911 Brakes 3" vs 3.5", What am I missing and Options

[jesiv]

Ok so I am upgrading to a 911 suspension (Seperate Thread http://www.914world.com/bbs2/index.php?showtopic=87337 ). Then I hear brake caliper bolt spacing 3.5 vs 3.0. So (IMG:style_emoticons/default/WTF.gif) WTF is 3" vs 3.5" Am I making a mistake going with 3.0 vs 3.5? I really don’t understand the issues. Do I care?

Thanks for real world opinions!

Regards,

James

[sww914]

The bolts that attach the caliper to the strut are either 3" apart or 3.5" apart. All 914's were 3" spacing. The 911 T's were 3" spacing, the 911 S's were 3.5" and all of the SC's and Carreras were 3.5" spacing. I'm not sure about the '75'76'77 cars, I think they went to 3.5 mid '75. If you want vented rotors and 5 lugs the easiest thing to do is just change the struts, hubs, and brakes to S, SC, or Carrera. There were 2 different ways to mount the strut to the ball joint, a pinch bolt and a wedge bolt. Either type of ball joint will attach to either the 911 control arms or the 914 control arm, but it must match the strut. 911 control arms are not superior to 914 control arms, the only difference is the splines on the torsion bars are different. If you use all the 911 stuff you use the 911 torsion bars.
Bigger calipers are available for 3.5" spacing than for 3" spacing. The biggest calipers for the 3" spacing is the BMW caliper which is about the same as the "M" caliper. With 3.5" spacing you can go up to the "A" caliper, Turbo calipers or with adapters you can use Boxster calipers. There are many more options and many more adapters, 944, 944T, etc., but I'm not that familiar with what all is out there because I already have a set of Boxster caliper adapters so I stopped looking.
If you're not racing seriously you won't need anything more than the "M" or BMW caliper with vented rotors so the 3" spacing will be fine and the 3.5" spacing will just cost you more money that you don't need to spend.
You can put your front 914 calipers on the rear with "M" calipers and replace your master cylinder with a 19mm master cylinder and have a well matched setup that will stop you really well, but you'll loose the parking brake without more adaptations.