Porsche Brembo 996 BBK Conversion-- let's figure out how to fix the dust boots/seals

[r4dr]

Also, as far as I know, the widest rotor I know of that comes from the factory with those Megane calipers is a 30mm-thick disc. I have to measure the calipers, but my question would be whether the caliper has clearance for something like a 34mm disc plus full thickness pads. And a few mm of space for stuff like titanium pad shields and allowing for pad tolerance.

[r4dr]

r4dr Is it possible to make larger rotors, like 355 mm and have them work with 996 calipers? Y’all sell larger rotors with caliper spacers for a bunch of Porsches, so why couldn’t it be done for our cars? 🤔

Anything is possible. And you're correct, since these calipers are all radially mounted, it would simply be a matter of caliper spacers and correspondingly longer caliper bolts. But it would end up being a custom hat (we could probably use an off-the-shelf Porsche ring so replacements are easy), and the price would be more reasonable if 5-10 people wanted to jump on.

However, we're also in a thread talking about free rotors... how many people would want to pay $1200 or so for a pair of assemblies?

For most of the time I ran the Brembo GTs, I had no ducting beyond factory/stock.



There's also free pads 🤣



I mean, it's not a fallacy if we can get it to work. Pads/rotors are probably 1/4 to 1/3 the cost of tracking, so if they can be made free, reliably...

That said, not gonna lie-- I miss my Brembo GTs. They were lighter, they had better pedal feel, I swear braking was better (as in stopping distances, though I understand why that should not be), and they were idiot proof-- with no effort I'd just run them till the pads were done, then on to the next pads. In the almost 15 years they were on my car, I had only 100% positive experiences with them.

What pads are you currently using via the FCP program?

TBH, if I were building a track car, I would just buy a 355x35mm Brembo Pista kit. IMO it's the best consumer track day setup for the front of these cars, but you can't get free consumables and the kit costs money.

[repoman89]

It’s no longer “free” though. Yeah we all buy plenty of BMW parts but there’s a limit. Store credit is a lot less useful to me these days since both of my M cars are in very solid mechanical shape. Half the time I want some small cheap part I struggle to even get to the $50 free shipping threshold without buying things I don’t need.

I haven’t done the math but the GTs with their larger 345mm rear rotors might move brake forces at the tire slightly rear which would decrease braking distance up to a point. I’m not sure the usual bias calc of torque applied to the rotors accounts for the extra lever arm.

[Obioban]

I remember you saying this and I've always kept it in mind. What's interesting is that the mass of the 355x32 rings isn't *that* much greater than the GiroDisc rings. They both have 48 vanes, but perhaps it might help having a proper rear setup as well. You were running a full cooling system with ducts and hoses, correct? Are you still using that setup with the CSL rotors?

For most of the time I ran the Brembo GTs, I had no ducting beyond factory/stock.

I know I'm biased and I don't pretend not to be, but there are more factors at play here than free rotors.

There's also free pads 🤣

Yeah, you're not wrong...

Turns out this "budget" kit isn't all that budget at all if you track your car. Love getting sucked into the sunk cost fallacy, so determined to get it somewhat tolerable!

I mean, it's not a fallacy if we can get it to work. Pads/rotors are probably 1/4 to 1/3 the cost of tracking, so if they can be made free, reliably...

That said, not gonna lie-- I miss my Brembo GTs. They were lighter, they had better pedal feel, I swear braking was better (as in stopping distances, though I understand why that should not be), and they were idiot proof-- with no effort I'd just run them till the pads were done, then on to the next pads. In the almost 15 years they were on my car, I had only 100% positive experiences with them.

[SQ13]

r4dr Is it possible to make larger rotors, like 355 mm and have them work with 996 calipers? Y’all sell larger rotors with caliper spacers for a bunch of Porsches, so why couldn’t it be done for our cars? 🤔

[heinzboehmer]

The lifetime replacement savings are at the cost of higher consumable wear, more labor swapping consumables, and shorter lifespan of wear items in the calipers. You might have more pad left which will get you through your upcoming 2-day event, versus putting new pads in and keeping the old set as "spares" that never leave that shelf again...

I know I'm biased and I don't pretend not to be, but there are more factors at play here than free rotors.

Yeah, you're not wrong...

Turns out this "budget" kit isn't all that budget at all if you track your car. Love getting sucked into the sunk cost fallacy, so determined to get it somewhat tolerable!

