Rear caliper fit?

[vwmike911]

Hi all will 87 3.2 rear calipers fit a 81 3.0 SC?
Regards
Mike

[spuggy]

Originally Posted by vwmike911

Hi all will 87 3.2 rear calipers fit a 81 3.0 SC?
Regards
Mike

Don't see why not, they fit my '77 just fine. Note that you would need to swap out the rear rotor as well, because the 3.2 rotor is 24mm instead of 20mm like the SC.

Most people don't bother. The rear 3.2 caliper pistons are over-sized and require the 3.2 proportioning valve to maintain brake bias (read: not lock the rears), and the rear brakes don't do much anyway so the additional thermal capacity in the rear is no big win.

You're probably better off swapping in 3.2 front rotors/calipers (which has the same piston size and rotor diameter as the SC, so does maintain the same front/rear bias when used with the SC rear calipers) and calling it good there.

[KTL]

Spuggy is right on. Don't bother with the calipers from the '87. Not worth the effort.

[vwmike911]

Hi Gents

Thanks for the replies the reason i asked is one of my calipers on the rear is knackerd and Ive been offered the later 3.2 calipers the fronts have already been changed to 4 pots
I take it these rear calipers will fit? i might have to change the rotor's? and will need to look at the brake biase?

Regards
Mike

[KTL]

Well you need to tell us upfront that you have 4 piston front calipers already installed! In that case, the larger piston size of the Carrera rear calipers is better suited to the typical Brembo 4 piston fronts.

How about sharing with us which 4 piston fronts and rotors you currently have installed?

[spuggy]

+1 what KTL said.

3.2 rear calipers bolt on - but not over SC 290mm x 20mm rotors, they're designed for 3.2 290mm x 24mm rotors. Which also bolt straight on.

The 3.2 rears, with the 42mm pistons, when used with 4 pot Brembos up front and NO proportioning valve, will likely improve your current front/rear bias by reducing the front bias until only a tad more front biased than the factory used. Depends on exactly what front rotors you're running, and what calipers/pistons.

Another consideration is that, with 4-pots already up front, the 3.2 rear calipers might easily nudge you over the line into needing a 930 master cylinder because your SC one won't push sufficient fluid.

[uwanna]

Originally Posted by spuggy

+1 what KTL said.
Another consideration is that, with 4-pots already up front, the 3.2 rear calipers might easily nudge you over the line into needing a 930 master cylinder because your SC one won't push sufficient fluid.

Don't think you'd need the 23mm master cyl, the early 964s with 4 pot Brembos up front and single piston in the rear still used the same 20.5mm master cyl as the SC! Have this setup on my '80SC (968 front Brembos and Carrera rear calipers/w 24mm rotors all around) and braking is superb!

[KTL]

Agreed. The small 4 piston calipers with Carrera rears do just fine with the SC/Carrera m/c. The m/c sizes are nearly the same size as the later cars have. Its the vaccuum boosters that are different (SC is a bit smaller)

[spuggy]

Originally Posted by uwanna

Don't think you'd need the 23mm master cyl,

Pretty sure I've seen both TRE and Bill V state in the past that you should use the 930 M/C for the Boxster conversion if you use the 986 4 pot calipers front/rear.

And I've never seen anyone suggest to run 930 calipers front/rear with an SC master cylinder.

10 minutes with a calculator demonstrates that a front pair of basic 36mm/40mm Brembos matched with a 3.2 twin-pot 42mm rear caliper has very close to the same total piston area as the factory 930 setup with 8 38mm pistons up front and 8 30mm pistons at the rear.

The stock early 964 setup you mention (with basic 36mm/40mm Brembos up front and twin-pot 44mm rear calipers) has even more total piston area than the 930.

Which surprised me, but that's why you do the math. Gee, learning stuff is great.

the early 964s with 4 pot Brembos up front and single piston in the rear still used the same 20.5mm master cyl as the SC!

That is interesting, that the early C2's and the RSA's used the small M/C with the twin-pot 44mm rear caliper.

Which doesn't seem to make sense on the face of it, considering that the factory also used the larger 23.8mm M/C for the 89-94 C4 with the 4-pot rears - which has less total piston area.

Maybe they just had a big pile of the smaller master cylinders to use up...

"Single piston in the rear", BTW, would actually be the cheap floating caliper design, and these suck. The early 964 rear caliper is an opposed twin-piston design.

