Do I really need new rotors? 300SD

Took my 1984 300SD in for an alignment and had them check the brakes at the same time. The guy said I needed new pads and rotors because there was only
10% left on the pads and that mereceds rotors are soft and they have to be changed when the pads get that low.
Am I being hustled or is it necessary to change the rotors when the pads get low?
How hard a DIY job is this?
Thanks, Jeff
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If I was doing the job for a paying customer, I'd highly recommend new rotors. MB rotors are intentionally soft by design and replacing them one to one with the pads is SOP. Some experienced DIYers may elect to replace pads only but it should be a carefully considered choice. Personally I'd rather replace the rotor than have to do both again prematurely because the rotor wore out.
Rooster wrote:

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Rotors do wear out. So there's a minimum allowable rotor thickness measurement whose number, I believe, is cast into the rotor's outer edge. One then just measures the rotor's worn area vs. the minimum.
The shop's claim that one replaces the rotor because the pads are worn is technically bogus, but in real life is about a ratio of 3 pads to 1 rotor in my experience. My '80 300SD still has its original rotors after 112K miles but they're probably now overdue for replacement.
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What the shop told you is bogus.
I recommends changing the rotors every 100,000 miles or so. If you are over 150,000 miles, change it out.
The pads on W126 is definitely a DIY job... quite simple.
The rear rotors are very easy to change out... just remove the two bolts holding the caliper... hang the caliper on a rope... NEVER HANG CALIPER ON BRAKE HOSE... Then get your biggest ball peen hammer and whack the face of the hub... where the lugbolts thrreads through... 24 oz hammer and higher is recommended and the rotors will pop out.
The front is a doozy, but you need time. Not terribly hard though but you do need muscle and right tool. Pop out the wheel... pop out the dust cover.... loosen the allen bolt on the hub nut... and remove hub nut and bearing... Remove two caliper bolts and hang the caliper on rope... pull out the rotor with hub.
Mount the hub on the wheel you took out... three bolts is enough and snug it up. You need allen bolt socket to remove the rotors from the hub... you will need breaker bar... 18" and some extension and 1/2" to 3/8" adapter as the allen socket will be 3/8" socket and the breaker bar will be 1/2"... Put some weight on the wheel to keep it from sliding and unbolt that allen bolt.
Put a rag in the wheel bearing hole and use the ball peen hammer to hit the rotor all the way around until you can remove it. New rotors... put blue threadlocker on the bolts and torque to 85 lb/ft. Reverse all steps... Caliper bolt torque is also 85 lb/ft.
Takes about 4-5 hours DIY. Back can be done in an hour both side... Front will take you 3-4 hours. Go for the ATE Premium One (slotted) rotors and Akebono pads at buymbparts.com... don't forget 4 sensors too.
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I forgot to say the rear rotors have one allen bolt each... small size... remove this before banging on the rotor.
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Rotor wear depends on how hard you drive and stop, and how hard the pads are. No definite statement about wear can be made. My experience is that my rotors need replacing once for every two sets of pads replaced.
If you don't replace the rotors when you replace the pads you sometimes will have a case of brake squeal that can last a long time. If the brakes squeal, they will squeal until the pads seat.
EJ in NJ
Rooster wrote:

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wrote:

It is not necessary, but if the rotors are worn too thin to be serviceable, or if the pads have - now or in the past - been allowed to wear so low that the rotor braking surfaces are scored or worn unevenly, the new pads may wear far too quickly, and/or braking effect will be lessened. Used to be we'd cut the faces of the old rotors on a special purpose lathe machine especially for this to make them smooth again. But again, this may make the rotors too thin to work properly - depends on the spec.
Other problems can be uneven wear on the faces, making the surfaces not flat anymore, causing excessive wear on the new pads and/or brakes that do not function properly.
Newer designs, especially on GM cars, have made the rotors so easy to change, and the parts so reasonably priced, that no one re-cuts the faces any more.
If you suspect you are being hustled, get the serviceman to show you what the problems are - are your surfaces pitted, grooved, or scored, are the rotors thinner than spec. (what is the spec. anyway). Inspect the old pads to see if they are worn smooth and straight to indicate if there are problems with the rotors that are not apparent. Always get him to leave the old parts in the trunk, so you might possibly have a chance at not being outright defrauded as well as being hustled for possibly unnecessary new rotors.
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As others have mentioned, the rotors may not need to be changed. However, from a service point of view, the shop carries the liability to get the job done right the FIRST time. If the brake squeals or vibrates after changing pads (without rotors), will you think the shop cuts the corner or tries to save you money? Will you trust the shop in the future? Or will you tell friends (or newsgroup here) about your BAD experience?
Also, all shops adds profit on the parts they sell. So, of course they would recommend changing the rotors. Unlike American cars, MB rotors are not serviceable. I have not encountered any MB shop/dealer not recommending rotors with the brake job.
I replace rotors with every 2 sets of pads. Now the front pads on my 190D is the 2nd set. The rotors have slight vibration.
I would rate the disk brake job a "2" (5 as the most difficult). The procedure actually is not that difficult, but more tools are required for a beginner. For example, floor jack, stand, good socket/wrench (don't buy the cheap ones), allen (hex) bit, and maybe a long/strong wheel lug wrench. If the wheels were tightened by power tool last time (most shops do so), it may be too tight for the factory wrench. Oh, wear gloves and mask (the brake dust is harmful to your lung).
A first-timer may take 2-3 hours for both wheels. Once you are used to, one hour is the most. Do ONLY one wheel at a time so there is always a reference in case you are confused. Also, do NOT try drum brake unless you are sure what to do. I don't do drum very often. The last time I did it took me more than 3 hours because I had to redo due to mistake :-(
If you do decide DIY, check on Google or come back here to ask. Good luck.
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Wan-ning Tan wrote:

