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Replacing Mercedes Benz Front Rotors and Calipers
 
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Pelican Technical Article:

Replacing Mercedes Benz Front Rotors and Calipers

Steve Vernon

Time:

4 hours4 hrs

Tab:

$150

Talent:

**

Tools:

10mm, 19mm wrench, 14mm flared-nut wrench, Flathead screwdriver, drain pan

Applicable Models:

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

Parts Required:

Caliper assemblies, rotors, pads

Hot Tip:

Make sure you return the old core

Performance Gain:

Better, safer braking

Complementary Modification:

Replace your brake lines

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.

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. When replacing the calipers you do not want to fully press the piston back until you have removed the brake line. This avoids returning contaminated fluid to the master cylinder. You want to press the piston back into the caliper just enough to allow you to remove it. 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 gets 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.

Begin by removing the wear sensor housing from the caliper. It is attached by a 10mm bolt, remove the bolt and pull the housing from the caliper. With it removed, open the housing and pull the sensor plug out. If you can remove the sensor from the brake pad, great, if not do not worry about ruining it as you are going to be replacing it anyway.

Move to the caliper and place a large flat head screw driver between the pad and rotor and push the piston back in the caliper back just enough so the pads will clear the rotor. Do not forget to check the reservoir to make sure fluid is not overflowing. You are going to be disconnecting the hydraulic line in a few steps but this way you can leave the system closed, and you will have less spillage, especially if you have to leave the job and come back to it.

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 when doing each side it will help. Remove the two 19mm bolts holding the caliper and mount to the steering knuckle. Use a zip tie or piece of rope, and tie the caliper up and out of the way while you remove the rotor. Do not let it hang by the brake line! Inspect you lines for wear, excessive dryness, cracks, bulges or leaks, and replace if necessary. I strongly recommend replacing your lines if you can not be sure they have been changed in the last eight years or if you see any signs of external damage.

With the caliper assembly gone, the next step is to remove the rotor. It is held in place by a T-30 Torx screw. Remove the screw and the rotor will come off the hub. The rotors can get corroded onto the hub and sometimes you need to give them a hit with a mallet to free them up. Anything except the lightest corrosion on the hub face must be cleaned with scotch brite and/or 80 grit sanding discs to keep the mating surface true.

Install the new rotor taking care to line it up with the locating pin and secure it with a new screw or put some Blue Loctite on the old one.

Install the new brake pads into the caliper assembly. The piston will already be in its fully retracted position, but the new springs on the pads will be stiff, so make sure you wiggle them into place on both sides.

Mount the new assembly and pads over the new rotor, onto the upright and torque the 19mm bolts to spec. Remember the bleed nipple must be at the top of the caliper or you have them on the wrong side. Attach the wear sensor to the brake pad, attach the sensor housing to the caliper, and plug the sensor in.

You are now going to remove over the brake lines from the old calipers to the new ones. You will need to bleed the system after this, so while there will be a little spillage you should be prepared for, you really want to make sure no dirt, debris of foreign matter gets into the new calipers.

Remove the rubber grommet from the top of the new caliper. While being careful not to get anything into the opening, use a 14mm flared wrench and remove the line from the old caliper, and attach it to the new one.

When you have installed either sides or all four corners, you are now ready to bleed the system.

Please see our article on bleeding your brakes. DO NOT drive the car until you have bled the brakes!

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).

Remove the 10mm bolt holding the brake wear sensor housing to the caliper.
Figure 3

Remove the 10mm bolt holding the brake wear sensor housing to the caliper.

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 a large 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 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 wear sensor, don't worry, as you are going to be replacing it any ways.

Remove the two mounting bolt connecting the caliper assembly to the upright (yellow arrows, only top one shown).
Figure 6

Remove the two mounting bolt connecting the caliper assembly to the upright (yellow arrows, only top one shown).

With the caliper assembly removed, unscrew the T-30 Torx screw and remove the rotor.
Figure 7

With the caliper assembly removed, unscrew the T-30 Torx screw and remove the rotor. If it is corroded on, just give it a hit with a mallet to free it up. Anything except the lightest corrosion on the hub face must be cleaned with scotch brite and/or 80 grit sanding discs to keep the mating surface true.

Install the new rotor and secure it with a new T-30 screw.
Figure 8

Install the new rotor and secure it with a new T-30 screw. If you are going to be reusing your screw put a little Blue Loctite on it.

Install the new pads into the brake assembly.
Figure 9

Install the new pads into the brake assembly. The springs will be a little tight but just wiggle them into position (green arrows).

Install the new caliper, pads and assembly to the hub/upright and torque to specs.
Figure 10

Install the new caliper, pads and assembly to the hub/upright and torque to specs.

Reattach the sensor housing to the caliper.
Figure 11

Reattach the sensor housing to the caliper. Insert the new sensor through the opening in the caliper, clip it into the brake pad and plug the sensor into the housing (red arrow).

Remove the rubber plug from the new caliper to install the brake line (yellow arrow).
Figure 12

Remove the rubber plug from the new caliper to install the brake line (yellow arrow). Take care that nothing gets into this opening.

Using a 14mm flared nut wrench remove the brake line from the old caliper and attach to the new.
Figure 13

Using a 14mm flared nut wrench remove the brake line from the old caliper and attach to the new. Don't worry about how much fluid you lose, as you are going to be bleeding the brakes next, just make sure nothing gets in the opening of the new caliper. The yellow arrow points to damage on a brake line. If you see something like this, replace your lines. Remove the zip-tie or rope you had hanging the old assembly and be sure to return the core for your core fee. MAKE SURE YOU BLEED THE BRAKES BEFOR YOU DRIVE!

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Comments and Suggestions:
Mike Comments: Are brake caliper mounts identical/interchangable between the 190D and 190E. I was doing the front brakes and the sliding pin in the mount sheared off on me. Can I grab a new mount from a 190E or has to strictly be 190D. Mine is an 1984 and would year matter?
Also is is possible to drill out the other half of the sliding pin still stuck inside?
Thanks
September 9, 2016
  Followup from the Pelican Staff: I am not 100% sure. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.


You can drill, extract then repair the mounting hole. Might be easier to replace though. - Nick at Pelican Parts
 
tyler.cameron Comments: Oh, and I forgot to mention, I did this on a 1992 Mercedes-Benz 190E 2.6.
July 19, 2015
  Followup from the Pelican Staff: Ok, got it. - Nick at Pelican Parts  
tyler.cameron Comments: I did this, but I only replaced one wear sensor. The other side had the old wear sensor dangling and I removed it... Now my ABS light stays on. Is it because I need the wear sensor on the other side as well?
July 18, 2015
  Followup from the Pelican Staff: The wear sensor should not turn on the ABS light. I would check the vehicle for fault codes. The wheel speed sensor wiring may have been disturbed, uncovering an issue, setting fault. - Nick at Pelican Parts  
Greg Comments: I have a 2008 Mercedes R350. It has 120,000 miles and I noticed what appears to be brake fluid on my garage floor on the inside of my left front tire. I'm assuming I have a possible brake caliper leak or brake line. However, It doesn't seem to leak when I park it in the driveway. Would it only leak when I push on the brake peddle?
March 26, 2015
  Followup from the Pelican Staff: It could leak more when you apply the brake, as pressure increases. However, the leak would always be present. I would inspect the master cylinder, brake lines and calipers for leaks. - Nick at Pelican Parts  
Me Comments: So what's the "torque to specs" values??
March 3, 2015
  Followup from the Pelican Staff: You didn't mention what vehicle you are working on, so I can't check if I happen to have the specs. 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
 

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