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Brake Bleeding and Flushing
 
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Pelican Technical Article:

Brake Bleeding and Flushing

Tom Morr

Time:

1 hour1 hr

Tab:

1 Liter of Brake Fluid ($12.25-$17.25

Tools:

Line wrenches, combination wrenches, ratchet/sockets

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Brake fluid

Hot Tip:

A pressure bleeder makes it a one-person job

Performance Gain:

Restores brake performance
One of the easiest, most reliable one-person bleeding systems is the vacuum-style Mityvac MV6830 bleeder, available from Pelican Parts (MVTC-001).
Figure 1

One of the easiest, most reliable one-person bleeding systems is the vacuum-style Mityvac MV6830 bleeder, available from Pelican Parts (MVTC-001). It can also be used to bleed hydraulic clutch cylinders.

Residual pressure in the brake booster normally dissipates when the car is shut off.
Figure 2

Residual pressure in the brake booster normally dissipates when the car is shut off. To make sure, gently pump the pedal a few times with the car off.

Removing old fluid from the master cylinder expedites flushing.
Figure 3

Removing old fluid from the master cylinder expedites flushing. A turkey baster, rags, and a cup are the traditional method. Higher-tech is using the Mityvac vacuum bleeder with its suction-tube attachment. Stirring the fluid with the tube helps dislodge sludge. Leave enough fluid in the bottom of the master cylinder so air won't enter the lines.

The Mityvac kit includes a fluid refill kit: various master cylinder plates and spouts that screw onto brake fluid bottles.
Figure 4

The Mityvac kit includes a fluid refill kit: various master cylinder plates and spouts that screw onto brake fluid bottles. This keeps the master cylinder topped up during bleeding. Alternately, check the level frequently to ensure that the master cylinder doesn't run dry.

The job can be done with the tires on the car.
Figure 5

The job can be done with the tires on the car. Raising and securing the car eases access to the bleeder screws. To guard against bleeder-screw stripping, spray the threads with penetrating spray.

Use a line wrench, box wrench, or socket to crack the bleeder
Figure 6

Use a line wrench, box wrench, or socket to crack the bleeder--open-end wrenches tend to round off bleeders' shoulders, creating more work. Begin with the right rear corner or the one that's farthest away from the master cylinder. (Our left rear was the most photogenic.)

Various-sized bleeder boots are included in the Mityvac kit.
Figure 7

Various-sized bleeder boots are included in the Mityvac kit. Select the one that fits snuggest and install it on the vacuum hose's barbed end. Then crack the bleeder screw a half turn or more with an open-end wrench. The Mityvac unit has a throttle on its handle that turns air pressure from a compressor into vacuum force. The kit also includes a hook for hanging the reservoir.

Bleed until fresh fluid comes out.
Figure 8

Bleed until fresh fluid comes out. Mityvac's instructions list 20-30 seconds as typical bleeding time. Unlike manual bleeding, air bubbles will be visible in the hose throughout: Vacuum pressure sucks air through the bleeder screws' threads. If this is objectionable, Mityvac recommends coating the bleeder threads with silicone grease to form a seal. Once fresh fluid appears, close the bleeder screw and move to the next-farthest-away-from-the-master-cylinder caliper.

After bleeding, clean up any residual fluid.
Figure 9

After bleeding, clean up any residual fluid. Turn on the car, gently pump the brakes, and check for leaks. Then test-drive the car. If the pedal feels spongy or has excessive travel before the brakes grab, repeat the bleeding procedure.

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Comments and Suggestions:
Gman Comments: Does a spongy brake pedal indicate that new fluid and bleeding system is required? Car has not been driven in over 6 months. Will brake fluid seep out of system if no used regularly. In other words,does lack of use cause problems with brake systems?
May 7, 2016
  Followup from the Pelican Staff: Spongy pedal is more likely a faulty master cylinder, brake line or a leak. - Nick at Pelican Parts  

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