[r4dr]

Totally agree that having the boots fail this quickly seems like more a symptom of too high caliper temps than anything else. However, even with the full cooling setup you mention (like mrgizmo04 has), the boots still fail after some events. I'm not really too concerned about the boots, as they're fairly easy to swap, but more concerned about the seals inside the caliper. If those are made of the same materials, then they're likely not doing too well. Would not be fun to find out that they've failed at the end of a straight.

The seals are a few degrees of separation away from the pads / rotors and aren't in direct contact with the pads themselves. Heat in brakes is more localized than people realize -- even the rotor tabs (where the hat fixes) can be noticeably cooler than the swept surface itself, and they're only an inch or so away from each other.

I guess what I'm saying is that I hear your concern but I've never seen anything that would lead to caliper seals failing and causing catastrophic loss of brakes. Even when they get tired (and they do, which is why we rebuild calipers) the pistons will still apply pressure to the pad, but the rollback behavior might not be as clean as a fresh setup.

That being said, I would pay good money for dust boots made of a material that's more tolerant to the temp these calipers see, just to avoid the pain of swapping them every once in a while.

You and me both.

And to address your cooling suggestions:

- Rotors: I'm running the subpar CSL rotors not because I think they're better than the Girodiscs, but because FCP sells them and having the lifetime replacement from them lowers track day cost. I suspect most people here are in the same boat.

The lifetime replacement savings are at the cost of higher consumable wear, more labor swapping consumables, and shorter lifespan of wear items in the calipers. You might have more pad left which will get you through your upcoming 2-day event, versus putting new pads in and keeping the old set as "spares" that never leave that shelf again...

I know I'm biased and I don't pretend not to be, but there are more factors at play here than free rotors.

- Pads: I'm running PFC08 pads all around (+ Girodisc titanium shims), so this should not be an issue.

Agreed. Love PFC pads.

[heinzboehmer]

One thing that jumps out at me is that different people seem to be running optimal hardware for different parts of their systems, but I don't think anyone is running a full setup. Though I'll admit I've lost track of who's running what from jumping into this thread late. Here's my take on the different components:

- Rotors: Going from the 30-vane CSL rotor to the 48-vane GiroDisc rotor is pretty big. That's over 50% more vanes, which just compounds the cooling capabilities when you add in the parts below. There are two pairs of rear prototype rotors that are in production now, and once fitment is confirmed with both stock and Porsche calipers, they will be available. These are 48-vane as well.

- Cooling: It's unfortunate that the cars you need cooling on the most (full interior street cars that are the heavier E46s) are the ones that would be most hesitant to run traditional cooling methods (ducts, hoses, backing plate). I'm a fan of the "scoops" that Vorshlag makes for the E46s (I first tried them on a GT350 and they seemed to work well). I don't have any 3rd party data to rely on, but based on 1st party testing, they seem to work well and you don't have the hassle of hoses. I will note that I would trim back all the backing plate material that isn't covering rubber dust boots or other hardware to maximize their effect. The advantages of active cooling are magnified by the 48 vane count in the GiroDisc rotors as well.

- Pads: Someone touched on this earlier, but the rear pads matter. Not as much as front pads, but if you have some low-end compound in the back that fades 5 minutes into your session, all you've done is work your fronts harder. I think people with race suspensions can probably run a square compound (or very slight stagger toward the front), but even if the rear is a lower-friction compound, it should be a quality, proper race pad that maintains that same friction throughout the temperature curve of a track session. I'm not going to name and shame brake pad manufacturers, but some are better than others.

- Caliper pistons: AFAIK, Brembo GT kits and other higher-end Brembo systems (like Porsche factory calipers) also come with aluminum pistons. Titanium pistons are interesting, but they need some kind of coating in order to maintain proper function with the pressure seals. Aluminum pistons are hard anodized. I've seen some issues with RB stainless steel pistons that make me stay away. I had to troubleshoot with a Porsche Cayman owner recently because he was getting some kind of metal binding noise from his caliper when applying the brakes. Turns out that the piston was binding on the caliper bore due to poor tolerances, and he ended up buying a new pair of calipers from Porsche. YMMV.



