Mark in Baltimore

Eric - Yeah, that's what I thought.

Chris - Why is that? I just swapped out all four rotors and all four pads with fresh sets. I really didn't like the grooving I was getting with the old pads.

Also, the factory doesn't install old pads with new rotors, so I'm not sure I understand the rationale.

chris walrod

While at work, I have my racing train of thought -on- and should have said for high performance braking applications, old pads should be used to bed new rotors.

These days, that train of thought has changed somewhat due to the advent of pre-bedded pads or pads that have had oils and resins torched out of the friction material already. Not long ago we always bedded new rotors with old pads simply to put down a clean and uncontaminated transfer layer from the pad. In other words, we didnt want the oils and resins from the pad to contaminate the friction surface of the rotor.

geolab

Calm down cowboy. The thread is meant to give your opinion to 95 carrera.
You don't install new pads with new discs? don't
I do install new pads everytime I change the discs, and I strongly recommend it.


When and where I choose to give evidence,
at least I don't copy from the workshop manual and claim its my opinion.
Hearing you, its as if you wrote that page.

TheOtherEric

Huh?? Re-read my post, please. It begins: "The workshop manual states..."

I still think that if you're going to give expensive recommendations like this, that you should be able to state some basis for it.

JasonAndreas

TheOtherEric

Thanks Jason. The page right before that states that the max allowable crack length is 5mm.

And by that, I am referring to the Porsche Workshop Manual, which I DID NOT WRITE, nor have any involvement in, apart from my numerous online references to it, occasional quoting of it, and possible copying and mailing to others.

FGL28

This is getting silly.
So Eric;
Based upon what you have written my independant mechanic, who has been working on Porsches for over 25 years, did a bad thing last month when he replaced the rotors and pads for our 993?

I think not. Maybe a REAL mechanic needs to weigh in and give both the pros and cons of new vs old pads with new rotors.

Greg Fishman

Either way is fine. I usually didn't replace both at the same time because the pads wear out quicker than the rotors. Either way you need to take a bit of time to bed the two surfaces together.

Traffic53

what the hell are y'all talking about here? since when is it recommended to replace pads when replacing rotors? ...and bedding new rotors with old pads? huh? am i the only one who occasionally uses the car at the track and swaps from street to race compound pads (produced by different manufacturers too!) without problems? i've never noticed anything except for how absolutely capable the 911 brakes are. i'll run nearly glazed pagid yellows on the same rotors i run street textars. the yellows bite hard with no warm up. can't imagine the car stopping any quicker.

no offense intended, just not sure where some here are coming from. it is possible to be too 'thorough' in servicing these cars. have quality fluid, bleed them, and change out warn parts. i wouldn't fuss about "material transfer" and "bedding". few are able to successfully bed brakes to manufacturer standards anyway. read pagids instuctions and get back to me

happy motoring.

BrokenE

My experience is that for road cars, it is a commonly accepted practice to replace the pads when you replace the rotors.

Thinking about how mechanical force is transmitted to the disc brake...it's really a system of components at work. The system includes the mounting point for the brake caliper, the brake caliper, the pistons, and of course the brake pad and the rotor. In all these components there are manufacturing and machining tolerances. What a brake system is ideally trying to accomplish is to transmit clamping force as squarely as possible to the disc.

The thinking behind not using old pads with new rotors comes from the fact that because components will have tolerances (they are not perfectly square) and because brake calipers flex as they apply clamping force, a used pad will not be perfectly worn. Each of the four corners will exhibit different wear thickness. This can be measured easily to the backplate.

So if you have a used pad that is slightly more worn in on the inside diameter for example, and you use it with a new disc. Then you can expect that at least for the first few miles, you are not going to get the full braking potential, until the pads wear in. Where this wear difference is extreme, it can be a sign of a component problem and installing worn pads on new discs will only exagerate the problem.

That said, if you inspect your pads and they are evenly worn, then I don't see why there would be any problem with installing them on a new set of rotors.

Marv

Another reason to replace rotors is if they have grooves worn into them. I don't have a quantitative answer for the size of the grooves.

New rotors have a slight advantage in mass over worn rotors. The extra mass sinks heat better and improves brake performance when using brakes often and hard. That is not normal driving conditions.

The final reason to replace rotors is if they are warped or warp when heated up after a few stops.

I recommend replacing pads and rotors as a pair and be don with it. I run OEM pads and rotors and have zero complaints.

Marv

Where is the picture of the shattered rotor? Also, not suitable for service anymore.

chris walrod

I guess it needs to be said once again that using old pads to bed rotors is a TEMPORARY measure. Once the rotors are bedded, install new pads! YES, new pads are OK to use with NEW rotors