How do you change the brake pads?

Submitted by	Category	Chassis	Public
Ken K. Yee on 06/14/2000 at 12:35 AM	DIY, Frequently Asked Questions	W163

How do you change the brake pads?

From Brent Nemec (blnemec@home.com):

I took Harold at his word and changed my front pads a couple of months ago. Unfortunately, it had been about 20 years since I last changed brakes. If you are somewhat mechanically inclined, its not too difficult.

I believe you need a heavy duty C-clamp with at least a 4.5 inch opening; a sturdy set of Allen wrenches, a wash pail (or strong box) to hold the caliper during the process; a regular (flat) screw driver; pliers?; and a 1x4x6+ inch board to compress the caliper piston.

As I recall - no guarantees:

Remove the tire/wheel (do the passenger side first - the driver side has the wear sensor, so its better to start with the simpler passenger side).
Remove the small semi-flat steel piece (about 1 by 3 inches) which you can see directly after removing the wheel. I believe this is attached with one or two small screws, and this piece seems to serve as a "scrapper" or "deflector" to deal with brake dust.
Loosen the two Allen head bolts on the backside of the brake caliper. This can be a knuckle-buster with short wrenches. The bolts have rubber bushings, so after you have unscrewed them, you have to pull the heads out SOME by hand to free them from the wheel.
Use the screw driver to pry the old pads away from the retaining clips.
Use the C-clamp and wood board to compress the caliper piston "back down" (as I recall, you have to do this before you install the new pads).
The caliper is somewhat heavy (maybe 10 to 15+ pounds) so have the pail/box handy while lying under the car to rest the caliper, as it is somewhat awkward and will remain attached to the car via the brake fluid hose.
Mount the new pads, put the brake caliper back on the wheel, re-insert/tighten the Allen bolts, re-install the little steel part on the front side of the wheel, and re-mount the wheel.
I asked the dealer to check the torque on my Allen bolts during my next service, since I did not have very long wrenches. - Does anyone have advice on how to know when these bolts are tight enough?

From James Quan (james.p.quan@ontariopowergeneration.com):

Just a few pointers to add for the do-it-yerselvers:

When removing the calipers, don't overstretch the rubber brake hose. It would be wise to devise a system with a coat hanger for hanging the calipers when you are not handling the calipers.
I find that you don't really need a piece of wood to push the piston back into the caliper. Since the brake pad is thin anyway, just put one end of the c-clamp on the pad. The pad will be discarded anyway. If you added brake fluid, you will have to remove some from the reservoir.
MB has a type of grease that comes in a silver pouch. I can't remember the name. It is a type of anti-seize, anti-clatter compound that should be applied to the surface of the piston only. Don't get this stuff on the brake pads!
I thought the bolts had a torx head. I used a torx bit that fit into a socket and that worked. When replacing this bolt/pin, clean the pin and put some "loctite" on the thread. There was the original blue stuff from MB for that purpose. It did not take much force to break the original seal. Therefore, I did not apply too much torque when tightening. I believe that the "loctite" will hold the bolt/pin in place.
My brake kit contained two sets of two stainless steel guides on which the pads glide/move when they wear. On previous MB's, this was not in the design and that would cause the pads to seize, especially on the rear brakes. The old ones can be pried off and should be replaced. They can be pounded (lightly) in place with a wooden mallet or something softer than an old Stanley claw hammer.
I didn't have to work from beneath the car. It can be done entirely from the sides of the car (oops, truck).

My front brake pads lasted 42,000 Kms.

From Clifton Lee (cliflee@hotmail.com) on the MB grease in the silver pouch:

That product is called "Brake Paste" and the part number is 001 989 10 51 (costs $1 each). You would normally use up to one pouch per pad set so it will take 2 for the whole car. You can also substitute an equivalent aftermarket paste.

From Craig Weems:

Rotex makes pads that have a lot less dust than the MB pads. They also don't squeal. You can get them from the Brake Warehouse (800) 814-0702 or from http://coximport.com/rotex/.

From DAN MACDONALD (DMAC@lifetouch.com):

I just replaced the front pads on my 2000 ML320 at 29,900 miles. The warning light was not on yet, but the pads worn to within a hair of touching the sensor. Note that the sensor will touch the disk when the pad is only about 1/2 gone. However, I wonder if the sensor could damage the disc?

