Help me replace my brake pads

[David Langsam]

I've never done it and I decided now was as good as time as any to learn. I got a set of Pagid pads and am all ready to go. I have the factory manual, but, typically, it's not that clear. The car is an '88 560sl (my baby). Any help is appreciated.

David

[DavidSoine]

Step one is do a search on this forum and on the "Tech Help" forum.

Since no one else is chiming in...here is a barebones procedure. USE IT AT YOUR OWN RISK! Please if anyone notices anything wrong here let's get it corrected right away.

You need:

-brake fluid (maybe)
-something to suck up fluid from the brake reservoir(turkey baster, vacuum pump, paper towels in a pinch)
-something to compress the pistons back into the calipers. C-clamps, channel lock pliers, etc
-something to drive out the pins - I use the end of a small rat-tail file and a hammer
-brake lubricant (if you want, not critical)
-brake cleaner - in case you accidently get grease on the rotor or pad

If possible get:

-new pins and anti rattle springs
-new pad wear sensors (4 total)

Other things to consider: did you check the thickness of the rotor to see if it is too thin? If not, do so right when you pull the wheel so you can STOP and get new rotors before proceeding with the brake job...this brings a new level of complexity and risk for the DIYer. These instructions do NOT cover rotor replacement! How about the brake lines...have they been replaced on your 15 year old car? Also, this would be a great time to refresh the brake fluid if you haven't done so already this year...(also not covered here).

If you are comfortable with the above, the procedure goes something like this...

1. Raise a wheel off the ground (use safe jacking procedures), remove the wheel.

2. Put some rags around the master cylinder and suck some brake fluid out of the reservoir. It will only come out of the front half of the reservoir, which is OK

3. (front only) unplug the pad wear sensors (ribbed connectors)

4. drive out the pins & remove the rattle spring

5. before removing the old pads, compress the piston(s) on one side of the caliper while the pad is in place. Use a C clamp or vice grips on the ear of the old pad, or right on the face of it...the pistons must be driven back so they are flush with the inner face of the caliper. You may need to pull the old pad out and clean some crud out to make space. Keep an eye on the brake fluid level in the reservoir, and suck more out if necessary to avoid a spill.

6. Once the pistons are pushed in, remove the old pad, inspect the piston/dust boot for leaks or damage. If there are leaks (looks wet) or dust boot damage STOP and get some more advice...

7. (front only) Carefully transfer the pad wear sensor to the new pad (or install the new pad wear sensor). If you need to reuse it, pull the pad wear sensor prior to compressing the pistons to avoid damage.

8. Carefully lube the back and side of the pad with brake lubricant (follow the instructions given) and put the new pad in place.

9. compress the piston(s) in the other side of the caliper, inspect, and install the new lining in a similar manner to steps 5-8.

10. install the new pins and spring - you will probably need to tap the new pin into place.

11. (front only) plug in the pad wear sensors

12. install the wheel & lower the vehicle

Repeat for each wheel.

The rear compartment of the reservoir is for the rear brakes - I have not found a way to remove fluid from it. As the piston is pushed back the fluid will be forced through a small hole near the cap into the front part of the reservoir.

When finished, add fluid if necessary. Clean up brake fluid spills immediately to avoid damage to paint. Pump the brake pedal to push the pistons back out (use shorter strokes, try not to push it to the floor) until you feel good hard resistance through the pedal. If you never get resistance - check for obvious brake fluid leaks...

Drive the car, use light pressure on the brakes when stopping to get the linings bedded in to the rotors. You will feel reduced brake performance initially, which should improve as the brakes are used and further bedded in.

With that being said:

Be ready for bad news on a 15 year old car. I just finished a complete brake system overhaul on my '87 with new calipers, rotors, linings and brake lines. Cost was in the "restoration" category, as you can well imagine. I was just planning to do linings and rotors.

best,

Dave

David Soine 87 560sl
Liberty, MO

[yeldogt]

I do not know if this is the case with the MB set up -- but you have antilock brakes -- it was my under standing that you should not push the calipers back in -- I use a "C" clamp also" unless the bleader is open.

The reason for this is to not push fluid/ dirt the wrong way through the antilock valves -- I know for a fact a few manufactures have this procedure.

I just open the bleeder and attach a hose anyway so my procedure is to always bleed the brakes anyway.

Also the pads and rotors for that model are not very $$ at the dealer -- much cheaper than most cars!

[David Langsam]

David,

Thank you, that was a very detailed list. I'm only going to do the fronts, I'll let you know how it goes. One of my goals is to finally have breaks that don't squeal. A friend suggested I file the edges of the pad, kind of round them over and that he's had good luck with that. Any comment? Also, I didn't know that the wear sensors were only on the fronts. I wonder why that is.

David

[dmorrison]

Well David and David this is David *G*

My 2 cents.
Everything that David of the second part told David of the first part is very good.

Now for what I can suggest.

If your wear light has not come on you do not have to replace the wear sensors, the little wires plugged into the pads. The outside plastic coating is warn down by the rotor as the pad is warn and the rotor makes the ground for the light. So if it was not on, don't worry about replacing them.

Flush your brake fluid now while your all greasy and have the tools out. Do a search on bleeding the brakes, it has been covered. Weather you buy the auto bleeder or get your significant other to press the brake pedal for you.

DO NOT ALLOW THE BRAKE FLUID TO TOUCH YOUR BODY PAINT. it will remove it.

