Hey all- I've been noticing lately I have to bear down on the pedal a lot harder to get ol' Pearl to stop. I took a front wheel off to look at pads and rotors and found that pads are getting quite thin. However, the rotors are what I'm wondering about. They are still real smooth, with very minimal grooving, absolutely no scoring, but they do have a bit of a "wear ridge" at the outside edge. I must say I've never seen rotors so well built on any other car. The backing plates are seemingly near as thich as most modern brake rotors! So I'm wondering- could I get by with just replacing the pads real soon and ignore changing the rotors for now?

Dave

1976 W115 300D "Pearl"
1970 W115 Euro 200 "Earl" Parts Car

Yes it is perfectly OK to change only the pads. That is what you are supposed to do unless the discs are shot. Unfortunately cars today (and for the last 20 years) are so shoddy that the discs are always shot (except Mercedes).

Reasons for replacing discs:

It is worn down thinner than the manufacturer recommends. Most discs are so thin that even the slightest truing cut brings them down this thin.

Reasons for turning discs:

The disc is warped, resulting in a pulsating pedal. If the pedal doesn't pulsate under foot, the discs are not warped enough to need truing.

The disc is so rutted it will chew up a new set of pads in no time.

Usually nowdays the disc is so cheap it only costs a couple of bucks more to replace than have them turned. So they seldom turn them, and when they do the disc is so thin it soon warps and you need to buy a new one anyway.

So just put pads on. If you do this before the metal backing hits the disc, and you make sure your calipers aren't frozen, your discs may go through 2,3 or more sets of pads before needing to be turned. And there is nothing wrong with turning them if there is enough thickness of metal. Now if you are real hard on your brakes you can warp even good discs, but if you know how to drive and baby your brakes they will never warp. I have seen discs worn down so thin you could cut bacon with them but they never warpes because the driver was easy on the brakes and never overheated them.

turning a 'warped disk' will make the problem come back more quickly, and your rotor will have even less material to disipate heat.

Use them as is or replace them.

My VW rotors have 90K miles on them, no scoring. Rotor quality is more a product of the supplier, and not the OEM. Buy from a good brake company (Brembo, Zimmerman, etc) and you will be find)

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2002 VW Golf TDI-169,000 miles B20

I agree that when you turn a warped disc the problem usually returns because the driver is still as hard on the brakes and now they have less metal to absorb the heat.

It is customary to use them as is or replace them. But as I pointed out this is more a product of the low quality of today's parts and the corresponding low price. If my discs could be turned and it cost less than new ones by a significant amount I would have them turned. PROVIDED they were good quality to begin with.

Like many here, I've had great success with replacing them. At $40 for quality rotors paying half that to get them turned might not make sense since you'll be right at or near minimum thickness, and you won't know how true of a turning job was done until you are driving on them.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

I have a spare set of rotors that I'm going to try to have turned. That way I can just swap them out when changing the pads next time. I feel rotors are good up until the minimum thickness specified is reached. I've never had problems in the past by using turned rotors on other makes.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

MB's official line is don't turn the discs just replace them. MB's tend to eat front brakes I would expect to do the rotors every 3rd pad change. But they are cheap so no big deal.

The rears however usualy last well over 100k.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If MB's line is not to turn the rotors then why is there a minimum thickness dimension on the edge of the rotors?

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

To determine if the pads wore the discs down to the point of being unsafe?

Ask the techs but I am 90% sure the company line is don't turn the discs just replace.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

If you still have pads left, there shouldn't be additional effort required to stop the car. I am wondering, if you don't have a vacuum leak that is reducing the power brake assist? Do you have any other vacuum related symtoms, i.e. slow engine shutdown, poor power door lock performance, etc.?

Perhaps I am wrong about worn pads requiring more effort, but I never noted that on any of my vehicles.

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

i agree that worn pads and rotors shouldnt increase pedal effort. they will however increase pedal travel. increased effort indicates vacuum problems or possible failure of one part of master cyl. (this would include increased pedal travel, accompanied by increased pedal pressure when it does catch).

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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.

I disagree, disc brakes are self adjusting and pedal travel should not increase as disc/pad wears. Remember you have 4 wheel discs.
The parking brake may have increased travel as the shoes wear, but not many prople would notice.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

Agree with above posts. Time to check out vaccum system for the booster. It's cheap to check out if working properly or not and lots of information in archives to help as well.

Hey,
I wasn't aware that you could get discs turned anymore. If someone does it anywhere near me I don't know about it.

Also I haven't seen it mentioned but as pads wear the fluid level in the reservoir drops. this could cause problems especially if it drops below the level of the divider in the reservoir.
Simply adding brake fluid can solve this problem.

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination

i am well aware that i have four wheel disc brakes. i do think that when the pads are worn that the pedal travel increases, though.

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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.