A930Rocket

Did a search and had no luck.

I'm rebuilding a pair of S4 front caliprs for my 930.

I ordered my rebuild kits and diassembled the caliper pistons, seals, etc.

When the kits arrived, they were different than what had been in there!?

Did they update the rebuild kit or do I have the wrong ones?

Here are two pics of the original parts and the new parts.

Old parts

New parts

Paul D

I'm a newbie to S4 brakes. I just bought a set off a 86.5 928. This was the first time the 4 piston calipers were factory installed on a 928. My pistons and seals look like the ones in your old parts pic. I beleive the new parts pic is a later style 4 piston caliper which had an outer dust boot seal. This outer dust boot fits into the ridge in the piston and mates to a ridge in the caliper to effectively seal out dirt from getting into the piston bores. I dont know if you will be able to use this kit on your calipers. I'm hoping someone else chimes in as I am very interested in the answer as well.....

BC

Well, The bottom is what is on my S4 calipers, and on my new Big reds (now black).

If the bottoms are the same OD for the actual piston, couldn't you just use the whole bottom assembly?

A930Rocket

The O-ring has the same color markings on it as the old one. So that seems ok.

The pistons are the same size, but obviously different.

The seal does go on the piston, but I'll be darned if I can get it in it's postion in the cylinder. I compared sizes of the new and old seal and the new one seems to be ever so slightly larger. It seems to be covered in rubber too making it harder. The old one was bare metal.

I was looking at my PET and it seems like I have the right parts, I just couldn't get the seal in!

I just needed some confimation that I had the right parts before I opened all the pkgs.

BTW. I only ordered enough for one caliper. Who has them at the best price? I got the first set from Pelican and they got them from PCNA, so there must be a cheaper way...

borland

There were two modifications to the front S4 Calipers. Mod I (MY1987) was an increase in the bore diameters. Mod II (MY1989) for both front and rear calipers, changed from scraper ring to a protective cap. This is all detailed in the Porsche 928 Shop Manual.

Doesn't discuss parts being interchangeable. I remember seeing the older parts still listed on the PET database.

A930Rocket

Borland,

How can I tell which caliper I have? I bought them used and believe they have 36 and 44 pistons. I'll re-confirm tonight.

I don't have the 928 manual as I have a 930.

I looked at the PET last night and I think it gave only one part number for what I thought were my calipers, but I picked '90 as my year. I'll look at '88 or others and see if there is any difference. Thanks,

Jim

John Veninger

The first S4 brakes (late 86 into 87) had pistons of 36mm and 42mm.
Some time in 87 they switched to 36mm and 44mm pistons. This was to help with even wear of the pads. Both of these versions used the scraper ring setup like your top picture.

From 89 to 91 the pistons size stayed the same, but the pistons themselves were changed and used the dust boot setup like you have in your bottom picture.

borland

I purchased a dust seal for the later front S4 calipers from 928 International, a Porsche Parts supplier and RENNLIST sponsor.

The part wasn't available separately from Porsche, so 928 International got them from BREMBO USA.

A930Rocket

Here's the PET I'm looking at. They seemed to change in '86-'87 as John says.

I measured mine tonight and measured 36mm and 44mm.

I would like to go with the scrapers from the earlier version if they are still available. Installing the pistons with the outside seals, it doesn't seem they can extend out very far? I'll try 928 International.


Thanks for all the help guys!

Jim

Jadz928

Also note the manuals highly not recommend disassembling the caliper bolts. At minimum, they must be replaced, and torqued properly.

namasgt

So for future reference, does any one know if the rebuilt kit for 89 with the dust boot setup can be used on the earlier style (86.5/87/88) scraper style calipers?

I took one of my 88 S4 rear calipers off to rebuild it with new sealing ring and dust boot only to find out the pistons don't have grooves. I did not know the S4 calipers had differences, thought they were all the same until the GTS models came out.
Does anyone know if one can just buy the scraper rings for the earlier style S4 brakes? The rebuild kit with new pistons (that I don't need) is too expensive.

Thanks
Ali

fraggle

You can use the later style IF you replace the piston$$$. Early S4 calipers, (like mine dammit) have NLA scraper rings. I was screwed two years ago and it sounds like no new solutions have come up. Sorry guys. LAte '87 and 88+ should be the same.

cpayne

https://rennlist.com/forums/928-foru...2-12-11-a.html

This link discusses a change mid year 88 as noted by Bill Ball in the thread

fraggle

Whoops sounds like I've got my cross over date wrong.

I never split mine, just pulled pistons, cleaned everything and carefully put everything back. Been working great since.

namasgt

Thanks for the response,
No you did not take the scraper rings out? Unfortunately I did and they are not reusable.