Machining 320i calipers for late model 914 front brake conversion

[tabmaster]

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:

1. I took a digital caliper and measured between the brake caliper mounting bracket and the outside of the disk ("d1").
2. Then I measured the thickness of the disk ("d2").
3. 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.

[SirAndy]

Originally Posted by tabmaster

BMW 320i calipers, '75 914, stock brakes, tee in place of the proportioning valve, braided steel lines

Oh boy, i hope you have a nicely fitting flame suit ...

[jess p]

Thanks for the info

I did the same on my 71, but didn't need to modify anything as they
are a direct fit. Another thing I did was eliminate the brake valve in the engine
compartment. I picked up my 320 calipers for less than $150 bucks, rebuilt.
Stopping power was dramatically improved. I did install new brake rotors
as they were shot.

Great article,thanks for the info.

[dmenche914]

one thing to consider is the type of brake pad used, this can have huge influence on braking. I like Porterfeld race pads on my stock caliper 914, stops very good, a little bit noisey and dusty, but they do what there supposed to do. take some time in your selection of pads, that can make or "brake" your caliper upgrade projects.

[racer]

Brake pads, and oh, maybe the only thing touching the road like tires, as well as fluid and working components can be issues too. Not a fan of the BMW conversion, but if you like it, then thats great! thanks for sharing info should others follow your idea.

[tabmaster]

Sir Randy: didn't have one before, but now I'm ready! It's still German though...

Jess P: Yeah, you early model guys have it nice! Glad to hear you still like your bimmer brakes. What pads are you running? I've got MetalMasters/XBGs front and rear. I figured the semi-ceramic might be helpful with the solid rotors.

dmenche and racer: you're probably right, grippier pads may have achieved the same result with less time and money. But then I would have to spend my time wrenching on the engine, which I'm still working up to :-) Question: how noisy are those porterfields?

[SirAndy]

Originally Posted by tabmaster

Question: how noisy are those porterfields?

Their street pads are not that noisy. They make noise when cold and when you apply the brakes just a little bit. No noise under harder braking.
But they *do* create a lot of (reddish) dust!

Btw. do *not* use racing pads on a street car!
You will never get them up to operating temp and your brakes will not work properly.

[TargaT]

Hi I have 320 calipers on my race car. When I bought the car it cam with a bunch of new spare parts. I install new drilled rotors and porterfield pads. After a couple of sessions I was getting bad brake chatter. I just took them apart and found the rotors warped and the pads worn unevenly either front to back or top to bottom ie tappered. Not sure why this is happening? I notice the pistons on the 320 calipers are not fully 360 deg. on the mating surface. Could this be putting uneven pressure on the pads. Does the raised part of the piston need to be in a specific location? Any other thougths?

I just ordered some new solid rotors and pads. My old pads are still very meaty. Should I just try to surface them to flat?

[TheCabinetmaker]

Originally Posted by TargaT

Hi I have 320 calipers on my race car. When I bought the car it cam with a bunch of new spare parts. I install new drilled rotors and porterfield pads. After a couple of sessions I was getting bad brake chatter. I just took them apart and found the rotors warped and the pads worn unevenly either front to back or top to bottom ie tappered. Not sure why this is happening? I notice the pistons on the 320 calipers are not fully 360 deg. on the mating surface. Could this be putting uneven pressure on the pads. Does the raised part of the piston need to be in a specific location? Any other thougths?

I just ordered some new solid rotors and pads. My old pads are still very meaty. Should I just try to surface them to flat?

A Belt Sander works great for truing up brake pads.

[TargaT]

I found out the raised portion of the piston needs to be in a very specific location. I will post a diagram later.