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Rear Brake Pad Replacement
 
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Pelican Technical Article:

Rear Brake Pad Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$40 to $75

Talent:

**

Tools:

Punch or screwdriver, hammer,

Applicable Models:

Mercedes-Benz W203 (2001-07)

Parts Required:

Brake pads

Hot Tip:

Check your brake discs when replacing your pads in case they have worn too thin

Performance Gain:

Better braking

Complementary Modification:

Caliper rebuild, brake disc replacement, install stainless steel brake lines

Replacing your brake pads is one of the easiest jobs to perform on your Mercedes-Benz. In general, you should inspect your brake pads about every 10,000 miles and replace them if the material lining of the pad is worn down enough. In reality, most people don't inspect their pads very often and usually wait until they loose braking power or start doing damage to the rotor. While the C320 models only have sensors on the front brakes, it's a wise idea to replace the rear pads and inspect your discs as soon as you see that warning lamp go on for the front brakes.

If you ignore the warning lamp, you may get to the point of metal-on-metal contact, where the metal backing of the pads are contacting the brake discs. Using the brakes during this condition will not only give you inadequate braking, but will also begin to wear grooves in your brake discs. Once the discs are grooved, they are damaged, and there is often no way to repair them. Resurfacing will sometimes work, but if the groove that is cut by the pads is deeper than is allowed by the rotors specifications you will need to replace the rotors. The smart thing to do is to replace your pads right away.

Brake pads should only be replaced in pairs--replace either both front pads and/or both rear pads at a time. The same rule applies to the brake discs.

This article will show you how to replace your rear pads, if you are doing the fronts please refer to our Pelican Parts Technical Article on replacing your front pads. The first step is to jack up the car and remove the wheel (slightly loosen the lug nuts before you lift the car off of the ground). Please see our article on jacking up your car. This will expose the brake caliper that presses the pads against the disc.

The pads are held within the caliper by a single retaining pin. There are also a small retaining clip that hold the retaining pin in the caliper. Start by tapping out the retaining pins using a small screwdriver or punch and a hammer. When the retaining pin is removed, the anti-rattle spring that holds the pads in place will fall out.

Now the pads can be pried out with a screwdriver. Work the screwdriver between the rotor and outboard brake pad. This allows you to pry and press the piston back into the caliper with no risk to the rubber dust boot. Be aware that as you push back the pistons in the calipers, you will cause the level of the brake reservoir to rise. Make sure that you don't have too much fluid in your reservoir. If the level is high, you may have to siphon out a bit from the reservoir to prevent it from overflowing. Use the small holes on the pads that normally surround the retaining pin as a leverage point for removing them. They may require some wiggling to remove, as it is sometimes a tight fit. It is important to keep in mind that the caliper piston is also probably pressing against the pads slightly and will add to the difficulty in removing them.

Once you have the pads removed, inspect the inside of the caliper. You should clean this area. Make sure that the dust boots and the clamping rings inside the caliper are not ripped or damaged. If they are, then the caliper may need to be rebuilt or replaced.

At this point, you should inspect the brake discs carefully. Check for any deep grooves. Using a micrometer, take a measurement of the disc thickness. If the disc is worn beyond its specifications, then it's time to replace it along with the one on the other side. Most discs have the minimum thickness stamped on them, if yours don't, please refer to your owner's manual.

The installation of the new brake pads is quite easy. You will need to take a small piece of wood or plastic and push the caliper piston back into the caliper. If you are worried about damaging the dust seal around the piston you can reinsert the old pads and use a large wrench to compress the piston back into the caliper. This is because the new pads are going to be quite a bit thicker than the old ones, and the piston is set in the old pad's position. Make sure that you push both pistons (inside and outside) back in the caliper.

Be aware that as you push back the pistons in the calipers, you will cause the level of the brake reservoir to rise. Make sure that you don't have too much fluid in your reservoir. If the level is high, you may have to siphon out a bit to prevent it from overflowing. Make sure that you have the cap securely fastened to the top of reservoir when you complete the job.

