cobalt

DO you have better pictures of the calipers with the 40/36 pistons also what sized pad do they use.

They look more like 964 calipers or 944 turbo/S2 non MO30 calipers that had been machined to fit. This would be the correct piston size for these calipers and would use a 44 x 98mm pad vs a 48 x 132mm of the medium S4's vs the 58 x 132mm pad of the big red/blacks. The 40/36 piston caliper would also use a 298 x 28 mm rotor vs a 304 x 32mm rotor.

bfellows

Hi,

Pad size seems to be standard 88 S4 size as pic shows a pad from my old caliper fitted. Other pics show the only serial numbers i've been able to find - the 93 one is a little confusing? Also shown are the milled flats.

Thanks for the help!

cobalt

Ok its a long shot but I am thinking one of the calipers is from a 993. The large 93 in the circle is the casting manufacture date. I have some big red,little reds here and i have some that have a 92 on one side and a 93 on the other half of the same caliper. SO one half of the caliper was manufactured in 1992 the other in 1993.

The 993 used basically the same medium S4 caliper as the 928 although IIRC the pistons on the 993's had a larger reduction in dia to accommodate a revised dust seal. I believe if you remove the outer seal and measure the dia of the piston as it enters the caliper you will see that it is the correct size with a larger reduction where it contacts the pad vs that of the 928 Medium S4 caliper.

It is a long shot but the closest thing to an answer i can think of.

I am curious to see what you uncover.

good Luck


Sorry couldn't be of more help.

bfellows

Looks like you were correct! Question now though is can I fit the caliper?

cobalt

To be honest that is a good question. I don't think there should be an issue. The same amount of force is being applied by the hydraulics but how does the smaller dia of the 993 piston pushing against the pad affect the clamping force? I can't tell you. I would think the difference would be nominal but that is a guess.

I would mount both and using new pads, once seated, do a series of hard stops. If one locks up constantly before the other than it might be an issue if not you should be good to go.

I wish I could be of more help.

Good Luck

bfellows

Thanks to all who have tried to help, i think i have an answer! According to Chris Sanderson at Loe Bank (928 specialist in the UK) the caliper is definately 928 - most likely late GT, or GTS that has been rebuilt with later pistons and revised dust seals. The milled flats on the bottom of the caliper seem to indicate that at some time the caliper has been modified for use most likely on a 944 or 968 and would be where the mounting spacer block would have sat. As the internals of the caliper are the same as the earlier style caliper the braking pressures would remain equal as the contact area of the piston to the pad has little effect on the stopping ability as long as the overall piston sizes are equal.

Vilhuer

He ain't no expert if he said GT or GTS caliper. Those are two totally different castings and very different size compared to each other.

cobalt

I have to agree. If the production dates on the casting say 1993 it might be a 928 caliper but could not be for a GTS. It is possible they made some changes due to available parts and this was sold later as a spare part. Although I might be wrong but I believe you will find you need a 993 rebuild kit to replace the seals on the one caliper.

the flyin' scotsman

As we've said all along the GT and S4 caliper are same.

The GTS is different in caliper dimension (larger) but has same pistion size as the S4/GT caliper.

ROG100

IIRC in the middle of MY 89 the larger piston in the front caliper changed from 42mm to 44mm.
That covered from mid year MY89 to MY91. All the other pistons remained the same size.

bfellows

My mistake, should be "S4 or GT caliper, not GTS"

Vilhuer

That makes more sense.

Piston size change was few years earlier. There are three variations of "S4" front calipers. '86 MY have 36/42mm pistons, early style seals and raised letters in "Porsche" text. '87-very early '89 MY have 36/44mm pistons, early style seals and raised letters. From early '89 to last '91 S4/GT calipers have 36/44mm pistons, late style seals and flat letters in caliber body.

martin D

Roger , you are confusing the seal change which occurred in '89 , not the piston size which was '88.


As far as I can make out there are 4 different Brembo front brake callipers for the 928. IIRC The rear callipers remained the same '86-'95

Below is a basic list, as some of the changes were between year (model year not calender year),sorry I don't have my tech info books to hand to be more specific.

ROW,USA S & UK S2 & all S4...'86-'87 42-36 mm pistons.......old style seals

All S4 ..........................................'88 44-36 mm pistons .....old style seals

S4 & GT..................................'89-'91 44-36 mm pistons ......New style seals

GTS........................................'92-'95 44-36 mm pistons......New style seals

928drvr86.5

[QUOTE=ROW,USA S & UK S2 & all S4...'86-'87 42-36 mm pistons.......old style seals

All S4 ..........................................'88 44-36 mm pistons .....old style seals

S4 & GT..................................'89-'91 44-36 mm pistons ......New style seals

GTS........................................'92-'95 44-36 mm pistons......New style seals[/QUOTE]

Are you sure? I once had a very difficult time finding dust seals for my 86.5. At that time i was conversing with one of the Brembo Reps via email about where i could source the seals and i was told that the seals were no longer made for my caliper. I was also told that Brembo changed the dust seal design in '87. Perhaps Porsche had a large inventory of the brakes with the old style seals to use up and it took until 89 to get the brakes with the new seals on a 928?

Trivial i know, but i had first hand experience with this. You cannot get new (old style) dust seals for the early Brembos up to mid '87 according to Brembo.

ROG100

Very interesting - I was basing my knowledge on the damper pads which changed during MY89. From my records and based on what I supply they increased from 42mm to 44mm which I thought was based on the piston diameter. Why do the damper pads change in diameter?