Dust seal ID numbers from E92 M3 Brembo GT6/GT4 calipers - please?

[Captain Caveman]

After all the talk recently comparing retrofit BMW M4 calipers, Stoptech and Essex AP Racing kits, I am curious why we have no data regarding the piston sizes of the equivalent aftermarket Brembo GT6 & GT4 front and rear calipers??

I've scoured the Brembo literature, and although they share a little basic data, they don't seem to publish the piston sizes or pad heights for their kit on our cars.

These calipers are of course very common across a multitude of OE fitments, however they vary in piston sizes depending on the weight of the car and the intentions of the car manufacturer. As a potential customer, I really want to know what the spec is for our cars.

Could anyone with a full Brembo kit care to publish their different dust seal ID numbers found on the rubber dust seals (3 different on front, 2 different on rear)?

Either way, it's very short sighted of Brembo to assume that they can sell a brake kit without revealing to potential customers the exact specification and resulting behaviour of the product they are selling. Every BBK manufacturer has decided on a spec which will have a very deliberate impact on brake torque, front/rear bias, pedal travel and feel and modulation. It is the buyer's right to have this information to hand in order to be able to make a decision on the best BBK for their needs. Withholding this info makes it impossible to make an informed decision.

Cheers,

M.

[pbonsalb]

You will find the piston sizes will all be very similar for bmw applications. BMW might use a large single and others use 3 small ones Per side but the area is virtually the same. They don’t change the braking force from stock. That could cause bias changes or screw up the ABS.

Aftermarket brakes offer more pistons for better pedal feel, perhaps rotors that dissipate heat better, but no better stopping for the first few stops. If you go larger on rotor diameter, they reduce the piston sizes do the brake torque remains the same. The bigger rotors have more heat dissipation capacity so they are good for racing. But you don’t need that for stopping on the street. It is next to impossible to overheat stock brakes on the street without getting arrested.

aftermarket brakes are for racers. Or for street drivers who want to look like they are racers. Which is perfectly ok, but be real about it

[Captain Caveman]

Originally Posted by pbonsalb

You will find the piston sizes will all be very similar for bmw applications.

Sorry I am asking about the aftermarket Brembo GT kit for the E92 M3 - they don't disclose the piston diameters on their kits, however some many forum members have this kit that they should be able to provide the information.

I am interested in comparing piston sizes between aftermarket kits compared with OE stock pistons, so this information would really help. We know Stoptech and Essex-AP sizes, just Brembo missing.

Cheers.

[Captain Caveman]

Pretty please, with sugar on top - somebody must have access to this info! Loads of M3 owners have the Brembo BBK - would anyone care to supply the piston dust seal IDs on their front & rear calipers?

You'd be doing your M3 community a huge service and resolving the freedom of information issue we have with Brembo.

Thanks!

M.

[M43S7RO]

Have you tried reaching out to race technologies to inquire? I have the 365 fronts that I have to take off in a couple weekends. I'll measure if you havent gotten an answer.

[pbonsalb]

The piston impression on the pads may not be the same as the piston size. Perhaps Brembo offers support to determine the piston size based on the piston head diameter. Stoptech does. It is also possible the piston size is labeled on the dust bolt like on Stoptech. If not, you will have to remove the boot to measure the piston. Also, a Brembo caliper for a 365 rotor may use some or all different pistons than a Brembo caliper for a 380 rotor.

[wyatth]

^ Indeed the 380/380 and 365/345 kits have different piston sizes in order to maintain Brembo's desired and relative bias/torque.

[Captain Caveman]

Thanks for all the thoughts so far - this info is not published anywhere, but I will indeed reach out to Race Technologies. Its hard to buy a kit blind - they should be freely providing the info so customers can make an informed choice!

If anyone can have a quick look at their dust seal ID numbers in the meantime that would be amazing!

