Musing out loud again......
I thought that this is both a smart and dumb question..or possibility.. that it needed it's own thread, to assess properly. I also needed to get the attention of some of the brake experts who are on this forum, who might weigh in with their thoughts. Pulled from another thread I was contributing in:
I found this on Ebay:
What it is..is the GM OEM!!BBK upgrade
..for a Corvette ZO6.
It is designed for 14" (355mm)x 35.56mm thick Front rotors. The brembo BBK is 355x32mm rotors, on the front. Oh, wait,.. you can get 35mm thick rotors for the M5. Stoptech has a slotted disc at that thickness and diameter. Brembo has a slotted disc for the rears..at 345mm diameter. The GM BBK rear caliper is looking for 340..that's 2.5mm extra depth and a slightly less shallow arc. How much that small change in arc is handled, is not something I'm aware of in terms of affect on the brakes.
What I DO see in a set of brakes, is that the wear is even and INSIDE the arc of the outer edge of the rotor. I suspect there is an issue with the arc being too shallow as opposed to being too sharp. Ie, keep the pad fully active, across all of it's surface. I'm thinking this is to keep the pad from breaking apart. Uneven stressing, and all that. That would mean..that the smaller rotor is the one that needs be in use. To keep the full pad surface fully on the rotor? How about edge issues on the rotor? somehow I don't think that it is as much of an issue, the arc in that respect (brake pad arc) being slightly 'open'. All depnds on clearance inside the caliper, when deciding the cut and layout of the 'to be machined' mounting braket for the caliper.
The GM BBK... front caliper...is a 6 piston design.
That's not all. It includes a 4 piston rear set!
. yes, you heard that right.
For $1300, street price, you get TWO sets of calipers. a six piston set and a 4 piston set. Both front and rear calipers -appear- to be single body forged designs. Cool.
These might easily be adaptable to the M5. A few machined brackets...and you're in business.
One big issue..I am ignorant of: How to deal with the different thickness of rotor required. I know that rotors wear...but do shims work in such places? what is the stock rotor thickness..oh..that's right. 31.5mm, up front. back, 28mm.
It's got me thinking. I know that the rotors for these cars are not cheap..ie, the rotors for the different stoptech and Brembo kits. What are the stock vette BBK kit rotor sizes and thicknesses?
Front: 14 x 1.3 / 355 x 32
Rear: 13.4 x 1 / 340 x 26
Ok. Between brembo and stoptech, they have the rotor sizes, insofar as diameter goes. The diameter is a bit off, at 2.5mm on either side of the rear rotor (either too big, or too small, so that does not really equate to an issue in terms of arc covered..this is the rear vette rotor compared to what Brembo and Stoptech have available. I'd guess they may have the thicknesses available, for their glorious multitude of other brake calipers.)
The vette rear caliper is looking for a 26mm thick rotor..and a 332mm diamter rotor. Brembo has a 345mm x 28mm rotor. Now, how does one deal with the extra 2 mm thickness issue? That's a biggie, from my limited knowledge on the subject. Pad thickness is the issue, I'd guess. and 2mm in a brake system is certainly quite alot.
Can you shave pads? Or find the right brembo or stoptech rotor thickness?
Well...it's a project. Who knows.
Price is right, but you'd certainly have to be willing to futz around,and figure a few things out.
As for the whole thing being potentially..unsafe, well..All you'd be doing is figuring out how to build the exact right mounting bracket. And, to add..I'm sure that CLEAR engineering drawings, with measurement numbers, for both the ZO6 and the M5 are both readily available.
Oh yes: Weight of the ZO6 BBK front caliper:9 lbs
I realize this sound like alot of work..but you'd end up with 6 pistons on the front, with 4 pistons on the rear. HOWEVER..that 'kit' as a solution for GM..was engineered on a 500hp car..but the WEIGHT of the vehicle..is stated as 3200lbs. That's 800 lbs less than the M5. Now, how that factors in, I've no idea, but I do know that it is important to remember. Premature fade and brake burn..all the way to broken calipers - is the gamut it could run, in terms of possible issues. Remember, I speak from ignorance here. Spacing issues are there (wheel clearance needed), I'm just not saying much about that..as all aftermarket BBK's suffer from that one. See the auction.
Ah, whatever. A million ways to skin a cat.
But at $2500 and building a few mounting (4) brackets..you'd be at F&R BBK. Now, that's not too shabby. And I'm sure the GM brakes aren't all that bad, either. GM has always been rather picky about taking their chances with lawsuits. In one twisted way or another.
I'd say the odds are, that the brakes are over engineered, as these sorts of devices DEMAND a range of over engineering as a safety factor. (back to the M5 weight as an issue)
Also.. just remembered.. the mounting method and design. It may not work with the Brembo or Stoptech rotors..but I'd doubt that . But it is an issue that definitely needs to be looked at, and should be one of the first to be adressed. For example, the mounting points for the adapter brackets might interfere in the caliper's mounting requirement....to that same bracket. But I doubt it.
In reality, the number of obstacles appear
to be quite low.
I think that someone might chime in and say "You know, its not a good idea to fool with the brakes, as they are important." I'd quip back..yeah definitely true..but you have to remember, it is at -LEAST- twice as dumb to be trying to drive the car fast enought to need them.
Why do it?:
Because I have a budget, I want it NOW....I like challenges, it's mostly an exercise in engineering and intelligent assessment.... it's entertaining to ponder..and even more entertaining to follow through. I'm very much a DIY, proudly 'dunned it myself' kinda guy. It also amuses me to put a GM product on a BMW. Just because it gives people pause. It is also my job to figure such things out at times. Engineering challenges, all over the place. This is just simply....another one, is all. A day in the life.