections on the left side of the master cylinder (green arrows).
Figure 3

Note the fluid line connections on the left side of the master cylinder (green arrows). These are 11mm fittings.

Use an 11mm flare nut wrench to loosen the fittings for both the front and rear braking circuits.
Figure 4

Use an 11mm flare nut wrench to loosen the fittings for both the front and rear braking circuits. Be prepared to have some fluid leak out.

It is a good idea to have a small glass or cup directly below the fittings to catch any residual fluid in the master cylinder.
Figure 5

It is a good idea to have a small glass or cup directly below the fittings to catch any residual fluid in the master cylinder.

Use a pair of pliers to carefully pull the clutch master cylinder feed line (green arrow) off the brake fluid reservoir.
Figure 6

Use a pair of pliers to carefully pull the clutch master cylinder feed line (green arrow) off the brake fluid reservoir.

Loosen and remove the 13mm nut (green arrow) securing the left side of the master cylinder to the brake booster.
Figure 7

Loosen and remove the 13mm nut (green arrow) securing the left side of the master cylinder to the brake booster.

Loosen and remove the 13mm nut (green arrow) securing the right side of the master cylinder to the brake booster.
Figure 8

Loosen and remove the 13mm nut (green arrow) securing the right side of the master cylinder to the brake booster. At this point, carefully maneuver the master cylinder out of the brake booster, around the brake line fittings and out of the engine bay.

Shown here is the master cylinder removed from the car.
Figure 9

Shown here is the master cylinder removed from the car. You'll need to transfer the reservoir from the old master cylinder to the new one. The reservoir is held in place with a plastic pin (green arrow).

Use a pair of needle-nose pliers to pull the retaining pin (green arrow) up and out of the master cylinder.
Figure 10

Use a pair of needle-nose pliers to pull the retaining pin (green arrow) up and out of the master cylinder.

Now pull the reservoir out of the old master cylinder.
Figure 11

Now pull the reservoir out of the old master cylinder. It is now ready to be transferred to the new master cylinder.

When fitting the new master cylinder, take care that the end of the mounting bore fits correctly over the drive piston (green arrow) in the brake booster.
Figure 12

When fitting the new master cylinder, take care that the end of the mounting bore fits correctly over the drive piston (green arrow) in the brake booster. At this point, you're ready to fill the system with fluid and bleed the system. See our article n Bleeding Brakes for more information.

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