[judge]

I bought my 1993 968 Cabrio in April this year, with only 40,000 kilometres [ about 25,000 miles] on it and it has been babied since birth! The PPI was done by one of Melbourne's most reputable independent Porsche shops and come back with the following details about the brake dics; "Front 27.3mm - Min 26.00mm; Rear 23.36 mm - Min 22.00mm" The pads were 70% good front and rear. This seems to me to suggest that the discs are original and I have about 1.3 mm left before I will need to change them. I would also guess that and the pads have been changed not too long ago.



So, my question is, how long will it take before I have to change the discs. The car still leads a pretty pampered life and is rarely driven hard; and out here in the bush there is limited need for heavy braking, unless you come across a kangaroo or a fox crossing the road in font of you. <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" />



Given the expertise here I should also ask if you agree with the minimum disc thickness as quoted in the PPI.



Finally, if I change the discs soon while there is plenty of life left in the pads, what are the pros & cons of keeping the old pads, or changing them at the same time?

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[Eric_Oz_S2]

The minimum rotor thickness is stamped on the edge of the rotor. The figures form in thickness you provide are correct. New thickness is 28 and 24mm, so they are not even half worn. As far as remaining life goes, that depends completely on driving style. If not driven hard, then you would easily get another 40,000 km on them.



PS - that must be one of the lowest km 968 cabs in Oz.



Eric

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[flash]

many factors determine rotor wear - pad hardness is one of them - what kind of pad you have will change the wear rate a lot



as rotors get thinner, and pads get thinner, heat goes up - this accelerates the wear of both components - so, as an example, while you may get 25k out of the first half, you'll likely only get 10k out of the second half



age of the pads will play into this as well, as pads get hard over time and don't stop as well



when you change pads, you should surface the rotors - this is to remove the deposits and prevent chatter - in doing this though, this removes material and shortens the rotor life



if i had to guess, i'd say you might need to change rotors when those pads are gone (maybe fronts but probably not the rears) - almost certainly all of them after the next set of pads though

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[ds968]

I have 50,000 mi on the current rotors, and they are still "out of the box" new.. no evidence of the slightest wear on them, no grooves, not even hair-line marks, certainly no lip of any kind. And to make things even more bizarre the brake pads which ostensibly would be as soft as can be to preserve the rotors in this manner, have more than 70% left after the same 50,000 miles, and they produce zero dust. I don't mean a little dust, I mean NO dust at all ! My mechanic keeps insisting that I must be going to someone else and having the brakes replaced because he claims he's never seen pads wear only 30% after 50k miles on any car, nor rotors looking brand new after all this time and wear.. As great as this may be for mwe, it's nonetheless frustrating because eventually whaen they do need replacement ( I'm guessing in about 3 million miles from now <img src="/forum/images/smilies/968/rolleyes.gif" class="smilie" alt="" /> ) I want to get the exact same rotors and pads but I have no idea what brand either one is- the P.O. changed all of them right before I bought the car at 58 k miles, and the work worder does not show the brand which was used, nor does he have any idea what was put in there. <img src="/forum/images/smilies/968/dry.gif" class="smilie" alt="" />

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[flash]

ds968 - you do seem to have a magic combination for the kind of driving you do



as a rule, ceramic pads like the ones you have don't wear very fast, and don't wear out rotors - the trade off is that, while they stop quite well, they don't stop as well as some other ones, and don't handle heat as well - that's just physics though - no getting around that - you really have to be using your brakes to tell the difference though, so for street cars, they work very very well



also, the same pad compound can act different on different rotors - i have R4-S pads on the denali and the 968 - i have rotor wear on the Zimmermans on the first set of pads matched with them which are at about 60%, but none whatsoever on the Baers and i'm on the second set of pads



basic physics lesson - something has to give - one material or the other must wear if they are doing their job - if they aren't wearing, they aren't working fully - so, if it's the rotor, and not the pad, then the pad is not heating up well enough - if it's the pad, there will be dust - whether or not it sticks to anything is the question, and different pads dust differently - some are heavy and sooty - others are very light and blow away - still others are in between

