Modified m-calipers on stock 914 rotors anyone?

[gshiwota]

I read the tech article about the BMW 320i front caliper upgrade and was intrigued by the mention of using modified 911 M-calipers (removal of spacer) for use with stock 914 rotors.

I just happen to have a good set of M calipers and 19mm master cylinder leftover from my '75 911 project that I'd love to install on my 914. However before I get into this endeavor has anyone actually performed this upgrade? If so, how's the brake feel and performance compared to stock 914 (is it worth the effort)?

I tried searching the forums but I couldn't find anyone actually performing this upgrade.

Edit- Oops, sorry I meant "914 rotors" in the title. I wish i could change this.

[Dave at Pelican Parts]

Happily, I can change the title for you!

I don't think the M calipers would gain you much, frankly. (But I'm not much of a fan of the 320 caliper upgrade, either.) I don't know of anyone who has done what you suggest, which is another hint to me that it probably isn't worth the bother.

If you change over to M calipers, and you have the ones with the spacers that allow you to do so, you'll gain a larger and heavier caliper than stock. (I think!) Larger is good, as it is more of a heat sink and more surface area to radiate the heat away. Heavier is bad, as it is unsprung mass that your suspension will have to work harder to control.

I believe the pistons in the M caliper are larger than the stock ones as well, which means that you will change the brake balance of the car. It should make the brakes more front-biased than they already are, which is good because you don't want the rear brakes locking before the fronts, but which is bad because the rears will wind up contributing less overall to the braking performance. You could modify, swap out, or remove the "proportioning valve" for the rear brakes, which will also change the brake balance, but that's getting into really re-engineering the system.

With the larger pistons, you will need to move more fluid. Your stock master cylinder will travel further to push the additional fluid the M caliper needs, making for a softer-feeling pedal. You can get that back by going to a 19mm M/C, of course, but again we're drifting into the "re-engineering" realm.

The major benefits as far as braking goes with the regular 911 front suspension setup are the larger calipers and the ventilated rotors. Those shed heat much much better than the regular solid rotors do.

As for braking performance, there should be very little if any difference. Remember, brakes only stop the wheels from turning. The tires stop the car from moving. Once your brakes have locked up, there is nothing more that they can do for you in this particular stop. If you're doing stop after stop, then heat management is the biggest thing.

If you cannot lock your brakes with stock brakes, something is wrong with them. They should be fixed. We know people who regularly out-brake BMW M3s on the track using stock four-cylinder brakes, in tip-top condition.

--DD

[gshiwota]

Dave - As always, thanks for your input. This is a big help! I started doing more research and it looks like upgrading to the larger 911 rotor with the M-caliper is the way to go.

I saw that there was once a billet hub available - anyone know if these are being made again?

On another note, I was going through my stash of old parts and I found that I have a set of 944 front rotors / hubs that were machined to fit a type-1 VW spindle. I understand that type-1 and 944s have the same spindle size so it seems like this may work. I also believe that the 944 rotor is the same as the 911 rotor. Maybe this will allow me to get "911 brakes" onto my 914. I'll start measuring it and post back here if I can get it to work.

Thanks!

[Dave at Pelican Parts]

I don't think the billet hubs are being made any more. You can try pinging Mike Mueller on the 914world BBS (his handle might be "mueller"?) as I think he did the design work for them originally.

Good luck with the 944 stuff! I always figured it would be easiest to do 911 stuff because there is no machining required.

Don't forget, if you go with 5-log fronts, you will have to convert the rears as well!

--DD

[larrym]

removing the goofy spongy 914 brake proportion-er and replacing it with a race-car type adjustable proportioning valve is the essential secret to better 914 brakes - maybe all you really need

i did the BMW conversion long ago (on a car i no longer have) - it was GREAT

- all those kits used one of two types/brands of adj valve - i put mine in the cockpit behind the shifter so i could adj it on track instead of under the engine shelf where you can't

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