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

[Obioban]

Obioban

you may have mentioned it already, but why did you change your Brembo kit out for the 996 calipers?

The Rennlist forums have a lot of good information that might be helpful.

FCP sells 996 track pads and CSL/ZCP rotors. That eliminates... 1/4-1/3 the cost of tracking

In every other way, the Brembo kit is hugely better. Lighter, pads last longer, rotors last longer, better pedal feel, no dust boot issues.

... I'm not entirely sure I made the correct choice.

[nyc951]

Obioban

you may have mentioned it already, but why did you change your Brembo kit out for the 996 calipers?

The Rennlist forums have a lot of good information that might be helpful.

[Obioban]

In terms of rebuilding the calipers frequently...

If Girodisc pressure seals hold up (I'll remove some dust boots to see if I find shavings like with stoptech ones pictured above), then they should be good and I'll be a happy camper. Because replacing the pressure seals gets messy with all the fluid.

If I keep playing musical chairs with dust boots between Girodisc, FCP Brembo, etc, that's not that terrible as they can be swapped with caliper and fluid line connected to the car (in worst cases at least the fluid line and pistons don't need to be removed and nothing gets messy with fluid everywhere).

If someone is trying the magical blue dust boots, report back, assuming that's the only variable you change.

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My friend with the brake failure in the video is going to try just the blue boots, and is going to try them as the only change at his next event.

I really want that to be enough of a solution, as I don't want to be fiddling with heat shields for the rest of time...

[Obioban]

If I remember correctly, the silicone is not impervious to brake fluid. If you manage to get them installed, I'd be curious how much of a difference they would make in your scenario.

But if brake fluid is in that area, something has already gone pretty wrong, no?

I’m debating what combination of them and titanium heat shields I should try…

[r4dr]

Girodisc dustboots seem to be holding up to temp after a few events (need to run a few more events to confirm), but as I posted in one of the pics above, they slide out of the bores (stay attached to pistons and get pulled out).

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Whoops, missed your post. I'll PM you and get you taken care of.

Doing some reading this morning, it seems silicon can deal with heat significantly better than EPDM. Other than install potentially being a PITA, what issues are your foreseeing in the high temp silicon stuff being fragile?

If I remember correctly, the silicone is not impervious to brake fluid. If you manage to get them installed, I'd be curious how much of a difference they would make in your scenario.

[Obioban]

Your difference in experiences with the factory rotor vs your Brembo BBK is interesting. I'm assuming you had a 355x32 kit, and while I don't have the weights of a Brembo ring, the GiroDisc 355x32 ring weighs in at around 17 lbs. The GiroDisc E46 M3 ring (ring only) weighs in at around 16 lbs, so the thermal mass is very similar. This passes my sniff test, because while the D1-012 factory-sized ring is 345x28, it has at least 10mm more annulus which makes it up. I don't have a recorded weight for the factory ring only, because we would have to cut the co-cast "hat" out...

Both the Brembo 355x32 ring and the GiroDisc 355x32 ring (and the E46 M3 ring) are 48-vane count. The factory rotor has 30 vanes, if my notes are correct. So the Brembo rotor would have more than 50% higher vane count, which lends itself to much more effective cooling. Brembo has also sold a 72-vane 355x32 (I think they call it Type 5) but I would suspect the ring in your kit was 48-vane.

tl;dr: it makes sense that your Brembo BBK was much more effective at cooling than the factory rotors, which matches your real-life experience. The factory rotors suck at cooling, relatively speaking.

Dust boots get toasted with track use, even the boots in my 997.2 GT3 with the 380mm setup (more than enough rotor for the car) are beyond disintegrated. Titanium pad shields will help, but at the end of the day the most robust boots are the EPDM units. The "high-temp" stuff is silicone if I remember correctly and tend to be fragile as heck.

Doing some reading this morning, it seems silicon can deal with heat significantly better than EPDM. Other than install potentially being a PITA, what issues are your foreseeing with the high temp silicon stuff being fragile?

[mrgizmo04]

Brembo, GiroDisc, and I believe Pat's seals/boots are all EDPM.

As far as I know, Brembo uses the same parts bin of seals and boots for their OEM calipers and BBK calipers.

Girodisc dustboots seem to be holding up to temp after a few events (need to run a few more events to confirm), but as I posted in one of the pics above, they slide out of the bores (stay attached to pistons and get pulled out).

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[r4dr]

Anywhere we can get edpm?

Brembo, GiroDisc, and I believe Pat's seals/boots are all EDPM.

As far as I know, Brembo uses the same parts bin of seals and boots for their OEM calipers and BBK calipers.

[Obioban]

Anywhere we can get edpm?

