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Pelican Technical Article:

Brake Line Replacement

Steve Vernon

Time:

4 hours4 hrs

Tab:

$10 to $100

Talent:

**

Tools:

11mm wrench and flare-nut wrench, 17mm, 14mm wrench, flathead screwdriver

Applicable Models:

Mercedes-Benz W124 (1986-95)

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:

Rebuild calipers, replace brake pads, flush brake system, replace master cylinder

One of the most popular projects for the W124 is the replacement of the flexible brake lines that connect the hard line from the chassis of the car to the brake calipers. These 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 strange characteristics, such as 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.

Faulty brake lines in the front of your vehicle can cause all sorts of steering problems when braking. It is common for bad hoses to cause a car to dart from side to side when braking. Bad hoses allow pressure to build up in the caliper, but sometimes do not release this pressure properly when the pedal is depressed.

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 each side of the car, as this will make it much easier to access the brake lines. 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 basically 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 use only one of these wrenches, as it is very easy to damage the fittings using a regular crescent wrench.

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.

The rubber brake lines (red arrow) connect the hard line from the ABS pump to the caliper and are often responsible for poor brake performance.
Figure 1

The rubber brake lines (red arrow) connect the hard line from the ABS pump to the caliper and are often responsible for poor brake performance. As the car ages, the rubber begins to break down and can clog the lines, leading to very little pressure getting to the calipers. The brake lines should be renewed if they are old or if you are having problems with your brakes.

A required tool is an 11mm flare-nut wrench (red arrow) that fully wraps around the brake line.
Figure 2

A required tool is an 11mm flare-nut wrench (red arrow) that fully wraps around the brake line. If you use a standard wrench, then there is a high chance of rounding off the corners and permanently damaging the hard brake lines.

The flexible rubber line connects to the hard line (yellow arrow) and then runs down to the caliper (red arrow).
Figure 3

The flexible rubber line connects to the hard line (yellow arrow) and then runs down to the caliper (red arrow).

Separate the hard line connection by using an 11 mm flared nut wrench on the hard line connection (red arrow) and a 17mm wrench holding the rubber line (yellow arrow).
Figure 4

Separate the hard line connection by using an 11 mm flared nut wrench on the hard line connection (red arrow) and a 17mm wrench holding the rubber line (yellow arrow). The rubber line should be held firmly in place by the connection but put a 17mm wrench on it just to be sure. These fittings are not very strong and will become stripped if you don't use a flared nut wrench. 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. Be careful when you are removing this fitting to make sure that you are not twisting the line.

This photo illustrates the end of the hard line.
Figure 5

This photo illustrates the end of the hard line. You can see the flare on the end of the line (yellow arrow) that fits into the rubber line. The connection nut (red arrow) is made of a soft metal and can be stripped easily. If the nut strips it cannot be replaced separately so take your time and use a flared nut wrench. Never use any form of Teflon tape or Loctite on the connections.

The rubber flexible line connects to the top rear of the caliper.
Figure 6

The rubber flexible line connects to the top rear of the caliper. Use a 14mm wrench and remove the line (red arrow). It is much easier to remove the connection to the hard line first as the line will twist and bind if you try and remove it from the caliper while still attached to the hard line. The rear lines are the same connections as the front. Removal is similar. Installation is the reverse of removal. You must fully bleed the brake system before driving the car.

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Comments and Suggestions:
oldtrucker Comments: When I purchased a used 95 W124 and inspected the flex lines, I found that they were installed in such a way that they rubbed against the tire. It is important to install them, so that the line is away from the tire. There is a I call it star mounting template near the strut since the lines may be shaped to push them outwards. You'll have to turn the line until it faces backward and then secure the hex into the template. Also, there is a clip to place tension onto the line, pulling it into the star template. They may have to be replaced too. Check for clearance between the tire, after the vehicle is back on it's feet.
June 9, 2015
  Followup from the Pelican Staff: Thanks for sharing your installation process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
 

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