JunoJim

I've run brake pads down to the metal, the rotors were scored, maybe half a millimeter deep in places. I didn't notice any difference in braking, so I just put new pads on, and they worked fine.

It seems to me, that new rotors should have grooves in them anyway, for more surface area. What is the real story ??? Unless there's a performance problem, why replace them ???

SkiNNy_p1mp3n

becose wen there is hi and low spots the pad only grips onto the hi spoots and not the whole rotor

tcesario

you might also see pads wearing faster than normal ,does it pull to one side ?

mleskovar

What's more important is the thickness of the rotor and if there's any cracks in it. Cracks mean overheating. One adverse affect of using worn rotors is they may not bed the pads in properly and you'll get squealing or poor stopping power. Starting out with virgin surfaces on the rotors is obviously more desireable and at only $110 for the set it's worth it.

JunoJim

mleskovar - that makes sense.

The other things would affect performance, which I would notice...

I've done other experiments on my cars, like NEVER changing the oil, just adding when low, and changing the filter once every couple years... never had a problem...

The cars you see burning oil have most likely run OUT of oil, and ruined the rings. They're lucky the car runs at all...

I had a 2 cylinder Volvo deisel in my sailboat. We ran it out of oil, and another time ran it out of water, and every time, after a cooldown, and fixing the problem, it started up, and ran (like a deisel).

It's all a matter of degree; like how much lead did you eat off the wall, or drink from your soldered plumbing system when you were a kid ??? Probably a billion times as much as they allow today...

AH1W-COBRA

never changing the engine oil will absolutely show pitting and oxidation effects on soft metals,brass,bronz,nickle,aluminum.the acidic effect on engine oil is more dramatic on unleaded vehicles,the oils are not developed/designed to suspend solids like a diesel oil.unleaded engines are held to a much stricter emission standard therefore tighter tolerances and less oil burned,so less oil replenished.it just isnt a correct method of ownership.when you sell the car you should hang a big sign on the window that announces "the oil in this engine has never been changed".im sure prospective buyers will consider that a plus when making a decision to purchase.no disrespect,im just a mech and would hate to end up with one of your used vehicles.

JunoJim

Interesting - I was hoping to get an expert opinoin... Thanks

To ease your mind, the vehicles I buy, I usually drive until they won't go anymore, so they go to the junkyard (usually after a couple hundred thousand miles) the best were 1974 & 5 RX7's, which burn oil in their cumbustion process, so I was cheating a little. Also, they have fewer soft metals and moving parts...

Of course, my wife's MB gets premium treatment. I'm an aerospace engineer, and some of us tried various self designed tests over several years... we even found a marine engine "zinc" that would screw into the RX7 cooling system, and it seemed to extend the radiator life...

vettdvr

If the rotor does not have any run out greater than .004 lateral and you have less than about .020" groove depth you probably could reuse them. I have at times in the past 40 years had to do this. The new pads will mesh into the gooves and still brake satisfactorily. However you must NOT be below the minimum thickness and the lateral runout should not exceed .004". If you meet these and have the grooves you will probably be ok. But in the future I would try not to wear this much into the rotor face and replacement would be a option.

If you reuse them you MIGHT,, have squeel until they fully bed the pads. I would say if you are within the criteria and want to try it give it a shot then report back. But otherwise I would buy new rotors.

Don't consider myself an expert,, but have had to make many things work and I have made grooved rotors work. Best of luck.

sosh

I believe that the rotors would be much more likely to crack along the grooves particularly if they are deep. The bottom of the groove could very well be beyond the min thickness spec for the rotor.

JunoJim

vetdvr - thanks - the more knowledge the better... no squealing yet...

sosh - I've never heard of rotors cracking. Besides, I would guess they'd crack radially (greater stress) rather than circumferentially.

I've studied crack propagation, and you are right, the crack very often is deeper than you might think...

sosh

I have seen and even once experienced a rotor cracking around the entire circumference in a worn groove. It was not in a car but an aircraft. made quite a mess out of the entire wheel and strut assembly. I, in fact have never seen one crack on a radius. I have seen partial cracks on the circumference. A grooved rotor is also more inclined to warp. Any squealing would be the least of your problems. Quite frankly you sound as if you are running your own personal destruction derby.

vettdvr

I have also seen rotors crack and lead to failure. this is why there is a specification for thousands of inch maximum as a specification. I have also failed an entire multiple disc system when landing at 170,000# Total weight and the antiskid system malfunctioned and landed with locked wheels. made for really smoky landing.

So for groves follow the specs. If your depth of grove is within spec as I previously said.. it might work. The depth of the grove is the real issue.

sosh

When it happened to me I was landing at CDG and I was lots heavier than that!! Fwd right side truck, thought it would be ripped off the aircraft (A330). Shut down that runway and had to take all pass off and they did something to free up the wheels to get the aircraft to the gate where they had to inspect the entire truck, struts, replace lots of parts. One of the multiple discs cracked all the way around and separated locked everything up. This A/C was pretty new at the time and all discs were well within limits and it had just come out of a B check.Opinion was that it was a defective disc that had previously been grooved with something stuck in it like a pebble.

Kar don

What airline do you fly for? USAir?

JunoJim

LOL - I've worked for Pratt & Whitney for 30+ years, on the military side. We've seen some pretty horrendous stuff that doesn't get released to the public...

I assume you know that most commercial aircraft use retreaded tires...

AH1W-COBRA

when we bought our last CPO S500 it was a lease turn in and the dealer gave me a list of everything that was replaced which included brake pads front and rear.the front rotors were grooved and it took the service manager to convince me that this is standard maint procedure.replace pads only, as long as the rotor thickness and runout were within tolerance.he also said that if you dont abuse the brakes most MB rotors will go three pad replacements on a set of rotors.

JunoJim

Ah Haa !!!

Very interesting

Fikse

that's what they tell you when they would have to foot the bill, take it in again when it's on your tab and see what they say...... they'll say you MUST replace the rotors.....

JunoJim

I believe that !!!

AH1W-COBRA

by the time we were finished buying this car we could not get them to even throw in the star service dvd at $94.these guys were finished and told us to either take it or leave it.the car was listed at $45.900 and we bought it for $30.000.they said there was absolutely no profit left in the car so they were not going to replace rotors unless i wanted to pay for them.the brakes work fine and some of the grooves have smoothed out,maybe because i drive the car like a grandpa on rorer-714.

AH1W-COBRA

those drag videos are way cool but the hair stands up on the back of my neck watching them.you guys are nuts!.that car should be valet parked at the Palms tower in las vegas,but maybe thats where you were headed after the races.gotta love Mercedes Benz.ill post a quick video of me on the 500 jawa,no brakes,burns alcohol,only turns left and will give you a rush like none other.

JunoJim

Yes !!! Post your video !!!