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[ds968]

Not sure how effective my braking is because I never really tested the car,s stopping distance ,and on the rare occasions I drive someone else,s 968 , it,s not something to which I pay attention so as to have a frame of reference and compare. I,m also not on the brakes all that much since the majority of driving is highway, and on fun runs the gear shifter does most of the braking so once again, there aren,t a lot of times when I stomp on them hard enough to get a good sense how well they perform under trying conditions. The sole exception was when I tracked it at the Speedway in Fontana, and I honestly did not like how they felt, so perhaps they,re not necessarily great brakes, but they clearly last without typical wear of either disc or pad in apparent defiance of physics theory. My MBZ rotors on the other hand, already have grooves and a moderate lip after only about 30k on them and the wear rate would indicate I might get only another 10k before they need replacement. Incidentally, the pads on the MBZ turn the wheels black with dust in no time. So I,ll take whatever magic is at play with the 968 because I am convinced at this rate the rotors have AT LEAST another 100k miles left on them, if I replace the pads with the same make ( and we,re speculating those are ceramic compound Metalmasters , but can,t be absolutely certain of that ) when the time comes and my driving remains pretty much the same as it has been.

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[flash]

them lasting so long is not in defiance of physics - what it means is two things:



1. that you don't use the brakes that much relative to the number of miles you drive (miles per stop kind of thing) - since you acknowledge your driving is mostly freeway, this is something of which you are already aware



2. that they are not grabbing like others, and rather more slick - your notice of their performance on the track is a good indicator of this



so, as long as you are happy with them, stick with them - obviously they have been stopping you when you need to stop, so i can't say you need to change for any reason



as for how long your rotors will live, i'll take another look the next time i see the car, but from the sounds of it you could easily get another set of pads of life out of them - lucky you

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[ds968]

Those must be the reasons for the longevity but I,m a bit weary as to how these slick brakes wiill do if I ever find myself in a situation where I have to break really hard in an emergency with no margin for extra distance. But as you said, they stop just fine for what I need currently, so I guess I,ll stay the course. Once again I choose aesthetics over function ; the biggest selling point to me is no brake dust on the wheels.

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[flash]

that' a big one too - i hate having to constantly clean brake dust - now that i am getting some wear on the front rotors and pads, the amount of dust has quadrupled - i may change them for fresh ones for that reason alone

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[Cloud9...68]

I have the same combination on the front as Flash - Zimmerman drilled rotors with Porterfield R4-S pads, and I get very little dust. It's not nonexistent like DS968's, but it's pretty minimal. My rears (Zimmerman drilled rotors, no idea what type of pads) actually produce more dust than my fronts. I did bed the fronts in after I installed them, and turned the rotors. They work fine for my purposes (never felt brake-limited, although this may change once I start driving on longer, faster tracks).

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[flash]

yup - mine were like that too, right up until i showed some wear - then it got worse - a LOT worse

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[Cloud9...68]

I've had mine a couple of years now, including a lot of track driving (although primarily on short, technical tracks where I never braked a whole lot), and no sign of excessive dust yet...

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[flash]

how much wear on the pads and rotors? maybe you just haven't gotten there yet? mine are now about 5 years old - maybe it's an age thing?

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[Cloud9...68]

Not a lot - the pads look like they have maybe 70% of their life left, and the rotors have very minimal signs of wear. I guess I just have to be harder on my brakes. I just don't use them a whole lot. When I was a kid, I had more than one car whose charging system failed while I was driving, so I had to get home without using ANY electrical components, including the brake lights. The first time it happened, I was very worried I wouldn't make it very far without using the brakes, but I was surprised to find it was very easy to drive without hardly using them. I just drove as slow as I could get away with, downshifted to slow down, and then just barely tapped the brakes to bring the car to rest at intersections.



Guess I just like Fangio's philosophy of "More gas, less brake." Although, before we start another debate on this subject, I fully realize this doesn't work on tracks with even moderately long straights.

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[flash]

nah - i think you just haven't gotten there yet - we'll see how it is when you get down where i am in wear

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