Brembo Big Brake retrofit kits for E28/E23/E24

[BenGerman]

Hi y’all,

After the last project of high strength S38 crank hubs the mill is empty again and the next project in line is ready to be accomplished.
I had Brembo E31 calipers sitting in my basement for a while now, but never got around to mount them.
Main reason for it: I’m not to thrilled with the brake bias of the factory M5 setup under heavy braking/cornering and the Brembo would make it front heavy again, even with E34 rears.

The idea: let’s fit Boxster rears with the Brembo fronts. The first calculations show a nice brake bias of 67/33% F/R.
Then I thought of the E23, where no real BBk is available at all. Now I have a 996 Turbo brake kit coming.

The goal is to come up with solutions to use Boxster/996 brakes with 16” and 996 Turbo brakes with 17” wheels, all while using standard BMW rotors.

There is a lot of different calipers out there from Porsche.
The only real difference I could tell so far is the Turbo front caliper, which has 36/44mm pistons.
All the others have 36/40 Front and 28/30 Rear. (986, 986S, 996C2, 996C4)

And while E31 fronts are getting more and more expensive and hard to find ($600-750 for the last sets), Boxster calipers are readily available for $150-200 per set of 2. They also have a way better choice of pads.

The following combinations will be developed:

E31 Front, 986 Rear
986 Front & Rear
996 Turbo Front & Rear
955 Cayenne Front & 996 Rear

The plan is to have three versions available: mild steel zinc plated, stainless steel, Titanium.

The goal is to have the first sets available for sale at the Vintage.
I will also bring a car fitted with these brakes.

[BenGerman]

986 Rear with E34 540i rotor (300x20)



Pad size comparison E34 540i Rear / 986 Rear



E31 Brembo / 986 Rear / 540i Rear

[dsmith]

Did you make your way through this thread yet?

http://www.mye28.com/viewtopic.php?t=100050

[BenGerman]

Yes sir. Unfortunately there was never a final product.

[BenGerman]

More calipers came in today. Still have to find a decent set of 996 calipers or confirm that they are exactly the same as the Turbo Rears...

The Turbo calipers with decent pads and a 345mm rotor should be plenty of stopping power.

[adam_poll]

I'd be interested in a set of brackets to mount 986 calipers front and rear onto E34 540i discs under 16" wheels on an E28 when they are available. The weight of the Porsche calipers, pads and brackets compared to stock 540i calipers pads and brackets would be very interesting to see. What master cylinder do you plan on using with these, stock 23.8 mm or the E32 25 mm unit?

Thanks,
Adam

[BenGerman]

I'd be interested in a set of brackets to mount 986 calipers front and rear onto E34 540i discs under 16" wheels on an E28 when they are available. The weight of the Porsche calipers, pads and brackets compared to stock 540i calipers pads and brackets would be very interesting to see. What master cylinder do you plan on using with these, stock 23.8 mm or the E32 25 mm unit?

Thanks,
Adam

I hope to have the first prototype for 986 Rear brackets done this weekend.
They should easily fit the 16" wheels with 300mm E34 rotors, potentially even with 325mm E46 M3 or 324mm E31 840Ci rotors up front.

I will do the calculations for the weights and brake bias this weekend and post the combinations here.
The Cayenne 6 Piston Caliper is around 4500g without pads. That is lighter than the factory M5 caliper (5000g).
This should give a good reference for now. Sure, the adapter will add some weight. But for that reason we will be offering the Ti versions.
A M5 rotor in 300x30mm is 8600g while a solid 325mm M3 rotor is 8200g, Euro 2 piece 325mm M3 rotor is 7600g and the 2 piece 345mm M3 Comp rotor is 8600g.

Other weights:

Front:
733i - E23 4 piston: 5100g
745i - E23 4 piston: 5300g
535i - E28 - Caliper + Carrier: 4500g
540i - E34 - Caliper + Carrier: 5100g
840i - E31 - Brembo: 3300g
M5 - E34 - Nürburgring Package: 6700g
730i - E38 Brembo: 3200g

I guess that a Boxster caliper with M3 rotors up front saves you about 1-1.5Kg of unsprung weight compared to a E34 540 brake.

