One of the most popular projects for the Mercedes-Benz is the replacement of the flexible brake lines that connect from the main 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 Mercedes-Benz 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 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 first step in replacing your lines is to elevate the car. 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.
Now it's time to disconnect the brake lines. Make sure that you have some paper towels handy, as there will be some brake fluid that will leak out of the lines. Brake fluid is perhaps the most dangerous fluid to your car, as any amount spilled on the paint will permanently mar it. If you do get some on the paint, make sure that you blot it and don't wipe it off. Be aware that your hands may contain some brake fluid; don't even touch anything near the paint on the car with your hands.
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 open 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 you do damage the hard line or strip the fitting, then the replacement line might be a special order part that will have to be shipped in from Germany. You can usually find the correct length line at your local auto parts store, but then you will have to bend it into shape, and most of the time, this is a very difficult process that requires a few special tools. The moral of this story is that you should use the right tool for the job (the flare-nut wrench).
After you have disconnected the hard metal line, you can now remove the flexible lines from the car. It is best to remove the line where it joins the hard metal line first, and then remove the line from where it joins the caliper. If you attempt to remove the line from the caliper on this car first it will twist up and bind, and make the job a lot harder and messier than it needs to be.
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 you turn full right or left or your car goes over a bump, it may stretch and break the line.
When it comes to replacing brake lines, many people install stainless steel braided lines on their car. The rumor has it that the stainless steel sheath keeps the rubber line from expanding under pressure and actually delivers better performance than do the standard lines. While this reasoning sounds good at first, it's mostly hype. The stainless steel braided lines are often made of the same rubber underneath and are simply protected by the outside sheath. Even if the sheath were tight enough and strong enough to prevent the lines from expanding, it really wouldn't make a difference in braking. Even if the lines expand a little, the resulting pressure that is exerted at the caliper will be almost the same.
Regardless of the rumor mill, I will recommend that you place the stainless steel lines on your car because the outside sheath protects the lines from dirt, grime, rocks, small animals, and other things you might run over with your car. The stock lines already have a metal "spring" that insulates them, so the gain is minimal.
The other thing that might warrant your consideration is the label of DOT (Department of Transportation) certification. With the original rubber lines, they were required to be certified under a certain set of specifications dictated by the DOT for use on U.S. highways. Often, the stainless steel lines are aftermarket components that are not DOT certified and are subsequently listed for "off-road use only" we recommend these line only be used on the track and not on public roads. Pelican Parts does sell a complete line of DOT certified stainless steel lines.
After you replace your brake lines you MUST bleed the brakes. Please see our article on brake bleeding. DO NOT attempt to drive the vehicle before properly bleeding your brakes.
The rubber brake lines 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. The red arrow points to the flexible brake line on the front of the car that needs to be replaced. The yellow arrows point to the fittings on the hard brake lines that need to be released using a 14mm flare-nut wrench.
This is the front of the 190. You can see where the line connects with the hard brake line (green arrow) and the caliper (yellow arrow). You need to support the rubber line end with a 14mm wrench while removing the hard line with an 11mm flare-nut wrench. The line into the caliper is removed with a 14mm flare-nut wrench.
This is the back of the 190e. You can see where the line connects with the hard brake line (green arrow) and the caliper (yellow arrow). You need to support the rubber line end with a 14mm wrench while removing the hard line with an 11mm flare-nut wrench. The line into the caliper is removed with a 14mm flare-nut wrench. Have a bucket or drain pan ready to catch any fluid that will spill as it is very toxic (red arrow).