I suspect that my latest front caliper replacement had something to do with using a set of rotors with three sets of pads instead of my usual two sets. I developed a leak in one of them when the pads were getting thin. Replacing a pair of calipers was significantly more expensive than replacing just the rotors; lesson learned.

Mercedes FSM specifies to not have the rotors turned on the w123/w126 and probably all of their cars or cars with non vented rotors.

However, I just buy new rotors and pads. New rotors whenever they are below or last known change known.

What page would that be on in the W123 FSM?

somewhere, But I remember it being discussed here that Mercedes rotors should never be turned.

Plus... $40 a rotor.. come on.

I remember Columbus being told that the Earth was flat. But the fact that someone said it didn't make it so.

Who cares what the FSM says you can or can't do, why would anyone waste time on a $40 part? That's up there with recycling dental floss.

I just looked in the W126 FSM, and it never mentions turning the rotors period. Now that I think about it, even though I have access to a full machine shop, I can't think of a single situation where I'd turn any of the rotors on my car. I'd never turn the fronts because it takes too much time to R&R them with all the bearing disassembly garbage involved. If i'm going in there, i'm going to put in new rotors (and inner bearing seals) so I can put off going in there again for as long as possible. As far as the rears go, they cost $30, not even worth my time to throw them on the lathe.


Just follow the FSM. "Replace disks with open cracks and score marks deeper than 0.5 mm immediately." Or wait to replace them until they've reached the thickness wear limit. Seriously people, a digital micrometer costs like $15 from harbor freight.

__________________
-Brian

1984 300SD, 375XXX miles, Light Ivory w/ Palomino TEX

I am left to wonder why folks who place such a high value on their time are driving old cars in the first place.
In any case, the technical feasibility of machining brake rotors is completely unrelated to whether the practice is convenient or economical.

I place I high value on my time because my time is valuable to the market. I drive old cars because I like old cars better than new cars. When I need my old cars fixed, I usually take them to my shop and have them fixed in a way that will last as long as possible. Therefore, I use new rotors instead of turning old rotors. For similar reasons, I recently gave up on buying used engines instead of reman engines.

If folks want to spend several hours of their time to avoid spending a few $100 on new rotors, they should enjoy themselves. I have other things to do.

Then here are some clues.

FSM doesn't tell you to turn the rotors each time you change the pads because it tells you to replace the rotors each time you change the pads.

$60 to make them thinner... because it's the difference between doing a good job or an average/crapy job, taking the warp out if it/they have some, no glaze left over from previous pads, less chance of squeal, new pads break in/seat better, etc.

you can often turn a rotor twice before it has to be replaced, so do the math. you save money

it's not like you are driving a race car where the rotors can never be turned and are subject to red hot temperatures. a little thinner on a slow sedan won't hurt unless they are out of spec.

W126, and they are vented. was assuming it was a W123. my recommendations have not changed.

i'll take your word for it, but the previous owner did a pad change before i bought the car and the brakes sounded bad and felt rough upon braking.

i did the pads and turned the rotors and there is no sound. however, i will not be turning the rotors a second time.

Could you quote the FSM verbatim?

I agree 100%. In my post on the first page, I said that if done properly, turning the rotors simply evens them out with a negligible affect upon the minimum thickness. Therefore it should also have a minimal affect upon the rotor lifespan. Without a question it's technically feasible, and if you have a set of too-deeply scored rotors (as specified by the FSM) that still have some usable thickness left, turning the rotors to eliminate the scoring is an alternative to replacing them.

...and my second post I simply said that I will always choose the 'replace them' alternative on mine because I consider turning them inconvenient.

__________________
-Brian

1984 300SD, 375XXX miles, Light Ivory w/ Palomino TEX

Yeah sorry I agree with Tangofox, FSM procedure 4251 for the 126, 124, 140 and a few others has tables of permissible pad and rotor thickness, and recommends replacement of rotors and discs independently once they reach their respective wear limits. Also, I think the 123 and 126 have the same front wheel hubs...

__________________
-Brian

1984 300SD, 375XXX miles, Light Ivory w/ Palomino TEX

sure, read it all the time.

turn the bolts and make sure they don't stay in. then use some tool to get all the old parts off the Binzy. put the old parts on a hot smelting iron of choice. (if you do not have one handy you can make one with some tape, aluminum foils, and 3 lifetimes of women's vindication). once the old parts are properly melted, sprinkle a little fairy dust and ferret fur on the new parts.

after the dust and fur has properly cured, Harry Potter must use his spell of choice to seal off any muggle or mud-blood tampering effects. once Dumbledore, or in the exceptional case Hagrid, has signed off on the rotors and pads they are ready for installation.

to install be sure to put everything on in such a way that you can get a wheel on it.


ok,ok. i paraphrased and slandered the FSM deliberately. i didn't know it was held in such high regard or perhaps even sacred. maybe not rotors every time by FSM. but i stand by the claim that new pads shouldn't go on old rotors unless turned.

and if you turn them to clean them and remove minor imperfections and they remain within spec, you have better rotors for your new pads than you would with the same rotors unturned.