And yes, the Cayenne Caliper will clear 17" wheels.

Source: http://www.318is.de/300mm/new/325mm/rc041/rc041.htm

[George]

This is cool. I like.

[tig]

This is cool. I like.

Me too. Makes me wonder what Porsche calipers will fit 16" wheels. Thinking Porsche calipers on Minerva, which will be painted a Porsche color (Minervablau) might be neat.

[BenGerman]

I just did some measurements a bit ago.
As far as I remember, Kohler confirmed that E31 Brembos with 324mm rotors fit several 16” wheels.
The Turbo caliper is only 1-2mm wider, but about 25mm longer. I’m convinced this can be worked out somehow.
If not, the 911 caliper for sure is smaller than the E31 Brembo.

I’m still not 100% sure what Porsche caliper is identical and where the exact differences are.
Some are just colored different (C2/C4), some share the same pads, some share the same pads but use wider rotors.
Not really thrilled to buy all of them.
Seems like autozone can get some. Maybe just order and return them?

At the end, the front / Rear combinations have to make sense in regards of the brake bias. Doesn’t help if one axle locks up before the other. We could use an adjuster valve, but I’m not a fan of that.

[BenGerman]

Some progress today: Measuring and modeling of the rear 986 adapter completed.
The biggest problem with the E28 trailing arms is the position of the ABS sensor. As it sits directly between the two caliper mounts, it makes the design way more complicated than in E30 applications.

The good news is: The Boxster caliper fits like a glove, with only slight modifications to the dust shield. The pads cover the rotor surface completely. Just by eye, I would say the contact surface is about 50% higher than with the 540i pad. Also, this combination works perfectly fine with 16" wheels, as seen with the 8X16 ET23 wheel.

image1 by Ben St, auf Flickr
image4 by Ben St, auf Flickr
image3 by Ben St, auf Flickr

[athayer187]

Very nice work! Let me know if you want an early adopter who will get some significant track time on your solution.

[Karl Grau]

I’m still not 100% sure what Porsche caliper is identical and where the exact differences are.
Some are just colored different (C2/C4), some share the same pads, some share the same pads but use wider rotors.
Not really thrilled to buy all of them.

I have a set of 996 Mk I calipers on the bench right now. I know they're the same sized used on the Boxster S. If you don't already have the info, I'd be happy to take any measurements you might need.

[BenGerman]

Very nice work! Let me know if you want an early adopter who will get some significant track time on your solution.

Thanks! I'll keep your offer in mind!
What setup are you currently running? The E32 750i as in your signature? What pads? I'm still working on a overview with some numbers and brake torque values.
The pads (friction coefficient) have a significant influence on the ultimate values.
At the end that's only one of the factors, but most likely the one that everybody can feel right away.

I have a set of 996 Mk I calipers on the bench right now. I know they're the same sized used on the Boxster S. If you don't already have the info, I'd be happy to take any measurements you might need.

That would be awesome. Let me have a look at my calipers and I'll send you a message.
Do you have front and rears?

[BenGerman]

Good news for the rear axle rotors: it seems like the E38 750iL rear rotors with 328x20 will bolt up right to the E28 hub. Even the E-brakes seem to match.
That was my biggest concern in using E46 parts in the rear, as adapter rings for the E brake shoes would have to be made. I will order a set and see what it looks like. They are only $100 a set of 2.

Im still looking for big options for the front axle, as the E46 Rotor has a complete different layout.
The E34 M5 Nür rotors (345mm) are $599 a set by now. Which is kind of... pricey.

I will also do the math for a combination of 324mm E31 rotor with cayenne caliper up front, combined with the 328mm E38 rotor and 991 calipers in the back. This would be the biggest set available, combined with 17“ wheels.

The advantage of using a Cayenne/Touareg/Q7 6 piston caliper is simply the availability and price.
They are available for $200-250 all day, while 911 Turbo Front calipers are easily double the money.
Plus the pads are a lot bigger. But, they can only be used with 17“ wheels.

Update 1:

Trying to bring some order into this rotor chaos. Will be updated as I look at other options.