I changed pads myself in about 1-1/2 hours, including about 30 minutes for cleaning the wheels. The job is very simple. You need:

- a Torx bit for the caliper bolts (I don't recall the size)
- a torque wrench for the lug nuts (bolts actually), 110 ft/lbs
- a floor jack and jack stand
- a "C" clamp to compress the caliper pistons

I bought the Mintex pads - they are supposed to have less brake dust, and last longer. I purchased from http://www.germanstar.net/163bp.htm. When ordering I asked if they come with the wear sensors, and they said no, so I ordered two. However, the front only uses one sensor, and the pads came with one - so I now have two spares. My discs were smooth, so I retained them and did not have them machined. I did not bother sanding them - as the new lining material is rough and semi-metallic and should do a great job of sanding by themselves.

So far the brakes feel fine, with no squeal or other problems. I'll have to wait and see about brake dust.

Pete Fagerlin put up some details on how to replace the pads *and* rotors:
http://www.petefagerlin.com/ML/brakes.htm

From Frank Kuehnl:
Excellent instructions, however, the "slugs" do not need to be removed, just lightly spray penetrating oil around the hub, and a little in each lug-hole, and hit the rotor on the surface where the wheel mounts with a large hammer (may take several beatings, good for removing frustration).

The rear rotors need to have the e-brake released prior to removal. Shine a flashlight in through the lug holes and slowly rotate the rotor until you see a small star-wheel. This is the adjuster for the e-brake, use a small slotted screwdriver to rotate the wheel, I forget which direction, so you must rotate the rotor after a few clicks. If it stops turning, go the other way. After the new rotors are installed, turn the wheel in the other direction until you feel the e-brake dragging on the rotor, then back off 3-4 clicks.

From Frank Kuehnl (kuehnl7r@chartermi.net) on what to do if one of the rotor allen bolts is stripped:

After the brake caliper and pad carrier is removed, turn the steering wheel to move the spot where the caliper was located. You should have both front wheels off the ground and the parking brake on before you do this! Install 1 lug bolt, thread it in about 1 cm. Use a 5lb hammer to strike the rotor, hitting from the vehicle outward (assuming that you are replacing the rotors). Turn the rotor about a quarter turn and repeat, the bolt will break off.

From drew888@sbcglobal.net:
The 2002 320 only has a sensor on the driver's side, and OMG! this was the easiest pad change I have ever done.

I now think my wife can handle this one (if she could get past the brake dust).

1) Gather tools; 17mm for lug nuts, breakerbar, T40 socket, 'emergency spare wheel pin (as coined by the parts guys- # A140-403-0-074 $7.95), floor jack, one jack stand, standard screwdriver and the part that made life so much easier = the piston spreader ($6.99 @ AutoZone). Oh yeah don't forget the new pads and BEER!
2) Loosen all lugs on both front wheels while on the ground
3) Jack up the truck on the side you'll do first and insert the jackstand. Lift the ML just enough to remove the wheel.
4) Remove top most lug and insert wheel pin (faster this way, trust me. last lug gets stuck under the weight of the wheel) and remove the rest and then the wheel.
5) Remove the 2 T40 bolts from the back side of the caliper. You will find them inside a plastic shroud. Take note of how tight they feel. You will need to remember this during the installation!
6) Use the standard screwdriver, locate the threads of the T40 bolts (just look inside the caliper). With the tip of the screwdriver gently push these bolts from the threaded hole they screw into. Although you have unscrewed these bolts all the way out the friction within the 'plastic shroud' and the fact that you cannot get a good hold on the head of the bolt makes it necessary to use the screwdriver. If you don't push these bolts up a bit they still catch on the caliper preventing you from removing the caliper.
7) Look at the outer most part of the brake pads. You can see that they rest on the caliper carrier(?)/caliper mounting bracket (?). I believe the lower one (the pad edge that faces the bumper) is more easily remove by just pulling it up. I remember that one didn't want to budge and the other came up easily...you'll see). Remove the caliper and swing upward resting it upside down on the top of the rotor.
8) Remove the outer pad by pushing it out at the top and then sliding it upward. There are 2 small studs on the pad backing that won't allow you to simply slide it upward.
9) Leave the inside pad there. It's needed to press the piston back in evenly. Now use the spreader and push the piston in (I'd leave it about 1/8 out as there are probably an inner seal as well. If so it may be damaged by pressing it in too far).
10) Remove the inner pad.
11) Take notice, by examining the old pads, just where the piston and caliper made contact with the back of the pad. This is where you may want to put some anti-squeal compound (spray, gel, grease, etc.). I didn't put anything and so far so good. I had an appointment and ran out of time. I may have done it faster if I had another beer!
12) By now you realize how simple this is and installation is the reverse of the above. The T40 studs should just be snug. Remember how it felt when you removed them?...yeah like that.

