Reasons to change (upgrade) one's brakes

[m110]

As far as I can tell, changing or upgrading the brakes on our cars comes down to several reasons. I am thinking of changing mine and just want to get people's opinion on the reasons one might do so.

1) Brake Fade: those that track and have fade problems would appear to address cooling by
a) diverting air to the discs to dissipate heat with deflectors or tubing




b) increase the thermal capacity of the system by having more mass to transfer heat (ex, bigger rotors)


c) changing fluid to optimize boiling point



d) ventilated and other exotic disc treatments

2) Brake torque: My understanding is that this is a function of swept area, clamping force, line pressure, pad material, piston size and many other factors which at the limit are bound by the limits of adhesion of the tire. This would appear to be the reason people change Carrera A caliper front brakes to Boxster calipers while keeping stock rotors (or perhaps #6 below). Also 944 turbo, 928 S4 and Big red upgrades.


3) Brake Modulation: A combination of caliper condition and run-out, mounting rigidity, balance, mechanical advantage of the pedal, pad composition, piston and MC size/matching. Not unlike Potter Stewart's definition of hard core pornography as hard to define but "I know it when I see it"; When I use the brakes on a 993 Turbo and it feels like I am stepping on the disc itself..I like it.

4) Unsprung weight savings: Alloy S calipers, PCCB and other lightweight options that reduce unsprung weight.

[m110]

5) Service cost: Namely removing pricey systems with high wear rates for cheaper options.

6) Esthetics: Can't argue with this: 917 etc, Zuffenhaus, 993 Turbo S yellow








7) Money burning holes in pockets

[javadog]

7) Bling factor
8) Can't leave their car alone. Must modify something.

I think you've pretty well outlined the reasons. I've added a couple. Few people seem to change the brakes because they need to; most change them because they want to. There's a big difference beteen the two and I'd wager that often the reasons you suggest aren't well understood by the people that change their brakes and they wouldn't matter anyway.

There are a lot of 911s running around in PCA club racing and other series that must run the stock calipers and rotors, or stock rotor sizes, etc. and these cars have no problems running a full race distance. The guys I know that run these cars don't seem to have any problems with service life either, so I can't see that anybody would ever need to change the basic components for any car that is not a dedicated track car, as there is no way to use the brakes on the street as hard as you can use them on the track. And, for track use, an experienced driver will use the brakes a lot less than a new guy.

A 3.2 Carrera already has brakes with more thermal capacity than prior 911s. If it were my car, I'd probably limit any modifications to pads, fluid and cooling. Taking weight off of the car would be a higher priority to me. I'm in the middle of changing the braking system on my Carrera 3.0 to the lighter, unboosted system of the 1976 and earlier cars and that will probably pay dividends as well in the feel of the system, as the booster removes some of the effort and the feel from the pedal.

My .02,
JR

[Bill Jennings]

Javadog,
Your C3 has boosted brakes mine doesn't and its a 77.
Mine is the UK version is yours german?
I was not aware of any boosted brakes on the ROW C3.

Cheers
Bill

[ChrisBennet]

Bigger brakes do have a convenience factor.

The pads last a lot longer and they fade less and, in general they "just work". Before I went to 993/930 brakes I remember getting 7 track*person days on the rear pads of my 3.2L car and having to bleed the brakes during a 3 day event with 2 drivers. I think I was getting 11 track*person days on the front with cooling ducts. (I was also having to take a few slow laps to get the brake pedal back after my codriver used them to stop in the paddock.)

Now with big brakes, I just bleed them before a track event with normal Valvoline brake fluid from Pep boys and the rotors last forever.

That said, if you aren't experiencing a soft pedal or replacing your brake pads every few track days you don't "need" bigger brakes, their associated costs and huge unsprung weight.

[javadog]

Bill,

Mine's a left hand drive '77, originally delivered to Germany. Yours might actually be a '76, but wasn't registered until '77. Several countries listed the "year" of the car as the first year it was registered. It's also possible that the RHD cars didn't get the booster until 1978. I've heard that but never confirmed it.