Bildschirmfoto 2018-01-22 um 17.08.49 by Ben St, auf Flickr

Update 2:
E38 750iL front & rear order for test fitting purposes.

[athayer187]

Very nice work! Let me know if you want an early adopter who will get some significant track time on your solution.

Thanks! I'll keep your offer in mind!
What setup are you currently running? The E32 750i as in your signature? What pads? I'm still working on a overview with some numbers and brake torque values.
The pads (friction coefficient) have a significant influence on the ultimate values.
At the end that's only one of the factors, but most likely the one that everybody can feel right away.

I generally run Performance Friction pads - for the last few years I've been running the -08 or -11 compounds (no mixing though). I'm not a fan of using friction material to change brake bias, as then you have wear and temperature expectation differences which just overcomplicates things to me. Yes, I run the E32 750i calipers all around (E36 M3 pad shapes - the only thing that's going to be hard to walk away from!).

[Karl Grau]

I have a set of 996 Mk I calipers on the bench right now. I know they're the same sized used on the Boxster S. If you don't already have the info, I'd be happy to take any measurements you might need.

Do you have front and rears?

Yes.

[tig]

Bildschirmfoto 2018-01-22 um 17.08.49 by Ben St, auf Flickr

This should be a FAQ/Sticky. Hugely useful and informative. Thanks Ben.

[BenGerman]

I have a set of 996 Mk I calipers on the bench right now. I know they're the same sized used on the Boxster S. If you don't already have the info, I'd be happy to take any measurements you might need.

Do you have front and rears?

Yes.

Thanks for your help! Curious to see what the differences really are.
That's the Boxster rear caliper dimensions. I will take the same measurements for all the other calipers I currently have.







Sorry, couldn't find my metric steel ruler.

This should be a FAQ/Sticky. Hugely useful and informative. Thanks Ben.

I still need to confirm these, so far I only put together what I could find online.
Maybe we can extend it and combine with some other brake Thread in the FAQ section.

Update:

Bildschirmfoto 2018-01-23 um 13.32.19 by Ben St, auf Flickr

Couple more rotors added. Still looking for something that fits the rear axle.

Seems like there is 3 different versions of E23 rear axles:

Old style - Until 9/81
New style without ABS and Dogbones - 9/81 to 9/82
New style with ABS and Dogbones - from 9/82

As the old style rear axle seems to require something totally different, I will not dig any deeper into a big brake solution for these cars.
For everything after 9/81 the E32 750i rotors seem to be a straight fit.

Update 2:

Found another potential option for the front rotors: E60 545i 2 piece rotors, 348x30mm, 10.2 Kg, $289 / set from Pagid.
Bildschirmfoto 2018-01-23 um 15.16.13 by Ben St, auf Flickr

This seems to be a promising option compared to the $600 E34 M5 3.8 Nür rotors.
With that being said, I will stop looking for rotors now and get into calculations.

This is what the Nür calipers and 345mm rotors look like under a 17" wheel. I believe 911 or Turbo calipers should fit in there as well. 6-piston Cayenne might be a little tight.

IMG_8449 by Ben St, auf Flickr

[Karl Grau]

As I mentioned, these are from a '99 996 C2.

Here are the rears, I'll do the fronts tomorrow.

[BenGerman]

This is good stuff! As 986 parts are usually cheaper, here is the first chance to safe some money.

The calipers seem to be completely identical, besides the 4 Pins that guide the pads.
And those are pressed in, so it should be possible to adjust or replace them.

Curious to see what the fronts look like!
Thanks a lot for helping out!

And by the way: Nice crank hub in the background.

[dsmith]

Dang. I want the motor to go with these brakes! As a side note, I just ordered 850i single pot 324 mm calipers and brackets for $130 from Autozone. I have found them to be the cheapest solution to bigger brakes, plenty of stopping power, though admittedly a bit heavy.

[BenGerman]

Dang. I want the motor to go with these brakes! As a side note, I just ordered 850i single pot 324 mm calipers and brackets for $130 from Autozone. I have found them to be the cheapest solution to bigger brakes, plenty of stopping power, though admittedly a bit heavy.