Us 320 guys REALLY have is easy. I literally completed the second wheel in less than 15 minutes (including lifting the ML).

P.S. I tried old pad large screwdriver pry against the rotor thing and it didn't budge a mm. This piston really needs even pressure all around with some extra umffftt or it ain't going nowhere. Buy the $7 piston spreader. After wasting almost 40 min. on the first wheel it took less than a minute after using this tool, very nice.

From Porterfield on whether the rear pads they sell include wear sensors:
Date: Thu, 27 Feb 2003 08:12:58 -0800
From: Wendy @ Porterfield's <sales@porterfield-brakes.com>
Subject: Re: Customer Contact - RaceBrakes.com

None of our pads come with the wear sensors some just have the provision for one to fit in. The AP 761 does not because that part number is for the years where the wear sensors were not called for. The part number they would want to ask for is AP 875 that does have the raised wear sensor cut out.

From howvood@direcway.com on opening the bleeder while changing the pads:

I usually place one end of a plastic hose on the bleeder, the other end at the bottom of a container. I crack open the bleeder, push in the piston and close the bleeder just at the end of the piston travel. This prevents any air from coming into the system. I then top off the fluid after the brake pads are replaced and the pedal pumped to move the caliper piston into position. Also, if someone had previously filled the reservoir, if the bleeder is NOT opened, and the piston pushed back, the reservoir will probably overflow.

Wolfgang found another 3rd party brake pad w/ the rear wear sensor:

Figured out how to install the rear wear sensor with ThermoQuiet pads. Just order part number MX875 for the rear instead of the MX761 previously mentioned. Added a picture next to my rear caliper:

http://www.whnet.com/4x4/brakepads.html

Another tip from Frank Kuehnl:
Spray around the hub and all of the lug holes, remove the rotor retainer screw. Then you want to wait a few min, and use a 5-lb sledge on the rotor, hit it on the top and side of the hat. It helps to think of all of the people that pulled out in front of you that day while hitting the rotor.
It will usually come off after the 3rd hard hit.

From David Hsu <dave@mur.com>:

As far as adjusting the e-brake, you'll be looking at the *side* of a star-wheel adjuster, at about the 2 o'clock position on the left side wheel, and 8 o'clock on the right side. It's akin to a cable-end adjuster like you'd find on bicycle brake, but viewed side-on.

Flick the visible side of the adjuster towards the rotor hub to retract/disengage the e-brake; flick it towards the outside edge of the rotor to expand/reengage the e-brake. When checking the wheel for e-brake drag every few clicks, be careful that you're not feeling the drag of the opposite-side rotor or the differential...just a little wiggle should be enough to detect drag.

This page describes the bedding/seasoning procedure for pads/rotors:
http://www.bira.org/bedding.html

From G Challis <gchallis@centum.com>:
Rear brakes - my ML had a wear sensor on the inside left pad. I didn't get one with the new pads, but the old one was only just starting to be exposed, so I reused it. My new rear pads were Mercedes originals, so they had the hole for the sensor (don't know if the aftermarket ones do or not).

To replace the rear pads, all you need is a 13mm socket wrench to remove the caliper (and to remove the little plate thingie if you are replacing the rotor; also need the allen key for the rotor).

I found no reason to back off the star wheel for the parking brake before taking off the rotor - my rotors came off fine, once I'd whacked them a few times around the lug nut holes to loosen them up. You possibly need to adjust the parking brake star wheel adjusters after you put the new rotors on, although I doubt you will need to as I can't imagine the shoes and drums will ever get any wear unless you have a habit of driving around with the parking brake on.

