After visiting the dealer for a “Service B” at about the 50,000 mile point on our 2002 CLK 55 AMG Cabriolet (W208), I nearly had a heart attack when he said it needed new front brakes, and rotors, and it would cost $1200 (on top of the $500 for “Service B”.) I have done brake jobs on other cars but generally speaking I’ve left the MB maintenance to the MB dealer. But a $1200 brake job was enough to get me looking at doing it myself.
Disclaimer: This DIY cannot address every issue that may arise, nor can it adequately train someone who doesn’t have the requisite skills and tools. This DIY was intended to document my observations since it may help others. You use this document at your own risk. I accept no responsibility for what you do with it. In particular, I don’t cover every safety concept that needs to be considered when working on cars, with jacks, etc. If you don’t know what you’re doing, this document will not help, and you should let someone else do the repairs on your vehicle.
A few upfront comments: I’m not an expert MB mechanic. This document may very well contain errors. If you’re using this document as a primary guide, please read and process the entire document before beginning. I’m not discussing every issue in this one paragraph. Regarding parts, one of the things I learned was that the MB dealer wanted over $900 just for the parts (2 new rotors, pad set, and 2 wear sensors). No wonder the brake job was $1200! I spent about $650 on the parts by going to parts.com instead, and I got actual MB CLK55 AMG parts, not aftermarket of any kind. You can certainly find the parts for less, but they may be aftermarket parts of some kind. My casual search showed that some parts outlets offered replacement rotors, for example, that were nominally 28mm with a wear limit of 25.4 mm. The correct MB AMG rotors are 32mm with a wear limit of 30.4mm. Does this make a difference? I don’t know. But since I didn’t know I went ahead and paid the $650 for the MB parts rather than dealing with aftermarket. If you’re willing to go with aftermarket parts you can probably do this job for ~$250 in parts. Also note that the MB rotors are unique to the left front and right front, they are not interchangeable. If you’re buying rotors that are the same part for the left front and right front, be aware that you’re dealing with a different animal there. Another thing I should mention is that I was advised to check my vehicle for the SBS/SBC system. This is a system that can activate the brakes even in circumstances when you’re not applying the brake pedal. Honestly I don’t know much about it, but I was able to determine that my vehicle does not have it. If you’re working on a different kind of vehicle, please check for this. If the SBS/SBC system actuates while you’re working on the brakes, bad things can happen, so you need to figure out a way to disable it, which I won’t cover here. Apart from that, this brake job turned out to be very similar to work I have done on other non-MB vehicles, so if you’ve done brake jobs on other vehicles, you will find this pretty easy to do. Overall I spent 2-3 hours on it, but I was moving slowly and I was showing my son how to do it at the same time.
OK let’s get started.
1. The first step is to get either a 17mm lug wrench, 17mm socket wrench, or your MB toolkit lug wrench to remove the bolts which attach the wheel to the hub. I did one wheel at a time; this document will show pictures pertaining to the left front wheel. There are no major differences for the right front wheel, but there are a few minor things I will point out. At this point just break the bolts loose, don’t remove them all the way.
2. Now jack up the car. You can probably use your MB jack, but it’s good to have a jack stand or blocks to support the car while you’re working on it. If you jack up the wrong place, you can damage things. Figure 2 shows how I positioned things. Once the wheel is elevated, you can remove the bolts securing the wheel to the hub. Remove the wheel and set it aside.
3. Now the brake caliper and rotor are exposed. (Figure 3.) At this point I went ahead and disconnected the wear sensor plug from the wiring harness (Figure 4). Later when we are removing the inner pad we can just pull it out and not have the wear sensor still hooked up. The next step is to remove the caliper mounting bolts. Figures 5 and 6 show the location of these bolts, on my vehicle an 18mm socket wrench did the trick. I had a half inch drive socket for this, but I think a 3/8 inch drive socket will work. These bolts are pretty tight and they also use some form of Loctite on the threads, so they can be difficult to break loose. Figures 7 and 8 show two methods that worked for me to break these bolts loose.
