[firefish]

I am about to put M030 calipers with 911 turbo rotors up front (thus replacing the stock non M030 calipers and rotors). I have read about moving the front calipers to the rear - some say it's good, others bad. What are the differences between non M030 calipers front and rear? Could someone who is knowledgeable about this share some info and explain to me why I should, or shouldn't, do this?

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[Big Dave]

Basically, DONT...
The front standard calipers have larger pistons fitted than the rears + when they are fitted to the rear of the car it totaly unbalances it. IE the car will want to swap ends. Not so much in the dry . But in the wet leathal....
I did this "mod" some time ago, + persiviered for a while, thinking i could "drive" around it.. But no.. Too many spins + a few visits to the gravel traps confirmed my thoughts....
Im sure that Pete "RS Barn" will also say a similar thing, as he recomended me not to do it...But i had to try for myself....

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[firefish]

<!--quoteo(post=72403:date=May 23 2009, 12:26 AM:name=Big Dave)-->QUOTE (Big Dave @ May 23 2009, 12:26 AM) <{POST_SNAPBACK}><!--quotec-->Basically, DONT...
The front standard calipers have larger pistons fitted than the rears + when they are fitted to the rear of the car it totaly unbalances it. IE the car will want to swap ends. Not so much in the dry . But in the wet leathal....
I did this "mod" some time ago, + persiviered for a while, thinking i could "drive" around it.. But no.. Too many spins + a few visits to the gravel traps confirmed my thoughts....
Im sure that Pete "RS Barn" will also say a similar thing, as he recomended me not to do it...But i had to try for myself....<!--QuoteEnd--><!--QuoteEEnd-->

Yes, I remember reading the thread about this. But, out of curiousity, what brakes did you run up front when you put the stock front calipers at the rear? What I am trying to figure out is how to best upgrade the rear brakes. Maybe it is not necessary yet, not by a longshot, but at some point it may be necessary.

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[Fox944]

with big reds up front, i would just upgrade the pads & get some cross drilled rotors for the rear. Get a brake bias valve to adjust the balance.

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[RS Barn]

My TS/RS has big reds OE . I installed a 964 Cup car bias valve vs 928. It's more agressive. OK for racing but it may be too agressive for some. For some reason rear brakes are a bit ouuchy when cold but after all warms up they are awesome with big reds
Pete

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[flash]

big reds up front and not increasing the rear creates a huge imbalance

if you increase braking on the front end, you need to increase it on the rear - the car is already too biased to the front - increasing front braking without increasing the rear will only DECREASE your total braking capability

i realize this sounds wrong, but it is the way it is - i know it "feels" like the car is stopping better because of the big nose dive, but if you actually measured the baking distances, you will see that they increase when you heavily bias the front end versus a balanced braking

it's all a function of how much weight is on each wheel during braking

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[Big Dave]

<!--quoteo(post=72420:date=May 23 2009, 09:43 AM:name=firefish)-->QUOTE (firefish @ May 23 2009, 09:43 AM) <{POST_SNAPBACK}><!--quotec-->Yes, I remember reading the thread about this. But, out of curiousity, what brakes did you run up front when you put the stock front calipers at the rear? What I am trying to figure out is how to best upgrade the rear brakes. Maybe it is not necessary yet, not by a longshot, but at some point it may be necessary.<!--QuoteEnd--><!--QuoteEEnd-->

I fitted a set of the M030 calipers at first, then went on to the "BigReds" with a 5-33 valve. It was still tail happy, so i refurbed the original rear calipers + refitted them. Now the car is spot on....
So basically just fit some M030 calipers up front with the standard rears at the rear. Get some better pads / change you fluid to "THE best" Castrol SRF, + fit some braided hoses....
Personally the Big Reds up front , on a street car are, in my opinion, to much.. But look good.
My car get used a lot on track....

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[firefish]

<!--quoteo(post=72440:date=May 24 2009, 01:05 AM:name=Big Dave)-->QUOTE (Big Dave @ May 24 2009, 01:05 AM) <{POST_SNAPBACK}><!--quotec-->I fitted a set of the M030 calipers at first, then went on to the "BigReds" with a 5-33 valve. It was still tail happy, so i refurbed the original rear calipers + refitted them. Now the car is spot on....
So basically just fit some M030 calipers up front with the standard rears at the rear. Get some better pads / change you fluid to "THE best" Castrol SRF, + fit some braided hoses....
Personally the Big Reds up front , on a street car are, in my opinion, to much.. But look good.
My car get used a lot on track....<!--QuoteEnd--><!--QuoteEEnd-->

I just think it sounds strange. Upping the brakes in the front to big reds and running the 5/33 proportioning valve on a car that is commonly known to be front biased I would assume that it would still make the car even more front biased, not more prone to go tail first (since 5/33 is recommended for street use with stock front brakes). But I'm guessing that with sticky tires and loads of stopping power in the front the tail gets so light that it gets loose.

