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Old 30th April 2006, 21:49   #1
KBK
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Corvette ZO6 BBK (6&4 piston) on a E39 M5?

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:

http://cgi.ebay.com/ebaymotors/2006-...ayphotohosting
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?

Found it:
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.
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Last edited by KBK; 30th April 2006 at 21:54.
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Old 30th April 2006, 22:01   #2
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i thought you HATED anything GM related ?????

Last edited by kees; 1st May 2006 at 00:02. Reason: Please don't quote the whole original post
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Old 30th April 2006, 22:04   #3
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very interesting.. hmm.. might be possible, but requires a bit of know how.. and some one to test it
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Old 30th April 2006, 22:40   #4
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Quote:
Originally Posted by fast4door
i thought you HATED anything GM related ?????
I have no problem stealing the candy out of GM's nasty little hands...

Roger is gone now, for quite some time. But until GM discovers some sort of social/ethical consience that is not specifically market/profit driven, I reserve the right to treat them like shite. (I'd like them to innovate their way to a reality that involves a future - not social, ethical, moral and planetary death) Things like: 'quarterly profit analysis will be the death of us all', can't be said enough times.

I duuno. No particular reason except that GM has always been an offender of note. To many times, companies take the course of least resistance..and follow a market instead of driving it. And when they drive it, they take the course of least immediate risk, which usually involves a path that leads to enviromental ruin. Too lemming, and too short sighted. They are, of course, in no way unique.

Anyway..back to the brakes in question.

6 and 4 piston, forged. There must be a way to make that work.... I'm gonna hit the GM dealer today and see if I can find some other info floating around the sales offices of a GM dealer. (Sunday..I'm sure the parts/mechanic shop is closed)

As I said..this is what I do. Last night for example, I was up til..ug..6am.. working on the modification and re-execution of an optics package for a projector manufacturer. Just so I can take it to them and say.."hey. You're the best in the world? Well...this is what it looks like when I re-execute what you have'. In the same way Discovery re-does a M5, I re-do just about anything that tickles my fancy. For the past five years I've been doing optics and projection/electronics work.

Contemplating the brakes is a hobby/fun thing, I guess. I think I can ace this one... I think.

Whatever the result, by the time I'm done... I'll know alot more about brakes than I do right now.

Oh yes. The fronts are a done deal, if you can get the brackets to fit and work. The Front calipers are available separately. As far as I know, it would be best to get the back working too, to equalize the clamping pressure and rate. Needs to be looked at.

As for stealing away business from brembo and stoptech, anyone attempting to do this is in for a world of hurt, unless someone else has done all the preliminary work...and we still have to buy our rotors and hats from someone. I don't think Dave Z or anyone else is going to loose much of any sleep or business over this.

Last edited by KBK; 30th April 2006 at 23:18.
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Old 30th April 2006, 23:16   #5
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Old 1st May 2006, 00:41   #6
Richard in NC
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The brake experts need to chime in here but....

I assume you'd use e39 designed rotors? The BMW hub/rotor setup would be completely different than a Corvette. My guess is there are insurmountable issues with using different rotors.

If the calipers fit the rotors and under the rims properly and if you could design proper mouinting brackets, I'd still be concerned about several things.

The brake brake balance front to rear could be off. The master cylinder is designed to move so much fluid front and back. 6 Pistons front could throw that off.

Having to move soo much fluid could cause a soft pedal. Search the archives, that seems to be a common complaint with BBKs, even 4 piston.
I honestly have no clue how well BBKs work in various cars.

ABS, DSC, and brake assist could be thrown way out of wack. I don't know their parameters but ABS & DSC may not be programmed to handle a totally different braking feel.
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Old 1st May 2006, 02:37   #7
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One would have to use the right hat..and I'd imagine that a given rotor design from either StopTech or Brembo will fit large numberof different hats..or..it makes sense if hats are designed, in terms of rotor size and car they go on. in that case..the right hat for a BMW, mixed with a different rotor from the same company.

The right diameter of rotor for that hat..will have a 'universal' mounting arrangement. It would be foolish to design many when one flange/mount design per rotor diameter will do, and also be optimum. So, as a question, that part is covered.

