RacingBrake

3rd option for stock brake replacement in this thread...

https://rennlist.com/forums/gt4/9393...is-thread.html

Alan C.

For PCCB equipped cars be sure you leave the retaining screws in until you have the caliper secured. If not you will run the chance of the rotor sliding off the hub. Next stop the floor.

texasviany

Thanks, I had MCS on the Viper TA.

JRitt@essex

Thanks gents...glad my post could help clear things up! Sorry again for the confusion.

AP Racing discs do not have a minimum thickness specification. Just about all of our customers will crack them before running them too thin. For reference though, I have had a rare few customers run them until the J Hook slots wore off of the disc face. By that point they are definitely due for replacement.

jphughan

Thanks Jeff! Are there guidelines about what types of cracks warrant replacement? I've heard the guidelines around drilled rotors that cracks connecting two holes or extending to the outside edge of the disc means it should be replaced or at the very least monitored closely from that point on, but obviously these rotors aren't drilled. Are cracks that reach the outside always an indicator of the disc needing to be replaced, or can they be run safely until there's a crack running all the way from outside edge to inside?

JRitt@essex

Below are some examples of our J Hook discs in various degrees of wear. The first stages of use show hints of little heat checks in the center of the disc. It's not uncommon to see these small heat checks after even one day on the track. They are a natural result of the iron expanding and contracting with the massive temperature swings experienced on the track.


Over time those little checks will grow larger and larger as shown below.



More abuse...more checks...



And more...



After enough cycles of expansion and contraction, the surface of the disc looks like a patch of arid ground.




If you see any cracks on the outer edge (OD) and inner edge (ID) where the disc attaches to the hat, then it's definitely time to replace the iron ring. Below is an example of a terminally-cracked disc.



Here's another example with a fracture on the outer edge:



Also remember that there is an inner disc face! Some people only peek through the wheels and look at the outer disc face. That's a no-no. You need to get your head inside the wheel and check the inner disc half (the part not attached to the hat) in case something like this is hiding from plain sight:




Please keep in mind that it's impossible for us to give a firm "yes" or "no" on whether a disc is still usable, safe, etc. There are simply too many factors involved. For example, running three 20 minute sessions in a Miata with a big brake kit installed at Willow Springs is going to produce dramatically less incremental stress on the disc vs. running a single lap in a 991 GT3 RS at Road America.

The responsibility is ultimately on the individual and their mechanic to keep a close watch on the discs. You should really be checking them every time you check your tires or oil when you're at the track (which should be frequently).

My personal advice is to never run a disc (or any component on your car for that matter) that you think is at all marginal, causes you any concern, makes you nervous, etc. Ask yourself if you would put your wife or child in the car for some hot laps with that part installed? If the answer is "no," don't be a knucklehead and tempt fate. It's not worth writing off a $150k car or being injured over a couple hundred dollar disc that is nearing the end of its life. Use your noggin!

Finally, it's never a bad idea to keep a spare set of iron rings and attachment hardware on-hand in your trailer, particular if you've been running your current discs for a while. Iron disc rings don't age like fruit. If you keep them in the oil paper in their original boxes, they can sit in your trailer virtually forever in as-new condition. It's a lot more fun to install a new iron disc ring during lunch than it is to pack up shop, forfeit your entry fee, say goodbye to your friends, and start the long drive home from the track due to a disc failure.

jphughan

^ Fantastic response, thanks again! I'll likely be installing your front rotors at the end of the year when I switch pads out. I already washed them with soap and water when I got them 2 months ago to remove the rust inhibitor to make certain I don't forget to do that later, but I've since put them back in their boxes wrapped in the oil paper they arrived in. I didn't realize that particular paper was significant to preserving shelf life -- that's good to know too! And it's great to see this kind of customer service having just bought your product!

ML///

@JRitt awesome post. Can you comment on if you consider the rotor hat a consumable? Another company was telling me that after I change my rotor rings five times I should buy new rotor hats. What is AP's take on this comment / suggestion?

JRitt@essex

Thanks gents.

The disc hat is definitely a consumable. Just as with the iron rings however, predicting a replacement schedule is nearly impossible due to the number of variables involved.

That said, our disc hats are going to last you a very long time. We now have complete big brake kits in the field that have been consistently pounded on the track by typical HPDE and club racers for 5 seasons without the customer replacing the hats. We use a very high quality heat treated billet aluminum with a hard anodized coating, and they hold up to a lot of abuse.

The way you'd be able to tell if your hats were getting worn would be slop in the mounting holes. The holes that the bolts go through would start opening up, and the hats would rattle around on the bolts.

When possible we use a 'float-in-hat' attachment system for our discs. That means the expansion of the disc is accommodated by the iron disc ring, rather than the hat. The holes in the iron ring are oblong, and the bobbin slides along that oblong channel. The holes in the hat are round and don't allow for vertical/lateral movement. That means the bulk of the wear due to disc float is placed on the iron ring (made from hard iron), rather than the aluminum hat (which is softer). That lengthens the service life of the aluminum disc hat.






