Does anyone do this? I saw a video of a guy replacing pads on a ML320 and he recommended scoring the discs with sandpaper.

Is it necessary or does it help?

PS - I posted this question on the ML part of the forum and expected to see it in my typical "New Posts" list but cannot see it unless I go to the ML section. News to me. I thought all posts went to everybody when they hit "New Posts."

Yes, that was standard procedure in the old days...
in case some surface hardening or some oils or something were on the surface... which would soon glaze over and not wear well... .
not too much sanding.... and keep it level...
rough sand paper.... 80 grit or so...just take off the smooth surface...a few strokes..
always use a block behind sandpaper.. not just on this ...

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

What I actually remember was roughing up the new brake pad with sandpaper.
Used to do that on the 6.3. But have not done that for years. Would take it out on the expressway and burn the new brake pads in slowly. Medium speed and a few stops. Higher speed and a few stops. High speed and a few stops.

These days I just put in new pads and forget it. Never had a problem - yet.

I'd say the best bet is to follow the directions of the pad manufacturer. Not all have the same process for bed-in procedure.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

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Visit the W123 page on iFixit for over 70 helpful DIY guides!

These days I just put in new pads and forget it. Never had a problem - yet

x2

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Score? Uh, no. Sand 'em, maybe. Just break the glaze.

In the early 80's AMMCO (the brake lathe folks, not the trans rebuilders) marketed an add on for their lathes that scuffed (maybe polished?) the rotors after they were cut. It used sanding discs that contacted the braking surfaces of the rotors while they were turning on the machine. We used it to quiet noisy rotors. My guess is that we had the cross-feed wrong on the rotors that made noise. (Mostly big GM trucks.) I worked with a mechanic that used an orbital sander w/200 grit to break the surface glaze on the rotor when doing a cheap "pad hanger" brake job. He didn't grind into the surface, just dull it. This was back in the days of transition from asbestos to semi-mets. Asbestos linings liked a slightly rough surface (like 300-400 grit paper), it helped them 'bed in'.The early semi-mets didn't care - they just chewed up rotors.

Did not mean really score; just scuff up with sandpaper. The video said to use 80 grit.

Think I will just disregard this completely.

New rotors will usually have some anti-corrosive coating over it to prevent corrosion while sitting on shelves and whatnot.

The only thing I've ever done was take a brake clean soaked rag and wipe that coating off the pad surfaces of the rotor.

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Allen Kroliczek
Oak Grove Autosport | Oak Grove Autosport
01 G500, 82 300TD, quite a few more.....

If you are installing new brake pads and new ritors: take the rotors out of their packaging and clean them very well with brake cleaner. They are coated in preserving oil so they don't rust, and that needs to be gone so just clean bare metal is left. New rotors SHOULD have a uniform, fresh crosshatch pattern cut into the friction surface like the honing on new cylinder walls. Install the clean rotor on the hub, lubricate points that need lubrication with silicone brake grease, apply thread lock to bolts that need it. Being careful to keep the brake pad contact surface clean, lubricate the sliding ears of the pad and install it. Bolt it all up, and read manufacturer instructions for bedding in the pads. The crosshatch pattern of the rotor will grab pad material and hold it (as it should) bedding in the pads. The pads are also heated by the bed in, and cure up the friction material boiling away any gases that are able to be released from the friction material. Usually, you do a few 25-10 stops, 40-10 stops, 65-10 stops, and NEVER come to a complete stop at any time in the bedding in procedure. Doing so will cause the fresh, hot friction material to weld itself to the rotor, and leave a high spot that will cause pulsation thereafter. After the bed in, drive carefully for 250 miles to avoid panic stops to 0mph, and then you're done.

If replacing pads only and reusing the rotor: the rotor needs to be measured for thickness. If too thin to be serviceable under manufacturer recommendations, get new rotors. If they are more than spec, you may proceed. You MUST have the rotors turned on a brake lathe to make the friction surface uniform and true, and to cut a uniform crosshatch for bedding in the pads. Once the rotors are turned and are uniform and true, measure again to confirm they are thicker than spec. With the rotor on the lathe, turn at max speed and with an angle die grinder with a scotchbright pad disc apply a uniform, consistent crosshatch pattern to the friction surface. From this point, proceed as if you were installing new parts.

Working in the field, this is the exact verbatim procedure I followed time and time again. I bedded in the pads before I returned the vehicle, and I instructed the customer to drive carefully for 250 miles after, avoiding panic stops to 0mph (hard, since everyone drives automatics). I never (not once) had a comeback for noise or pulsation. Also, I have fixed several cases of noise complaints with a proper bed in sequence to remove the glaze from the friction surfaces and cure up the pad compound the rest of the way. It is slightly more difficult since used parts lack the crosshatch pattern that helps the bed in process, but with a few extra passes it will complete eventually.

Sandpaper by hand is just too loose with tolerance for my taste. I also recommend starting with a new rotor each time as opposed to cutting. Brakes transform kinetic energy directly into thermal energy. The ability for the brake parts to soak up and reject this thermal energy is what makes them function well or not. The less mass a rotor has, the less metal is there to soak up the energy and become saturated. That means brake fade occurs sooner and stopping distance is increased. Rotors are cheap now so it makes turning a thing of the past unless the rotors are rare and still pretty pricey. Follow this advice and you will never go wrong.

Manny - thanks.

Manny - thanks, that is a keeper!

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Last time I replaced the pads on my car (Porterfield R4-S), the pads came with an installation kit and instructions to block sand the discs to a matte finish and then spray them with this stuff that looks like aluminum spray paint.

I did as the instructions stated and the results have been very good.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250