If yours is a '76, the serial number will be 91166xxxxx. A '77 would be 91176xxxxx.

JR

[Bill Verburg]

The boosted brakes were introduced at the beginning of the MY77 production run on Sportmatic cars, the manual versions got it well into the run

There are some advantages to the boosted system on a '77 C3
1) it's just that a booster and not a power brake in the old luxo barge American sense
2)you get the bigger 20.6mm m/c rather than the 19mm unboosted, this gives you a bit better pedal feel

If you are going to do brakes do them right

[SilberUrS6]

Hmmm, Boxster calipers on my Carerra? Sounds like a decent idea, especially if it leads to easier pad changes.

I am kind of a brake snob. I have always found the braking on my Audis to be inadequate, and have upgraded the brakes on every Audi I have owned. The first car I ever felt had adequate brakes from the factory? My '85 3.2. Shortly after I bought that car, I bought my wife a 2001 M-B E320 wagon. That car has excellent brakes - better than just about any car I've driven, before or since. Very large rotors (thermal mass, brake torque) big caliper pistons and beefy caliper structure (clamping force) and large pad area. I wouldn't have any trouble upgrading my 3.2's brakes if I could get some function increase, but the OEM brakes stop the car very well.

[m110]

Originally Posted by SilberUrS6

I wouldn't have any trouble upgrading my 3.2's brakes if I could get some function increase, but the OEM brakes stop the car very well.

That is my point. My 3.2 stops well. Fade is rarely an issue, torque could be better, modulation is fair compared to modern sports cars cars, weight could always be better, I'm ok with pricier parts, esthetics....sure.

As mentioned by javadog; I can't leave my car alone...but that's part of the hobby and not a bad thing.I either rebuild everything I have or replace...labour is the same either way.

The brake modulation and pedal feel is what concerns me most and the main reason to change them for me. Just wondering if anyone else has different thoughts since it seems there is a wide range of reasons to change.

[Bill Verburg]

I'll repost this comparison chart for various commonly used brake setups used on 911s '69 -89


The best feel comes from having the lowest slave/master ratio

Initial bite depends heavily on pad compound and temperature

remember it's the tires that stop the car, as long as it's adequate and appropriately balanced, brake torque is relatively unimportant

there will be differences in feel between calipers, A is stiffer than S, non boosted will have less play(feel stiffer) due to fewer and stiffer components

f/r ratio is important too, you want to run as much rear as possible consistent w/ getting the most out of the system as a whole. For most 911s ~ 1.45 is a great target, more front(higher numerically) thermally loads the front more which can be an issue, and gives up the work that can be added by the usually bigger rear tires, more rear(lower numerically) gives up work that can be done by the more heavily loaded fronts and tends to add instability. Effective lsd, low car, stiff springs all help braking stability.

the smaller wheel diameter and older wheel design the less room for calipers, 930s are the best in this regard as they can be fit into 15s, 944 Fuchs have more caliper room than 911 Fuchs of the same width and ET.

In general for 911s w/ stock brakes it's best to max cooling and use the best fresh high temp fluid that you can find because the brakes are stressed in track use and run at much higher temps than more modern designs. Because they are stressed the oe 911 brakes tend to require more maintenance, ie more frequent flushes and bleeding and pad changes. A lighter car is also easier on brakes, the energy converted from velocity to heat by the brakes is directly proportional to the cars mass more powerfull cars stress their brakes more, the energy converted to heat is proportional to velocity x velocity

[m110]

Originally Posted by Bill Verburg

The best feel comes from having the lowest slave/master ratio

What is the trade-off for this? Pedal effort?

Terrific input as always, you should publish your posts in a book. I read every one.

[Bill Verburg]

Originally Posted by m110

What is the trade-off for this? Pedal effort?