Note the round attachment holes in the hat...



FYI...the other attachment method would be float-in-hat (see below). Sometimes that method is required due to packaging issues on the car, but we prefer float-in-disc when feasible due to the lower wear and tear on the aluminum hat.

myBailey07

Kudos to Essex. This is a great example of how a vendor should handle customers on forums/social media. No marketing hockey pockey - just good, solid, factual useful information. Thank you for that. I am sure glad I went with the AP Racing rotors. Have been very happy so far.

ExMB

Jeff, for clarification; when you talk about rattling around you mean once the wheel is removed and the hat is only held on the hub by the set screws the disk ring could be moving around due to the hat/ring mounting holes sitting in enlarged holes?

jphughan

Not that I expect to reach the end of life on the AP hats anywhere in the near future, but out of curiosity, how would the bolt hole slop test be performed? Looking at my new rotors still in boxes, the bolts seem to be providing enough clamping force to prevent me from moving the hat with its bolts around even inside the deliberately oblong rotor holes, so I assume detecting slop in the hat this way would be impossible. Would an appropriate test be to suspend the hat with no rotor attached in the air with the inboard side facing the ground, drop the mounting bolts through all the holes, and agitate it quickly back and forth (in a washing machine motion) to see how much rattling occurs?

And a bit off-topic, but while you're here answering technical questions, if you're inclined to answer another, I've never understood how dual cast rotors work. I know they're technically two-piece rotors, but they're a single assembly, i.e. the hat can't be separated from the ring for replacement. How does one make a rotor that's a single assembly but that operates as a two-piece rotor?

bigskyGT3

JRitt/Essex thanks for informative posts.

JRitt@essex

Okay...I guess I need to elaborate. A hat is a consumable...but we're talking about a very long-term consumable! I would not expect our disc hat to be worn out in five iron ring changes.

There are some different ways an aluminum disc hat, or the mounting bobbins can wear out. The basic thing to keep in mind is that the iron disc is harder than the softer aluminum, even when the aluminum is anodized. A steel bobbin is also harder than aluminum. The main cause for wear and fatigue on a brake disc that is being tracked is heat. Repeated trips to track temps wear both the aluminum and iron out over time. Heat creates distortion and makes things soft and malleable. When harder objects press on softer objects at high temperatures, the softer object distorts.

Here's a shot of our hardware stack for reference when reading my comments below:


Some ways that you could see wear over time:

• If the hat was removed and placed on a perfectly flat surface (a granite surface plate for example), the hat wouldn't sit flat. That would indicate that the aluminum hat has fatigued and warped sufficiently to necessitate replacement. At that point, the distortion would allow play/movement in various contact points for all of the components, creating wear in those areas. That's what I was thinking about in my previous comments about wear. If you found the hat was warped, then you could proceed to checking for wear in other areas. In five years of producing our two-piece discs, I have yet to have a customer tell me this has occurred with their hats.
• Over time, the anodizing on the disc hat will shift color to a burgundy, maroon, or brown. Again, this comes with more and more heat cycles. There's no set rule about when to change out a hat based on color, but it does indicate that the hat is being taken to very high temps and back, and over time it will fatigue. Typically the hotter it gets, the more dramatic the color shift. FYI...I have customers with purple disc hats that were formerly black, and their hats are still in fine shape and exhibit no distortion.
• As a mounting bolt fatigues and loses tension, that could allow some slight movement of the iron disc against the hat. Any movement could allow the anodizing to wear out a bit where the hat surface meets the iron ring. That said, the AKB spring clip provides a little tension to quell movement, so that would help in that situation. Since you're going to be replacing your disc attachment bolts with every iron ring change, you'll essentially always have fresh hardware/bolts. In five years of producing our two-piece discs, I have yet to have a customer tell me that they've had a mounting bolt wear out before they replaced their iron rings.
• Over a long time you could see some wear on the steel bobbins, since it's sliding in the channel of the iron disc ring. We typically recommend reusing the bobbin until it wears out. When it wears out it will no longer fit as snugly in the oblong channel, could twist a tiny bit, and you'll start to hear some rattling noises. It would be more common for the bobbin to be replaced due to corrosion. Again though, I just surveyed a few of my sales guys. In five years of producing our two-piece discs, we literally can't think of one specific customer who has requested new bobbins. In NASCAR Sprint Cup, our teams aren't even replacing these that often. Sometimes they stick them in a tumbler to clean them up, then reuse them.

In summary...notice any trends above? You will likely never have to replace your disc hats during your time of owning our discs, and it shouldn't even be on your radar. Replace your nuts and bolts every time you install fresh iron, wash, rinse, repeat. Maybe in a couple years install some fresh bobbins and AKB spring clips. Enjoy your discs and don't overthink it! If you see something that appears odd one day, call us and we'll be here to help.

ExMB

Thanx for going into more detail Jeff