What about 993 Rear Calipers on 3.2 Front Rotors?

[bento]

i was wandering about on the net and i saw a set up on an 1988 carrera where the guy was running a 993 rear caliper on the front rotor. he says that the advantages include being able to retain the standard rotor size and that you pick up 4 pot calipers. sounds good to me. any of the brake gurus have any thoughts on this. it sounds like a reasonably afordable, modest swap which shouldn't involve a ton of fabrication and cost a fortune (ie big reds, s4s, 930s, etc.)

check it out, its at:
http://www.gagme.com/greg/911/hacks/rebuild.html
at the bottom of the page.

just a thought from a low-coster,

thanks

db
88 carrera

[cstreit]

Depends on the rear caliper. There are a number of different sizes and combo's, many of which could result in a rearward brake bias. Works okay on the street, but some of these combos would not work on the track...

I can tell you that I've had that particular combo, in fact, greg and I both learned it from the same guy. Greg's car is nice BTW.

What this accomplished for me was definitely better braking, but as my speeds increased, I really moved the heat problem from front to rear, and started demolishing rear disc's...

If you added a bias valve you'd be okay probably.

[bento]

interesting.
so it sounds like the calipers from the 993 plus a brake bias valve might be an effective brake upgrade for a mostly street driven DE and Auto-X carrera. three questions: 1) which 993 calipers work?, 2) what would the cost be for the calipers used plus a bias valve? 3) is there any fabrication required?

thanks for all leads

db

[AES]

You might want to try to get Bill Verburgs opinion. Here is a link to one of his brake oriented pages

Brake Info

[cstreit]

I used rears from a 96 993. The mounting holes will require a slight amount of modification. Here is a picture of what's required. (I've highlighted to show the difference.)

Bill will tell you exactly what he told me, and why I know.. TOo much rear bias... AND ...heat capacity is determined by disc size (thickness) more than calipers.

[89911]

Any increase in caliper size without an increase in rotor mass, either circumference or thickness, is a waste of money. A four piston caliper on a same sized rotor is going to either wear the rotor quicker or cause warpage due to the increased heat that will now be accumulating.

[Bill Verburg]

Chris is absolutly correct. Here are some potential biases

• stock 84-89 ~1.3 uses a p/v on the rear circuit
• normal 911 ~1.6 hbr no p/v
• 993rear on the front & stock 88 wide M rear ~1.17 hbr needs an even more agressive rear p/v

Even worse is the fact that the calipers are not the primary weakness that usually needs to be addressed when upgrading brakes. That primary weakness is the inability to absorb and dissipate the massive amounts of heat generated at track events. This fault leads to boiled fluid, glazed pads, and warped rotors. The cure efficient cooling ducts followed by bigger rotors.

I really encourage you to read this link

The link Alf posted is more of a data base of what's available from different models and years. Some pieces can be used on 911s some not. Just keep in mind that just because something can be done it doesn't mean that it's an improvement.

[bento]

nice. thanks for all the great info. i know that rotors would be the limiting factor still but the idea of going to a four piston caliper for cheap sounded, in theory, to be a very cost effective, mild upgrade. the pad size is measureably bigger so i thought that the heat dissapation of the pad itself might be helpful. seems like the best solution on the cheap is still the "little reds" as documented by Clark, sorry Chuck.

Member of the Low-Costers,

david

[ohecht]

I cannot find the reference to the "little reds" recommended by Clark". Can someone help me out?

On an 82 SC, I am replacing warped front rotors (and adding cooling ducts), and I am trying to get the right rotors for better than stock braking without going as extreme as 930, Big Red, etc.

The car sees a few autocrosses and one or two DEs a year, and is also a daily driver.

Any experieces with Powerslot? Frozen? I am interested in the longevity of the front rotors, braking performance seems acceptable to me now.

Can I use Carrera rotors, or are they too thick for the calipers? Bill's excellent site mentions ~4mm spacers that were added to SC calipers for the Carrera's. When I rebuilt my calipers just after getting the car a few years ago, they had spacers in there, and 4mm sounds about right. The thing is, I measured the remaining rotor material yesterday using dial calipers, and all were close to SC specs. I would think this would mean that the calipers are stock, but I want to be sure before I pass on the simple option of buying carrera rotors if they will fit between my caliper halves.

Also, does someone have the part number for the o-rings that go between SC caliper halves?

Thanks,

Olivier

[KTL]

Carrera calipers are referred to as the "Wide A" by Bill V because they are exactly that. An SC "A" caliper that has wider spacers in between the halves to accept the wider rotor. So if you want Carrera rotors, you'll need the wider caliper.

I have no experience with splitting the calipers, but I do know that many recommend against doing this. I guess there's some sort of magic or trick to this? Leaky calipers often result from splitting them, even with new o-rings used. Why I do not know. Just thought i'd throw that out there.

[ChrisBennet]

Just swap your rotors and calipers for Carrera ones for an inexpensive and effective improvement - designed by Porsche no less. You even get to keep you brakepads.
-Chris

[ohecht]

I have split the calipers before and replaced the o-rings without any leaks at all. (actually I had to early in the P-car ownership cycle before I knew any better than to not let a hack mechanic try to change the pads during a state inspection. He split the calipers trying to replace the pads, which I now know takes all of 2 minutes with minimal tools and no dismantling!)

