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TAV TAV is offline
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Thoughts on my planned brake upgrade (3.6 911sc)

I have a 3.6 conversion that is almost done. So now, Iíve turned my attention to the brakes.

After much reading, the plan is:

1) Rebel s racing 996 Caliper kit for the front to use 318x28mm rotors with 996/Boxster s Calipers

2) Carrera Calipers at the rear with 290x24mm rotors.

The reasoning being:
- there will be an increase in rotor sizes for improved heat management.
- The rear caliper choice will allow the hand brake to be retained, slight improvement in rotor size (thickness) and
- the F/R bias wonít be too bad at 1.642.

Am I missing anything? Any thoughts, suggestions?

The car will be 50/50 street/track.

Thanks
Old 10-11-2017, 09:01 PM
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Bias adjustment valve on REAR brake line. I installed mine beside the brake master cylinder just before the turn into the smugglerís box. Adjust it by threshold braking on a really wet road. I have set mine so the front locks up just before rear for street and dry track.
Johan

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Old 10-12-2017, 05:04 AM
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TAV TAV is offline
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Uwon, your setup would only work if you had a naturally rear-biased brake system, as the valve on the rear brake lines only helps in reducing the braking to the rear..?? Is that the case?
Old 10-12-2017, 05:16 AM
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Quote:
Originally Posted by TAV View Post
I have a 3.6 conversion that is almost done. So now, Iíve turned my attention to the brakes.

After much reading, the plan is:

1) Rebel s racing 996 Caliper kit for the front to use 318x28mm rotors with 996/Boxster s Calipers

2) Carrera Calipers at the rear with 290x24mm rotors.

The reasoning being:
- there will be an increase in rotor sizes for improved heat management.
- The rear caliper choice will allow the hand brake to be retained, slight improvement in rotor size (thickness) and
- the F/R bias wonít be too bad at 1.642.

Am I missing anything? Any thoughts, suggestions?

The car will be 50/50 street/track.

Thanks
You are sort of on the right track
The front is a nice improvement on A or S or wide A, but not as good as 930
bias actually is more like 1.743+/-,(hyd bias is 1.642 but mechanical effects of the rotors altar that #) this is more front biased than optimal for track use, fine on the street. If you could get a pair of the 2 piston 964 rears that would improve bias to ~1.53, which is almost ideal.

if it were my car I'd still hold out for full 930s
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Old 10-12-2017, 05:50 AM
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TAV TAV is offline
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Originally Posted by Bill Verburg View Post
You are sort of on the right track
The front is a nice improvement on A or S or wide A, but not as good as 930
bias actually is more like 1.743+/-,(hyd bias is 1.642 but mechanical effects of the rotors altar that #) this is more front biased than optimal for track use, fine on the street. If you could get a pair of the 2 piston 964 rears that would improve bias to ~1.53, which is almost ideal.

if it were my car I'd still hold out for full 930s
Thanks Bill. Iíd love to have 930 brakes... but the budget has to draw the line somewhere, unfortunately.

Is there an adaptor kit thatís readily available for the 964 early 2 piston caliper to be used on the 911sc? I didnít come across any when I was looking into all the various combinations of front/rear Calipers.

Thanks
Old 10-12-2017, 06:16 AM
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Originally Posted by TAV View Post
Uwon, your setup would only work if you had a naturally rear-biased brake system, as the valve on the rear brake lines only helps in reducing the braking to the rear..?? Is that the case?
Correct.
I run Ď79 930 front floating rotors and 930 rear rotors with 930 Calipers all around. Backing off on rears required.
BTW, I used to run 993 Calipers on these rotors which also required backing off the rears.
I personally prefer the 930 Calipers for performance over the 993.
Hope this helps.
Johan
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Old 10-12-2017, 08:26 PM
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Old 10-13-2017, 01:13 AM
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Set of 930 rears for sale here. Guy says they can be used on the front, is that correct?
Pair porsche 911 930 Turbo Rear Brake Callipers | eBay
Old 10-13-2017, 03:56 AM
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Originally Posted by Ian Comerford View Post
Set of 930 rears for sale here. Guy says they can be used on the front, is that correct?
Pair porsche 911 930 Turbo Rear Brake Callipers | eBay
Bolt pattern is the same but the Pistons are smaller.

