I have some new PFC in the box waiting to go into the front and rear but still have about 6mm left on the pagids (which seem to have heat cycled out). My mechanic has told me that the rotors need to be machined when changing pads? Yet I have also heard its most desirable to use new pads with old rotors and vice versa wherever possible.

I know there are lots of guys on here that DIY and track their cars a lot. Wondering what the consensus is on this? What are the implications for not machining then? I am using brembo type 3 rotors if that makes any difference.

Also if anyone has a link to brake rotor and pad DIY for these cars that would be great. For tips like which thread lock to use on caliper bolts, torque settings for this and whether the caliper bolts need changing every time?

Cheers

 

Absolutely do NOT machine anything. I change pads 3-4 times a summer and reuse the same hardware. I change/flush fluids 1 or 2x a summer.

If you do need machining, replace the rotors. Also find a new mechanic...

The mechanics of how the systems work and how pads break in can be found around...

Ray

 

Hi Ray, curious as to why not to machine? My rotors have a fairly large lip on them but slots remain and no signs of significant cracking to the edge but there are plenty of the usual hairline stress cracks (have not taken a measurement). Aside from the lip and slight rippled feel to the surface of the rotor, I have no unusual braking vibrations or other symptoms. How else would you know machining is required? I'd prefer just to drop the new pads in and run these rotors down until they're toast, but thought I'd ask the question on here based on what the mechanic told me. He mentioned something about machining being required as pads taper as they wear.

 

I dont machine the rotors.
With the new limits imposed by the feds and manufacturers (for your safety, nothing to do with profits ) any time you touch one its magically out of limits.
The new pads will work their way into the smooth wear patterns.

When rotors warp you will know it.

 

Aside from the fact that you probably shouldn't machine these rotors - how much is the cost to machine them? New rotors (cayenne 350s) are like 100 each.

 

The brembo type 3s are $870 per corner :S

Unfortunately in Australia we don't have the cheap cayenne rotors at our disposal and by the time you pay shipping on them over here it's not worth it for cheap heavy rotors. The brembos are still more cost effective than the OEM rotors in the long run.

 

If they have a significant lip replace them. Do not machine those rotors.

 

There's no Cayenne S in Australia??

 

What your mechanic is referring to MIGH be considered 'best practice' if money is no object...

What happens is that when you start afresh: new pads & rotors, there is this initial period where there is a transfer of material from the pad to the rotor. It is this friction surface that provides the necessary friction to stop/slow down the car.

If you are replacing the pads with a completely different type then the initial brake in period may take a bit longer as one material type replaces another.

This transfer of material (or spotty in some cases) is one of the causes of brake judder.

Hi Spiller,

In the past, some folks would use a very abrasive pad (used to be Hawk Blues) to remove this material on the rotor.

If your need is for the track then a roloc 3m pad: http://catalogue.3m.eu/en_eu/eu-asdt...ing_Disc~SC-DR not sure which would be the best color or abrasiveness can be used to remove the old material. the other option would be to simply drive the car and let the transfer occur.

PF pads don't need to be bedded, but in this case spend a bit of time getting this transfer started.

I would also suggest that you make sure that you get as much cool air into the brakes/calipers to help these last.

Rotors get replaced when the are to thin or when they warp..

Ray

 

I don't turn rotors, and as you say, try to bed new pads with old rotors and vis versa. Never had a problem, but when changing pad brands, you introduce a different variable. Brake pads don't "heat cycle out". With Pagids, I change them when they get to the thickness of the backing plate because they transfer heat and lose effectiveness, or at least I assume that is why their braking effectiveness deteriorates.. Is that what you are talking about? PFCs generally need no bedding, but I would drive 100 miles on cold PFC pads to try to get the Pagid material off of the rotor before doing some PFC bedding, just to be on the safe side.

 

If your goal is to get rid of the previous pad material when switching to a new compound, you can use a 3M scotch brite pad on a wheel to remove the old pad material. Just putting on the new pads and driving around works well enough for me

 

Hi guys,

Re: transfer layer onto the disc, I had planned on doing a couple hundred miles of street driving with the PF pads in there before going to the track. I've done this in the past and it has worked well. I just wasn't sure why else machining would be recommended. if this is the only reason then I will pass.

As for the pagids heat cycling out, I guess what I meant was they are no longer stopping the car well. Particularly since they've worn down past 50%. I'd say there is currently 4 or 5mm of friction material remaining. This was my main reason for switching the PF as I understand they work the same down to the backing plates.

I guess I really need to get a measurement on the rotor thickness remaining. What is acceptable measurement within the minimum thickness? i.e. when do you change? Money is not "no object to me" and given the expense of the rotor I don't want to be changing them out before they're done. On the flip side, I'm sensible enough to realise brakes are there for a reason.

This is how the front rotor looks today (mid way through a track day). Slots are still there but starting to become quite shallow.

 

Hey Spiller, machining rotors predisposes them to warping as they are made thinner and less able to cope with heat load. Additionally with yours being slotted, this is an additional issue as the results can be hit and miss...

If they are fine from a thickness point of view, I would do as others have said and just brake clean the disks, change your pads and drive on street for a period of time before bedding in the PFCs by getting heat into them.

PFC procedure for reference... Please note the recommendation about sanding/grinding

http://www.pfcbrakes.com.au/techtips.php?pageId=18

IIRC the minimum thickness is 32mm???...

 

From the picture, I would say that the rotor shown is getting on the thin side. Start saving for a replacement.

Isn't DBA a Australian co? I don't use their product, so don't have much of an opinion.

Pads will get affected by temp, they will heat check - cracks everywhere... Is this what you were referring to?

Ray

 

911rox, thanks for the link mate.

Ray, correct DBA is an Australian company, I can get rings to suit the brembo hats. They're probably cheaper but I've heard lots of stories about them cracking prematurely so I think I'll just eat the cost of the brembos this time and see how long they last from new. To be honest they weren't in great shape when I got the car and I've managed 6 days with them thus far. They actually wore considerably in the last three sessions yesterday after taking that photo which makes sense if they are done. And yes the pagids have some cracking through the pad - I don't think that is the fault of the pads though. Our club runs a few time attack events where you don't get a cool down so you literally sit in pit lane for 3 minutes waiting for your next lap with your brakes smoking F1 style. I won't be doing these events next year.