Brake Upgrades

for anyone thats interested..i just got some front calipers off an '87 944, non turbo, and they are direct bolts on for replacement of the 914 fronts, they bolted right on my '73 w/ no problem, im gonna take 'em off and put them on my '72 soon to be turbo..hopefully daily driver, just thought id let everyone know, if your looking for a cheap brake upgrade

[JP Noonan]

I would be very careful. I don't know a lot about (anything?!?) brakes, but aren't the 944's vented rotors?

In the 320i article the author talks about other calipers fitting but they are too wide because they are made for vented rotors. What I think will happen is that either the first time, or after the pads wear down, the

PISTONS MAY POP OUT OF THE BORE!!!!

This means

NO BRAKES AT ALL, A TOTAL LOSS OF PRESSURE!!!!!!

Once again I could be wrong (I hope so, 944's had pretty good brakes) but isn't it worth checking out, if you haven't already.

Then there is the issue of them being centered on the rotor. This is why the 320i calipers need machining.

[jamesm]

It's true that this ought to be checked, but caliper pistons tend to be quite deep. So much so that, on most calipers, you could remove them from the rotor completely and apply pressure so the pads squeeze completely together, and the pistons still don't fall out. If you have a very thin rotor, and totally worn-out pads, this might be possible, but I'd think it unlikely.

As for centering them, this isn't much of an issue. If they're a bit off center, then the only thing that will happen is the pads on one side will wear a bit more quickly.

There's a whole class of brake calipers that only have pistons on one side of the rotor, and rely on the ability of the whole assembly to float on pins. This kind of caliper is never "centered", and yes, the pads wear out faster on one side than the other.

The only time you'd need to worry about centering is if the caliper would actually rub the rotor.

[John Rogers]

JP is right, they will not work well if at all. I checked with a local manufacturer of racing brakes in San Diego and he noted: single piston calipers have about 60% of the clamping force of dual piston calipers. They are used because they are cheap and can still stop the car. Also, if the calipers are off center the clamping force will be reduced and uneven heating of the rotors will occur which will probably warp them. Calipers are designed to work with a specific thickness rotor as JP noted and if they haven to travel too far when the pedal is pushed, the seal will fail to pull them back and they can lock on the rotor and the wheel don't turn well. This will get worse as the brakes get hotter as in an autocross. Finally if the pistons are much bigger than the stock ones, the master cylinder would be unable to supply the necessary fluid to make the calipers activate correctly. That is why when upgrading to the BMW brakes, you need to use a 19mm master cylinder or the pedal feels terrible. I did this to our 914 last year and put the larger master cylinder in right away after driving the car.

[This message has been edited by john rogers (edited 03-25-99).]

oops...ran into my first problem today, when i tried to put the wheels back on, i found out that my old 15" steel wheels inside are to small for the larger size caliper, it rubs agaisnt the wheel and keeps the wheel from turning, time for the grinder, and im sure the 944 calipers, even though 1 piston, have more stopping power than the 914's, if not more pressure power, the pad area is almost 2 times as big, which will still give me more stopping power, and the piston wont pop out, the pad distance is off a little bit now, but thatll all be fixed when i put on the brakes hard the first time..any more ?"s??

[John Rogers]

Our BMW brake upgrade missed the back of the alloy wheels by very little, but cleared the outer rim easily. Instead I would check on some spacers as grinding any of the casting would probably weaken the body. As an aside, I checked with the tech inspection head of our autocross committee and he said a car converted like this would not be allowed to run since you are trying to use a floating caliper mounted rigid and they consider it unsafe? Good luck.

well..the rub on the outside of the wheels, the wheels arent wide enough so i dont know if spacers would help, and unsafe...WTF??, if theyre unsafe why have then been used so long..?. oh well..i like 'em

[jamesm]

The idea that more pad area increases stopping power is a misconception. It sounds right, but it isn't.

Stopping power is strictly related to how much clamping force can be applied on the rotor. Whether this is done through an area of 10 square inches or 1 square millimeter is irrelevant to actual stopping power.

Where additional pad (or rotor) area DOES make a difference is resistance to fade. More area means more surface area to dissipate heat, and heat is what causes brake fade. If your current brakes are fading, then more pad area will help. If they aren't fading, but the low braking force is due to a low clamping force (which, for example, can be caused by a caliper that isn't stiff enough, so it spreads under load), then more pad area won't help at all.

[paulhagedorn]

I was thinking about doing the same upgrade to my car. I have brakes out of an 85.5 944. What I think (this is my opinion only) is that the 944 brakes will give better braking because of the size of the piston. I would think that it could clamp down on the rotor much better than the stock 914 brakes. While it is true that the 914 brakes are double piston, the pistons in them are very small. The only problems that I see with doing the conversion is fitting a wheel on it and also one pad wearing out a lot faster than the other.

[J P Stein]

Let's talk brakes. The problems with 914 brakes are:

1). Lack of piston area in calipers
2). Lack of piston area and volume in the master cylinder.

3). Lack of cooling area in/on rotors
Without going into areas like adjustment of
rear calipers or air in the proportioning
valve all the items above must be addressed
to make any serious improvement.

If you want to fool around with oddball setups in regard to calipers,go right ahead
it's your ass.Porsche(or their subs) makes a load of calipers that fit 911 struts that
will WORK. A,M,& S all have larger pistons
which equates to more clamping force that is lacking in the originals.

I could never lock-up the fronts in the dry with the originals(I'm not as young as I used to be).

The 17mm master cylinder is inadequate for anything but a fishing weight.It lacks sufficient volume & piston area.It also makes for a soft pedal. 19mm cyl. is
cheap and WORKS.I have no experience with
the 23mm master cyl. but have heard that it
requires excessive pedal pressure(anyone
have comments ?).

Obviously,solid rotors have less mass & surface area and again,lots of rotors will fit 911 struts

My experience suggests that changing the master cly. to a 19mm and installing an after
market prop. valve is worthwhile. If one wants to go any farther,do it right, and change the rest of the stuff.The ass you save
may be your own.