I'm still in the middle of calculations, but there is a lot of interesting things going on with these BMW brake systems.
Especially the master cylinder question keeps me busy at the moment.
The E31 floating calipers are the same piston diameter as the E34 540i/M5, they are just made to be mounted on the slightly bigger rotors.



What MC, rear brakes and rotors are you going to run this with?
From the numbers, the bigger rotor in the front when going from 540 to 840 floating rotors will increase your front breaking torque by 1.6%, changing your overall ratio from 68.4%F to 68.8%F.


Here is the BMW factory MC options:
E23 MC = 22.2mm
E28 MC = 23.8mm
E32 MC = Early E31 MC = 25.4mm
Stepped E31 MC = 20/26mm

Does anybody know of anybody know of any other MC options for our cars, that will not require replumbing of the brake hoses?
The Stepped E31 design uses a FR+FL, RR+RL layout (only possible option when stepped), while everything else is a crossed layout of FR+RL, FL+RR.

[BenGerman]

Alright, let's stay with the science:



What do we know about MCs:

People have noticed an increase in pedal travel when using the 23.8mm MC with bigger brakes such as the E34 540 F/H. (Stage 5)

E32, E34 and E31: 25.4mm
Porsche 986 / 986 S: 23.8mm.
Porsche 996 C2, C4: 23.8mm
Porsche 996T, GT3: 25.4 mm
Porsche 997GT3: 27 mm (and a common upgrade for firmer pedal feel on other Porsches)
Cayenne: 27 mm

Fun fact: The Cayenne & 997 GT3 MC is $164 while the E28 MC is $474.

What affects the pedal feel?

The pedal feel is affected by the sizes of the caliper pistons. (Thanks Micah for the good discussion )
Larger caliper piston = more brake fluid needs to be moved through the system to move the pistons the same distance.
If you increase the MC piston diameter, the brakes will start locking earlier in the travel.

But the total pressure in the system will be lower as well, reducing the pressure on the pad and ultimately the maximum braking torque.
This can be seen in the above table, when comparing the E34 540i front caliper braking torque with both MC sizes. The maximum torque is reduced by 13%.
It is important to keep both things in mind.

It does not help to increase the braking torque to a maximum (combining a E28 MC with Cayenne calipers), if the brakes can not be controlled anymore.
Since the amount of fluid that needs to be pushed through the system to move the calipers pistons towards the rotor is going to increase significantly with the bigger calipers, it would actually feel like a weaker brake, as nothing happens in the first part of pedal travel. Only flooring the pedal would give you the maximum stopping power. And we don't try to do that too often...

Next step: compare the pistons to each other to determine the correct MC for every combination.

[Karl Grau]

And by the way: Nice crank hub in the background.

Here are the fronts:

[1st 5er]

Good work Ben.

[dsmith]

What MC, rear brakes and rotors are you going to run this with?
From the numbers, the bigger rotor in the front when going from 540 to 840 floating rotors will increase your front breaking torque by 1.6%, changing your overall ratio from 68.4%F to 68.8%F.
.

With the 850i 324mm fronts, I use stock MC and e28 rear brakes. I have done that combo on 2 cars and really liked it. An M5 and a 535is. If there was any change in pedal travel vs braking, it did not cause issues with heel & toe shifting. I may put 540 rears on the next one just to see how I like it.

Carry on. I love it!

[q20v]

Great info! Thank you very much for digging it up and posting it. I have an E34 and just bought E31 front calipers and have been considering upgrading the rears to the 540 calipers. Your post is motivating me to us Boxter calipers though. I have the ability to make adaptors but if you get some in production before I start making some, I might just buy some from you. I'd have to confirm compatibility between E34 / E28. Keep the updates coming!

[BenGerman]

I've been really busy in the last couple days and didn't really make a lot of progress.

I got a couple rotors in for test fitting purposes:
338x32 Front, 328x20 rear and for comparison the normal E34 upgrade, 300x20 rear.




338x32 fits perfectly with the Turbo calipers under a 16x8 Style 5 wheel.

[tig]

That's awesome. Enough room for balancing weights?