whats the limit on brake rotors? - PeachParts Mercedes-Benz Forum

ned2683 · #1 08-13-2003, 09:14 PM

i am looking to get my rotors grinded/turned to take some of the grooves and marks out of them while replace the pads with OEM pads (the PO used cheap pads). i was wondering what are the thinnest you can have your rotors before you need to throw them out. thanks

Gilly · #2 08-13-2003, 09:21 PM

The Min Thickness is stamped on the rotor if they're MB rotors. Usually if it's above the service spec you just reuse the rotors, I've never machined an MB rotor. The service spec is usually about .5 mm thicker than the Min Spec stamped on the rotor.
If you can't locate the Min Spec on the rotor, let me know which of your cars you're working on and I'll see if I can find the specs.

Gilly

psfred · #3 08-13-2003, 10:04 PM

Usually if the grooves are deep enough to need machining, the rotor will be at or below minimum by the time you get them out.

This is one of the drawbacks of the aftermarket pads - the ones that advertize long lifer are harder than the MB OEM pads, and you sacrifice the rotor for pad life.

I the old days, I got ahold of a set of asbestos pads for my Audi Fox -- rotors looked new, but the pads only lasted 10,000 miles! I switched back...

Peter

dc88168 · #4 08-13-2003, 11:18 PM

On my 1985 300D Turbo, the rotor stamps indicated:

Front: Min: 10.5 mm (=0.4134 inch)

Rear: Min: 8.3 mm (=0.3268 inch)

David

________________
1985 300D Turbo

leathermang · #5 08-13-2003, 11:47 PM

Get a FIRM quote on turning them first...
When I got mine turned it cost as much as I could have bought NEW one for....and they turned one below the minimum thickness...

ned2683 · #6 08-14-2003, 12:12 AM

i think the balo rotors go for 60 bucks a set on ebay. but i know a shop that would turn them for free so i was gonna see how long i can ride these rotors till i need to change them.

right now the passanger front rotor has grooves in them, shake and squeal when stopping. i don't think they are warped as i have inspected them before.

this is for a W126 300SD BTW.

so i suppose what i need to know is after turning them how much life can i expect. rephrase = how fast do these rotors wear down with OEM pads. i don't want to be turning them and wearing them down to the unsafe limit in 2-3 month. is there a general idea on how much 1mm would last assuming i don't use the brakes on a race track. since i bought this car about half a year ago i couldn't keep track on how old the rotors were and when they were changed, please help me out on how long your rotos typically last.

thanks guys

leathermang · #7 08-14-2003, 12:17 AM

I think the dealers offer" MB" and " other" ... my new one cost me $35 .

Gilly · #8 08-14-2003, 05:08 AM

Wht I've noticed is you can usually start out with new pads and rotors, replace the pads ONCE before again needing pads and rotors both, so the rotors should last through 2 sets of pads.

Gilly

Thomaspin · #9 08-14-2003, 11:27 AM

As for how long they last, there's no right answer. When I used to commute 15 miles using back roads, it was 12k miles on a set of front pads and 24k on the rotors. Lots and lots of braking. 1983 300SD.

Now my commute is 12 freeway miles and I brake maybe 6 times....looks like 30-40k on a set of front pads, and lots more on the rotors.

In CA shops that machine rotors will usually measure yours and tell you if they can be turned, keenly aware that lawyers will be all over them if they go below the stated minimum thickness and you have an accident.

rmmagow · #10 08-14-2003, 11:28 AM

FWIW, I've usually just changed the pads after doing a quick measure of thickness on the rotor to be safe. Not so much on my MB, but on my mazda 929 I've changed pads 3 times in 140K miles and the brakes continue to work fine even thought the rotors are a LITTLE grooved. No shaking or pedal pulse and I don't let the pads get too thin before swapping them out. I just changed the MB pads a while back and basically did the same thing and they seem OK. I think if the rotors are only a little grooved you can just let it go at that as long as they're more or less in thickness spec. Measure in a few spots before decideing if the rotors are OK.

Thomaspin · #11 08-14-2003, 11:43 AM

That's good advice from rmmagow. The place not to measure rotor thickness is at the edge, which is an unworn, original thickness, part of the rotor. You need a caliper that 'steps' over the edge, or use a couple of washers, nuts, whatever to step back the caliper on the main disc surface, measure, then deduct the thickness of the 'padding' for a true reading.

alan911 · #12 08-14-2003, 01:07 PM

If they are "shaking" when you come to a stop it ususally means the rotors are warped. Cheap Pads.......No amount of turning will fix them. Seems to be normal with MBZ after 75000 mi or so. Probably 2 or 3 sets of pads.

I just replace my rotors and pads and sensors (all OEM) for $119 total. Not a bad job really. And no dust yet.

I've never heard of anyone actually recommend "turning" them.

For a few dollars more you have the piece of mind with new ones.

psfred · #13 08-15-2003, 12:18 AM

The easy visual way to check MB rotors is to look for a disctinct lip on the outer edge, where the pads don't cover. When this appears, the rotors are under thick and need to be replaced. You can also check the inner side -- the pad rubbing surface must be above the central hub portion -- if it is level or near lever, the operating part is worn away to near minimum.

Figure rotors won't last any longer than three sets of pads, max, maybe only two.

That's quite a while for me, as I usually get 30,000 or more on a set -- lots of easy country driving, with the major milage on the highway for hour after hour without braking.

Peter