Then... the rotor for the rears, as the emergency brake drum is built into that. There lies a potential issue. In that case..the Brembo slotted rotor for the rears..at 28mm thickness..and 345mm diameter. The GM rear caliper is looking for 340mm diamter. Possibly shaving the rotor down? It may not be nessessary to go to the full 340mm..and you might be able to get away with shaving less.

Now, rotor thickness on the rears. The GM caliper wants 26mm. The Brembo BMW one is 28mm thick. 1 extra mm per side. now, pads wear alot, that's their job. Possibly, the rear rotors might be shaveable in their thickness and and up not being a critical issue. I dunno. something to look at. Wouldn't be slotted anymore.... also, possibly...thinner pads instead? A few minor obstacles. How's the weight balance of the vette compared to the BMW? If the balance is the same and the real issue is the extra weight, I'm not quite sure that the weight actually would be considered an issue. After all, you use up your brakes till they don't work anymore, etc. Same ole same ole. Thinner pads are possible, if the GM caliper is designed to handle aftermarket pads, meaning the pad mount is standardized. Thinner pad availability would nearly bring it down to a very definite possibility, for both the front and rear.

As for the BBK creating too much flow and mush..the BBK for the vette..does not specify a new master cylinder. So it should be good on that front. I can't imagine the fluid flow rates are all that different between the two cars (BMW and GM Vette).

~~~~~~~~~~~~~
So, a short idealized list:

Check brake fluid (pedal movement vs displacement) flow and rate between the two cars (BMW vs. Vette). If good, go to next step.

Check to see if the GM calipers accept standardized pad sizes. If good, go to next step.

Dimensional issues: check for clearance and mount points.

If mountable...look at machining the flanges.

Stoptech Slotted 355x35mm BMW E39 M5 front rotor and hat.
Thicker pads for the front, as the GM caliper wants 35.56 mm thick rotors. With titanium inserts for temp control.. you might be just fine. after all, you are only 0.255 mm per side off on the thickness of the rotor required..and the titanium insert adds a certain thickness. Check on that. I think you can even see the number written on the insert, in the picture on Dave Z's site.

Brembo slotted 345x28mm (Or StopTech)rear rotor and hat, shaved down in diameter. I prefer the StopTech Rotor, as their internal vane design appears as if it allows for the shaving down to the proper diameter. The GM 4 pot rear caliper wants a 340mm diameter rotor.

Thinner pads for the rear, as the GM rear caliper wants a 26mm thick rotor.

Install.

Test your Rube Goldberg brakes.

EDIT: potential problem. Just discovered..that the pads are specific to the caliper. Let's see how many companies end up making pads for them. It's nearly 6 months down the road after they have been introduced..so maybe there are more.

Now, these calipers fit on many Vette models, so the mount point is a standard GM one. But..the thing to find out is if the Rotors are a specific requirement for their use, ie, do any other GM Vette rotors work with them? Then it will be known if different thickness pads are available. I have feeling (after thinking it through) that shaving down pads is next to impossible..and if possible, the friction layer/compound could be micro-cracked. Not a good thing.

Last edited by KBK; 1st May 2006 at 04:53.
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Old 2nd May 2006, 06:54   #8
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Call me crazy, but....

Why not go diect to the source? Then you don't have to have "Corvette" stenciled on your brakes on your BMW.

http://www.pbrperformance.com.au/index.htm
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Old 2nd May 2006, 07:24   #9
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Quote:
Originally Posted by gtessier
Call me crazy, but....

Why not go diect to the source? Then you don't have to have "Corvette" stenciled on your brakes on your BMW.

http://www.pbrperformance.com.au/index.htm
they don't even BMW or Corvette brakes on your choices.. but maybe the ones for the daewoo will interchange...
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Old 2nd May 2006, 07:27   #10
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Quote:
Originally Posted by fast4door
they don't even BMW or Corvette brakes on your choices.. but maybe the ones for the daewoo will interchange...
As KBK suggests, this is a custom built setup. You'd need to buy individual components.
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