Course they are serviceable they can be machined but still must be within the minimum thickness.
Its just convenient that they sell new rotors - for the profit.
I have not encountered any MB shop/dealer not

as above

You could have machined them.
Third party rotors are just as good, plus you may find they were supplied as original equipment to MB.
Check around for the price. I bought drilled and slotted rotors plus pads at half the MB price, much better value.
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The best Mercedes shop in my valley recommends new rotors with every pad change. New rotors now cost less than the charge to turn them.
I did not change rotors when I last did a pad change, and now, after only about 3000 miles, I notice a pulsation or variation in the braking when I come to a stop. The rotors are almost certainly worn unevenly.
Considering the high cost of many parts for my 300 TDT, rotors are a bargain.
You mechanic does not sound like he is being dishonest when he recommends new rotors. It's a good idea.
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MB rotors can be machined. However, it is not worth the time that the shop needs to do so. To do the machining, it takes time... extra 20 minutes per rotors... to set it up and then have the machine cut it for you and then buffing it if you have older machine. You only charge customer like $15 or so per rotor...
For shop with no machine, they farm it out, but that will lock the car in the service bay that you can't use until you get the rotors back.
My experience with machined rotor is that they don't last long... less than 2 years before it warps. Consider that W126 rotors cost about $50 for front and $30 for the back each... it is cheap enough to buy... Of course, that's not the retail price... so double or triple the price for retail. Then this is quite pricy for customer.
As far as changing rotors with every brake job, that is a waste of money and resource. Unless you have something wrong in the first place such as pulsation or abnormal wears on the rotors, I don't see any reason to change it.
The biggest reason for alot of the rotor problems is simply the brake pad. Stick a OE pads in and you will get the same problem again. OE or OEM grade pads are not the best pads. They work the rotors so hard that it eats the rotors in no time. Time after time... everythime I saw OE grade pads on the car, I see abnormal rotor wear.
So what pad to use? Right now, ceramic pads are the best bet... Bosch or Akebono is my choice now. It stops the car good and easily... no black dust. PBR Ultimate ceramic pads are dusty... which is what I got on my car... but everyone else, I stuck in Bosch and Akebono ceramic pads.
Another reason for abnormal wear on rotors... far more common is use of impact wrench on lugbolts... it really screws it up.
Heav... you may have some other issue that cause the vibration during braking.
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Thanks everyone for all the replies. It's great to have a bunch of experienced people to hang out with on the internet to get advice from.
I'm taking Tiger's advice and getting the Akebono pads and ATE rotors from Rusty.
I found a couple of experienced indie MB mechanics through a guy I know. I think I'll contact them and see what they'll charge before I spend my weekend learning how to put in the rotors.
Jeff
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re the minimum thickness, my rotors have 260k km on them are are worn much below this minimum.... I think I'm down around 175 mm. What 'exactly' is the problem at these lower thicknesses? Is it that the calipers may not retract properly; ie they come out too far? rotors get too hot? I really don't know In any case, I'm doing my rotors asap as well, and hope that it won't be as complicated for my W124 as Tiger described it for the W126. I was supriesed, very actually, that there it was required for the bearings to be removed
cheers

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I did my W124... all new rotors and pads. W124 is a ton easier... simply one bolt holding the rotor in place and it pops out with a whack of ball peen hammer.
Only the W126 is that tough one. I actually did it twice... two different cars.
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On Sep 26, 11:27 am, snipped-for-privacy@sciborg.uwaterloo.ca (Guenter Scholz) wrote:

The caliper pistons need to push out further to take up the extra slack of the thinner rotors as the pads wear down When past the wear limit on the rotors, I've actually had part of the piston break off and it gave the brake pedal that "soft" feeling. Then ya end up not only replacing the rotors and pads, but the calipers too. The rotors on my l07 are fairly easy to replace.
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The last time I tried to have the rotor machined was more than 4-5 years ago. I don't do that anymore (even with US cars) since, like Tiger mentions, it's not worth the time and cost.
When I took the MB rotors to be machined, 2 shops rejected even though they did other rotors for me before. Both cited the same reason: not serviceable. OK, maybe it can be done mechanically, but no one wants to do it for some reason.
Anyway, I change rotor for every two sets of pads. The parts cost isn't much when DIY and buying parts online.
Rob wrote:

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