So either a 20.64mm master cylinder is OK for piston areas above 930 sizes, or you need a 23.8mm 930 master cylinder once you start using configurations with a larger piston area.

I already own a 930 booster and master cylinder, so I already made my choice.

[vwmike911]

Hi gents

Thankyou for the info this much appreciated for further info the front 4 pots are 944 turbo calipers with the lower hole elongated slightly?

Regards
mike

[uwanna]

Originally Posted by spuggy

Pretty sure I've seen both TRE and Bill V state in the past that you should use the 930 M/C for the Boxster conversion if you use the 986 4 pot calipers front/rear.

And I've never seen anyone suggest to run 930 calipers front/rear with an SC master cylinder.

10 minutes with a calculator demonstrates that a front pair of basic 36mm/40mm Brembos matched with a 3.2 twin-pot 42mm rear caliper has very close to the same total piston area as the factory 930 setup with 8 38mm pistons up front and 8 30mm pistons at the rear.

The stock early 964 setup you mention (with basic 36mm/40mm Brembos up front and twin-pot 44mm rear calipers) has even more total piston area than the 930.

Which surprised me, but that's why you do the math. Gee, learning stuff is great.



That is interesting, that the early C2's and the RSA's used the small M/C with the twin-pot 44mm rear caliper.

Which doesn't seem to make sense on the face of it, considering that the factory also used the larger 23.8mm M/C for the 89-94 C4 with the 4-pot rears - which has less total piston area.

Maybe they just had a big pile of the smaller master cylinders to use up...

"Single piston in the rear", BTW, would actually be the cheap floating caliper design, and these suck. The early 964 rear caliper is an opposed twin-piston design.

So either a 20.64mm master cylinder is OK for piston areas above 930 sizes, or you need a 23.8mm 930 master cylinder once you start using configurations with a larger piston area.

I already own a 930 booster and master cylinder, so I already made my choice.

To clear things up, I miss spoke when I said "single piston rears" I obviously meant the early 964s had 4 pot brembos up front and twin piston in the rear!
By the way, when I first installed the 4 pot Brembos up front and Carrera twin pot in the rear, I too thought I needed a 23mm MC. Bought a new one from a Pelican on the buy sell forum. I installed it and removed it! Didn't like the short throw or the "modulation" of the brake pedal and the "extremley hard" pedal! Went back to a 20.5 MC and am quite happy. I like you don't understand why Porsche used the the 20.5 MC in the early 964s, but maybe it's something to do with 2 pot rears reacting different than 4 pot rears regardless of the total piston swept area of the system! I'm sure they had a good reason.
All that being said, I'm very pleased with the performance of my particular setup!

[KTL]

One last clarification, no 911 has ever used floating calipers. Any rear caliper from 1965 to present has used fixed calipers. Which we shoild give Porsche credit for, since floating/sliding calipers are cheap & perform crappy IMO

Thanks also for doing the piston calculation, as that's the key to determining m/c sizing

[Bill Verburg]

The m/c has to be sized for the brake pistons and the intended users/use

Porsche used the 20.6mm boosted m/c on 964s because the intended users/use were/was doctor, lawyers and indian chiefs along w/ their s/o's to get to the club or spa, not young, fit race car drivers. The smaller m/c requires less leg to operate.

w/ 964 front and wide M rear 20.6 is fine for most users, as long as the booster still works it's good to use 23.8mm m/c to get a better pedal at the expense of more leg. W/o a booster you'd want a very healthy leg to operate it in the latter config.

I've said it before and i'll say it again, using 964 or Boxster calipers on 3.2 Carrera rotors isn't a good way to do this(I'm trying to be polite here)

[RWebb]

"doctor, lawyers and indian chiefs" - xlnt! I am going to use this quote


We should have a little bot that keeps count of how many time Bill (has to) repeat the same advice...

[spuggy]

Originally Posted by vwmike911

Hi gents

Thankyou for the info this much appreciated for further info the front 4 pots are 944 turbo calipers with the lower hole elongated slightly?

Regards
mike

Mike, you need to be clear about the intended use of the car, and what your aims are.

You should also be careful. The 951 front Brembos are designed to be used with a 28mm rotor (only the rotor from the '86 951 is even close to the correct offset for use on an pre-ABS 911, (the '87 951 had ABS) - even with the '86 rotor you either have to space the wheel out or notch the A-arm to use the rotor on a 911).