I used the Motive Products power bleeder -- it's great! Really makes flushing the old hydraulic fluid out of the system a breeze. I'd recommend alternating the color of the fluid each time you flush the hydraulics (ATE
makes red, blue, and original clear), so that you'll know when you've flushed the old stuff out of each line. It's not strictly necessary as the old fluid is always a bit darker and cruddier than the new, but it would make it really easy to tell when all the old stuff is out (I used the clear, but next time I'll use the blue - or red!). 1 liter is enough to flush out the system.

I have 66,000 miles on my ML (quite a bit of stop and start driving in the SF Bay area plus lots of hills), and these were the 3rd (!) set of front pads, and 2nd set of rears. The rotors hadn't been replaced before. The pads appeared to have worn fairly evenly (outer vs. inner). The sensors start warning you when there is still about 2mm of pad left so there's quite a safety margin. I think the dealer is overly cautious on replacement, so you can save some money by waiting until the sensors come on. The dealer wanted to replace the pads and rotors at about 55,000 miles, I guess because the rotors were no longer to spec.; I went another 11,000 before the light came on.

From Mark Jennings:

I just did the front brakes on my 2000 ML320. It is not difficult, but it helps to have some experience with doing disc brakes before.

I didn't bother replacing or turning my rotors so I didn't bother removing them - they looked nearly perfect to me, so I didn't bother. I'm of the belief that you shouldn't turn them unless they're obviously scored. I'll probably just replace them next time.

None of the DIY info on the net matched what my brakes looked like. Here is the basic step-by-step:

1. Jack car up, remove wheel. Do passenger side first since it doesn't have the wear sensor.

2. Remove two Torx bolts on the back side of the caliper. They're in plastic sleeves so the caliper can slide on the pins. Just leave sleeves in place and back bolts out until they've disengaged from the hub.

3. Compress caliper piston enough to get caliper off. I used a hand wordworking setup clamp and then rocked the caliper some to get it to come off - you just need the piston to retract enough to get some room for the pads to get over the ridge at the edge of the disc. I'd loosen your brake reservoir cap to allow air to escape. It will disengage from the front side first and then rotate as it comes off. It will take some firm force and a bit of cussing.

4. Remove pads. The non-piston side comes off first - it helps to pry the two retaining clips on the front a bit. The back side just pops out from the piston.

Putting it back together is basically the reverse. I used some disc quiet stuff on the back side of the pads and some caliper grease on the pins, but I don't know if it is critical. It appears the caliper bolts also had some loctite on them, so I cleaned up the pins and re-loctited.

I paid $75 for the pads - the dealer wanted $600.

Drew mentioned you have to watch the brake fluid reservoir levels when you push the piston in so the fluid doesn't overflow. Also, pump the brake pedal a few times after each brake is done to bring the levels back down so it doesn't overflow on the 2nd brake you change.

Paul Dick also found the WIS instructions:

From sam_ml500 on Benzworld:

I replaced my rear brakes with Mintex pads and Brembo rotors. Here are the pics of rear brake mechanism that are missing in Pete's web site. (Pete, feel free to use them on your site if you wish to. Your page motivated me to do brakes myself.)
Notes:
1. My 2002 ML500 has 4 wear sensors on all four wheels. Luckily I checked before removing brakes and picked one sensor from local parts store.

2. Brake pistons can be pushed back with pad spreader, C-clamp or the easiest is following.
If you are replacing rotors and pads both you do not have to worry about scratching old ones. So insert two big flat screw drivers between pads and rotor on both sides and twist them together. If you twist one side alone other side piston will pop out. Also if the both pistons are all the way in flush with caliper body, you are good to insert both side pads effortlessly.

3. Rear wear sensors are connected to the outer pads. Both of my inner L & R pads were worn beyond sensor activation point.

4. Front caliper bolts are 21mm. Rear Caliper Bolts 17mm.

5. My brake fluid level was slightly below low mark on reservoir. Once all pads were replaced level came back to high mark. So I did not have to add fluid nor spill.

I am not a qualified mechanic. All of above are my observations and I assume no liability for any or all problems you might encounter following these notes.

sam_ml500 has attached this image :

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And here's another 1998 ML320 brake pad and rotor replacement page:
http://www.furgasonhomes.com/ml/brakes98ml.htm

This is one covering the 2002 ML320:
http://members.aol.com/dominic888/howtoreplaceml320brakepads