So I've looked at the links using Boxer callipers and it looks quite complicated where as some where I read one can do a straight swop using BMW callipers. Has anyone done this and was it an improvement? Yours thoughts in this direction welcomed.

I'm doing exactly this on the 75 I am resurrecting.

Changing piston size to the larger BMW caliper mimics the 914-6 calipers.
If you're using a 3/4 bore master (more common, cheaper) you will regain the stroke you lost when you changed to the 3/4 master. This also slightly affects brake balance, Changing the front without also changing the rear pushes the balance slightly rearward.
If you're using the standard valve in the rear this won't be an issue.

The larger pads on the 320i caliper should wear slower and you might get more miles out of them.

You will need to modify the lines a bit. Mine came with new copper/nickel lines.

You will add un-sprung weight to each front corner (not good).

I did mine for cost and appearance reasons. I needed everything anyways and the BMW calipers were less expensive in my case. I like the look of bigger calipers and the set I purchased had just been re-plated and are very pretty.

If you think you're going to improve the brakes in a way you can feel you will be disappointed...

If your stock stuff is working properly, I would not suggest it.

Changing the stock pads to a "performance" pad will have a FAR greater "feel" improvement than anything else IMO.

I'm using Porterfield R4-S on all corners.

Alpha calipers on a 914-4 front suspension with 911 Carrera hubs vented disks. Done by PMB Performance for Mark Sonners Raby Engen 1974 Turquoise 914

I think you should consider this set up. Look up on 914world and see the postings by our members.

Bob B

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You can use bmw calipers on 914-4 struts. Alfa and M calipers require 3” - 914-6/911 struts. Boxster brake calipers require 3 1/2” struts & adaptors.

My mistake I guess. Mark S says he was invoiced for 911 struts. The stock 4 ones that I took my shoulder out, we put on that made the car a roller to get it to Utah last year.

Bob B

I have BMW brakes on my 72 914-4. It came with the car when I bought it. I just started driving it after a full car rebuild… including the calipers, and I have issues.

On the earlier cars the calipers bolt on… without machining. However, the caliper/mount doesnt mount in the center of the rotor. You have to shim the bracket to get it close. I don’t love this arrangement. Also.. my Fuchs wheels just barely clear the caliper and I’m probably going to have to add a spacer… 1/4 should work. Right now I have a steel wheel for a spare.. that won’t fit at all… so I have to work all this out.

Finally… the brakes are dragging a little… I’ll relube the pins… and see if that fixes it… otherwise I have to tear them all apart and see what’s hanging it up. It might be a piston clocking issue… which I thought I had right when I rebuilt the calipers. Frustrating!

Things to consider….

What problem are you trying to solve? If you haven’t added horsepower, stock breaks work great when functioning properly.

Hmmm from boxster to bmw brakes that’s a huge swing. What is your car/motor, and what are you looking to achieve, will you be modifying more in the future?

I’m of the mindset of do it once and do it right…. Are you considering 5 lug down the line? My -4 track car, has Porsche A calipers up front and Ms in the rear with a 19mm MC. IMO it’s perfect for the car, great feel, great modulation, correct bias, and more than enough brake for a 914. You have to go with 3.5 in struts, and you lose the brake, but you get the 5 lug with it…

Brakes are all about weight and velocity. HP has very little to do with it. And remember, when the brake calipers get big, so do the rotors. Then you increase unsprung weight and potentially decrease your suspension performance. Brakes are a system so plan it out before you just go bigger. Eric Shea has some excellent articles on “upgrading” brakes.

I did a BMW front caliper swap with a 19mm master cylinder. The back brake pads were hardly worn so most of the braking was done by the front. I switched back to 914 calipers in front and installed Porterfield R4-S pads all around. Even braking on all 4 corners.
Rebuild your calipers and the proportion valve in the rear. Install ss braided steel brake lines and Porterfield pads, you will be fine.

The conversion to 5 lugs also gives you a vented rotor for heat sink and the option of wider wheels for additional traction

The bmw caliper alone creates an unbalanced system that can thermally overload a stock rotor

Better to buy high end pads on stock calipers

Not trying to offend anyone
But for 20 years we have been discussing this and many/myself included do not recommended the bmw caliper. Not always an upgrade

GO to Classic Section and DO your homework. Covers everything you need to know.

Well thanks guys for all the input, I just want the car to stop! the wheels never skid or lock, can that be right? I've replaced the master cylinder because it was leaking, the callipers look like they have had some attention before me (ie they were painted red!!). Am I too use to driving a morden car? can you lock your brakes? I would like to keep it simple if possible. Please keep the ideas coming.

Yes you can lock them. You cannot compare to ABS braking.

Well if the calipers were painted red . . . They already have been upgraded

Setting aside the fact that OP says they can’t be locked, I’m really stating to believe that people have become too accustomed to brakes with power assist and very often - over boosted and completely lacking decent pedal feel and modulation. ABS only compounded that by teaching people to just mash the brakes and let ABS do the modulation.

Get back to 100% functional stock brakes and you’ll be in good shape. Something clearly wrong as-is.

I can share what worked well with mine. I put steel braided brake lines, a 19mm master cylinder and these great pads from Shea’s place. Can’t remember what they are but call PMB and they’ll fix you up. With that setup, on my honor I’d have to modulate my brake foot on hard braking to keep it out of a skid…But it chirped. I submarined a coworker into the footwell. It has 205’s which makes a skid even harder. If I stomp the brake pedal it will skid.

Now that is out of the way, this is going on the front of my car.
For me it is more about shedding heat to prevent loosing a consistent pedal corner to corner. That and a whole lot more choices on rims and tires.

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@mepstein
Guru of Porsche wisdom. What spacing is a 3.0 strut?
Matt

I’m not sure what you mean by spacing? M & Alfa calipers are a direct fit on 3”-911 struts. They will use 911T vented calipers. Contact PMB for more info. They are the brake guru’s.