My car has 930 calipers with Rebel hats.

Einmalig probably has a dozen rebuildable rears in a box on the shelf

All kinds of "secrets" modifications need to be done to rears, but oh man is it worth it.
Old 10-13-2017, 06:19 AM
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Originally Posted by TAV View Post
Thanks Bill. Iíd love to have 930 brakes... but the budget has to draw the line somewhere, unfortunately.

Is there an adaptor kit thatís readily available for the 964 early 2 piston caliper to be used on the 911sc? I didnít come across any when I was looking into all the various combinations of front/rear Calipers.

Thanks
No, you would have to DIY
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Old 10-13-2017, 06:22 AM
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Originally Posted by Uwon View Post
Correct.
I run Ď79 930 front floating rotors and 930 rear rotors with 930 Calipers all around. Backing off on rears required.
BTW, I used to run 993 Calipers on these rotors which also required backing off the rears.
I personally prefer the 930 Calipers for performance over the 993.
Hope this helps.
Johan
Sounds like there is something else that is off

930s are really well balanced but if anything are a tad front biased

if you had 993 front and 930 rear than would be even more front biased.
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Old 10-13-2017, 06:25 AM
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Originally Posted by Ian Comerford View Post
Set of 930 rears for sale here. Guy says they can be used on the front, is that correct?
Pair porsche 911 930 Turbo Rear Brake Callipers | eBay
As Doug says the 3.5" bolt pattern is the same and they are narrower for use on 26 to 28mm rotors.

The issue w/ using them in front is 2 fold
1) gotta find a 26 to 28mm rotor that fits
2) find a rear setup that is balanced
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Old 10-13-2017, 06:27 AM
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TAV TAV is offline
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Thanks for all the feedback

So I have come across a set of brakes front and rear that have come off a similar project:

993 NA front calipers size (44/36mm pistons)
964 4 piston rear calipers size (30/28mm pistons)

The above setup is too front biased with F/R ~ 1.9

So my plan is to replace the rear ones with 993 rear calipers (34/30mm pistons) which would bring back the hydr bias to around 1.57

I don’t have this current brake set in front of me, but I would think the rear 993 calipers would just bolt on replacing the 964 rear ones as they’re exactly the same from the outside (just different piston sizes). Is this correct?


Also, once I get these, I’ll be servicing with new dust boots and seals.
Are the pistons generally changed as well at some stage? Should I be changing the pistons “while I’m there”?
Old 10-13-2017, 03:43 PM
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Originally Posted by TAV View Post
Thanks for all the feedback

So I have come across a set of brakes front and rear that have come off a similar project:

993 NA front calipers size (44/36mm pistons)
964 4 piston rear calipers size (30/28mm pistons)

The above setup is too front biased with F/R ~ 1.9

So my plan is to replace the rear ones with 993 rear calipers (34/30mm pistons) which would bring back the hydr bias to around 1.57

I donít have this current brake set in front of me, but I would think the rear 993 calipers would just bolt on replacing the 964 rear ones as theyíre exactly the same from the outside (just different piston sizes). Is this correct?


Also, once I get these, Iíll be servicing with new dust boots and seals.
Are the pistons generally changed as well at some stage? Should I be changing the pistons ďwhile Iím thereĒ?
The devil is in the details, yes the 993 f/r is pretty good but it depends on the rotors used too.

First you will probably need 17" wheels, 944 16 may work in front but I haven't done that one so can't say for sure.

993 calipers f/r will want the same f/r rotors as 930, you will need either the 1978 -1980 930 rotors or aftermarket equivalents. Later '80 up 930 front will not work unless you also have 930 front fenders, if 930 fenders are there then you also use 930 hubs.

