Long story short, I don't want to pay $6,000+ for a big brake kit for my daily and vendors won't sell me just the adapter brackets so I could finagle my own BBK.
I have my fronts figured out, mostly, if my current test caliper fits. The issue will be the rear as I know for a fact the car I'm using test calipers from won't fit as I currently have a floating single piston in the rear with shorter mounting points ('06 BMW 530xi wagon).
My question is, to bypass fabbing up/bribing a buddy to fab up an adapter bracket for the rear calipers, would it be possible/is it advised to grab a dual piston front caliper and put it on the rear if I could find one with the same mounting distance? I know I'll need the proper rotor, but I'm just 'concerned' that a front caliper can't/shouldn't be on the rear.
As always, any help is greatly appreciated.
Thanks!
There's no inherent reason not to put a front caliper on the rear, but the usual hydraulic conditions apply - you'll need a MC with a rear circuit bore that moves an appropriate amount of fluid for your new rear calipers.
The vendors won't sell you the adapters because that's the part with all the R&D in it.
Depending on how the parking brake is implemented, you may lose your parking brake with this setup. And instead of trying to find a MC with a stepped bore, it's probably easier to pick a set of calipers with the right bore size for the rear. It will almost definitely be smaller than the front. Watch for rotor width as well, it's not uncommon for the rear rotors to be solid with the fronts vented.
the front brakes do about 70% of braking. upsizing your rears won't help a ton.... I'd just leave them unless tracking...
In reply to GameboyRMH :
I was also worried about the MC, but it appears it's the same exact MC for the M5, M6, etc all the way up to the 2015 7 series. I also haven't seen any complaints/issues when people did buy the vendor kits that would do 6 piston fronts and 4 piston rears. Anecdotal, but it is nice to know on my end.
In reply to Keith Tanner :
Haha, I wouldn't complain about paying a premium for the R&D cost of the adapter bracket; I just don't want to pay for the calipers, rotors, and pads along with it 
I forgot all about the parking brake...I'll have to look in to that as well, now.
In reply to Fueled by Caffeine :
As true as that is, I'll never say no to larger calipers! Unless I get beyond frustrated with it, then singles will do.
We put front brake calipers on the back of our leMons car. The calipers were off an early 80's Monte Carlo and te rotors were rear rotors from a mid-90's Impala SS. Apart from loosing the parking brake function, they worked fine. Welded on adaptor brackets, stainless flex lines (floating calipers).
If the parking brake function is controlled by an inner drum brake on the rear rotor, then whatever caliper works in the setup.
$6000 for a BBK? I just checked turnermotorsports, I can put StopTechs with 2 piece rotors at all 4 corners of my 135i for less than $6000, and that's not even bothering to shop.
Why not properly size the front pistons to work with the current size of the rear pistons? Are you fighting fade on the track? Want a more common pad size? I'm assuming you're putting the this on the 530ix mentioned in the first post? Even that boggles my mind.
FuzzWuzzy said:
In reply to GameboyRMH :
I was also worried about the MC, but it appears it's the same exact MC for the M5, M6, etc all the way up to the 2015 7 series. I also haven't seen any complaints/issues when people did buy the vendor kits that would do 6 piston fronts and 4 piston rears. Anecdotal, but it is nice to know on my end.
In reply to Keith Tanner :
Haha, I wouldn't complain about paying a premium for the R&D cost of the adapter bracket; I just don't want to pay for the calipers, rotors, and pads along with it
I forgot all about the parking brake...I'll have to look in to that as well, now.
In reply to Fueled by Caffeine :
As true as that is, I'll never say no to larger calipers! Unless I get beyond frustrated with it, then singles will do.
Larger isn't better. Larger is different. It may be worse. You more likely want larger diameter rotors, but not necessarily larger calipers.
The reason that big brake kits work with the stock master cylinder is because the guys specifying the kits are specifying the correct piston size. If you go from 4 piston to 6 piston calipers, you'll use pistons that have 50% less area. If you're going from a floating caliper to a fixed, you'll halve the area. If you want to increase the bias at one end or trade off travel for effort, you'll play with the piston sizes. Generally speaking, masters are expensive to change so you use them as a constraint.
