Safety Margin for Minimum Disc Thickness?

[spooltime]

While replacing a defective ABS speed sensor yesterday, I took disc thickness measurements of the two front discs on my CTTS. The disc shows minimum thickness spec as 36mm. Both measured in at about 35.7mm. Obviously, I've got to do the brakes in the relatively near future, but I'm wondering how much more I can let these wear down before I'm putting my safety at risk? 35mm? Or should I just plan on biting the bullet and popping for the uber-expensive multi-part front discs now? Are there any alternative discs available?

[Loren]

Are you doing pads soon also?

What was their thickness?

[spooltime]

Pads will be done, too. Pad have maybe 35% - 40% of their friction material remaining. Looks like a prior owner may have done pads previously, but skipped doing the discs at the same time.

[Loren]

With the weight of the Cayenne it is not unusual to replace discs with each pad replacement. Driving style may have some influence too.

I would say plan on changing both pads and discs in the next 5,000 to 10,000 miles.

If the brake fluid has not been flushed and replaced in the last two years - do that too.

[ALEV8]

Loren shouldn't we get a warning on the dash? That's probably just pads though I'd guess. My brakes pulsate like crazy but there's plenty of pad thickness. No warning either.

Maybe my rotors are due.....

[White987S]

My brakes pulsate like crazy but there's plenty of pad thickness. No warning either.Maybe my rotors are due.....

Sounds like your rotors are warped. With your cross drilled rotors, look for checks/cracks that are at or very near the rotor's outer edges. Time to replace.

[Loren]

Loren shouldn't we get a warning on the dash? That's probably just pads though I'd guess. My brakes pulsate like crazy but there's plenty of pad thickness. No warning either.Maybe my rotors are due.....

The warning tells you when there is not much left and the sensors have worn through.

No sensor for old brake fluid - just poor braking and potentially brake failure in an emergency situation (due to moisture in the fluid).

If your brakes are pulsating then you could have enough pad separation and deposits on the discs to cause that (no such thing as warped rotors - http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths).

Sometimes discs can cleaned and pads replaced to control that but chances are it's time for a full brake service (pads, discs, and fluid).

[ALEV8]

Need to look up in my service records when pads and rotors went on last. PO was super meticulous and have all service records since original purchase in VA 2004 at Tyson's Corner. If anything the rotors look worn. Plenty of pad. I was told to always replace them at the same time so I always do. Fluid was changed about three weeks ago....

Edited August 17, 2013 by ALEV8

[clarksongli]

cayenne rotors come NEW with not a lot of meat to begin with. Combine this with the weight of the car, as Loren said, it is not unusualy to have to do everything during pad changes.

That being said, in my opinion, there is plenty of meat to run low on the rotors. The risk you run is that the rotors will warp more easily the thinner you get, but if you are taking it easy and just trying to make it to the next pad change, you will be fine. my rotors were <35mm when they came off last year.

there ARE less expensive options. In some of my other posts and my DIY, i use Centric (makers of Stoptech and a few other names). Many rotor blanks get pulled from the same castings since these companies generally outsource the steel forming these days.

Look up Centric, they run 30ish a piece, so maybe 150 bucks for rotors from amazon (free shipping). Just make sure you cross reference the PNs since amazon doesn't always get that right. The feature you do lose is the zinc plated rotor hats.....but some paint will fix that pretty easily.

[ALEV8]

I was wondering about Centric. I've used Brembo and Zimmerman up until now. I'm thinking rotors first since my pads aren't worn that much. My previous owner used drilled and slotted rotors but I can't get an idea of manufacturer. I so have casting numbers.

[clarksongli]

I've run the centrics for maybe 20k so far.....I do everything from pulling stumps, highway driving, daily commuting, and towing at roughly 8k lbs of equipment. The rotors have never failed, or warped in anyway.

Again, Rotor blanks are fairly generic these days, yoo don't see a foundry for each company these days, generally that is outsourced and a centric blank may be the same as a OE without the final processing (final hat cut or zinc plating).

a note on drilled/slotted rotors.....i ALWAYS stay away from them. If a rotor was cast with the holes, that's one thing, but most companies simply drill holes in a rotor blank.....without the structure behind the holes, the rotor become weaker. For daily driving, you would most likely be fine, but then why would you need drilled rotors??

My track car i have always run blanks....and will continue to do so. Pad material is a key factory in stopping.....And i have seen drilled rotors at the track crack in half.....my CTT will only ever see blanks.

[spooltime]

Maybe for the regular turbo 350mm discs, but unfortunately I can't seem to find any lower cost options for the 380mm CTTS front discs.

there ARE less expensive options.

[clarksongli]

Centric makes them....have you done a search?

PNs: 125.37048 and 125.37049 (left and right).

[mcbit500]

Nice price range, $700+ to $1,000-

[spooltime]

Nice price range, $700+ to $1,000-

Unless that's the total for a pair, that price is significantly more than I can buy the factory front discs for. If that is for a pair, who is the vendor at that price?

[mcbit500]

Nice price range, $700+ to $1,000-

Unless that's the total for a pair, that price is significantly more than I can buy the factory front discs for. If that is for a pair, who is the vendor at that price?

Looks to me like it's for one.

Autoanything $945

Amazon $725

Zeckhausen Racing $1094

ebay $748

and probably some more...

Edited August 22, 2013 by mcbit500

[spooltime]

Ouch, just ordered a set of genuine Porsche discs for the front and rear of my CTTS. I suppose I can take some consolation knowing that those 911 drivers with factory ceramic discs get a list price of over $7,000 each on front disc replacements; the just over $500 each I paid for my front discs pale in comparison. :)