So...can I just try to find the wider spacers, widen my own calipers, and then get Carrera rotors?

Or would a rebuilder accept my SC calipers as cores on Carrera rebuilds, since the only loss would be the spacers?

Any good or bad experiences with the Frozen and Powerslot rotors? It seems that Frozen last a long time, I wonder how the Powerslots hold up.

Olivier

[Bill Verburg]

To my knowledge the wider spacers are not available as separate items, but the wide Carrera calipers are cheap new(Wayne has them new @ $219ea.). The Carrera rotors are also available at reasonable prices. The Carrera rotors and calipers are a bolt on for any earlier S or A strut car. No change is needed or desireable at the rear.

They are even cheaper at salvage yards and I am sure there are a bunch floating around in garages from big brake upgrades.

I see no advantage in cryo treatment but do like slotted rotors. The advantage of one geometry for placing the slots over another also escapes me, I always assumed that the different geometries were the machinists choice, except that the slots should follow the internal architecture of the rotor so as not to compromise its strength.

[ohecht]

Thanks for the advice, Bill. I think I will try to go with Powerslot rotors for a Carrera in the front and find some decent Carrera calipers rather than rebuilding mine again.

Does anyone have some old Carrera calipers laying around? Or just the spacers?

What pads to you recommend to be easy on wearing the rotors but still stand up to the occasional track event? With the ease of changing them, I suppose I could also just switch pads before any event if the compromises are too great with a do-it-all pad.

Olivier

[Don Wohlfarth]

ohecht, your stock brakes should be fine for a daily driver, ax, and 1 or 2 de's a year. Since you are adding brake cooling you are going to improve the cooling. You can't generate enough heat to warp a rotor at ax so that's not a problem. Don't know your driving experience but new drivers can overuse the brakes and over heat them. Some drivers install very agressive pads in an attempt to have more brakes that can lead to warped rotors.
Make sure you properly bed the new rotors with old brake pads and new pads on old rotors.
Would think you would be having brake fade even with Super Blue fluid if you're getting the rotors hot enough to warp them.
Rotors will turn a deep blue if heat is the source of the warping. It could be something as simple as the way the wheels are torqued that can lead to warping.
Has this happened to several sets of rotors or only the current set?
You are doing the cheapest thing by installing a cool brake kit.
The last thing you want to do is screw around and get some bastardized braking system that may or may not work on the track.

[Bill Verburg]

Using Carrera front calipers and rotors does not change the brake bias in any way, it does provide ~20% increase in thermal mass.

I use Pagid Blue, but they are a bit expensive as are the equally good Ferodo DS 2500. A reasonably priced street pad is The Axxis Metal Masters or Mintex ~$30-50

The Ferodos and Pagids are nice because of their linear C_f from ~ 100&degC to ~700&degC

Here are the curves for the softer DS 2000 the 2500 is a better all around high performance pad.

Pagid has an improved Blue pad also.

[ohecht]

Don,

These are the rotors I got with the car, and I think the front one warped because the caliper was partially frozen when I got the car. I rebuilt the caliper and had the rotors turned, and they were judged to be marginally OK by the shop at the time.

I may be hard on brakes, as I think I brake late and hard. I have not experienced any fade even on the track, and the braking force has always felt excellent. I use ATE Super Blue and bleed it often.

I think the Carrera option is a good compromise while I am replacing wear parts anyway to give me more room to grow in the braking department.

Olivier

[Don Wohlfarth]

Olivier, you may have solved your problem, sticking caliper. There's usually something that causes a rotor to warp.
Turning the rotors is usually a waste of time as a rotor that is warped will require the removal of so much metal that the rotor will be marginal when it's true. To add to the problem the warped rotor has developed hot spots that can change the temper of the metal in these spots and you want to have the same temper around the surface. At the same time you want to remove as little metal as possible so you can retain at least the minimum thickness.
Rebuild your calipers, install new slotted rotors, and install the cool brake kit. You don't run enough track events (yet ) to upgrade the brakes. It sounds like you run more ax so you have 2 problems there: 1)changing the calipers will move you out of a stock class 2)because you will have more mass to absorb heat you will have a problem getting the brakes hot enough to work properly.
Of course if you're like some of us with a small and easily solvable problem you'll be on the phone this afternoon to Wayne with your order for Carrera calipers and rotors.

[BK911]

Another question for the experts:

I have f/r Carrera calipers to put on a 73T. Do I need to update the master cylinder? Mr. Verburg stated, "No change is needed or desireable at the rear." Does this mean I shouldn't put the rear calipers on?

Thanks!
BK

[ohecht]

Still on the fence between the current and Carrera caliper/rotor route, and your point about classes in autocross and heating up the brakes to a good level is a good one. The autocrosses so far have been very casual in their classes, though, as I have been in the same class with highly modified cars with race rubber, usually basedo nthe mix of cars that show up!

Regarding rebuilding A of Wide A calipers: Are the o-rings included in some rebuild kits? They were not in the ones I used last time. If not does anyone have the part number?

One more question after seeing some S calipers on Ebay: Are they any better than my A calipers?

Olivier