I recently went through the process of fitting front BMW 320i calipers to my '75 914. Since it has the late model struts (apprx 72-76), the calipers needed to be machined in order to fit properly. Thought I'd share how I did it.
NOTE: the measurements in the following pictures are from my car only, they may not match other cars. If you want to use this method, make sure to measure your own car before doing any machining.
WARNING: Brakes are a safety critical component. Modifying the calipers from their original state may cause brake system malfunction or failure, resulting in damages and/or serious injury/death. The following is for informational purposes only. Modify at your own risk)
Measurements:
- I took a digital caliper and measured between the brake caliper mounting bracket and the outside of the disk ("d1").
- Then I measured the thickness of the disk ("d2").
- The distance from the mounting bracket to the center of the disk = d1 - d2*1/2
Why care about the distance to the center of the disk? Most of the caliper is rounded cast surfaces, which makes it hard to clamp down to machine. if you unbolt the two halves of the caliper, the mating surfaces are nice and flat to locate off of for machining (marked as datum "A"). My goal was to have this splitting surface centered on the disk. Here's my multi-view "drawing" used as machining instructions
My buddy did the machining work, and they came out great!
FYI, he used a 3/8" 4 fluted carbide end mill bit at 1200 RPM. Made some .100 passes then climb cut to finish it off.
I used a carbide dremel bit to add fillets to the sharp edge of the cuts just to prevent any cracks from getting started there. Probably overkill (ok ok, definitely overkill
), but I'm not taking any chances with my brakes! If I had thought ahead, I could have had my buddy do this with the mill. Good ol' hindsight.
for installation, see Pelican's technical article:
Pelican Technical Article: Upgrading to BMW Calipers on the 914
Installed, and perfectly centered around the disk. Sexy!
Results:
With the stock brakes, I was concerned about whether I'd be able to stop in time for an emergency situation. Now it feels like I have real brakes! I'm running the tee in place of the proportioning valve and braided steel lines, which seem to work just fine. If I find otherwise, I'll let you know.