pcar928fan

Try a different pad material and use the anti squeak stuff on the back side of the pads when you put them in...should help. My Pagid oranges sounded TERRIBLE the stock pads dusted bad and were not much good on track... Since I have the race car now I went back to stock pads on the S4. They did fine at first but are a touch squeaky now.

Neither of my GTS's stop as hard as my S4...not even close. I went out in the S4 tonight for the first time in awhile and the first time I hit the brakes it brought a smile to my face that car stops SO GOOD!

pole position

This hat for the 965 should fit http://www.zeckhausen.com/StopTech/consumables.htm#Hats

This rotor ring will fit the above hat http://www.racingbrake.com/Rotor_Rings_s/3262.htm

That is your 14 inch (355/32) set up right there plus caliper spacers and longer mounting bolts.

Cheburator

There is no way ever that a S4/GT will stop better than a GTS when comparing apples with apples i.e same discs and pads across the two cars. The GTS benefits both from higher leverage due to the increased disc diameter and also due to significantly bigger pad area... How can people call white black and black white is beyond me...

When upgrading from S4 to GT you only need bigger disc shields and longer bolts. There is absolutely no need to change the brake bias valve Brett! Standard stock 16" wheels will just about clear the calipers, but you will not be able to use stick-on balancing weights. Custom 3-piece 16" BBS wheels will fit without issues, but I doubt many people on the list have wheels like this...

Brett928S2

Hi

You seem to have some sort of problem with me...and I have no idea why...but this list is not the place for it...

My advice was a general mechanical principle...from a QUALIFIED mechanic and race mechanic...

You change brakes and you ALWAYS make sure that the front/rear bias is correct or the car WILL swap ends under hard braking.....

For all we know the OP may have been hoping he could just change the front or rear brakes alone....

I have no idea why you do not believe "pcar928fan" in his statement.....I do....

MY S4 (on my S2) brakes have stopped me from huge speeds perfectly adequately ....

All the best Brett

AO

While Brett may be technially correct, in pratical terms it's really a non-issue.

I recently did the GTS swap and based on my experience, it's the pad that makes the most difference. On my S4 calipers I ran a set of Hawk HPS-Plus pads and they were awesome. The car would stop immediatly. No fade, no sponginess, just rock solid brakes. I loved them.

Now I have the GTS calipers and am running standard HPS pads and they don't stop nearly as well. They feel soft and a bit spongy. I think I'll try re-bleeding the system to make sure it's not air, but this was the same feeling I had on the old calipers before I switched to the HPS-plus pads.

BTW, Here' the writeup on my GTS conversion... https://rennlist.com/forums/928-foru...oot-whoot.html

Cheburator

Brett, I don't have an issue with you. Not at all... I have an issue with pointless drivel... If you look at the WSM/PET - you will realise that the brake bias valve is one and the same for the GTS and the S4 and even the 944 Turbo... The original poster asked about swapping GTS FRONT calipers, not rears. So, WHICH PART OF THAT DID YOU NOT UNDERSTAND? I have done the swap and have done tracks and races on it for 2 seasons without issues. But no, we need your opinion about cars swapping ends if you brake from high speed. One more time, in case you missed it, we are discussing GTS FRONT calipers, not rears since the latter are the same across the range of 928s and 944s. You are free to agree with whoever you want about S4s calipers being better than than the GTS ones... Let me break the bad news to you - I also made the point about comparing stock with stock... Of course S4 calipers with OEM discs and Pagid RS29s will be better than GTS calipers with Zimmermann discs and Jurid pads. Now then, what happens when you put OEM GTS discs with Pagid RS29s? You lock the front tyres with 265 cross section R888s even though you still have a working ABS, that's what happens Mr "QUALIFIED RACE MECHANIC"...

Lastly, in case you also missed it - Porsche did not design the brakes, BREMBO of Italy did. Porsche merely fitted the prototypes of our calipers on the 917 - a car which actually regularly went north of 200mph, unlike others... Cough! Cough! Cough!

Rant over... and appologies to the rest of Rennlist...

Vilhuer

If anything, that valve should be changed to make brakes less stable. Factory kept it same to make GTS run extra safe.

