Porsche Enthusiasts Club Forum

I have been offered some S4 front brake calipers that need a refurb due to some seized pistons.

I noticed that none of the pistons have dust seals -- is that right? I thought all S4 calipers had dust seals on each piston.

any insight you can give will be appreciated

Yes they should all have dust seals, but if you are refurbing calipers they should be replaced anyway.

Porsche sells repair kits which include the seals for a few quid. Different part numbers for the different piston sizes.

Hi

As has been said they get new seals on the refurb....BUT unless you are doing yourself , do you realise how much its going to cost for the refurb ???? it AINT CHEAP....

Plus , if the pistons are seized in the bores, the refurb company may well tell you they are scrap


All the best Brett

guys -- thx for the heads up.

calipers with seized pistons are probably scrap then!


now a 2nd question (double points for answering it!):

I notice from the parts manual that there are 3 types of S4 calipers, the earliest with 36 & 42mm pistons and 2 later types with 36 & 44mm pistons. Might anyone know what the difference is between the 2 later types?

Hi

I would GUESS the later ones are either for the GT or GTS ???

All the best Brett

right I think I have cracked it, the Porsche parts catalogue is very helpful, there are actually 4 types of S4 calipers . Each caliper does have a year of manufacture cast into it so that will help with indentification if you get landed with a pair.

1) the earliest S4 calipers are in fact from the previous model of 928 with 36 & 42 mm dia pistons. ie they used the parts bin up to 1987 ish (part nos: 928 351 421/2 00 for left & right calipers)

2) the next type produced until 1988 has the larger 36 & 44 mm dia pistons BUT uses a different dust seal (the dust seal is smaller than later models, so it does do not fit calipers made from 89 onwards) (part nos 928 351 421/2 01 for left and right)

3) Type 3, is as 2) above but made to 1991 and has the larger improved dust seals (part nos 1989-91 928 351 421/2 03 for left and right)

4) Type 4 is as 2) above but made from 1991 onwards and also has the larger improved dustseals. Not sure why it is different than Type 3 BUT it has the same part no and uses the same dust seals.

COST OF REPAIR KITS
This is where there is a catch:

Type 2 repair kits for all 8 pistons will cost at least £250, depending on how good you are at getting discount from an OPC

Type 3 & 4 calipers are out there in much greater numbers so the repair kits are much cheaper. Cost of repair kits for all 8 pistons is just over £100, again depending on how much discount you can get from your OPC.

a prize will be given if you get this far, without nodding off!

The GT and S4 have the same brakes.
The GTS has larger front brakes.

I spoke to my local OPC parts dept today (JCT 600 Newcastle). They told my they no longer stock any 928 parts on the shelves and all items are ordered in. I know the former flagship is more reliable than the rest of the range but I would have expected them to keep service items in stock.


Stephen

I took a bit of a punt and bought a used pair off eBay yesterday not knowing which variant it is...should arrive shortly.

Where is the year of manufacture stamped on the calipers?

if you imagine the caliper is made of 2 halves, the date stamp is on the surface at the top/bottom of the caliper that points towards the other half.

That is the case for the 944 as well, even filters etc. they order in. To be expected TBH, how many will they see for even a service?

Not all these calipers have dust seals, some have scraper rings.

Rich

Happy to report that my purchased 2nd-hand calipers appear to be Type 3 as per Paul's description above.

Given that they were acquired used, is it prudent to take out and rebuild the pistons/seals or can I get away with leaving them in if visually they look OK? Would rather not have to spend the time/money in taking the pistons out, and possibly rebuilding the seals, if not needed.

if the pistons are not seized, plate lift is not significant and no leaks when first used then just get on and use them.