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

[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).

[Slideways]

What about titanium alloy pistons - https://www.silverlakeprojects.com/p...ns-for-porsche

[BigRussia]

Sucks that you are already on Girodiscs and rb blue. I was hoping Girodiscs would help a tonne given number of vanes and proper 2 piece efficient design.

I'm also on ti shims, and I've been using the Vorshlag shovels (per pic). Trimmed my shield even more this week, so need to retest. Qualitatively speaking, these shovels move more air than when I had the 2" hoses. Are you running cooling ducts other than stock tunnels?

IIRC, conduction from backing plate/ti shim to dustboot is not a transfer mechanism, but I need to double check. With new pads, if boots are properly installed, tip of the piston should be first part pressing on the shim/backing plate. After installing new pads, you have to pump the pedal a few times and that seats and pushes out the pistons a bit. Also remember that in these budget kits pistons are aluminum (vs high end kits using steel or even ti), which has higher conductivity and less resistance, so first line of defense for the tip of the piston is the boot.

Do you by chance have a size diff for the front pad between stock and Megane, like I provided at end of post 22 above. Would love to see the diff visually.

Yeah I was bummed that even with the Girodisc and slightly thinner PFC pads the RB blue boots cooked. I wanted to run caliper temp strips for that last track day but UPS lost the package from Alcon... I will be running temp strips next track day, hoping I see under 400F.

I dont have any brake cooling besides the stock factory 'brake duct' tunnels. Brake cooling is is my current project rn, I tried DIYing my own setup using OEM C6 Corvette brake ducts (like how AAF kit uses) but turns out need to not have A/C for that (evap blocks the RH duct)... Im still searching for a cooling solution that's streetable and with A/C. BTW I've had your DIY brake cooling video on my Watch Later list on Youtube for a while haha, and was considering the Vorshlag deflector kit at one point at well but just didnt want to deal with cutting my dust shields and reducing heat protection for the arm ball joints (though hypothetically they should be getting some cooling air lol).

Damn I didnt realize the budget kits Brembos had aluminum pistons, figured they were steel! At least they werent ceramic so I didnt think much into that. Yeah with the new 16mm GLOC pads the pistons were basically at bottom and the Brembo boots 'fold' was still touching the backing plates. As the piston moves out w/ pad wear then the boots should not be folding upwards into the backing plate as much, I imagine.

Do you mean the pad thickness of the stock pad size vs the D1001? Or the caliper's max space for the pads? If the latter id assume the stock calipers had a much wider gap for pads, since Ive been having dust boots issues since moving to the Megane Brembos.

I should've mentioned in my previous post that I'm running rear 996 Brembos, their stock dust boots have been holding up fine. I didnt even rebuild them, just installed the used calipers with the factory boots since they looked good and still no cracks or issues, though I havent looked at them since the last track day with the PFC08 pads. I was running lower friction compound GLOC pads rear and I think the fronts were basically doing all the braking work so maybe that's why they haven't been heat stressed and cracked yet (no boots touching either with the 737 pad shape).

[mrgizmo04]

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

Per my last comment, they might use steel pistons which prob help. I'd also assume material composition for boots changed from originals to today. Folks have tried Stoptech, Brembo, Girodisc, RB with high temp variants and they all melt.

Essex is into something with their bootless kits for track.

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[mrgizmo04]

and new Girodisc rotors (no heatshields this time). While better, 3 of the 4 RB high temps had developed cracks next track day…

mrgizmo04 I was actually thinking the opposite, that as the pads for wear down in thickness with use maybe the dust boots will survive since won't (shouldn't) be touching the backing plates directly as much lol.

Sucks that you are already on Girodiscs and rb blue. I was hoping Girodiscs would help a tonne given number of vanes and proper 2 piece efficient design.

I'm also on ti shims, and I've been using the Vorshlag shovels (per pic). Trimmed my shield even more this week, so need to retest. Qualitatively speaking, these shovels move more air than when I had the 2" hoses. Are you running cooling ducts other than stock tunnels?

IIRC, conduction from backing plate/ti shim to dustboot is not a transfer mechanism, but I need to double check. With new pads, if boots are properly installed, tip of the piston should be first part pressing on the shim/backing plate. After installing new pads, you have to pump the pedal a few times and that seats and pushes out the pistons a bit. Also remember that in these budget kits pistons are aluminum (vs high end kits using steel or even ti), which has higher conductivity and less resistance, so first line of defense for the tip of the piston is the boot.

Do you by chance have a size diff for the front pad between stock and Megane, like I provided at end of post 22 above. Would love to see the diff visually.

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[repoman89]

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

[BigRussia]

Im in the same boat but with Renault Megane Brembos (Freakyparts kit). Melted the stock new dustboots with 16mm GLOC pads and only slightly worn ZCP rotors, since the pistons had to be fully compressed to fit them and was only able to put Ti heatshields on outboard side. I then replaced the inboard boots (which were completely melted vs the outboards) w the RB blue high temps, and put 14.5mm PFC pads and new Girodisc rotors (no heatshields this time). While better, 3 of the 4 RB high temps had developed cracks next track day… I mean it’s def from direct contact to the pad backing plates but still frustrating that even w a ‘thinner’ pad thickness they still touch n cook. I then installed new RB blues boots for the outboards along with the Ti heatshields both sides hoping now they will survive without cracking next track day, but I’ll have to replace the already cracked inboards again. This will get tiresome and expensive if I have to keep replacing dustboots after every track event.

mrgizmo04 I was actually thinking the opposite, that as the pads for wear down in thickness with use maybe the dust boots will survive since won’t (shouldn’t) be touching the backing plates directly as much lol.

[mrgizmo04]

Anyone confirm those blue RB ones hold up with pad less than 50%? Once pad starts getting low, heat capacity exits stage left and things start going south exponentially.

I'm getting tired replacing boots every other weekend. Although you really only need to do it if swapping to fuller pads where pistons need to be compressed back in (like to street pads). So I'm stopping swapping from track pads and will just let the pistons come out as track pads wear and when I need new track pads will clean off the pistons and replace dustboots. Hopefully blue ones are the answer?

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