Cheburator

I know... that's why the racer is getting an AP Racing brake bias valve grafted on next week instead of the stock one... To be fair I was surprised by how much braking is done by the rears once you start really pushing the car at very fast tracks which require sharp braking for hairpins or 90 bends

mark kibort

A couple of points here.
No, there is nothing to worry about with GTS brakes fitted to a stock S4 . the difference in all catagories is minimal. in fact, the larger caliper will require less braking effort for the same stopping torque, so less rear brakes will be applied. "Swapping ends" is just silly".

now based on driving style, the faster you go, the less rear brakes you will need, as there is more weight transfer to the front when more g's are generated, so it makes sense, for all things being equal, you will want LEsS rear brakes as you stop harder. just plain physics here. Now, very hard trail braking will want even less. Ive dont all sorts of combinations of pads and bias for the S4 chassis ending up with the GTS rotors up front and pagid blacks on the stroker. its a perfect set up with absolutely no compomises. Its really funny all the teams i run into that have brake issues. fade, squeaking, lockup, rear bias issues, etc etc. the porsche 928system is incredible. Did anyone catch my latest toe to toe video with a $180K porsche GT3 convered race car with a pro at the wheel? we were dead even in almost all areas, and he even had real slicks. a testimate to the 928 design, (and a few things Ive figured out)

mark kibort

Brett, if it is you that is a "qualified race and porsche "mechanic, you better go back and get recertified. Hey, nothing against you personally, as I love your passion for speed, but your comments are nonsense.
The car will not swap ends under braking with rear brake changes. i can have NO rear brakes, or I can have All rear brakes, and I willl NOT swap ends. It can change the characteristics in extreme racing situations, or in the rain, but it is certainly not a gurantee of any problem or issue. second of all, as I mentioned, if you put a bigger rotor up front, you will need less fluid pressure to stop, thus actually reducing your rear braking forces, and this hints of the issue of front to rear balance, with more front givng more stability at the edge of adhesion. the GTS full brake change or GTS rotor change is so minimal,it wont be noticed by most anyone on the street. only on the track and its a very minor change. on the street, this is more for looks than anything. Lets be honest here. the GTS and S4 brakes are equally capable of stopping the car under most any condition. it might take more foot pressure for the S4, but both are more than adaquate. Now, under repeated 150mph to 80mph stops, the larger diameter rotor will help with leverage and efficiency of managing the heat. thats it. more thermal mass is better too, but folks, we are talking less than .5" larger radius , so the reall difference is VERY small! best bang for the buck if you really care about performance, get some pagid black racing pads.

mark kibort

yes, they can stop the same with different pedal pressures.

larger pads?? well, thats not realy true. same width, but they are thicker down at the inner diameter.Ive have always contended that that area of pad is insignificant, and probably only generates heat. this is why most of the best racing systems have thinner pads, but WIDER pads or the same as the S4 pad, like the stoptech ST40 or F50 brake set up that anderson uses as proof of this point.

S4 16" wheels will NOT clear the GTS calipers and or S4 calipers with GTS rotors. Ive tried, the car doesnt move.

mark kibort

pad breakin is 90% of the squeaking issues.

Cheburator

Mark,

Last time I put a GTS pad over a S4 pad, the difference was kind of noticeable... Like 1.5cm height difference in favour of the GTS pad, you do the maths. Sorry, that makes no difference and I must go back to my maths and physics classes

Porsche must be really dumb, just look at them... After all, they fitted the GTS caliper and disc to the 964RS, 964 Cup, 964RSR, 993RS, 993RSR, 993GT2, 968 Turbo S race cars.... Why bother when they should have listened to you and gone with a F50 disc and a S4 caliper???

16" wheels clear the GTS caliper, but only if the wheels have non-stick balancing weights...



P.S. For a change I agree with a lot of the other stuff you say here... Thus have another one on me

mark kibort

Man, you have to read more carefully. the pad is the same width, but not radius ( from outer edge down to hub) this means that the real active contact area is really the outer 1/2 of the pad. just like airplanes wings produce most of lift at the outer 1/3rd. the inner part of the pad is really not that effective, thats why (and read this real carefully) most ALL racing pads are no larger than the S4 pads, but some are much wider, like on the 6 or 8 pot calipers.

so, i guess Anderson and all the racers in World challenge that use a pad like the S4 for their 14" rotlrs are dumb?? porsche now makes a very narrow pad , like the S4 for all the GT3's. the GTS caliper is a big street caliper, and all the racing companies dont have such a thick pad anymore. they all go wider, fitted to larger diameter rotors.

Now, I fitted the GTS rotors to my car, and used the GTS bolts to fix them with spacers. they rub on the 16" rims, as I couldnt roll the car during the building of the new racer. however, it might be a subtle difference between the S4 and GTS caliper at the outer most diameter points. it would be too close for comfort on a 16" rim, even if it did fit (i.e. rolled)

pcar928fan

Cheburator,

Sorry you don't believe my S4 stops better than any of my GTS's. I have had them on track and I think the GTS's fade a bit less, but they certainly don't stop as nicely as the S4's. I have not run them side by side each with Pagid oranges but have run them side by side on the street plenty enough to know the feel and stopping power (on a single stop) is greater from the S4's... As MK noted, at the same pedal pressures. I can only push so hard with my hand and am trying to get close to lock up but not engage the ABS... My S4 is superior.