If you run calipers designed for 28mm rotors on 3.2 24mm rotors, there are very real risks associated with the pads being allowed to wear too much (e.g. as far as would be "normal" for 28mm calipers on 28mm rotors).

This is to say nothing of the fact that 3.2 rotors have been known to crack from overheating with stock 3.2 calipers when driven very hard, let alone when you put over-sized calipers on them. The weak link is the thermal capacity of the front rotor and that's what needs to be addressed to upgrade the brakes - shiny/larger calipers do nothing to address that, other than in a negative way as they are capable of putting even more heat into them.

Unless the problem being addressed is that the brakes don't look nice when parked, of course.

I'll leave it to you to consider the use of a rat-tail file or similar to elongate the mounting holes on a brake caliper mounting bracket. Not a well-engineered approach or solution.

A better way to address the mounting issue is to plug the mounting hole(s) and re-machine in the correct place (search this forum for many people who adapted 930 rear calipers for use on 911 banana arms), or to machine off the ears altogether and convert with a radial mount bracket.

VCI went to a lot of effort to do this correctly with their kit 911 Brake Upgrades using 964/944T calipers.

299x28mm rotors is a sweet spot for some guys racing light early cars that don't need a 930 or larger setup, but it's not the best bang-for-the-buck, or even the best overall solution for heavier cars (yes, an SC is a heavier car) driven very hard (e.g. tracked), or those with substantially more power, IMHO.

By the time you've spent that much money/effort, you might as well invest a little more and do it right to get a solution that works.

[vwmike911]

Originally Posted by spuggy

Mike, you need to be clear about the intended use of the car, and what your aims are.

You should also be careful. The 951 front Brembos are designed to be used with a 28mm rotor (only the rotor from the '86 951 is even close to the correct offset for use on an pre-ABS 911, (the '87 951 had ABS) - even with the '86 rotor you either have to space the wheel out or notch the A-arm to use the rotor on a 911).

If you run calipers designed for 28mm rotors on 3.2 24mm rotors, there are very real risks associated with the pads being allowed to wear too much (e.g. as far as would be "normal" for 28mm calipers on 28mm rotors).

This is to say nothing of the fact that 3.2 rotors have been known to crack from overheating with stock 3.2 calipers when driven very hard, let alone when you put over-sized calipers on them. The weak link is the thermal capacity of the front rotor and that's what needs to be addressed to upgrade the brakes - shiny/larger calipers do nothing to address that, other than in a negative way as they are capable of putting even more heat into them.

Unless the problem being addressed is that the brakes don't look nice when parked, of course.

I'll leave it to you to consider the use of a rat-tail file or similar to elongate the mounting holes on a brake caliper mounting bracket. Not a well-engineered approach or solution.

A better way to address the mounting issue is to plug the mounting hole(s) and re-machine in the correct place (search this forum for many people who adapted 930 rear calipers for use on 911 banana arms), or to machine off the ears altogether and convert with a radial mount bracket.

VCI went to a lot of effort to do this correctly with their kit 911 Brake Upgrades using 964/944T calipers.

299x28mm rotors is a sweet spot for some guys racing light early cars that don't need a 930 or larger setup, but it's not the best bang-for-the-buck, or even the best overall solution for heavier cars (yes, an SC is a heavier car) driven very hard (e.g. tracked), or those with substantially more power, IMHO.

By the time you've spent that much money/effort, you might as well invest a little more and do it right to get a solution that works.

Hi Mate
Thanks for the reply the car is for street use i dont think the calipers will take a 28mm disc i will have to check that? possibly not 944 turbo? the calipers were proffesionaly elongated as this was only a couple of mm and was done in favour of the radial dirrection it was felt that this would be better than pluging the hole due to the heat involved?
Regards
Mike

[RWebb]

Porsche's stock brakes are more than enuff for street use, as well as some DEs.

The only real upgrade would be a smaller version of PCCBs but no such item exists.

People you see "upgrading" the brakes on their street cars are really downgrading them b/c they are increasing unsprung wt.

Some are entranced by the cosmetic allure of brake bling. I must admit that I too have been...

[Flieger]

Elephant Racing was working on carbon brakes in early car dimensions, but that was before the economy went to heck.

[john1234]

hello fraudster mike! members, avoid this guy vwmike911. he's a con artist. wants something for nothing and then claims goods are damaged and runs off with your money.