cobalt

After some helpful clarification from Mark regarding the S4 brakes he has for sale I find there are contradictions in many articles and info I have regarding the Medium S4 brakes used on the 928 S4 and other models.

I have seen 90 GT's and some S4's with brakes that look almost Identical to the big blacks used on the GTS. The differences are smaller rotors and slightly smaller size of the caliper. I believe the length was the same but the width is different. These calipers used the 48 x 132mm pad vs the 58 x 132mm pad of the big black/reds. The medium S4 calipers are also noted as the same calipers used on the 91-92 turbo and the 993.

According to the article on Brakes written by Bob Gagnon and Bill Gregory there were 3 versions of brakes supplied by Brembo in the mid 80's:

"Brembo provided four piston calipers, with different sized piston sizes through 1998: The smaller of the calipers, introduced on the 1985 944 Turbo, the medium S4 caliper introduced on the 1986 Porsche 928S4 and the large "Big Black" calipers introduced on the 1992 928 GTS (also used in red color for 911 Turbo applications) The calipers use two sizes of pistons in each caliper half, which reduces taper, or uneven brake pad wear, that can occur when equal pistons are used.

.....The Carrera RS and Turbo 3.3 used Medium S4 calipers in front and small calipers in rear, while the turbo 3.6 carries Big Reds in front and medium S4's in back. Note the medium S4 black calipers used on the front of the 993C2 and Carrera RS/Turbo 3.3 are different castings, to work with respective 304mm and 322mm discs."

So now the confusion. There appears to be a conflict with this info whcih has been corroborated by many experts. The pictures I have show the medium S4's used on a 951 S which is the same Medium S4 used on the 91-92 turbo yet the pictures Mark has differers.

Can people corroborate and post pictures showing that the Medium S4 used on the 928 is a different casting than those used on the other models and if that is the case can anyone measure the pads used to see if they measure 48 x 132mm.

I am posting 5 pictures the first is of the small 944 turbo brembo caliper the second is of the medium S4 caliper used on the 944 turbo S then followed by the medium S4 calipers as seen on Marks S4 and the last are the big blacks.

Any clarification would be appreciated.

Thanks

Vilhuer

There are several variations of middle version, commonly known as S4 version even though they first appeared in late summer 1985 in first '86 MY ROW 928 S cars. 928 variations are AFAIK

'86 = small pistons
'87-88 = large pistons, first type seals
'89-91 = large pistons, second type seals

AFAIK 250 hp 951 use exact same front calipers.

There is also visual difference in different year parts. Later calipers have less features in area where Porsche text is. Don't know when exacly this changed but it don't have any effect on how they are mounted or anything.

cobalt

OK so there are visually different castings used with the earlier using raised lettering and ribs and the later using decals. This would explain why i am seeing different looking calipers all being called medium S4's. I had never seen the earlier raised lettering version until marks post.

Thanks

heinrich

Anthony I bought "Beg Reds" from a VERY trustworthy 944 turbo S racer on this list. They are weird, they look like S4 but are slightly bigger. I suspect they *may* be the mediums you are talking about.

cobalt

I guess the only real way of telling is to measure the pads. The turbo S used medium S4's that look identical to the big reds just slightly narrower and only accept the 48 mm wide pad.

Vilhuer

996 GT3 front, 220 hp 951 front and big red (which is same as big black except for small details which can be changed)



996 GT3 and 996 GT2



On top 220 hp 951 front
From left to right, 996 GT2 front, 996 GT3 front, 993 front (almost same as 928 S4 AFAIK), 996 GT2 front, 996 GT3 rear and 996 GT3 front.



Weights of the front calipers:
220 hp 951 2.86 kg
928 S4 3.36 kg
996 GT3 3.11 kg
996 GT2 3.67 kg

Reason why its difficult to mount 996 GT2 or GT3 calipers into 928 which use medium or big black calipers.

dr bob

So all I need is a set of offset SH capscrews and I could use the bigger calipers? Off to the custometric hardware store again!

worf928

The (black) brakes you show were not used on US 928s after the '88 model year. Starting in '89 they are visually similar (except in size) to the later-style GTS calipers. The pre-89 calipers are a few mm wider.

Vilhuer

Same change was done in ROW cars also. Early style and late style is same in all meaningful measurements allowing them to be interchangeable. Late style were meant to be used with asbestos free brake pads. Outside styling change was done for the heck of it while more important piston seal change also had fuctional meaning.

atb

Something else to note.
I have the "big red" rear brakes (993TT), which use the S4 size calipers but... the piston sizes are way smaller. They are even smaller than the stock S4 rear pistons. So, you get a bigger caliper than stock, a bigger pad than stock, but smaller pistons. I don't understand why the big red rear brakes don't use the S4 pistons, any ideas?

Vilhuer

It could be balance thing between front and rear brakes. There has to be some difference in force what comes out from piston at given pressure since there are large and small piston in each caliper. Reason given for this is that this will allow even pad wear. If it works within one caliper it should work between calipers also. Don't know how exactly Porsche wants to change front/rear brake ratio with that change though.

hinchcliffe

In looking at my '87 and my buddies '85? 951 his fronts calipers looked about the size of my rears and his rears were slightly smaller than that. Now the 951S is a different story, correct?

Vilhuer

Yes, 250 hp 951 has same brake calipers as 928 S4. Also drilled rear disks used in S4 etc have 951 part number. Porsche tried to rationalise number of different parts they used.

worf928

I thought that might be the case.
Other than the piston seal change, I think there are only two other functional changes. 1) Since the 'newer' calipers are a few mm narrower some wheels will fit a car with the newer calipers and not fit cars with the older calipers unless a small (<5mm) spacer is used. And 2) there was a change to one of the 'squeal' damper plates due to a change in the inner diameter of one of the pistons - which one I don't recall. BTDT though.

Alan

Erkka,
Great data - as usual!

Thanks for the visuals on these - you don't often get to see side by side comparisions across models like this

Alan