Since changing the proportioning valve seems like a pretty big hazzle, at least not something you do just for the fun of it, wouldn't the best way be a 5/45 valve and, like Fox says, installing a brake bias valve (ie a reduction valve on the brake lines to the rear)? That way you could adjust the bias on the fly depending on the conditions and on how the car feels and handles, and you could have a street setting with a safe amount of front bias without having to worry about the car swapping ends.

In my case I am not, a this point, looking for more stopping power. I have a heat problem and bigger pads, discs and improved cooling should sort that out. Not that I wouldn't mind more bite as a bonus... [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[Big Dave]

I think its the 5-33 valve. Its the one from the 928,s...
Im sure its the 5-33 though.....

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[flash]

heat is the primary reason for any car to have bigger rotors - they really don't increase stopping power as much as they dissipate heat

that being said, the larger calipers and pads do increase stopping power

5/18 is stock - i have a 5/33 with oem size rotors all around - a 5/33 on oem rear and large front will indeed be about as front biased as the 5/18 is stock - a 5/45 would be better but not without compromise

the problem that arises is that, if you are not good at braking and controlling it, setting the rear to be more heavily biased, can cause you to swap ends pretty easily - when you set the rear heavier, you have to learn to feather brakes - this can be as hard for some people to learn as gear matching or heel-toe can be

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[firefish]

<!--quoteo(post=72461:date=May 24 2009, 06:34 PM:name=flash)-->QUOTE (flash @ May 24 2009, 06:34 PM) <{POST_SNAPBACK}><!--quotec-->heat is the primary reason for any car to have bigger rotors - they really don't increase stopping power as much as they dissipate heat

that being said, the larger calipers and pads do increase stopping power

5/18 is stock - i have a 5/33 with oem size rotors all around - a 5/33 on oem rear and large front will indeed be about as front biased as the 5/18 is stock - a 5/45 would be better but not without compromise

the problem that arises is that, if you are not good at braking and controlling it, setting the rear to be more heavily biased, can cause you to swap ends pretty easily - when you set the rear heavier, you have to learn to feather brakes - this can be as hard for some people to learn as gear matching or heel-toe can be<!--QuoteEnd--><!--QuoteEEnd-->

Agreed on the rotors. Although a little more power should be available since the arm is longer - in my case 14 mm.

But back to my original question, and I wan't to emphasize on that I do not plan to do this, I am just trying to grasp the concept:
Would fitting non M030 front calipers in the rear, whilst keeping the 5/18 valve, give the equivalent change in front/rear bias as if a 5/45 valve were fitted and the rear calipers remained stock? Or can you not compare apples with pears?

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[Big Dave]

Like i said in a previous post. Its not advisable to do it..
I fitted the standard fronts on the rear. It gave a longer brake pedal as you are moving a bit more fluid.
It did make the car fabulous in the dry . In fact REALY fab. It helped buy reducing the front end dive under braking. And it didnt seem to have the weight transfer like usual. Making the rear squat down more into the tarmac...BUT,,in the wet was a nightmare....VERY lairy...........The rear would lock up before the fronts, making it VERY unstable....

It must be something to do with the larger pistons exerting more force onto the pad/disc...
I believe that the best mod is to fit the rear calipers from a 964 C4 [I think],on the rear of our 968,s, as these have slightly larger pistons than ours, but not as big a difference as fitting the 968 fronts to the rear...
Just consult a copy of PET for part no,s + caliper differences...

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[firefish]

So, since changing the valve seems like the first thing to do after upgrading the front brakes I guess that I'll try the 5/45 first and evaluate it - hopefully it'll be perfect.

Can someone please give me the Posche p/n for a 5/45 valve? Perhaps someone has one for sale that he/she doesn't need. Pm me if so.