I remember you saying this and I've always kept it in mind. What's interesting is that the mass of the 355x32 rings isn't *that* much greater than the GiroDisc rings. They both have 48 vanes, but perhaps it might help having a proper rear setup as well. You were running a full cooling system with ducts and hoses, correct? Are you still using that setup with the CSL rotors?

Someone noted that race calipers don't have dust boots, and I think we can all see why! Tracked cars end up frying their dust boots regardless, and generally speaking, you can just leave them as is until you completely rebuild the calipers. I wouldn't bother replacing them every track day, or every other track day. They don't have nearly enough benefit to warrant that much expense and labor.

However, that being said, the dust boots in this thread do seem to be frying pretty quickly. The dust boots in my GT3's calipers are completely toast, but that happened over the course of a half dozen of track days and I'm leaving them as is until I go to rebuild them. This is even with the ceramic pucks that Porsche includes in an attempt to create a thermal barrier and reduce direct heat transfer.

I would conjecture that having all the pieces of the puzzle I listed above would help, but I don't have any way of saying it's a magic bullet solution.

Totally agree that having the boots fail this quickly seems like more a symptom of too high caliper temps than anything else. However, even with the full cooling setup you mention (like mrgizmo04 has), the boots still fail after some events. I'm not really too concerned about the boots, as they're fairly easy to swap, but more concerned about the seals inside the caliper. If those are made of the same materials, then they're likely not doing too well. Would not be fun to find out that they've failed at the end of a straight.

That being said, I would pay good money for dust boots made of a material that's more tolerant to the temp these calipers see, just to avoid the pain of swapping them every once in a while.

And to address your cooling suggestions:

- Rotors: I'm running the subpar CSL rotors not because I think they're better than the Girodiscs, but because FCP sells them and having the lifetime replacement from them lowers track day cost. I suspect most people here are in the same boat.

- Cooling: The problem with the CSL rotors is not just the vanes, but also the hat design. The hat extends into the airflow path quite a bit and makes the traditional cooling ducts less efficient. They're still useful, but I didn't bother installing my ducts this last track day because of this (I should also mention that I saw no fade without cooling, just the melted dust boots). Bry5on recently did a bunch of testing on his own scoops and found that the mudflap blocked a decent amount of air: https://nam3forum.com/forums/forum/m...180#post255180 The Vorshlag scoops seem fine, but trimming that mudflap is probably a good idea to maximize the scooping effect.

In the future, I do plan on having adequate cooling, so the problem should be mitigated somewhat. Currently working on a caliper evacuation duct that should keep the calipers cool regardless of rotor design: https://nam3forum.com/forums/forum/m...081#post258081

And yes, these calipers are not meant for such heavy cars. My car is quite a bit lighter than stock (3200 lbs with a 1/4 tank of gas), but it's still a lot heavier than the cars these were originally designed for.

Anyway, my point is that efficient cooling with 996 calipers + CSL rotors is not trivial and even though it it's easy to bolt some aftermarket parts on, they might not be optimal.

- Pads: I'm running PFC08 pads all around (+ Girodisc titanium shims), so this should not be an issue.

- Caliper pistons: The issues you mention are exactly why I didn't go with aftermarket pistons when I rebuilt my calipers

In summary, I don't think it's fair to ask for a magical dust boot that works everywhere because most people running the 996 calipers are running them on a heavy car with subpar rotors, but I am a bit concerned about the caliper seals. Cooling will absolutely help, but it's not an easy problem to solve with the aforementioned setup.

[r4dr]

One thing that jumps out at me is that different people seem to be running optimal hardware for different parts of their systems, but I don't think anyone is running a full setup. Though I'll admit I've lost track of who's running what from jumping into this thread late. Here's my take on the different components:

- Rotors: Going from the 30-vane CSL rotor to the 48-vane GiroDisc rotor is pretty big. That's over 50% more vanes, which just compounds the cooling capabilities when you add in the parts below. There are two pairs of rear prototype rotors that are in production now, and once fitment is confirmed with both stock and Porsche calipers, they will be available. These are 48-vane as well.

- Cooling: It's unfortunate that the cars you need cooling on the most (full interior street cars that are the heavier E46s) are the ones that would be most hesitant to run traditional cooling methods (ducts, hoses, backing plate). I'm a fan of the "scoops" that Vorshlag makes for the E46s (I first tried them on a GT350 and they seemed to work well). I don't have any 3rd party data to rely on, but based on 1st party testing, they seem to work well and you don't have the hassle of hoses. I will note that I would trim back all the backing plate material that isn't covering rubber dust boots or other hardware to maximize their effect. The advantages of active cooling are magnified by the 48 vane count in the GiroDisc rotors as well.

