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!
