BMW Brakes.., ehhh...aint THAT great.. Options

[914ghost]

So, I gets a set of 320i brake calipers off a wrecked car the other day.
Very good clean condition, pads are like new. They were FREE, so what the heck right?
I got a 70' so ..they bolt right on -- RIGHT?
Not quite, but pretty slick.
Bend the brake line, I had to grind on the outside of the actual caliper body just a smidge (through the part# stamping) because my wheels hit'm - 2 liter fuchs, totally stock. Not sure about that - anyways,
Okay, bolt'em on, bleeed, bleed, bleed...adjusted the proportoning (big word) valve rod all the way in...tried IN and OUT not much diff.
Pedal is still a bit soft, but works. Summary is: No Big deal, maybe I need the big Master cylinder? They work about as good as before.
Pad area is like 40% larger, but it's not much of a difference-
did I forget something?
-Bob O

[lapuwali]

There's not likely to be a night and day difference, esp. in gentle to moderate braking. You'll have to stand on it to notice much of anything, and it should be somewhat easier to lock up the fronts than it was before. Increased pad area will make no difference in feel or in braking power, just fade resistance and pad wear. Pad material can make a substantial difference to power and feel, however.

If you swapped the 17mm master cylinder for a 19mm unit, braking power would go DOWN for a given pedal force. The feel would change, with less pedal travel before things started happening, but you'd have to press substantially harder on the pedal before you got maximum braking. Some people like this, others think it just feels wooden and unresponsive.

[campbellcj]

A 19mm M/C would work better with these calipers, I think.

But really the only thing that truly improves the braking system is to upgrade the rotors, pads, M/C and wheel-tire combination as an integrated system. Anything else is a compromise that will exceed the original design parameters of the Factory in some way...usually heat dissipation.

[914ghost]

Soo...basically it's a bunch of hype.
Wow, sweet deal, my pads will last 9 years instead of 5!!
Thats $21 every 5 years was gonna break me too!!
Newton would agree about the M/C I guess- larger piston = more force to move, BUT less distance to do same work as small piston M/C..
Whatever. Anyone want a set of BMW calipers?
-Bob O

[campbellcj]

No, it's not exactly hype, as you do have more pad surface area now and I guess some guys like the "feel" of these calipers better. However, any claims of significantly-improved braking performance/distances from JUST a caliper swap seem to be highly optimistic based upon various prior discussions here and on other boards. You are essentially just converting the same amount of kinetic energy into heat over a larger surface area, which is in turn conveyed into a mass of iron (the rotor) that has to try to dissipate that heat energy somehow regardless of how or where it acquired it -- before it can absorb another dose. And, maybe more importantly, you are asking your same old tires to do their maximum work even more quickly than before (i.e. threshold braking at the limits of adhesion, er, lockup.)

In practical street applications this is kind of a non-issue, but on the racetrack the concern is that you can overwhelm your rotors, tires, and other braking-related components by pumping more heat into them then they were initially designed to absorb and dissipate.

So, don't worry, be happy, unless you have a real reason to be concerned (such as a brake-intensive racetrack or a rulebook that you need to obey).

[banderson]

I did the conversion and was not impressed either. (IMG:style_emoticons/default/barf.gif) Stopping distance feels down, and I still get fade at the track.

As I see it, there are 2 separate issues:

1. STOPPING DISTANCE. This is controlled by BIAS between the front and rear. You want all for wheels to exert there own maximum stopping force on the road. This is best achieved by having a slightly oversized rear caliper and an adjustable proportioning valve. By increasing the front (320I) the rears became less effective, even with a "T".

2. FADE/HEAT BUILDUP. This is controlled by airflow. Vented calipers have squirrel cage fans built into them. This works best. An other good method is ducting. Adding mass or pad area is not a solution. This is what is great about the mythical 4 lug 911 hubs.

YMMV

[IronHillRestorations]

Brake fade can be attributed to a few more things, the age of your brake fluid, and the compound of your pads. This is why real racing pads aren't that good on the street, they work best when really hot, hotter than you'd ever get on the street.

A few comments and questions about your "upgrade". Don't use used pads, unless you are also using the same rotors that the pads were working on. The old pads are "bedded" to the old rotors. GET NEW PADS!
If you got the calipers off a junked car, you should probably rebuild them. More than likely, they've got stagnant, contaminated, old brake fluid, and you don't know if you've got a marginally working caliper.
Did you have your rotors turned?
How old is your brake fluid?

I've done the swap with new and/or rebuilt components and found a noticable improvment. Was it like bolting on Turbo brakes?? No, but it was better than stock.

Just my .02, your results have come out differently!

PK (IMG:style_emoticons/default/cool.gif)

[brant]

I still believe that the most bang for your buck in braking improvement will always come from pads....

I swear if people would go buy a set of Portefields, pagids, or something of that sort and put them onto stock calipers.... They will notice the biggest bolt on improvement.

What everybody has said above it absolutely true, and a full braking system will be superior (especially on the track)...

but if a street car wants to keep it simple and maybe spend 50-100 bucks... Buy performance pads.

brant

[Joe Bob]

Well, the big thing about them is that they are cheap and plentiful. There are more Beemers in the bone yard than 914s so the original premise was a source for replacements as opposed to an upgrade.....somehow over the year's the term 40% bigger pad equated to more horsepower or something.....

Unless you have a stronger leg...you won't notice a big difference....just less fade....

I have the same brakes on my SC that I do on the 914/6. Only diff is the SC is power assisted. But that is a BIG diff....

[914ghost]

LIke I said. HYPE!
(IMG:style_emoticons/default/beer.gif)

I have new pads, I can try those, and new rotors, I can try those too.
BUT, I didn't have a problem to begin with, my car is a daily driver- I'm just hyperactive.
It was another project I could "finish" in an hour or so.
Easy come, easy go..
Comes down to the science- Conservation of energy- theres no way I was somehow going to make the car slow down faster with LESS effort by only increasing surface area of the friction pad. I guess then I'd be rich and the worlds energy crisis would be over.
I could add a vacuum booster, eh?
Maybe next summer.
-Bob O

[phantom914]

.......I could add a vacuum booster, eh?

It would take about an hour. (IMG:style_emoticons/default/wink.gif)


What is the piston diameter on the BMW calipers?

Andrew