- Pads: Someone touched on this earlier, but the rear pads matter. Not as much as front pads, but if you have some low-end compound in the back that fades 5 minutes into your session, all you've done is work your fronts harder. I think people with race suspensions can probably run a square compound (or very slight stagger toward the front), but even if the rear is a lower-friction compound, it should be a quality, proper race pad that maintains that same friction throughout the temperature curve of a track session. I'm not going to name and shame brake pad manufacturers, but some are better than others.

- Caliper pistons: AFAIK, Brembo GT kits and other higher-end Brembo systems (like Porsche factory calipers) also come with aluminum pistons. Titanium pistons are interesting, but they need some kind of coating in order to maintain proper function with the pressure seals. Aluminum pistons are hard anodized. I've seen some issues with RB stainless steel pistons that make me stay away. I had to troubleshoot with a Porsche Cayman owner recently because he was getting some kind of metal binding noise from his caliper when applying the brakes. Turns out that the piston was binding on the caliper bore due to poor tolerances, and he ended up buying a new pair of calipers from Porsche. YMMV.

It does not. Ran the same seals for 10+ years on my brembo GT kit…

… but they don’t have FCP rotors…

I remember you saying this and I've always kept it in mind. What's interesting is that the mass of the 355x32 rings isn't *that* much greater than the GiroDisc rings. They both have 48 vanes, but perhaps it might help having a proper rear setup as well. You were running a full cooling system with ducts and hoses, correct? Are you still using that setup with the CSL rotors?

Someone noted that race calipers don't have dust boots, and I think we can all see why! Tracked cars end up frying their dust boots regardless, and generally speaking, you can just leave them as is until you completely rebuild the calipers. I wouldn't bother replacing them every track day, or every other track day. They don't have nearly enough benefit to warrant that much expense and labor.

However, that being said, the dust boots in this thread do seem to be frying pretty quickly. The dust boots in my GT3's calipers are completely toast, but that happened over the course of a half dozen of track days and I'm leaving them as is until I go to rebuild them. This is even with the ceramic pucks that Porsche includes in an attempt to create a thermal barrier and reduce direct heat transfer.

I would conjecture that having all the pieces of the puzzle I listed above would help, but I don't have any way of saying it's a magic bullet solution.

[Slideways]

It does not. Ran the same seals for 10+ years on my brembo GT kit…

… but they don’t have FCP rotors…

How often are you replacing rotors?

[Obioban]

Does this happen with the real deal Brembo GTs? Those aren’t THAT expensive compared to the budget kits.

It does not. Ran the same seals for 10+ years on my brembo GT kit…

… but they don’t have FCP rotors…

[heinzboehmer]

Booo. r4dr works at Girodisc, right? Is there any shot we can get this feedback up the chain and find a solution?

+1!

[Pklauser]

Booo. r4dr works at Girodisc, right? Is there any shot we can get this feedback up the chain and find a solution?

[heinzboehmer]

Just another data point. Girodisc dust boots did not survive either:




Pads were at about 50% and I was using titanium shims. No brake cooling though.

[BigRussia]

Not to derail or take this thread off topic from 996 Brembos but I think its still relevant; speaking of piston 'upgrades' from aluminum got me looking for my Megane Brembos and found this SS piston kit from RacingBrakes. Seems the FK8 CTR Brembos use the same size pistons as the Megane Brembos. What sucks is that it's so hard to find info on the exact size of the Megane pistons, I know theyre 40/40mm diameter but the depth I'll just have to assume/hope they're 30mm like the CTR's.

https://racingbrake.com/bh-41p/

For $266 it's not baaad, like yeah it sucks having to spend more money on the budget BBK (and spend the time and labor to rebuild), but even with the full rebuild kit they also sell ($407 with high temp boots upgrade https://racingbrake.com/bh-41bsp/) the Freakyparts Megane Brembo kit + Girodisc 345mm rotors is still cheaper than a Brembo GT 355mm front kit but not by much maybe after the rebuild kit I'd have saved $1k, but still much cheaper than any of the AP Racing kits on Essex (besides the 325mm kit they sell).