Terrific input as always, you should publish your posts in a book. I read every one.

Correct, Several of the local shoes have gone so far as to use 23.8mm m/c w/ oe S/M brake set ups in non boosted applications, that is a slave/master ratio of 26.467 that's comparable w/ what was used on the old 3.0RSRs, 24.26

It takes a lot of leg to get the most out of those brakes, the lowest i've used in my cars is 32.342 which still takes a lot of leg if unbosted

[manbridge 74]

Brake feel is sooo subjective but I've been enjoying the non-boosted S/M brakes in my 74 with original M/C. I've actually had all three front caliper choices available on this car with oe discs. Rears were never changed.

The small M calipers actually had the shortest pedal travel and seemed to require the least muscle. Point of lock-up being hard to discern being the only real negative.

The later A calipers had more travel but better modulation.

Current S calipers have the best feel as far as point of lock-up and almost, but not quite, as good pedal travel as the Ms. I'd like to try a more aggressive compound in the rear to see if I can get some more bite before the fronts lock.

Interesting to me that Porsche didn't spec a different M/C size for the different caliper piston sizes (38mm vs 48mm) in 1974 or perhaps ever?

But ALL 911 brakes are fantastic in stock form considering what was on other cars 40 years ago.

[Bill Verburg]

Originally Posted by manbridge 74

Brake feel is sooo subjective but I've been enjoying the non-boosted S/M brakes in my 74 with original M/C. I've actually had all three front caliper choices available on this car with oe discs. Rears were never changed.

The small M calipers actually had the shortest pedal travel and seemed to require the least muscle. Point of lock-up being hard to discern being the only real negative.

The later A calipers had more travel but better modulation.

Current S calipers have the best feel as far as point of lock-up and almost, but not quite, as good pedal travel as the Ms. I'd like to try a more aggressive compound in the rear to see if I can get some more bite before the fronts lock.

Interesting to me that Porsche didn't spec a different M/C size for the different caliper piston sizes (38mm vs 48mm) in 1974 or perhaps ever?

But ALL 911 brakes are fantastic in stock form considering what was on other cars 40 years ago.

All 911 '69-89 front M, S, A, wide A calipers use the same size pistons 2x48mm per caliper, all '69 rear M '69-83 use the same pistons 2x38mm per caliper, for 911 '84-89 rear m were increased to 2x 42mm per caliper.

The difference in feel for all of them is a function of pads, temp, boosted or nonboosted(boosted all use 20.6mm m/c for improved feel over the non boosted 19mm, though there were a few '69s w/ a neat 20.5mm non boosted m/c).

Aluminum S are slightly less stiff than any of the iron versions, there is slightly more flex in the boosted linkages and bulk head mounts than in the more direct non boosted setup.

[manbridge 74]

I goofed on the piston sizes, and all 3 had different pads now that I recall, (been too long)......

Thanks for clearing it up and posting the chart!

[stevie 77 930]

Here is my upgrade....On my 77 930, i went from S to Boxter, and now the real deal 930 calipers and rotors. New calipers, brake lines, hats from VCI and OEM rotors from Zimmermann. The fronts are done... the new rear calipers are currently being modified at Rennsport.

[m110]

Looks great stevie 77 930.

I have decided to go the same route; mostly (being honest here) for brake modulation, fade, esthetics, and can't keep fiddling in that order.

[PrimeMvr]

I have 993TT brakes on my 87 930 and they are spectacular. They will brake at (and beyond) tire adhesion all day long. Feel/modulation is clear. My only complaint is they are too easy to lock all four wheels if you stomp on them. Learned that one the hard way at the end of a straight. I'm sure it looked great from the outside with all tires smoking as I left the road

[H-viken]

Can the S caliper be used in the rear, or does that cause unbalance?

[Bill Verburg]

Originally Posted by H-viken

Can the S caliper be used in the rear, or does that cause unbalance?

no, yes(at least most sane people think so)