[r4dr]

Your difference in experiences with the factory rotor vs your Brembo BBK is interesting. I'm assuming you had a 355x32 kit, and while I don't have the weights of a Brembo ring, the GiroDisc 355x32 ring weighs in at around 17 lbs. The GiroDisc E46 M3 ring (ring only) weighs in at around 16 lbs, so the thermal mass is very similar. This passes my sniff test, because while the D1-012 factory-sized ring is 345x28, it has at least 10mm more annulus which makes it up. I don't have a recorded weight for the factory ring only, because we would have to cut the co-cast "hat" out...

Both the Brembo 355x32 ring and the GiroDisc 355x32 ring (and the E46 M3 ring) are 48-vane count. The factory rotor has 30 vanes, if my notes are correct. So the Brembo rotor would have more than 50% higher vane count, which lends itself to much more effective cooling. Brembo has also sold a 72-vane 355x32 (I think they call it Type 5) but I would suspect the ring in your kit was 48-vane.

tl;dr: it makes sense that your Brembo BBK was much more effective at cooling than the factory rotors, which matches your real-life experience. The factory rotors suck at cooling, relatively speaking.

Dust boots get toasted with track use, even the boots in my 997.2 GT3 with the 380mm setup (more than enough rotor for the car) are beyond disintegrated. Titanium pad shields will help, but at the end of the day the most robust boots are the EPDM units. The "high-temp" stuff is silicone if I remember correctly and tend to be fragile as heck.

[Obioban]

Was just talking to some local people about heat management with these calipers the other day. The stock noise isolators that stick to the pads are made of what appears to be steel with a rubber coating. Bry5on ran the math and found that a heat shield made of 0.1mm elastomer and 1mm steel would result in the same thermal conductivity as 1mm of titanium. Any thicker on the elastomer and it outperforms Ti.

Point of this is that the calipers are designed to have those isolators installed. Heat getting to the dust boots is probably much higher without them. The problem is likely extra bad with track pads, as most of them have a backing plate made of just steel and lack that HDPE-like layer that street pads like textars have on them. I know that layer is probably mostly on there for noise, but it should make a pretty big difference regarding heat transfer as well.

My plan is to use the OE Porsche/Brembo dust boots and a heat shield. Haven't decided yet if I want to run the titanium shims or the stock Porsche ones with the metal cylinders removed (pic below). Will likely buy the Ti stuff and run a quick experiment to see which one does a better job at track temps.



I know this didn't answer your question, but I figured I'd share, as less heat there should help prolong the life of the seals.

These are the appropriate dust boots:

- https://www.fcpeuro.com/products/por...or-95135191700
- https://www.fcpeuro.com/products/por...or-95135191701
- https://www.fcpeuro.com/products/por...or-95135291700
- https://www.fcpeuro.com/products/por...or-95135291701

I suspect the rubber coating would melt off, rendering the plate thermally conductive.

[heinzboehmer]

assuming that's the only variable you change.

I think you might be asking too much with this statement...

[mrgizmo04]

In terms of rebuilding the calipers frequently...

If Girodisc pressure seals hold up (I'll remove some dust boots to see if I find shavings like with stoptech ones pictured above), then they should be good and I'll be a happy camper. Because replacing the pressure seals gets messy with all the fluid.

If I keep playing musical chairs with dust boots between Girodisc, FCP Brembo, etc, that's not that terrible as they can be swapped with caliper and fluid line connected to the car (in worst cases at least the fluid line and pistons don't need to be removed and nothing gets messy with fluid everywhere).

If someone is trying the magical blue dust boots, report back, assuming that's the only variable you change.

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[Casa de Mesa]

Essex has a whole section on why your track car don't need dust boots:

https://www.essexparts.com/essex-designed-ap-racing-competition-brake-kit-front-cp8350-e46m3

Yep, well aware. Look at post #11.

They are a very helpful bunch though and might have ideas, was my thought. Even if they are anti dust boot 😛

[mrgizmo04]

I want to say that the last few 996/7s I saw at the track had aftermarket BBKs on them. It seems a little ridiculous to expect heavy track use out of a caliper designed for a street application.

They would be ok, if seals and dust boots would not blow out. On budget racecars, e36 and e46 guys have been running 996 kits for ages.

Has composition and formulation of the materials changed vs 5-10 years ago so they don't last as long now? Possible.

One of the inherent problems with 996 kits that folks forget about that gets lost among some "benefits" like "lighter", "pedal feel", is that they were originally on cars lighter than ours and with rear bias. So rear pads actually add significant size upgrade to deal with heat vs stock m3 pads (few pics below). For front bias cars like ours, 996 fronts just don't provide enough heat capacity (+ inefficient rotor cooling setup as I discussed before). I shove as much air as possible into the rotor, but that semi floating hat just deflects most of it back. Not surprising that newer m3 gen guys switch brake kits with similar style semi floating rotors to expensive kits. I think simply a proper rotor would go a long way to evacuate the heat. But swiss cheese rotors were all the rage.

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