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Pelican Technical Article:

Bleeding Brakes

Steve Vernon

Time:

2 hours2 hrs

Tab:

$10 to $40

Talent:

**

Applicable Models:

Porsche 944 Turbo (1986-89)

Parts Required:

3+ quarts of brake fluid

Hot Tip:

Use different-colored brake fluid so you know when your system is flushed

Performance Gain:

Quicker, firmer stopping

Complementary Modification:

Rebuild brake calipers

Bleeding brakes is a DIY project that should be part of your regularly scheduled maintenance. While it may seem like there is a bit of black magic involved with the bleeding process, it is really just a straightforward process of getting the air out from your brake system. The best strategy to follow when bleeding your brakes is to repeat the procedure several times in order to make sure that you have removed all the trapped air from the system.

The basic system can be bled using the traditional method. One method of properly bleeding the brakes uses two people and the other is to use a power or pressure bleeder. Pressure bleeding uses a reservoir of brake fluid that has a positive air pressure force placed on the opposite side of the fluid, which forces it into the brake system. This basically replicates someone constantly pressing down on the brake pedal without having to worry about air flowing back up through the bleed nipple.

The first step in bleeding your brakes is to jack up the car and remove all four wheels. Please see our article on safely raising and supporting your Porsche 944

Before you begin you will want to clean around the top of the reservoir (red arrow).
Figure 1

Before you begin you will want to clean around the top of the reservoir (red arrow). You do not want any dirt or debris getting into the brake fluid system.

Remove the cap with the level sensor and gasket (red arrow).
Figure 2

Remove the cap with the level sensor and gasket (red arrow). Inspect the gasket for wear, as it helps seal the system and replace it as needed. Set the cap off to the side where it cannot get dirty.

Next, fill the Motive Power Bleeder with two quarts of brake fluid, if you are flushing the system.
Figure 3

Next, fill the Motive Power Bleeder with two quarts of brake fluid, if you are flushing the system. Make sure that you check with your owner's manual and use the correct brake fluid. It is wise to start out with 2 quarts of brake fluid in the pressure bleeder and another quart on the shelf in reserve. Depending upon your car and the mistakes you may make, you may go through a lot of fluid, especially if this is your first time doing a brake bleed. Also, only use new brake fluid from a sealed can. Brake fluid is hydroscopic, meaning that it attracts water and water vapor, which diminishes its performance. Brake fluid containers left exposed to air will have the fluid inside compromised after a short period of time. There are a few little tricks that you can use when changing your brake fluid. It's a smart idea to fill the bleeder with a different-colored fluid and then bleed the brakes. When the new-colored fluid exits out of the caliper, you will know that you have fresh fluid in your system. Attach the bleeder to the top of the reservoir making sure it is tight; you do not want to have leaks when you are pressurizing the system (red arrow). Place the lid on the bleeder and use the hand pump on top to pressure the system to around 15 pounds; there is a scale on the front of the bleeder that shows the pressure (yellow arrow).

If you are flushing or bleeding the system you will want to start on the brake furthest from the reservoir, which is the right rear.
Figure 4

If you are flushing or bleeding the system you will want to start on the brake furthest from the reservoir, which is the right rear. The bleed nipples on the calipers are always on the top. If your bleed nipple is on the bottom someone has installed your caliper upside down. The front calipers on the 951 have two bleed nipples on each caliper (red arrows), one for each side.

Remove the protective cap on the nipple (green arrow).
Figure 5

Remove the protective cap on the nipple (green arrow). The nipples see a lot of weather and road grime over the years (yellow arrow), so you always want to use a flared nut wrench when working with them (red arrow). The flared nut wrench will grasp four sides of the nipple and help prevent stripping.

Attach a clear plastic hose to the nipple and have a catch bottle handy.
Figure 6

Attach a clear plastic hose to the nipple and have a catch bottle handy. You want to use a clear hose so that you can see bubbles in the fluid. With the system pressurized, open the bleed screw or nipple and watch the fluid flow into the catch bottle (red arrow). When the fluid changes to the new fluid color and there are no longer air bubbles in it, close off the nipple and move to the next one. Repeat the bleeding process at each corner. If you are using a pressure bleeder system, make sure that you often check the level of brake fluid in the bleeder reservoir so that it doesn't accidentally run dry. The pedal should now feel pretty stiff. If the pedal still feels spongy, you may need a new master cylinder, have a leaky caliper, or have old spongy flexible brake lines. You should flush and replace your brake fluid every two years. Deposits and debris can build up in the lines over time and decrease the efficiency of your brakes. Regular bleeding of your system can also help you spot brake problems that you wouldn't necessarily notice simply by driving the car. Also, never reuse brake fluid. Always use new, fresh fluid. In addition, don't use brake fluid that has come from an open can that has been sitting on the shelf or sitting in your Power Bleeder for a while. The brake fluid has a tendency to absorb moisture when sitting on the shelf. This moisture "boils" out of the brake fluid when you start using the brakes and can result in a spongy pedal.

If you are bleeding the brakes the old fashion way with one person working the brake pedal and one the caliper, it's very easy to forget to check your master cylinder reservoir. As you are removing fluid from the calipers, it will be emptying the master cylinder reservoir. If the reservoir goes empty you will have to start all over. Keep an eye on the fluid level and don't forget to refill it. Make sure that you always put the cap back on the reservoir. If the cap is off, then brake fluid may splash out and damage your paint when the brake pedal is released. Take care not to push the brake pedal all the way to the floor, as you can actually damage the master cylinder by driving the piston into an unused portion of the master cylinder and damaging the seals. Then open the bleeder valve on the right rear caliper. The system should lose pressure, and the pedal should sink to the floor. Open and close the valve, and then tell your family member to let their foot off of the pedal. Do not let them take their foot off until you have completely closed the valve, or it will suck air back into the system. Repeat this entire procedure at least three times on each caliper in the same order as described previously. I recommend that you use this procedure as a final step, even if you are pressure bleeding. The high force associated with the pressure from the brake pedal can help free air and debris in the system. If the brake fluid doesn't exit the nipple quickly, then you might have a clog in your lines. Brake fluid that simply oozes out of the bleed nipple slowly is a clear indication that your rubber lines might be clogged and constricted. Don't ignore these warning signs. Replace the brake lines while you are working in this area.



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Comments and Suggestions:
DJS Comments: Hi,

I used the suction method, and found that you should remove the little cup inside the reservoir opening. It restricts how fast the reservoir can be refilled so there is a real hazard of drawing the reservoir down too much. I found out the hard way.
August 18, 2016
  Followup from the Pelican Staff: Thanks for sharing your process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 

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