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Pelican Technical Article:

Replacing Brake Hoses

Time:

1 hour1 hr

Tab:

$50

Talent:

**

Tools:

set of flare nut wrenches

Applicable Models:

Mercedes-Benz W210 (1996-03)

Parts Required:

New brake Lines

Hot Tip:

Make sure you have a drain pan

Performance Gain:

Safer brake hydraulics

Complementary Modification:

Flush out brake fluid

The brake lines in your car should be inspected every time you service your brakes and/or change your tires.

Some facts about brake hoses:

  • The industry standard average safety life of a brake hose is six years.
  • Brake hoses deteriorate from the inside as well as the outside.
  • Moisture is absorbed into brake fluid systems through brake hoses.
  • Contaminants in brake fluid act abrasively on the inner wall of brake hoses.
  • The brake hose reinforcing fabric deteriorates though expansion and moisture.
  • High operating temperatures contribute to the deterioration of hoses.
  • Brake hoses swell with age and restrict flow.

Generally, all brake hoses on a vehicle deteriorate at the same rate, so all hoses should be replaced if one is found to be faulty.

Additionally, brake hoses can fail in one of three ways,

Rupture: (burst hose) = due to age, too many miles or an impact are the typical cause.

Partial Internal Collapse = The inner ply becomes damaged/detached acting as a partial restriction and/or one way valve.

Full Internal Blockage = The inner ply becomes damaged/detached acting as a plug; the brake pedal still feels good but there is no brake application.

These rubber lines can break down and corrode over many years of normal use. Eventually, a brake line can fail by bursting open, although there will usually be a tell-tale sign, such as blistering or cracking. If a line does burst while you are driving, you will lose all the pressure in one-half of your braking system.

Faulty brake lines in the front of your car can also cause steering problems when braking. It is common for bad hoses to cause a car to dart from side to side to 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 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 only use a flare-nut wrench for this job, as it is very easy to damage the fittings using a regular crescent 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. If the fitting is corroded, spray it with a good penetrant spray for a few days prior to removing the fitting. I've had stellar results with Aero-Kroil in the past to loosen up corroded fittings.

Installation of the new lines is straightforward, and the easy part of the job. Before you start attaching the lines, make sure that you have the correct ones for your car. There are a few different types, and a few different lengths, so make sure that the ones that you are putting on are the same length and have the same fittings as the ones that you are removing. If the line you install is too short, then when your car goes over a bump, it may stretch and break the line.

After the lines are installed, you'll need to bleed your brakes to remove the extra air you introduced into the system by removing the old lines. Please see our article of bleeding brakes for more info.

Here is a set of new OEM brake lines for the Mercedes W210 Chassis.
Figure 1

Here is a set of new OEM brake lines for the Mercedes W210 Chassis.

Shown here is a rear rubber brake line on our project car.
Figure 2

Shown here is a rear rubber brake line on our project car. Over time, the rubber can dry out and start to crack, eventually causing the hose to burst. In this article, I will go over the steps involved with replacing the lines.

Use an 11mm flare nut wrench to loosen the top connection of the brake line to the hard metal line.
Figure 3

Use an 11mm flare nut wrench to loosen the top connection of the brake line to the hard metal line. The line itself has a pin cast into the underside of the crimped fitting to center it inside the sheet metal. Make sure you have a drip tray under this connection as it will start leaking brake fluid.

On the caliper side, use a 14mm flare-nut wrench to loosen the connection.
Figure 4

On the caliper side, use a 14mm flare-nut wrench to loosen the connection. Once it its loose enough, you can thread out the old brake line by hand. Like before, make sure you have a drain pan underneath to catch the fluid that leaks out.

Shown here is the compression fitting on the end of the metal brake line.
Figure 5

Shown here is the compression fitting on the end of the metal brake line. It's important to keep this fitting clean before installing the new line. Also, make sure that the new line threads into the fitting correctly. It is very easy to thread this fitting in the wrong way and strip the threads. Take your time and thread it in by hand. If you feel any resistance, stop, back the line out and try again.

Thread the new line into the caliper first and tighten it down with the 14mm flare-nut wrench.
Figure 6

Thread the new line into the caliper first and tighten it down with the 14mm flare-nut wrench. Then connect it up at the metal line. The new lines may or may not have the centering pin cast into the crimped fitting. Ours didn't, which means you need to counterhold the new line while you tighten the 11mm fitting on top.

Shown here is the new line installed on the car.
Figure 7

Shown here is the new line installed on the car. Now all that's left to do is bleed the brakes and you're rolling again.

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Comments and Suggestions:
dave Comments: on my new lines the large end that connects to the metal line does not have a locating point which sits inside the metal pipe when connected together. does this matter as my garage says it does and they will not install these lines because there will be possible fluid leakage. the supplier says the lines are ok and will work please help as this has been going on for 3 weeks now and i need the car.
October 6, 2012
  Followup from the Pelican Staff: I am confused by this question.
The lines are self aligning metric Bubble flare.

If they are talking about the body front brake hose mounting point, many aftermarket hoses have a smaller external hex size that does not lock firmly into the mounting/orientation bracket.

This can allow them to (over years) vibrate, damaging the steel line or mounting tab.

I prefer the correct MB hoses on my personal vehicles, but have used thousands of the aftermarket hoses at owner request due to cost..

Your options; If the shop refuses to install the parts:
* You can buy the correct MB part.
* Have the car moved to another shop.
* Install the parts yourself.

roy@pelicanparts.com

- whunter
 

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