So I have BMW front calipers on my car from the PO. I know many on this site don't feel that this is an upgrade. But, is it at least as good as stock 914 calipers? Will I run into problems if I want to use Portfield pads and ss braided brake lines? If anyone has these, what options are there for improvement. I'm going through my entire brake system and don't experience with BMW stuff.

I just read an excellent tech article on Pelican about the BMW upgrade. It sounds like the calipers from the 320i was the popular upgrade. These take Pagid, Mintex etc. pads. These should be easy to get at FLAPS. The author was very convinced of the braking improvement with this upgrade as 320i calipers have bigger pads/pistons.
He also had warned againts using ss braided lines as these are for off-road/racing use and can have sudden catastrophic failure. I think I'll stick with stock lines.

Not an upgrade. At best equal...

Most people who claim it is an upgrade were actually replacing worn out stock systems with rebuilt 320i calipers. Not a fair comparo

Do yourself a favor. Under the Lapuwalli Classic Threads Forum here on this site you will find an excellent article by James Montebello who died in October of last year with some technical assistance by Eric Shea. It goes over not just the hows of your brakes but the science behind them.

The stock system in good serviceable condition with good quality pads are very good for almost all applications short of track days, hill climbs and, racing. I am going to guess that you don't do any of those or you would not be asking this question...

My car has stock 914 brakes in like new condition. It stops so well it will scare you. No foolin'

The "problem" w/ factory brakes is their ability do get rid of heat. They are capable of locking up the tires when in good shape. The BMW "Upgrade" makes it a little easier to lock up the brakes, but it also adds even more heat into the front rotors, and the larger calipers means there is less rotor exposed to the air, diminishing the heat control capabilities.

The car will stop just fine, but it is adding extra stress to an already marginal system.

BJH

since you already have the BMW calipers I wouldn't loose sleep over them being on your car.
If you are not tracking your car they won't be a problem.
I also agree to leave the braided lines to some one else. The stock lines when in good condition are very good.
the BMW calipers are similar to a M caliper (larger pistons than stock calipers) that is not spaced, so it can be used with a solid rotor instead of a vented rotor.

why do you feel you need to use Porterfields?


I have M calipers with vented rotors on my car....I use the magical mythical billet front hubs so I still have 4 bolt wheels.

After you spend 200$ on master, 50$ on front callipers and 100$ on stainless hoses, you should just wait to get a five lug conversion ready and use them hot rims you really want. Five lug is the way to go brother.

Dan, I'm going to use this car for some autocrossing as well as street. Porterfield RS4 seems to be a popular pad for this. Would this be overkill for me? I don't know, maybe just getting my brake system back to stock specs would be adequate for my use. Or at least it's a good start.

I don't think the heat dissapation of the rotors will a problem with my use. There are no long mountain descents or tracks around here. Looks like I'll be fine with some new pads and brake fluid.

for street and occassional AX Porterfields will work just fine....there are some pretty good local sources for them...
I use the Porterfield R4Es on the front of my car (M calipers) with stockish pads in the rear (running stock front calipers on the rear)...not for the faint of heart of lack of experience.
For Occ. AX and street your BMW calipers will be fine.

I didn't know that Eric Shea lent this kind of assistance. I might need some too, if things don't start looking up soon.

As Dan mentions, I wouldn't lose any sleep over the current BMW brake system. It's been spelled out here fairly well though...



Let's work off this.

A well working 914 brake system will "never" fail at that/those tasks. It's well designed for those tasks as is any brake system from Porsche. In fact, an informal poll here found no brake fade ever (on narrow bodied cars) with the exception of serious road racing. Even then, some professional 914 drivers state an over-dependency on the brakes caused those issues. I'm one to side with some of the road racers that have the vented rotors up front. It's a nice upgrade for those punishing environments.

If you think Porsche makes great engines, their brakes are even more famous. The BMW brake caliper itself is fine too, it's basically a precursor to the 911 A-Caliper (48mm piston, widows peak fluid inlet etc.) it's just a bit too much for that solid rotor as explained by BJ. Dan is running basically the same caliper (48mm piston and same pad area) but he has:

* Vented 911 rotors
* 43mm pistoned calipers in the back
* No handbrake (it's a racecar)
* Different pads front and rear

If I were you I would simply go back to a working 914 brake "system" (term as defined by the system the vehicle engineers designed for the car) and get some great pads.

If I were you and I decided to keep the current mix of calipers on the car I would cryogenically treat the rotors or buy some that are cryogenically treated. I would then get a AJ vent kit to cool the entire thing. Those are the ones with the scoops that zip tie to the A-Arm and direct forced air into the rotor eye. Top it off with some good pads and then go readjust the proportioning valve so the rears come on in a progressive manner. The factory valve is epoxied (sic) in place but it's fairly brittle by now. You should be able to chip the epoxy away and free up the shaft and lock nut. With a video camera or a friend you can trust, you should be able to reset the valve for optimum performance.

Cool Brake Kit

Damn it, I was going to post the same thing.

Hey Eric you need to come see my Nieghbor. She needs your assistance more than anyone in the world.

After her, there's this dog next door to me ......................... The Cap'n

One other thought about the BMW caliper conversion....if you have a 19mm master and the stock front calipers, the leg-effort required to make the car stop goes up some. I've done the calcs and, naturally, don't remember the numbers now, but the effort goes up by 15-20% for the same force exerted on the pads.
The much-vaunted "increase in stopping power" some people mention when going to the 19mm master is really just a somewhat stiffer pedal, all else being equal, and there is actually a DECREASE in effective braking effort (at the pads) given the same push (your right leg) at the pedal.

Enter the BMW calipers....the pistons are larger than the stockers and, coincidentally, almost exactly equal the percentage increase in area that the 19mm master offers over the 17mm. Leg effort vs. "stopping" effort remains just about the same as stock. For those curious enough to do the numbers, the formula (courtesy of Blaise Pascal) is Force = Pressure x Area....assume that pressure and force (your right leg again) remain the same for the illustration and you'll see that the area comes out rather neatly.

There are other variables, of course, one being the ~20% larger pads and the fact that the rear calipers are now a bit underserved, pressure-wise. But I have two cars with 19mm masters...one with stock fronts and the other with BMWs....and the BMW equipped car has a nearly-stock feel, brake-wise. Is it an upgrade? IMO, it isn't, not really. It does restore the leg effort/braking effort balance, though, and for a street car I can't imagine it would have a downside.

other than...



Again, nothing to lose sleep over but I'm one to like both front and rear calipers playing nicely with each other.

Thanks for the comments, it's good to hear rational input from someone who has both systems.

When I first got my car I bought in to the BMW "upgrade" and got the brakes working. My calculations show the rear braking is really reduced. I have since got my calipers and M/C back to stock and they work great! I have removed the "proportioning" valve and now am very happy with the system with the one exception that the pedal always feels a little soft to me. The stock brakes work great!