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Flexible Brake Line Replacement
 
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Pelican Technical Article:

Flexible Brake Line Replacement

Steve Vernon

Time:

4 hours4 hrs

Tab:

$7 to $200

Talent:

**

Tools:

14mm, 11mm flare-nut wrench

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

New rubber or stainless steel brake lines

Hot Tip:

Make sure that corroded rubber from old lines didn't end up in your caliper

Performance Gain:

Better braking performance

Complementary Modification:

Bleed brake system

There are flexible brake lines or hoses that connect the hard lines from the master cylinder to the brake calipers. These lines are designed to be flexible to allow movement of the suspension and steering. The lines are made out of rubber and have a tendency to break down and corrode over many years. The rubber lines should be carefully inspected every 10,000 miles or so. They can exhibit signs of failure, such as damage from road debris, bubbling and expanding prior to actually bursting. Needless to say, failure of these lines is a very bad thing, as you will instantly lose pressure in one half of your brake system. The lines can also fail from the inside where broken down rubber can end up getting into the calipers.

Faulty brake lines in the front of your W123 can cause all sorts of steering problems when braking including causing a car to dart from side to side. Bad hoses allow pressure to build up in the caliper, but sometimes do not release this pressure properly when the pedal is released. This can lead to uneven wear of the pads and unsafe operating temperatures as the pad never comes off the rotor.

The first step in replacing your lines is to elevate the car. Please see our article on safely jacking up and supporting your vehicle. Remove the wheels from the car. To prevent a large amount of brake fluid from leaking out, I recommend pushing the brake pedal down just to the point of engagement and block it there. If you do this, you will lose less brake fluid, and also less air will enter into the system.

The brake lines themselves can be very difficult to remove. The goal of this job is to remove the lines without damaging anything else. In this case, the easiest thing to damage (besides your paint) is the hard steel brake lines that connect to the flexible rubber lines. These lines have relatively soft fittings on each end and often become deformed and stripped when removed. The key to success is to use a flare-nut wrench. This wrench is designed for jobs like this one where the fittings are soft and might be heavily corroded. The flared end of the wrench hugs the fitting and prevents it from stripping. It is very important to only use one of these wrenches, as it is very easy to damage the fittings using a regular crescent wrench.

NEVER put any sort of Teflon tape or Loctite on the threads or fitting. You must properly bleed the entire brake system after replacing your brake lines. Do NOT attempt to drive the vehicle until you have properly bled the system.

Front- The front brake hose (red arrow) connects the hard line (yellow arrow) to the caliper (green arrow, not shown).
Figure 1

Front- The front brake hose (red arrow) connects the hard line (yellow arrow) to the caliper (green arrow, not shown).

Front- You must remove the hard line fitting first as the line attached to the caliper needs to spin to remove or install it.
Figure 2

Front- You must remove the hard line fitting first as the line attached to the caliper needs to spin to remove or install it. There is a mount attached to the chassis (blue arrow) that supports the brake line connection. The hard line (red arrow) enters from the top and the fitting on this line is the only thing that should turn when loosening. The flexible hose line going to the caliper (yellow arrow) enters through the bottom and is held in place by corresponding notches in both the hose and mount. There is also a metal clip on top that holds everything still.

Front-A required tool for the hard line connection is an 11mm flare-nut wrench that fully wraps around the brake line nut.
Figure 3

Front-A required tool for the hard line connection is an 11mm flare-nut wrench that fully wraps around the brake line nut. If you use a standard wrench, then 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. The other disastrous thing that can happen is that the fitting can get stuck to the rest of the hard line. The fitting is supposed to turn and rotate on the end of the line, but sometimes it becomes too corroded to break free. When this happens, the fitting and the line will usually twist together, and it will break the line in half.

Front- Carefully clean around the fitting and place the flared nut wrench on the fitting and turn.
Figure 4

Front- Carefully clean around the fitting and place the flared nut wrench on the fitting and turn. Be careful when you are removing this fitting to make sure that you are not twisting the line. If the fitting is stuck try some penetrating oil. If you are going to be installing the new line at a later time make sure to cap the end of the hard line fitting.

Front- Remove the hose line from the bracket at the base of the strut and using a 14mm flared nut wrench remove the line from the caliper.
Figure 5

Front- Remove the hose line from the bracket at the base of the strut and using a 14mm flared nut wrench remove the line from the caliper. The line will need to spin to be removed and installed so you must remove this connection last and install it first. Installation is the reverse of removal. NEVER put any sort of Teflon tape or Loctite on the threads or fitting. You must properly bleed the entire brake system after replacing your brake lines. Do NOT attempt to drive the vehicle until you have properly bled the system.

Rear- The rear hoses are similar to the fronts.
Figure 6

Rear- The rear hoses are similar to the fronts. The hose (yellow arrow) attaches to the hard line (red arrow) and the caliper (blue arrow). You must remove the hard line connection first.

Rear- The 11mm fitting on the hard line (red arrow) is removed in the same manner as the front line.
Figure 7

Rear- The 11mm fitting on the hard line (red arrow) is removed in the same manner as the front line.

Rear- Use a 14mm flared nut wrench and remove the line form the caliper.
Figure 8

Rear- Use a 14mm flared nut wrench and remove the line form the caliper. The line will need to spin to be removed and installed so you must remove this connection last and install it first. Installation is the reverse of removal. NEVER put any sort of Teflon tape or Loctite on the threads or fitting. You must properly bleed the entire brake system after replacing your brake lines. Do NOT attempt to drive the vehicle until you have properly bled the system.

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