When the piston is pushed all the way back, you should then be able to insert the pad into the caliper. If you encounter resistance, double check to make sure that the inside of the caliper body is clean. When the pads are in place, insert the retaining pin and spring clip back into place. It's wise to use a new set of pins and clips when replacing your pads.

In general, I recommend removing and replacing the brake pads one side at a time. When the piston is pushed back into the caliper, it will try to push out the piston on the opposite side of the caliper. Leaving the brake pad installed on one side keeps the piston from being pushed out too far.

You also may want to spray the back of the brake pads with some anti-squeal paste. This paste basically keeps the pads and the pistons glued together and prevent noisy vibration. Some brands of pads may come with anti-squeal pads already attached to the rear surface. Anti-squeal pads can also be purchased separately as sheets that are peeled off and stuck on the rear of the pads.

When finished with both sides, press on the brake pedal repeatedly to make sure that the pads and the pistons seat properly and make sure that you top off the master cylinder brake fluid reservoir if necessary. Brake pads typically take between 100 and 200 miles to completely break in. It's typical for braking performance to suffer slightly as the pads begin their wear-in period. Make sure that you avoid any heavy braking during this period.

This picture illustrates the different parts of your braking system; the rotor (blue arrow), the caliper (red arrow) the retaining pin (yellow arrow) and the spring clip (green arrow).
Figure 1

This picture illustrates the different parts of your braking system; the rotor (blue arrow), the caliper (red arrow) the retaining pin (yellow arrow) and the spring clip (green arrow).

To remove the old pads, tap out the retaining pin (red arrow) with a punch or screwdriver and a small hammer.
Figure 2

To remove the old pads, tap out the retaining pin (red arrow) with a punch or screwdriver and a small hammer. They should slide out pretty easily, as there is usually no load on them. If there is much difficulty encountered during the removal process, then tap on the pads slightly to remove pressure from the pins.

Remove the spring clip (red arrow).
Figure 3

Remove the spring clip (red arrow). It is a good idea to replace the retaining pin and clip when changing your brake pads, especially if you live in an area that sees winter weather.

Pulling out the pads usually involves the use of a screwdriver for leverage.
Figure 4

Pulling out the pads usually involves the use of a screwdriver for leverage. The pads are loose in the caliper, but it's a pretty tight fit, and there is usually lots of dust and debris in the caliper. Wiggle the pads back and forth in order to pry them free.

When you are ready to install the pads back into the caliper, use a wooden or plastic handle to push back the two caliper pistons.
Figure 5

When you are ready to install the pads back into the caliper, use a wooden or plastic handle to push back the two caliper pistons. If you are worried about damaging the dust seal around the piston you can reinsert the old pads and use a large wrench to compress the piston back into the caliper (red arrow). Don't use a screwdriver, as you might damage some of the piston seals.

Keep your eye on the fluid level in the master cylinder reservoir (yellow arrow) it can overflow when you push back on the pistons.
Figure 6

Keep your eye on the fluid level in the master cylinder reservoir (yellow arrow) it can overflow when you push back on the pistons.

Install the new pads into the caliper.
Figure 7

Install the new pads into the caliper. You may have to install pads into one side of the caliper (red arrow), and then push the piston on the other side back in to get the next pad in. Don't forget to reinstall the small retaining clips for the pad retaining pins. The completed assembly should be carefully tested before you do any performance driving. Brake pads can also take several hundred miles to fully break themselves in. Exercise care when driving with brand new brake pads.

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Comments and Suggestions:
hli Comments: does the 2002 c320 have a rear brake sensor that needs to be replaced as well?
April 24, 2014
  Followup from the Pelican Staff: Yes - Nick at Pelican Parts  
amaher Comments: I am wondering if it is necessary to replace the rotors when doing the rear break pads. If so, what is the procedure for a CLK320 W209? Additionally whether you replace the rotors or not, is there a requirement to machine the rotors and what is the best method to achieving this?
April 22, 2014
  Followup from the Pelican Staff: You have to measure the rotors, if they are close to or under spec, replace them. We don't currently have that tech article. If we get the chance to perform the repair, we will be sure to document it. - Nick at Pelican Parts  

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