RyanPerrella

well start by measuring the disc size. The mid 89 plus calipers look the same.

if you have 304mm or S4 rotors then you should have the same issues with pads coming loose and have a rust ring on the rotor. Post a pic we can compare.

RyanPerrella

I measured the calipers as you suggested Jim and find 7 5/8" from point to point.

Now for Rotor selection, there seem to be a number of OE Porsche 322mm rotors available.

The GTS rotors which i dont believe have cast holes in them, which are probably the most expensive.

The 993 TT rotors which are compound and fairly cheap but which would require an expensive new aluminum hub. Ive heard each corner could drop from 1 to 4lbs. 4lbs would be nice but if its just one lb, then it wouldnt be done to save any money.

Then i see two 965 rotors available. I see on the 928 SP site that they list 965 351 045(and 046) 00. I haven't called for a price on these yet but Pelican lists them for $200 each.

Also there is a 3.3L 965 turbo rotor with the 043 and 044 numbers but they are more expensive and i don't know their spec's

The cost on the 993 rotors would be over $650 for everything. Nearly half the cost coming from aluminum hats because the hats that come on the rotors a cannot be used.

I would love to have the bling factor of the compound rotors but at nearly twice the cost I cant see it being worth it. I wouldn't be surprised to find the 965 rotors for $150-$175 each which would make the disc swap a total bargain.

I am curious if there are any other options out there for 322mm rotors that I am missing?

mark kibort

are you sure these are GTS pads and calipers?
I just measured the width of the S4 pad and they are 53mm wide. based on the micrometer reading, those pads look identical to the S4 pads. why are you not measuring the exact thickness (width) of the pad material?

that looks like a S4 caliper to me. maybe i have GTS calipers too!

one of the pics that you posted showed the spring out of place. that would allow for the pad to move outward and give you that funky wear pattern. I also positioned the micrometer like you have on your pads. was one of those pads S4 and the other GTS? Im a little confused on what im looking at. I tried to replicate it below.

mk

mark kibort

those calipers are definitely different. could they be 993 calipers or something that is the same as the S4 size, but different? the bottom line is the pad size i would imagine.
mk

bfellows

https://rennlist.com/forums/928-forum/385988-s4-gt-brake-confusion-more-pics.html

See if this helps, I have early and late S4 fitted....... long story....

John Veninger

Early ones, the later 89+ S4/GT calipers had printed lettering.

dprantl

I didn't have time to remove the wheel so I don't know how useful this picture is. However, my calipers and rotors like the same size as Mark Kibort's. It also looks like my dust shields are sized correctly for the rotors.

Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*

RyanPerrella

Dan,

Those calipers look like S4 calipers to me, they have the raised lettering so much as i can tell from the pic. This would seem to eliminate my idea that the late S4's had at some point been given the newer style caliper with the stick on "Porsche". The sticker is the easy identifier to GTS calipers, but I thought I saw the same on another 90 recently.

Kibort,

I don't know the correct way to measure pads, so i duplicated my measurement to compare. The pads that read 57.6 were in the car when i got it (Pagid's) and as you can see by the huge wear marking don't correctly fit the rotor. But they fit the caliper. Your calipers aren't the same i know just because of the raised Porsche lettering.

Also the spring was just removed, but you can see that when the spring is in place the part thats supposed to hold the pad down is about 6-8mm away from the top of the pad. Thats why they are loose, is because i now assume the pads are mounted to deep in the caliper, because there is no rotor at the outer edge. If i throw in a larger rotor which i will do then the pads can sit further out of the hub and the spring clip will be doing its job.

Would this give me more braking leverage? Having the pads grip a larger caliper such as a level will do for torque. Is that one way larger brake rotors work is by using the larger disc's size for torque to slow the car?

dprantl

Nope, the lettering is not raised. I can run my finger over them and it is flat-smooth. Also, like I said, these calipers are a good deal longer than the fronts on my wife's 968. I understand that the 968 has the same size brakes as an S4, is that right?

Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*

RyanPerrella

well your lettering looks bigger then mine. Or the lettering is the same size but the size of your caliper is smaller so it appears larger.

Wanna pull a wheel off and take that measurement as Jim suggested? Or did you already say you measured?

dprantl

Yep, I measured and they are 7 5/8".

Dan
'91 928GT S/C
'86 928S 5-spd w/LSD *sale pending*

bfellows

Pics show early S4 type (top) and late S4 / GT type bottom - any help? Pad type is the same.

RyanPerrella

Bert,

I can tell by looking that the calipers I have are larger.

Dan,

I will take a pic of my caliper with measuring tape and post it.

RyanPerrella

Couple things ive not noticed after seeing the late S4 GT calipers.

1) The directional arrow on the late S4 calipers is long, the directional area on mine is very short, see pics.

2) I believe i also had S4 pads, my measurement of 57.6 mm is incorrect and that would explain why the pad bottoms out but is still not on the spring retainer. I NEED GTS pads as well as 322mm rotors. The pads I have will not work.

Take a look at how i measured the calipers and try and do the same to yours and let me know what you get.

Also in the pics you cant see where the 1" line is, but trust me when i say its at the base of the block where the pipe screws into. The measurement is 7-5/8"

RyanPerrella

As For which rotors to use I think i am going to eliminate the 993 TT with aluminum hats for the time being because the cost will be $650. Altogether not very much had the 965 3.6L TT rotors not been available for $304 for the pair from Porsche.

GTS Rotors which i assume are the same as the 965 rotors only they are without the cast holes are $189 each

965 3.6L rotors $151.46 each which is what the aluminum hats alone would cost. I think I will go with the 965 rotors, seems like a no brainer to me honestly.

Now for GTS pads

I hear Pagid's are preferred pads but their description seems to be for racing cars and mine is strictly a street driver. I see pads from Textar for $50-$60 and Hawk'e in the $120 range. Pagid's are in the $250 range which when there is on version for 20% of that cost i would never do on a street car. It appears that the pads I have are S4 as well and i am simply measuring them incorrectly. This would explain again why the pad spring clip doesn't touch the tops of the pads. I need GTS Pads which are no doubt bigger.

Anyone with pad suggestions? Actually my biggest concern is dust, i dont want to deal with brake dust at all. The Pagid's were turning the cup II's black all the time, so a low dust pad something i would really prefer. Suggestions?