Hi,
I may need new brake pads, I don't know yet. Haven't taken it in.
But what are Rotors?. I've read that sometimes they need to be replaced
as well. Why and when do they usually need to be replaced?
Thanks

Rotors need to be replaced when they are worn too thin or worn so unevenly that they cause problems, like a shaking steering wheel when braking.

There are few situations when rotor replacement is critically necessary.

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I agree with tangofox.

Indeed original OEM Mercedes rotors were well made.

If its not too badly scored or if the outer edge does not have a very high lip on it (as the center material surface wears, the outer edge that is not in contact with the brake pad remains at the original thickness. So you can see and feel the contrast.)

The rotor is the disc that the brake pads embrace to stop the car.

Imagine yourself clamping both your hands over a moving bicycle tire.

The tire is the rotor and your hands are the pads.
Clamp down and the tire stops.

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
********************
1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD

Rotors:

1983 Mercedes-Benz 300D Base Sedan - Brake Pads & Rotors - Page 2

They're the thing the brake pads rub against when the brakes are applied. Common reasons for replacement are being worn thinner than the minimum thickness (checked with a micrometer), or warped (feels like ABS activation even though you don't have ABS). On a 123 or 126, the rear ones are extremely easy to change. The front ones are little more involved since you have to repack the wheel bearings and then set the bearing preload. The factory recommends using a dial indicator for this. American manufacturers usually recommend a certain torque setting instead.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Do the front and rear brakes/rotors generally wear the same?
If you need one rotor do you usually need all four?
I'm wary of an unscrupulous mechanic saying I need rotors
when I don't really need them right now...Been putting off
taking my car in to a shop.

Fronts usually wear faster than rears. They should generally be replaced in pairs, so if you need one front, it's a good idea to do both fronts.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

You may want to spend $100 / $200 and get a documented appraisal or survey of your car. Sorta a mechanical check to see whats wrong ''as you are thinking of selling'' or something like that.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

if you still have the 83 mercedes, the rotors are easy to tell if the DEFINITELY need changing, because they will feel like described above. you'll feel a pulsing in the pedal, and the steering wheel will shake as you apply the brakes. other things can cause this shaking, so it's not 100% sure, but it's a good sign. also, if one pad is worn unevenly, or more than the others, it's a good sign that the calipers will need service or replacement.
front rotors on the benz are not easy to change, as in addition to the bearing repacking needed, also, there are small bolts on the inner edge of the hub that need to be removed, and they are VERY tight.
if you are inquiring about a different vehicle, please let us know.

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My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
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Note that the Rotors are also called Discs and the reason they are called Disc Brakes.

While I have replaced the Pads Only on some Vehicles due to not having the Money or being in a hurry to get the Car Back on the Rod in general if the surface of your Rotors are not very smooth they should be replaced or turned (metal is removed to make the Flat again).

My experience has been that if I put new brake pads on an old Rotor the Pads do not last as long.

Also if you measure a used Brake Rotor you will find that the outer portion where the Brake Pads make contact of the Rotor is not going to have the same thickness as the inner portion of the Rotor.

This is different from warping which can also happen.

If the Front Rotors are removed on a W123 the whole Hub has to be removed because the Rotor blots together from the inside.

Besides the mentioned re-greasing there is a Procedure in the Factory Service Manual to adjust the Hub end play/Bearing End Play with a Dial Indicator.

I had been a Diesel Mechanic for 18 Years and though I could adjust the End Play by Hand as I had always done and ended up overheating the Grease in the Hub because I got it to tight.
I did it again with a Dial Indicator and after years of use have had no issues if I used the Dial Indicator as the manual wants you to do.

I am saying the above because if you have a Mechanic do the Job and one or both of the Front Wheels gets too Hot not using a Dial Indicator to adjust the Front Hub end play could be the issue. Don't let the Mechanic BS you on that.

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84 300D, 82 Volvo 244Gl Diesel

The list below is for engines, what car do you have?

A 240D is a 616, a non turbo 300D is a 617.

There is a bunch of info there including the minimum rotor (disc) thickness. This will let you know if they need replacing.

The fronts wear much faster than the rears, as they do most of the braking.


Model 123 Maintenance Manual Index

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83 SD

84 CD

My experience has been that, when I need to replace the pads, I generally need to replace the rotors as well. Even if the rotors technically have life left, I can only be confident that I have nice, squeak-free braking if I replace the rotors too. And least this has been the case with the fronts.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Which brake light is it?

BTW, you might want to stick to one thread per issue so that the rest of us don't get confused .

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1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

Thougth I would add something. I tend to buy Cheap Rotors and Cheap pads locally and buy Car is a Beater.

so I replaced the Rotors instead of turning them because it costs about 1/2 of the cost of a new Rotor to have the Old Rotos resurfaced. And, if I have the Old Rotors resurfaced I have to drive several miles away drop them off and come back for them later and maybe they are too thin to reuse.

The local Auto Parts store is only 1/4 mile away and is saves a lot of time on things I need right away.

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84 300D, 82 Volvo 244Gl Diesel