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Mercedes Benz Front Brake Pad Replacement
 
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Pelican Technical Article:

Mercedes Benz Front Brake Pad Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$50

Talent:

**

Tools:

13mm and 15mm wrench, 19mm socket, C-clamp, flathead screwdriver, Zip Ties

Applicable Models:

Mercedes-Benz W124 (1986-95)
Mercedes-Benz W201 (1984-93)

Parts Required:

Brake pads, wear sensor

Hot Tip:

Have a friend help

Performance Gain:

Better, safer braking

Complementary Modification:

Bleed your brakes

Mercedes-Benz engineering proportions approximately 75% of the vehicle braking capacity to the front brakes, therefore most models have larger calipers, pads and rotors on the front. While both front and rears brakes work on the same principle, this article is only applicable for the front brakes.

The front brake system on the 190E are floating calipers, and while you do not need to remove the caliper mount from the steering knuckle you will need to remove the caliper from the mount to change the pads.

Before we begin I would like to spend a minute and talk about your brakes. This article demonstrates how to change your pads without having to bleed your brakes afterwards; however I am a strong believer in changing your brake fluid and bleeding the brakes at least once a year and highly recommend you do it every time you change your pads. That being said, if you have just changed the fluid or do not feel a need to, this article will show you how to change your pads without having to bleed the brakes.

First thing you need to do is get the car up on jack stands. Please refer to our article on jacking up your car for more information.

With the car safely up on jack stands and the wheels off, open the hood. You will be pressing the piston back into the caliper to make room for the new pad and you want to check the reservoir to make sure there is enough room for the fluid that is going to travel back into it. If your reservoir is completely full you are going to need to remove some of the fluid. Again, a word of caution here, brake fluid is extremely toxic and will quickly destroy any paint it comes in contact with. Clean around the cap area before you open it. The hydraulic lines and seals in the brake system are very susceptible to any foreign matter and you do not want to have anything but clean fresh fluid in the reservoir. Take a clean syringe or turkey baster and suck out enough fluid to make room for the compression of the caliper piston.

Before you remove the caliper you should inspect the rotor for any damage or excessive wear. It is alright for there to be a small ridge along the outside diameter of the rotor, but if you have any concerns about wear, measure them with a micrometer. Be sure to measure the disk in several different places, from the inside to outer rim. Most rotors have the minimum diameter stamped on them. If you can not find this, please refer to the owner's manual for your recommended minimum wear.

Also while you are there, spin the rotor to make sure they turn free and are not warped, inspect them for cracks. If you find any problems, replace the wheel bearing and/or rotors as required. You should inspect your brake pads every time you check or change your oil. The pads should be replaced when it is worn down enough to trigger the wear sensor or is below a quarter inch of pad left.

With the car safely supported turn the wheel to give you more room to work. The mounting bolts are on the inside of the caliper and if you can give yourself a little more room to work when doing each side it will help.

Looking at the back of the caliper you will see the wear sensor. It looks like a small box with a wire coming out of it and going to the brake pads. Open the lid on the sensor housing and pull the rubber lead straight back and out. Insert a large screwdriver between the inside pad and rotor and push the pad back in towards the caliper. If you break the wear sensor, don't worry as you are going to be replacing it anyways. Once you have pushed the pad back far enough for the pads to clear the rotor you can begin removing the caliper. Note: If there is excess resistance from either caliper piston while compressing them, this is a strong indicator they need to be rebuilt or replaced now.

There are two bolts holding the caliper to the mount. These bolts allow the caliper to move so it will stay centered on the rotor as the rotor wears. Using a thin-walled 15 mm wrench to hold the mount side of the bolt, remove the 13mm bolt on the caliper side. With the bolts removed the caliper can be pulled back off the mount and rotor. Inspect your caliper for any signs of damage. Look for cracks, tears in the dust boot or leaks from around the cylinder. Replace or rebuild the caliper if you find any issues trouble. Hang the caliper by a zip-tie or rope from something on the car so that it does not hang by the hydraulic lines. Inspect you lines for wear, excessive dryness, cracks, bulges or leaks, and replace if necessary.

With the caliper gone simple remove the pads from the mounting bracket; if they are badly worn it may take a little effort to remove them. Inspect the rotors again, and replace the old pads with new ones. The new pads will have a place to insert the wear detector on them. It just clips into the hole in the top center of the pad.

With the new pads and wear detector installed in the mount you need to prep the caliper to reinstall. Depending on the wear of the old pads, the new pads will be thicker. You will need to push the piston in the caliper back into the caliper body far enough to make room for the new pads. One of the best ways to do this so that you do not damage the piston, caliper or dust seal is to use one of the old brake pads and a C-clamp and slowly compress the caliper and piston, checking the reservoir to make sure the brake fluid does not overflow.