4. Now we can remove the rotor retaining bolt. This bolt has an Allen head so I used a 5 mm Allen wrench.
5. Once the caliper retaining bolts are loosened and removed, it’s necessary to expand the brake pads so that the caliper can be lifted off the rotor. However before we do this, it’s necessary to start paying attention to the fluid level in the master cylinder (Figure 10). During this step and some of the following steps, we’ll be compressing the brake slave cylinders which are in the caliper assemblies. This will force brake fluid back into the master cylinder. We will probably be forcing enough fluid back into the master cylinder that if you didn’t do anything about it, it would spill out and make a mess. Brake fluid is nasty stuff, so we don’t want this to happen. So keep an eye on the fluid level. If it rises above the max indication, it’s time to remove some. I used a turkey baster that I keep for this type of job. Don’t let dirt or other contaminants get into the brake fluid. Once you remove some fluid, discard it in an environmentally friendly way, for example by taking to the same place that you recycle used motor oil. Do not put used fluid back into the system. Try to keep the system closed as much as possible, only removing the lid when you need to withdraw fluid. Wipe up any fluid spills immediately. Brake fluid can damage paint and other substances.
6. Now we can expand the caliper. The method I used is shown in Figure 11. Note that I intended to replace my rotors (and pads) so I wasn’t too concerned about nicking the rotors. If you don’t plan to replace the rotors, it’s good practice to have them turned at a brake shop, which will put a new surface on them. If you’re just doing a “pad slap” and leaving the rotors as-is, you don’t want to damage the surface with the screwdrivers. If you’re careful, you won’t, but you may want to investigate another method to expand the caliper. Anyway, I put a flat-bladed large screwdriver in between each outer pad “ear” and the rotor, and then pulled the handles towards me. This puts pressure on the caliper to expand, forcing the pistons back into their cylinders slightly. This method should give you enough clearance to remove the caliper. Later we will continue compressing the slave cylinders all the way. Once the calipers are sufficiently compressed (and the caliper retaining bolts removed) you should be able to lift the caliper off the rotor. Have a coat hanger ready to go as a support mechanism for the caliper once it’s removed (Figure 12).
7. Once the caliper was removed, I was able to just pull the rotor off the hub. I live in a warm climate (roads are not salted) so the vehicle is not highly corroded underneath. If you have lots of corrosion, it may be difficult to get the rotor off. Tapping the rotor around the hub spindle to break loose the corrosion should help. If you’re not replacing or refinishing your rotors, you can skip this step.
8. Next it’s time to remove the pads. The outer pad is the one that is not in contact with the slave cylinder pistons. The outer pad can be removed by prying it towards the inner pad with a screwdriver, then lifting it out of the caliper assembly. Before removing the inner pad, it’s time to compress the slave cylinders “all the way”. For this step it’s very helpful to have a large C-clamp, with about a 12 inch jaw opening or so. Leaving the inner pad in place, place the Cclamp as shown in figure 13, and tighten the clamp until it won’t go any more. You’ll feel the resistance suddenly get stiff, this is when to stop. Now you have compressed the cylinders all the way, to give maximum clearance for the new pads going over the rotor. Reminder: keep an eye on the fluid level in the master cylinder as you’re performing this step. Remove fluid as needed.
9. Now you can remove the inner pad. Pry it out using a screwdriver. This one is more difficult because it has tabs which are grabbing onto the slave pistons.
10. It’s time to begin putting the new pads in. We’ll start with the inner pad. This pad is the one that has the wear sensor installed in it, so assuming you bought new wear sensors (they’re not terribly expensive) go ahead and install a wear sensor in the cutout slot for it in the inner pad. Figure 14 gives a picture of the correct orientation. You want the wire that exits the sensor to be exiting out on the pad material side, not the backside of the pad. This sensor just snaps into place. You can push it in with your finger until it clicks in. Now insert the inner pad into the caliper, mating the tabs with the piston openings. Once I get the pad aligned correctly, I go ahead and use the C-clamp again to get it seated all the way down on the pistons. You have to make sure the “ears” on each end of the pad are in their respective slots before you will be able to get the pad installed. Since the caliper is in 2 pieces (a “fixed” piece that is attached via the bolts to the car, and a “floating” piece that rides with the outer brake pad), these 2 pieces tend to squeeze together, making it difficult to get the new pads in. Use a screwdriver to pry these two pieces apart so that the channel for the “ears” is wide enough to slide the “ears” in. Then use the C-clamp to finish the job on the inner pad.