[Captain Caveman]

Originally Posted by M43S7RO

Have you tried reaching out to race technologies to inquire? I have the 365 fronts that I have to take off in a couple weekends. I'll measure if you havent gotten an answer.

Thank you - that would be amazing!!

[Captain Caveman]

I have emailed Race Technologies and emailed Brembo directly, however I'm not holding out much hope tbh.

I believe the only way we're going to get this information so we can make proper informed purchase decisions in future is if someone can take the trouble to measure the pistons on their kits, front and rear. It's a hassle I know, but would be invaluable to the community in the interests of fairness and transparency for anyone who's looking to buy a BBK now or in the future.

[DRLane]

Not sure what you're trying to achieve. All of these kits have been tested with thousands of track, TT, and endurance racing including professional teams.

What about your application is so unique that you couldn't be happy with any of these? You want a firm pedal buy new pads often, run a high quality fluid and keep it topped up.

[Redd]

Pad material, fluid compressibility and (in a small part) steel hoses will have a far larger impact on pedal feel than piston size.

[Captain Caveman]

Originally Posted by DRLane

Not sure what you're trying to achieve. All of these kits have been tested with thousands of track, TT, and endurance racing including professional teams.

What about your application is so unique that you couldn't be happy with any of these? You want a firm pedal buy new pads often, run a high quality fluid and keep it topped up.

Wow, that's a seriously blinkered point of view tbh. I like to know what I'm buying. Same as buying a coilover kit and wanting to know what spring rate the manufacturer has decided is 'optimal' for the car - it's their opinion, not necessarily what I want. Same goes for BBKs.

If it were that simple, all BBKs would come with the same piston size, pedal feel, pedal travel and modulation, but they don't. Same as suspension, each manufacturer decides on what they feel is the best for a particular application, but it's totally subjective. It's an opinion. Stoptech has a piston area almost identical to stock, but more rear bias. Essex Racing has a 10% smaller piston area, with the resulting decrease in pedal travel and increase in pedal firmness whilst maintaining the stock bias, and Brembo - no idea, they won't tell us.

See the issue. As a consumer I have a right to make an informed decision as to the relative behaviour of a product compared to stock, or other equivalents. If I'm gonna spend over £7K+ on a BBK, it's not a big ask to be able to make my own decision. Maybe I prefer a larger piston area with longer pedal, more modulation and greater overall torque, or perhaps I like a firm pedal and to press a little harder for my brakes to perform fully. Either way, I like to be able to make my own choices and have the information to do so.

I don't have the luxury of being able to try each BBK solution before I buy to decide which is right for me, however with a logical brain and some basic calculations, it's straightforward to work out what the resulting impact of a particular BBK solution will be when you crunch all the numbers together, (disc diameter, disc annulus, pad height, pad COF, piston area) especially when you have the stock numbers as a baseline. Pretty simple maths.

Again, like coilover kits, most buyers are happy to buy kits off the shelf and ask no questions, however those with a little more appreciation of what they're buying, or simply want the freedom to make their own choices, have the information on spring rates available, even if they have to ask for it. The info is available.

The same should be the case for BBKs. Not sure why this is an issue?? Why would anyone criticise anyone's right to this information!?? Weird.

[DRLane]

You're right - There is no need to criticize and I also appreciate knowing what you're buying / customization. Just seems like you're not going to get much in regards to the Brembo caliper pistons. AP, Alcon, ST, and PFC all make considerable solutions and would hate to watch the season pass by without the upgrade. Hence the "just make a decision" because I don't think you'll regret it. There are fast drivers on every kit and I just don't see these as a critical. Aerodynamic? I get that!!!

Anyhow, best of luck to you finding the perfect fitment. There is no sense in being a jerk. I apologize!