With the piston compressed place the caliper back onto the mount passing the wear sensor through the opening in the caliper and attach the mounting bolts. With everything secure, plug the wear sensor back in and close the wear sensor housing.

Get into the car and slowly press the brake pedal. It may take several pumps of the pedal to expand the piston back out to the brake pad, but after a few pumps you should have a good firm pedal. Take care not to push the brake pedal all the way to the floor, as you can actually damage the master cylinder by driving the piston into usually unused portion of the master cylinder and damaging the seals. If you had a firm pedal before you started and can not get a firm pedal after finishing, you have gotten air into the system and will need to bleed your brakes. If you had a soft pedal and there are no external leaks you will probably need new brake lines and/or a master cylinder.

Before you begin working on the brakes, check your brake fluid reservoir.
Figure 1

Before you begin working on the brakes, check your brake fluid reservoir. You are going to be compressing the caliper piston which will cause brake fluid to travel back up into the reservoir and you need to make sure there is room for it. Carefully clean around the reservoir before you open it, as you do not want any dirt or debris getting into it.

This photo shows the brake rotor (blue arrow), caliper mount (red arrow) and the caliper (yellow arrow).
Figure 2

This photo shows the brake rotor (blue arrow), caliper mount (red arrow) and the caliper (yellow arrow). Inspect everything for signs of damage - such as cracks, gouges, leaks or excessive wear.

Turn the wheel to give yourself better access to the inside of the caliper.
Figure 3

Turn the wheel to give yourself better access to the inside of the caliper. You are going to be working on the wear sensor (green arrow) and the caliper mounting bolts (yellow arrows).

The wear sensor runs from the pad to the sensor housing on the caliper.
Figure 4

The wear sensor runs from the pad to the sensor housing on the caliper. The sensor is basically just a small piece of metal surrounded by ceramic. When the pads wear down to the point that the ceramic wears away on the rotor and the metal part of the senor makes contact with the rotor, it closes a circuit and sends a signal that your pads need replacing. Open the sensor housing and pull the rubber plug from the housing (insert upper left).

Insert a large flat head screw driver between the pad and rotor and push the pad and piston back enough so they clear the ridge in the rotor and can be removed.
Figure 5

Insert a large flat head screw driver between the pad and rotor and push the pad and piston back enough so they clear the ridge in the rotor and can be removed. If you damage the sensor, don't worry, as you are going to be replacing it any ways.

Remove the two mounting bolts connecting the caliper to the mount using 19mm socket.
Figure 6

Remove the two mounting bolts connecting the caliper to the mount using 19mm socket. Remove the caliper and inspect it for damage and leaks.

Next you can remove the old pads from the mount.
Figure 7

Next you can remove the old pads from the mount.

Install the new wear sensor into the new pad.
Figure 8

Install the new wear sensor into the new pad.

Install the new pads in the mounts.
Figure 9

Install the new pads in the mounts.

You'll need to prep the caliper to make enough room for the new pads to fit.
Figure 10

You'll need to prep the caliper to make enough room for the new pads to fit. Place one of the old brake pads over the piston and using a C-clamp slowly press the piston back into the caliper until you have made enough room to clear the new pads. Check your reservoir before and while doing this to make sure there is enough room for the fluid being moved back into it. With the caliper prepped, pass the sensor wire through the opening in the caliper and reinstall the mounting bolts and pull the sensor into the housing. Get in the car and pump the brakes slowly until you get a firm pedal. Take care not to push the brake pedal all the way to the floor, as you can actually damage the master cylinder by driving the piston into usually unused portion of the master cylinder and damaging the seals. If you do not get a firm pedal and you had one before you started, air has got into the system and you will need to bleed your brakes. If you had a soft pedal before the installation and there are no external leaks, you will probably need new brake lines and/or a master cylinder.

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Comments and Suggestions:
K-Man Comments: My 190e had 19mm mounting bolts for the caliper housing to the wheel, but the nut and bolt assembly you show during removal was a 13 mm for the bolt and a 15mm for the nut. Thanks though, the tutorial helped. You might also want to casually mention that the springs on the pads are to be depressed smashing them outward underneath the caliper vs. depressing them inward and inserting them into the cavity above. No big. It's your deal. It works. Thanks, K
April 14, 2015
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
georgielad Comments: Hi
Nice tutorial. However, The 190 had many different front calliper configurations and found it difficult to get a video of my particular breaks/disks. I know its not a problem to do but would be nice to have some information.
Thanks for the tutorial.
March 8, 2015
  Followup from the Pelican Staff: We don't currently have that tech article. If we get a chance to perform the procedure, we will be sure to document it.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
190owner Comments: Thank you from England on your excellent instructions on the mercedes 190 brake removal - came in really handy when I got stuck!!
August 3, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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