Rotors
The rotors on the 88 560SL are actually from a different body style. To remove them. After you take the wheel off look for a allen head bolt, just one, that is on the hub section of the wheel. Remove that allen bolt and the rotor comes right off. Mercedes uses the lug bolts of the tire to hold the rotor secure. The manual shows the rotor assembly to be part of the wheel hub and a bear to replace. The 88 is not set up this way. Look at the supplement section at the end of the service manual. Your 88 has a brake system that was installed on the 124 and 201 model

Service Manual Chassis and Body Model 107 Volume 2:
Go to page B42 way in the back. The upper left picture shows your rotor. Item #8 is the allen bolt to remove your rotor as I explained above. But you do have to unbolt the caliper to remove the rotor.

I would recommend opening the bleed valve to push the caliper pistons back into the caliper. I agree with the idea about getting dirt and such in the ABS.
My method is to actually do it with a large screw driver while the whole assembly is still on the car. Remove the wear sensors, the pins and rattle spring. Then put a large screw driver between the rotor and the pad. Open the bleed screw and push the tip of the screw driver towards the pad. You don't want to push the tip towards the rotor so you dont' damage it. Fluid will come out the bleed screw. Once the pads are full retracted against the caliper. close the bleed screw. Then remove the pads and clean the caliper aera with brake cleaner spray. Now you can check the caliper for any fluid leaks. Press slowly on the screw driver, A slow steady pressure will move the caliper, you don't have to muscle it. Once you do this method I would highly recommend bleeding the brakes to ensure that no air flows back into the system thru the bleed screw. I ALWAYS bleed the fluid and replace all of it when I do any brake service.

Anti squeel paste. I have tried a few differnt brands. A Mercedes mechanic recommended Permatex anti seize compound. Thats all they use at the local dealer. It works fine. Use a pea size amount on the edge of the pad and the round circle place were the caliper piston touches the pad.

Other things while you are there. Look at your rubber brake hoses that comes from the side of the wheel well to the caliper. If they look old and cracked you will want to replace these soon.

Check the black wire that is gong from the wheel well to the caliper area. This is your speed sensor wire for your ABS. If it is in bad shape you might start to get an ABS light on while driving the car. You can get this light if any of the wheel sensors is not inputing a speed due to a intermitent wire in that harness. I have had this happen.

Good Luck

Dave, Party of the 3rd part.

[DavidSoine]

I haven't seen any special instructions for lining changes/pushing back the piston with an ABS system on the MB service CD....

Brake squeal comes and goes....I had it on a back brake, I suspect due to a stuck caliper, worn linings and a thin rotor. It is usually a combination of things and changing one of them will often alleviate the noise.

Personally I would just toss in the new pads and see what happens (again, check the rotor thickness.) You can always chamfer them later- it is an accepted technique for reducing squeal (tho probably not OEM approved...). Also lubricating the back of the lining, where the pistons contact, is known to reduce noise.

Often OEM brake pads have an additional thin backing plate which helps reduce noise - I know either the fronts, rears or both Pagid linings have this feature (I forget if they both have it, but at least one of them does!)

best,

Dave

[kip Foss]

David Soine,

Just a note on safety. Using the end of a rat tail file and a hammer is an ccident waiting to happen. Files, everything except the very last litle square stem that goes into the wooden handle, is made of hardened steel that will shatter when hit by an equally hardened hammer face. One of these slivers in your eye at 100 mph and its all over but the glass eye. Brass or steel drifts are too cheap to buy to risk loosing an eye.

I hit a chisel once and a sliver came off the head. It cut a large blood vessel on the top of my hand. You can't imagine the amount of blood that can come out of such a small hole. I still have the scar.

[DavidSoine]

Kip:

Thanks for the safety tip - I'll have to add an assortment of drifts to my tool kit...

best,

Dave

[ned2683]

i have a quesion about the "pistons" in the calipers. do both of them push in? (outside one, pushing pad towards the car, and inside one pushing out from the car). do they both squeeze the pads into the rotors, or is only one suppose to move?

i thought btoh move. but i been told only one does. if i am right i mght have a stuck piston, and how would i fix this? thanks

ned

[maheath]

I just did the rear brakes on my SEL this weekend. Both pistons definitely move. I used a C-clamp and the metal plate from an old pad. If your piston is stuck, then it probably needs to be rebuilt. There are kits for that, but I don't know much about them. I bought rebuilt calipers when that happened.

My motto is don't try to get cheap with brakes. They're too important.

[ned2683]

thanks for your advice. i would like to make sure though if these are "floating calipers" (i believe that is the term). i have heard from several people that they are. so just want to make sure. can anybody shine in on this it is a W126 300SD

[DavidSoine]

FWIW, I don't know what the 126 brakes look like.

If it is a "floating caliper" setup there will only be one piston, on the inside, and the caliper is attached by "pins", most likely the pins are protected with with rubber boots. The pins are attached to a piece of metal that surrounds the caliper and bolts to the knuckle...called the "carrier". The carrier also provides the bearing surface for the front edge of the brake pads.

So if you look at the brakes and see a "carrier" along with the caliper, you have a "floating caliper" setup. If all you see is the caliper itself, you most likely have a fixed caliper, two piston design.

There are floating caliper designs that don't have a carrier, but I wouldn't expect to see them in a Mercedes...

best,

Dave