[Captain Caveman]

Originally Posted by DRLane

You're right - There is no need to criticize and I also appreciate knowing what you're buying / customization. Just seems like you're not going to get much in regards to the Brembo caliper pistons. AP, Alcon, ST, and PFC all make considerable solutions and would hate to watch the season pass by without the upgrade. Hence the "just make a decision" because I don't think you'll regret it. There are fast drivers on every kit and I just don't see these as a critical. Aerodynamic? I get that!!!

Anyhow, best of luck to you finding the perfect fitment. There is no sense in being a jerk. I apologize!

Hey, appreciate your reply - good man

For me, it's not about questioning what each individual company has put together as if I knew better (I definitely don't), however it's more about having transparency of information to allow for informed decisions.

I am guessing the main reason Brembo don't want to publish their piston sizes, is due to their GT6 and GT4 calipers being original equipment on so many cars these days, equipped with that information it would be too easy to make an identical retrofit kit with identical specs to their off-the-shelf solution, for a fraction of the cost.

That said, I'm determined to get the information, as is my right as a consumer. Hopefully someone will be able to measure their piston sizes at some point, there are enough Brembo BBK owners on here to make that possible!

[wyatth]

FWIW I don’t think the GT6/4 calipers are OE in many cars. The OE offerings you often see have the big bolt top center of the caliper (see Slonik’s offering as an example - these look like the model on CTS-V, AMGs, STIs, Range Rover Sports, etc.). The caliper face where the text is is also slightly different (squared on GTs, pointy on Slonik/OEs). I don’t know what other differences there may be, but it’s enough to conclude they aren’t exactly the same anyway.

[Captain Caveman]

Originally Posted by wyatth

FWIW I don’t think the GT6/4 calipers are OE in many cars. The OE offerings you often see have the big bolt top center of the caliper (see Slonik’s offering as an example - these look like the model on CTS-V, AMGs, STIs, Range Rover Sports, etc.). The caliper face where the text is is also slightly different (squared on GTs, pointy on Slonik/OEs). I don’t know what other differences there may be, but it’s enough to conclude they aren’t exactly the same anyway.

You're right, they are very slightly different, but only slightly. The share the same basic design, the rears are almost identical too.









Anyway, that's taking us off topic. Has anyone managed to measure their pistons?

[Captain Caveman]

Hi all -

I have found an easy and accurate way of getting the piston sizes from the Brembo calipers. If someone can give me the ID numbers on their rubber caliper piston dust seals, I can get the piston sizes from them easily. Piston seal IDs are in the following format; 204872 45

And look like this (rubber rings around the pistons) - you can see the ID numbers clearly.



Many thanks!

[slowdown_dan]

Originally Posted by Captain Caveman

Hi all -

I have found an easy and accurate way of getting the piston sizes from the Brembo calipers. If someone can give me the ID numbers on their rubber caliper piston dust seals, I can get the piston sizes from them easily. Piston seal IDs are in the following format; 204872 45

And look like this (rubber rings around the pistons) - you can see the ID numbers clearly.



Many thanks!

Attached picture is for the rear GT4 kit with a 345x28 rotor

Front pics didn't come in as clear so I won't attach but the part numbers end in 45, 43, and 41 for each piston. This is for a 365 gt6 front kit.

This happens to be the brand new kit that I currently have for sale, btw.

[Redd]

Curious is there any point to replacing the piston dust seals since they are going to get destroyed in a short time? Mine are obviously shot but some have told me not to replace just the dust seals if the caliper isn't leaking.

[derbo]

Originally Posted by Redd

Curious is there any point to replacing the piston seals since they are going to get destroyed in a short time? Mine are obviously shot but some have told me not to replace just the seals if the caliper isn't leaking.

The ones by the face of the piston are dust seals. They are separate from the piston actual seals. Outside of protection the actual seals from debris, it's not necessary.

[Redd]

Originally Posted by derbo

The ones by the face of the piston are dust seals. They are separate from the piston actual seals. Outside of protection the actual seals from debris, it's not necessary.

Yes I mean the dust seals. Corrected my post. Thanks.