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Brake Master Cylinder and Reservoir Replacement
 
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Pelican Technical Article:

Brake Master Cylinder and Reservoir Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$180 to $350

Talent:

**

Tools:

13mm socket, 11mm flare-nut wrench, pliers

Applicable Models:

Porsche 944 (1983-89)
Porsche 944 S2 (1989-91)
Porsche 944 Turbo (1986-89)
Porsche 944S (1987-88)

Parts Required:

Master cylinder, brake fluid

Hot Tip:

Watch for spills

Performance Gain:

Better braking performance

Complementary Modification:

Check your brake pads

Without a doubt, your brakes are 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 and reservoir have 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 or reservoir, you should probably replace it.

Replacing the master cylinder on the Porsche 944 or 951 is not difficult. It is just a tight fit, but it should take no more than three hours including bleeding the brakes.

You are going to be working with brake fluid so it is important to remember is that brake fluid is toxic to humans and paint. Brake fluid spilled on paint will permanently mar the surface, so be very careful not to touch the car if you have it on your hands and clothing. If you do get a spot on your paint, make sure that you blot it with a paper towel. Don't wipe or smear it. Then quickly rinse it with plenty of water. It's also important not to try to clean it off with any chemical or other cleaning solutions. Always make sure you catch and dispose of the fluid in accordance with the regulations in your area.

When completed you must properly bleed the entire brake and clutch system! Do NOT attempt to drive the vehicle until you have properly bled the system.

Before you begin clean the area around the cap (red arrow).
Figure 1

Before you begin clean the area around the cap (red arrow). Even though you are removing the reservoir you do not want dirt and debris getting into the fluid and possibly the lines. This is especially true if you are replacing the master cylinder and going to be reusing the reservoir.

Remove the cap and check the condition of the gasket on the level sender (red arrow) and replace as needed.
Figure 2

Remove the cap and check the condition of the gasket on the level sender (red arrow) and replace as needed. Use a turkey baster or fluid pump to suck out all of the brake fluid you can.

Remove the supply line for the clutch hydraulics from the reservoir and set it aside (red arrow).
Figure 3

Remove the supply line for the clutch hydraulics from the reservoir and set it aside (red arrow). You do not need to disconnect it from the clutch master cylinder.

You can now simply pull the reservoir from the master cylinder with your hands.
Figure 4

You can now simply pull the reservoir from the master cylinder with your hands. The reservoir is held in place by two rubber grommets (red arrows) in the master so you may need to wiggle the reservoir while you pull it out.

If you are planning on reusing your reservoir make sure to check for cracks and splits, especially around the spigots and seams (red arrows).
Figure 5

If you are planning on reusing your reservoir make sure to check for cracks and splits, especially around the spigots and seams (red arrows).

When removing brake lines you should use the proper tool, which is an 11mm flare-nut wrench that fully wraps around the brake line nut.
Figure 6

When removing brake lines you should use the proper tool, which is an 11mm flare-nut wrench that fully wraps around the brake line nut. If you use a standard wrench, there is a high chance of rounding off the corners and permanently damaging the hard brake lines. These fittings are not very strong and will become stripped if you don't use one of these wrenches.

Use the 11mm flared nut wrench and remove the three brake lines (red arrows).
Figure 7

Use the 11mm flared nut wrench and remove the three brake lines (red arrows). When you are reinstalling them always start threading them by hand until they are well seated. These have a tendency to cross thread and strip easily so take your time and make sure you are doing it correctly.

Using a 13mm socket, remove the two mounting nuts (red arrows).
Figure 8

Using a 13mm socket, remove the two mounting nuts (red arrows).

You can now pull the master cylinder out from the brake booster.
Figure 9

You can now pull the master cylinder out from the brake booster.

Whether you are reinstalling your master cylinder or installing a new one, always make sure you replace the gasket between the master cylinder and brake booster (red arrow).
Figure 10

Whether you are reinstalling your master cylinder or installing a new one, always make sure you replace the gasket between the master cylinder and brake booster (red arrow). Note: your new master cylinder should come with a new gasket.

If you are replacing the master cylinder the new one will come with new grommets already installed (yellow arrows).
Figure 11

If you are replacing the master cylinder the new one will come with new grommets already installed (yellow arrows). It helps to put a little clean brake fluid on the reservoir when seating it in the new master cylinder. Swap over the proportioning valve to your new master cylinder (red arrow).

Now is a good time to check the condition of the brake booster.
Figure 12

Now is a good time to check the condition of the brake booster. This one has some damage from spilled brake fluid but nothing a little sandpaper and paint can't fix. Just make sure to tape off everything well, as you don't want paint getting in the booster or brake lines.

You will now need to completely bleed the brake and clutch system.
Figure 13

You will now need to completely bleed the brake and clutch system. Please see our article on how to bleed your brakes and clutch slave cylinder bleeding for further assistance. Do NOT attempt to drive the vehicle until you have properly bled the system.


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