In back 930 rotors from 1978-89 bolt on, you will need to ditch the splash plates and cut of the mounts for same. Yes 964 and 993 rear are the same except for pistons, yes yu want 993 rear. To modify them for 930 rotors first plug the existing mounting holes w/ aluminum rod, then redrill to fit on the rotors.

It will look like this, you can see the old and new hole location


You will also need to grind bit in the throat area as the 930 rotors @28mm are 4mm thicker than 993


final install looks like this


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Old 10-13-2017, 04:02 PM
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The devil is in the details, yes the 993 f/r is pretty good but it depends on the rotors used too.

First you will probably need 17" wheels, 944 16 may work in front but I haven't done that one so can't say for sure.

993 calipers f/r will want the same f/r rotors as 930, you will need either the 1978 -1980 930 rotors or aftermarket equivalents. Later '80 up 930 front will not work unless you also have 930 front fenders, if 930 fenders are there then you also use 930 hubs.

In back 930 rotors from 1978-89 bolt on, you will need to ditch the splash plates and cut of the mounts for same. Yes 964 and 993 rear are the same except for pistons, yes yu want 993 rear. To modify them for 930 rotors first plug the existing mounting holes w/ aluminum rod, then redrill to fit on the rotors.

It will look like this, you can see the old and new hole location


You will also need to grind bit in the throat area as the 930 rotors @28mm are 4mm thicker than 993


final install looks like this




Thanks Bill. You've been very helpful.

I will be running 17's, so that part shouldn't be an issue. I have a wide body 911 sc, but not running 930 hubs.

After all the information you've given me, I know exactly what my plan is now in terms of callipers, rotors... i.e. a whole brake package with an acceptable F./R brake bias.

Thanks!
Old 10-13-2017, 08:08 PM
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Originally Posted by Bill Verburg View Post
Sounds like there is something else that is off

930s are really well balanced but if anything are a tad front biased

if you had 993 front and 930 rear than would be even more front biased.
Bill, I used to have 993 brakes all around, not just rears. And to restate for clarity, the rears needed to be backed off with the adjustable bias valve, otherwise Iíd be doing pirouettes every time I brake hard.
Johan
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Old 10-14-2017, 03:51 AM
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TAV TAV is offline
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Bill,
With the setup shown above using the rear 993 calipers and grinding a bit of the throat region, does one have to modify/shave new pads when they're due for replacement?

thanks
Old 10-14-2017, 05:03 AM
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Bill, I used to have 993 brakes all around, not just rears. And to restate for clarity, the rears needed to be backed off with the adjustable bias valve, otherwise Iíd be doing pirouettes every time I brake hard.
Johan
You are in a minority of one then, I reiterate there is/was something else amiss

Most people(I talk to 100s) w/ tracked 911s like a net bias of 1.42 to 1.49 for most conditions.

RSRs w/ adjustable bias have a range of 1.26 to 1.92 centered on 1.59 they generally run as much below the middle setting as much as possible as much of the time

Every 911 built up through 1983 has a net of 1.491

There are some guys at the extreme that like even more down to the 1.2 range, I wouldn't go that far myself but do run 993RS 1.426 on both of mine
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Old 10-14-2017, 06:17 AM
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Bill,
With the setup shown above using the rear 993 calipers and grinding a bit of the throat region, does one have to modify/shave new pads when they're due for replacement?

thanks
You may, it depends on the pad they are all a little bit different
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Old 10-14-2017, 06:18 AM
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Originally Posted by TAV View Post
Thanks Bill. You've been very helpful.

I will be running 17's, so that part shouldn't be an issue. I have a wide body 911 sc, but not running 930 hubs.

After all the information you've given me, I know exactly what my plan is now in terms of callipers, rotors... i.e. a whole brake package with an acceptable F./R brake bias.

Thanks!
On a widebody the cheapest way to get the 930 sized rotors that the 993 calipers need is to use 930 hubs and '81-89 one piece 930 rotors. w/o this you will either need spacers or wheels w/ more than usual o/s.

So it comes down to the wheels. If you already have the fronts 17s it depends on what ET they have.
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Old 10-14-2017, 06:22 AM
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