11. The outer pad will be easier once the inner pad is in place, but you will still probably have to pry the 2 caliper pieces apart slightly so that the “ears” will drop into their channels. A note about anti-squeal grease: Brakes may squeal when applied due to the metal-to-metal contacts in various places in the caliper assembly. Manufacturers use a variety of methods to work around this, including things like an anti-squeal “shim” which goes between the pads and the caliper, and anti-squeal grease in those places and elsewhere, such as on the “ears” of the pads. My MB OE pads had anti-squeal shims integral to the pads, but I went ahead and used anti-squeal grease anyway. I don’t know what’s best, but my brakes aren’t squealing. I think you will probably be OK without grease, but it’s cheap and easy to use. You can get a small throw-away pack at an auto parts store for a single use. Put a SMALL thin layer of it on the backs of the pads where they contact caliper metal, and also on the ears of the pads where they contact the caliper channels. DO NOT get this grease on the face of the pads or on the rotors. Use a very small amount. Obviously if you’re going to use this grease, put it on before installing the pads.
12. Once the pads are in place, put the new rotor on the hub and secure it using the rotor retaining bolt (with the Allen head). Hand tight on the Allen wrench is OK here. When replacing the rotors, at least if you are using MB OE parts, the left rotor and right rotor are not interchangeable! If you ordered parts, then keep track of which part number is which, and don’t mix them up. If you just want to eyeball it, then look at the contour of the ventilation slots that are between the rotor faces. The left and right rotors look very different in this area, and are easy to distinguish this way. If you are doing one wheel at a time, then make sure the rotor you are putting on matches the one you are removing in terms of the contour of these ventilation slots. (Although there is an inner and outer pad on each side, there is no distinguishing difference between the left side pads and the right side pads, so nothing to check there.)
13. Now it’s time to put the caliper assembly back on the rotor. If you’ve done things properly up to this point, you should have a fairly wide opening and it should pretty much just drop on the rotor. If you can’t get it on the rotor, it probably means you didn’t compress the pistons enough, or the pads are not properly seated in the caliper assembly (for example inner pad not seated all the way down on the pistons). You should not have to force it on the rotor. The pad material is soft enough that you can easily damage it if you manhandle the pads onto the rotors. If it won’t go on, inspect the caliper closely to decide where the missing clearance is.
14. Now you can replace the caliper retaining bolts. You will have to support the caliper with one hand and align things while getting a bolt in place. Once one of the bolts is in place, the other is much easier to align and get in. Tighten these pretty much as tight as you can with a socket wrench. I don’t have torque specs and I feel like replacing the Loctite is not a necessity. Others may disagree with me or feel that it’s critical to torque these correctly. If you’re unsure, then consult someone you trust, or locate torque specs and use a torque wrench and/or loctite. If you’re still nervous, then you shouldn’t be doing this job yourself, have someone you trust do it.
15. Now it’s time to re-connect the wear sensor to the wiring harness (Figure 16.). Just use your fingers to push the plug all the way into the socket. When you’re all finished later with the entire job, if the brake light on your dash is on, it means one of the sensors is messed up.
16. Finally, re-install the wheel, tighten the bolts, then lower the car and tighten the bolts again. Use a star pattern when tightening the bolts. Again, usual disclaimers here. If you feel like it’s necessary to torque these to a specific spec, then do so. If you don’t know how, you probably shouldn’t be using this DIY as a guide. I just tighten mine using a wrench until they feel very tight, until my strength runs out using just a lug wrench or socket wrench.
Now you can do the other side. It’s pretty much the same steps. The process of breaking the caliper bolts loose is different because of the orientation of things (the previous methods I showed won’t work the same way on the right hand side) but you will figure something out. I was able to get the upper caliper bolt loose by using a similar method, and for the lower bolt I used a long pry bar appropriately situated between the suspension and the wrench handle. Also, as already mentioned, the left hand side and right hand side rotors are not interchangeable (at least for MB OE parts.) Use the correct one on the correct side.
Once both sides are done, you should start the car but do *NOT* put it in drive, leave it in PARK (or leave the manual tranny disengaged in neutral) and pump the brakes until the pedal height returns. This is necessary because we pushed the pistons “all the way” in, and now we need to bring the pads back out until they are snug against the rotor. This step is *CRITICAL*, do not skip it or drive away without doing it. As mentioned earlier, if the brake light is now on in the dash, the most likely explanation is that one of the wear sensors is messed up. Finally, either before or after a test drive (make sure your pedal height is up again), it’s a good idea to check the brake fluid in the master cylinder one last time and adjust as necessary. Normally you should not have to add fluid after performing a brake job like this.
That’s it! Enjoy the money you saved.