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Old 12-09-2006, 12:20 PM   #3
Butt Dyno
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Join Date: Apr 2002
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06 Evo #7 STU, 05 Saabaru


I just bought new pads. Do I need to buy new rotors or have my rotors turned?
I just bought new rotors. Do I need to buy new pads?

This comes up somewhat frequently. Some folks have asserted that you need to buy them in pairs. So I sent this question to some of the NASIOC brake experts:
Originally Posted by ButtDyno
I've always wondered about this and I would like to add it to the brake FAQ. I have always gone by the rule "whenever you swap anything (pads or rotors), bed it in afterwards" and it's worked out fine for me - i.e. I have not always bought in sets. I would be curious to know what you guys think.
I got three replies. There is some nuance here so I don't want to add cliff notes

1. Eric @ StopTech:
Originally Posted by ESmooth
There's definitely no need to get new pads and rotors at the same time.

If you are getting new rotors only and your existing pads have good volume remaining, a bed in procedure is all that is needed to lay down a good transfer layer of pad marterial.

If you are putting new pads of the same compound on used rotors, a bed-in cycle is again all that is needed in order to put the new pads through green fade and to refresh the existing transfer layer.

If you are putting new pads on old rotors that were used with a different compound, its best to drive around normally for a few days or a week in order to clean off the pad transfer layer of whatever was being previously used. After the old material is gone, a normal bed-in cyle should be done to establish a transfer layer of the new pad material onto the rotor face and to put the new pads through green fade.

Some compounds dont play well with each other and trying to bed one compound in over another can lead to vibrations and poor performance. If you have some race pads for your calipers, its a good idea to drive on those for a day or so between pad changes since they are more abrasive and will make the clean up of the rotors go that much quicker and reduce the chances of contaminating the new pads with the old material.

Feel free to use that however you need it for the FAQ page.
2. Ken @ WRXBrakes:
Originally Posted by WRXBrakes
Well - as usual it's not simple.

Assuming pads and rotors are still flat and not tapered then used pads are good to bed new rotors with. They transfer material more evenly leading to less instances of pulsing/judder. They should be of the same or similar type for best results i.e. trying to bed in Carbotech ceramic pads after OEM Brembo semi-metallics can be problematic.

The chemistry at the interface is sensitive to a lot of things - but usually you can re-bed old pads to new rotors and vice-versa.

Another example is trying to bed in street pads after race pads - can be tough.

It's usually somewhat visible - smearing on the rotor surface etc.
3. Todd @ TCE:
Personally, I've not had any issues with old pads on new rotors or new pads on old rotors. Not like I toss out a set of race car rotors just because the car needs pads...I wish! lol I could make some money on that one.

I usually lightly sand the pads down and put them in if they are used and let 'er rip.
Might add that when you do change pads on old rotors however that you may want to consult the new supplier as to their suggestion for rotor prep also. I have seen where moving from a long time PFC use to another brand can cause issues. They put down a lot of carbon transfer and the new pads slip right over the surface if you don't scuff them when the new pads are installed. In short, I'd always suggest a hand sanding if you change compounds or brands.
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Last edited by Butt Dyno; 01-23-2008 at 10:39 AM.
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