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[flash]

do a search here using all the options for "brake bias valve" and "flash" - it should turn up - i listed all of the part numbers in it

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[Jens Ove]

What about installing Big Reds or similar in the front, and then using an adjustable brake bias valve, like this one: http://www.compbrake.co.uk/BRAKE%20ACCES...VALVE.html

The problem with moving the non-M030 to the rear, is that they will require a larger volume of brake fluid to pass to move the pads similar distance as the originals. Because the pistons are larger. This means that the brake pedal needs to move a longer distance to feed the brake pistons/cylinders. Unless you also change the master cylinder. But then it is getting even more complex.



I like to fit Big Reds to the front. I have non-M030. If i change to better disks and pads at the rear, and I can adjust the pressure to the rear, my thought was that this way I could increase the brake power at rear, and find a balance. Anybody who have tried this? Any thoughts?

I have read he part list for 968 Turbo S and RS. From what I remember, the brakes in a 968 Turbo S have larger calipers at front, larger than M030. At rear they have kept the M030-type (although in red), which I believe is the same as non-M030? And drilled disks. I assume that the bias valve adjustments must have retained the braking balance in these types of cars? Anybody who have experience with adjustable brake bias valves?

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[flash]

i'm fairly sure the turbo used M030, but i'll look into that



as for the conversion, it has been done, and it is a somewhat reasonable compromise. it would still be better if you fitted larger brakes in the rear.



the rear M030 disks are thicker, not just drilled. the calipers use thicker pads too.



if running the "big reds" up front, i would run the M030 rear brakes at a bare minimum, and would look for larger.

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[Jens Ove]

When placing front calipers at rear, I assume that is an attempt to get better break balance after upgrading the front brakes.

I guess Porsche had found the balance in both Turbo S and Turbo RS, so why not look at them instead of trying and failing?

I've looked at the original part list from Porsche. I have not fond the original calipers from 968 Turbo S or RS in any internet stores.



The Turbo S version:

Front brake calipers (in German like the document):

928.351.423.12 - Bremssattel VA links rot

928.351.424.12 - Bremssattel VA rechts rot



From my understanding this is the same kind as the 928 GTS Big Black Calipers from 1994 (928.351.423.02), but in RED.

928 1994:

Left - 928.351.423.02

Right - 928.351.424.02

928 1995:

Left - 928.351.423.03

Right - 928.351.424.03

These have 36mm/44mm piston sizes. I don't know if the 02-types from 1994 have different piston sizes.



Pads:

928.351.940.02 - Bremsbelag 928 GTS

Option:

965.351.940.90 - Bremsbelag VA Pagid RS 4/4 (orange)

Pads from the GTS are standard, with orange pads from the 964 Turbo as an option.



The Turbo RS front calipers:

928.351.423.13

928.351.424.13

I assume 968 Turbo RS use 928 Big Black calipers from 1995, but in red color.



Brake disks:

Front, both Turbo S and RS:

965.351.045.00 - left

965.351.045.00 - right

That's from the 964 Turbo.



Rear brakes, both Turbo S and RS:

951.352.421.12 - Bremssattel HA links rot

951.352.422.12 - Bremssattel HA rechts rot

I believe these are the same as the rear calipers of 86-89 944 Turbo and 89-91 944 S2 (part # 951.352.421.02) but in red instead of black.



Rear brake disks:

Not specified in the document, which means probably same as the drilled disks for the M030 option (951.352.041.91).



Brake master cylinder:

The RS use a special type, 968.355.011.00. Turbo S use the same as in a CS (951.355.011.01).



I cannot find any special kind of bias valve for Turbo S / RS in the document. That should mean they both use the CS-type.



The Turbo S / RS part list is available as a PDF document if anyone wants it.

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[flash]

hmmm - i'll have to look a bit farther - the numbers are EXTREMELY close to the M030 option, and the same piston size as the M030 option, but are S4 calipers, but not big blacks, though often confused with them

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[Jens Ove]

[quote name='flash' timestamp='1315083107' post='114942']

hmmm - i'll have to look a bit farther - the numbers are EXTREMELY close to the M030 option, and the same piston size as the M030 option, but are S4 calipers, but not big blacks, though often confused with them

[/quote]

I've e-mailed you the original Porsche part list for 968 Turbo S / Turbo RS in case you have not seen it before. The rear caliper type is specified with ID numbers there. Remember that the calipers of Turbo S and RS are in red.



I received the document from the official Porsche dealer in Norway, as I have a plan to spec my 968 CS into a Turbo S (with supercharger), and keep it street legal. I need to keep the brakes working well and in balance after the upgrade.

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[flash]

yeah - i have that - i think the parts are the same, though with slightly different numbers, likely a color change

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