911 Brakes?, ...or 320i brakes? Options

[CptTripps]

I was planning on doing 320i calipers in teh front, but before I plunk down that cash, should I be looking for 911 calipers? I hear people saying that they have them, but I didn't know if I needed other stuff to go with that too, or if the calipers would just bolt on.

Breakes are the first order of business on my new 73. Going fast is NO fun if you can't stop fast.

The rears are not working properly. They compress enough to keep the rotors shiney, but I don't think I'm getting a whole lot of stoping power. I bought a pair of rebuilt calipers, but if I get them on, and have the same issues, where should I look?

[Joe Bob]

Most 911 calipers use vented rotors.....soooooo, ya need the right struts.....320 calipers uses soild ones.....at least the most common ones do. There IS a 320i caliper that is vented as well....but more rare.

[jim912928]

With the 4cyl engines..properly maintained 914 brakes will stop you just fine. Upgrade your brakes if you are going to a six or if you are upgrading to 5-lug. The system is a balanced one with a proportioning valve in the back. Maybe all you need is to rebuild and rebleed?

I've kept mine 914 all around (even though I upgraded to 5-lug and vented..I just spaced the calipers. But I totally rebuilt the fronts and rears and put in a new master cylinder and I stop just fine.

I've heard pluses and minuses on the 320 upgrade..do a search here. But if I were going to drop the money for a 320..you might want to consider a 5-lug upgrade and put 911 brakes on the fronts with vented rotors.

Just another option.

[campbellcj]

There have been LOTS of previous threads on brakes here so a Search might be helpful.

Basically you have to identify "why" you feel you need to upgrade your brakes, and then assuming it is something you're gonna do, what is your weight/cost/fabrication "budget".

My personal feeling is that a straight caliper swap is not a great idea. Without bigger/better tires to generate more traction and bigger rotors to dissipate more heat, you are basically creating an "unbalanced" brake system. As mentioned above the stock factory system is actually about right for most street purposes and even many very quick racers run with it (however with appropriate race pads & fluid). I did that myself for 2-3 years of track events.

Your rear brake issue may just be the venting clearance -- many people including myself when I had stock /4 rear calipers -- believe in setting them fairly tight compared to factory specs. I don't remember the specifics but somebody else might pipe in with the exact feeler gauge specs.

You might also have a constipated proportioning valve i.e. it has air bubbles and needs to be bled; or in fact maybe the rear brake system overall needs a good bleeding.

Before jumping into some more expensive upgrades you may want to explore upgraded pads, fluid, and OF COURSE make sure every other component from the pedal cluster, master cylinder, lines, rotors, and calipers are in good working condition.

[mattillac]

(IMG:http://www.914world.com/bbs2/html/emoticons/agree.gif) well said.

[lapuwali]

What Chris said...

Remember that tires stop the car, not the brakes. If you can lock the wheels, you have enough brakes. If you can't, then you need to fix the brakes, but you need to determine WHY you can't. From your description, you simply need to get the stock brakes working 100%, then go from there.

The 320i calipers, or early 911 calipers that use solid rotors, will have bigger pistons, thus reducing the amount of pedal pressure for a given braking force. You also get a longer pedal, which many people don't like. Softer pads will also give more braking force for a given pedal force, w/o the long pedal problem.

[markb]

Repair the stock system first. If, when properly set up, they don't stop you the way you want, then look at an upgrade, starting with a new m/c. My stock brakes stop me extremely well. BTW, the BMW brakes aren't actually "better", they're just "different". Just my .02 .

[DBCooper]

QUOTE (lapuwali @ Jan 15 2005, 08:32 PM)

Remember that tires stop the car, not the brakes.  If you can lock the wheels, you have enough brakes.

Not quite true. Lots of brakes can lock the wheels but will fade when they're used hard or long. Not acceptable. At that point you at least need vented rotors. At least.

[CptTripps]

Thanks for all the great advise guys. Last night I re-blead the whole system but there is snow on the ground today, so I won't be test-driving.

I have a set of machined 320i calipers that I got from eBay cooming. (Listed here in the 'For Sale' section.) I was also going to put a 19mm MC on while I have the car apart this winter. Nothing wrong with replacing that preventatively...right?

[lapuwali]

QUOTE (Paul Illick @ Jan 16 2005, 05:28 AM)

QUOTE (lapuwali @ Jan 15 2005, 08:32 PM) Remember that tires stop the car, not the brakes.  If you can lock the wheels, you have enough brakes.   Not quite true. Lots of brakes can lock the wheels but will fade when they're used hard or long. Not acceptable. At that point you at least need vented rotors. At least.

Granted, but that means you can't lock the wheels anymore, so the brakes need fixing. Still a generally applicable rule, it just needs to be applied under all conditions, including repeated hard stops.

Vented rotors are not always the magic fix to fading brakes. Pad material can be the problem, as can fluid. The rotors are just one piece of the puzzle.

[Bleyseng]

The 320i calipers work fine only slightly better than the stockers IMHO. Mostly less fade if you track or AX the car.
For bleeding the brakes including the prop. valve get Speed Bleeders for each caliper. This is the only way I have found to really clean all the air out of the lines and get a rock hard petal. New 19mm MC is a nice upgrade. Install new rubber brake lines too.

I totally agree with Chris C says...

Geoff

[jim912928]

Yes..speedbleeders are a must! Get them for 914's here:

http://www.speedbleeder.com/

They manufacture them...great people to deal with.

Also, if your brakes have dual bleeders....Bleed the bottom first then the tops. If you just bleed from the bottom air in the top of the calipers will not be purged.

[fiid]

There are two things you need provided by the rotor and caliper.

1) Stopping "power" (enough to overcome the tire traction).
If you can lock the wheels up you have enough.

2) Heat dissipation. When you stop - your moving energy gets converted to heat. Bigger pads will do this more quickly than smaller ones.

The disc's job is to dissipate the heat before you need the brakes again.

So basically: if you can lock the brakes up - you have enough caliper. Concentrate on getting the disc cooler - that is best achieved by going bigger (discs) and vented. Or you could go to carbon if you have excessive cash and nothing else to spend it on :-)

Speed bleeders are awesome, and everyone should have them - if only as a guard against mistakes.

Fiid.

[lapuwali]

QUOTE (fiid @ Jan 16 2005, 12:25 PM)

2) Heat dissipation. When you stop - your moving energy gets converted to heat. Bigger pads will do this more quickly than smaller ones.

I can see we're going to get into the physics of brakes again. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Pad area has basically no effect on how much stopping power you get, or how quickly heat gets generated. Less pad area heats up the PAD more quickly for a given force, but not the rotor. Look in any physics textbook on the classic friction model, and you'll find area of the two surfaces providing the friction is not a term in the equation. Only the coefficient of friction between the two materials and the force applied to them matter.

Fade is primarily caused by the coefficient of friction between the pad and the rotor falling due to heat. If the rotor is too small, it will heat up too much and its coefficient of friction will fall. If the pad is too small, the same thing will happen. A pad with the wrong material may have its coefficient of friction fall too quickly with temperature. Such a pad may work well when cold and used sparingly, and thus might be a good street pad. A good racing pad with good friction properties at high temperatures may not work well at low temps, and thus won't work nearly as well on the street as it does on the track.

The other thing that can cause fade is the fluid boiling, so you want to use fresh fluid (added water will lower the boiling point, and all non-silicone fluids will absorb water out of the air over time), and you want to use fluid that works with your intended use.

So, while vented rotors MAY fix a fading problem, they're not always the magic bullet to fix one.