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@Alipapa , after how much use? Your use of the word “again” makes it seem like you’ve addressed this fairly recently already. If so, then it seems as though there might be something else going on here. I’m not sure that looking for a higher temperature option isn’t just treating a symptom instead of the underlying issue.

Is there any chance that the hand brake is not properly (fully) releasing?
Or, might the sliders not be free (pads not releasing after normal brake application)?
In either of these circumstances, I could see this happening. But I do not understand how, under normal circumstances, the rears would wear and heat up this badly.

I would do anything to get that kind of wear in my rear pads - it would be an indication that they are actually contributing to stopping. But most of us have found that the rear pads exhibit very little wear - even on a track. Basically, one set of rears for every three or four fronts (assuming the stock setup and same compounds front and back).

What front-pad wear are you experiencing?
The last time I changed the boot was November 2018. Previously, I also found the rear pads last 2-3 times longer then the front one. That's why I didn't pay too much attention to them, and never thought the pad would be gone like that.
Will get them fully rebuild as soon as I am back from business trip. Heading to some place far right after trackday is so freaking tiring lol

Here is a picture of the left rear rotor
 

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Just took my front OEM caliper apart and the pistons are 29mm in length. @DrPyro2k: can you please update your first post w/this info?

I just ordered the 30mm long piston kit @DrPyro2k listed, so we will see if they work!

Also, when rebuilding, folks will likely want to replace the oil seals in addition to the pistons and dust boots: Brake Fluid Seal Kit - 38mm (2 ea)
 

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Discussion Starter #25
FYI... @GMS is reportedly designing a titanium piston for the 4C. Both @kennebraun and I have spoken with him, but @kennebraun timetable is too short to wait on rebuild.
 
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Welp, just took apart my calipers... both are shot. The calipers themselves are warped, so no dice on a rebuild. Luckily, I bought a backup used set recently simply because the price was right. They arrived today, as luck would have it. So I just put my “new” used calipers on for now.

I’m gonna return the ss pistons since I haven’t had issues with my brake fluid cooking on me since switching to SRF. Sorry I won’t be able to verify the extra mm in length will work on these pistons. Best of luck to whoever goes first! But honestly, I think they should work just fine.
 

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Discussion Starter #27
@kennebraun - Mind taking a few photographs of the warpage and damage, so other 4C track junkies know what to look out for?
 
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Has anyone tried titanium brake shims or are they snake oil? I figured they couldn't hurt and bought some on ebay, but don't do enough tracking to know if they work or not.
 

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Discussion Starter #29 (Edited)
The idea behind these devices is to provide a "thermal break" between the back of the pad and piston in the caliper. The piston is made from Aluminum, so it has very high thermal conductivity (237 W/m K). Thus, it easily transmits the heat from the pads to the fluids. The back of the pad is carbon steel, which has a thermal conductivity of roughly 60 W/m k). Titanium has about half the thermal conductivity of carbon steel.

From an engineering perspective, there are a few ways to disconnect the heat of the pad from the fluid. Porsche GT4s (and GT3s?) use a ceramic puck to provide that thermal break. (Picture from Autoquest Motorsports)
108447


The ceramic can crack and break due to thermal shock and cycles and are sometimes replaced by Titanium pucks (aftermarket solution). Some more advanced pistons designs simply minimize the contact area between the piston and pad backing. The issue with this is that it could theoretically lead to uneven pressures and uneven pad wear. Other aftermarket solutions use Stainless Steel (cheap) or Titanium (lightweight) pistons to reduce the heat transfer of the aluminum by eliminating it all together.

Frankly, I would question how well a very thin sheet of titanium would be at reducing that thermal transfer. Thickness (like that of the GT4 photo above) is necessary for truly limiting that heat transfer. I could sit down and calculate the heat transfer rate, but don't think it is worth it.
 

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Shims are useless as they won't stay in contact with brake pads and will probably rattle and float in the calipers. High quality Titanium piston with small contact patch designed like a crown is what will keep the heat transfer off the calipers. Of course, let's not forget about cooling ducts. And what makes the discs damaged is brake pad deposits, so running high end racing calipers on racing rotors and low performance brake pads will destroy the discs in a heart beat. As deposits get stuck to the discs the brake pads keeps grinding down the disc, but where the deposit is stuck to the disc it doesn't grind the disc, but the pad, so this makes an uneven pattern on the disc and pad, so the discs will start to vibrate. Drilled discs are also prone to cracking between the drilled holes and larger 300m diameter or more, non floating discs are prone to getting warped, so high end cars use large diameter, floating discs and race cars use large diameter, thick, floating and slotted discs.

Steel pistons:
  • + cheap
  • + easy to CNC
  • + durability
  • ° medium heat transfer
  • ° medium thermal expansion
  • - heavy
  • + prone to rust
Aluminum pistons:
  • + easy to CNC
  • + light
  • + cheap
  • - high heat transfer
  • - high thermal expansion
  • - durability
Titanium pistons:
  • + low heat transfer
  • + low thermal expansion
  • + light
  • + durable
  • + low friction (AlTiN coated)
  • - expensive
  • - hard to get high quality Titanium alloy
  • - hard to CNC
As usually in the world of motorsport, the performance doesn't come cheap.
 

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2015 Alfa Romeo 4C w package 22C, Coupe Track package, leather upgrade and the forged 18s and 19s.
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I installed stainless steel pistons in the front calipers of both my Lotus Elises. I've never had an issue with any heat related brake issues since and when tracking a Lotus, late braking is where you pick up a lot of time on the higher horsepower folks. Here's some stats from the site I purchased the pistons from.
  • Approximate Thermal Conductivity of common caliper piston materials (BTU/hr-ft-F):
  • *Aluminum: 136
  • *Stainless Steel: 8
  • *Titanium: 13
  • As you can see, stainless steel has only about 5% of the thermal conductivity of aluminum. It’s typical to see stainless steel or titanium “vented” pistons in racing calipers.
 
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Sorry for my tardy response! I have been rebuilding the structure of my garage and it’s been all consuming.

No visible distortion on the calipers, but they are severely discolored (not a big deal in and of itself) and the bolts that tie them to the hub don’t fit into the holes anymore. That was my big indication that they had warped. The bolts fit fine in the new used set of calipers I got from a fellow 4C person.
 

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This gave me an idea: if anyone has a few front calipers for sale (cheap) to use as paperweights, I'd be interested. Thanks!
 

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I am running Nitto NT01s on race wheels (Matt's Advan 17x8.5F/18x9.5R). But really in this case it was due to me wearing to the backing plate on my brake pads (the inner pad wore faster than the outer, so I didn't have as much margin as I thought I had, combined with the fact that Pitt Race is exceptionally hard on brakes, which I didn't quite account for).
 

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This gave me an idea: if anyone has a few front calipers for sale (cheap) to use as paperweights, I'd be interested. Thanks!
Haha if you're serious, I'd be happy to send you one of my fronts for the price of shipping! only payment I'd ask is for some pics of the final product.
 
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