Vilhuer

Possibly because piston shape was changed due to seal type change. Early style pistons have straight outside and dust seal is on caliper side while late style dust seal is partly on piston and partly on caliper. See 1989 S4 service info tech for diagram. Text in it is not absolutely clear but I would interpret it so that same silencers would work on both early and late version as long as pads are thinner asbestos free version.

Nicole

OK, so you guys figured out the size of the front pistons - what is the size on the rear?

jon928se

Each fixed caliper 2x30mm and 2x28mm

The earlier question would have been easily resolved with a picture of the normally visible side of the caliper - raised "PORSCHE" letters means old seals, stuck/painted on "PORSCHE" letters means new style seals with what looks like smaller dia pistons, until you pop the seals off and measure the actual piston and not the sealing groove on the piston.

Hilton

You can determine the pistons you have by the size of the hollow middle section.

There's a Technical Service Bulletin from '89 that lists the inner and outer dimensions of the various pistons, and you can tell which you have by just taking out the pads and unbolting the brake caliper to get some vernier calipers in there.

I saw it the other day when hunting for similar info.. Bill Ball posted it in this thread here: https://rennlist.com/forums/showthre...+raised+brembo

edit: FYI my calipers have raised Porsche lettering, but are made after the changeover during '89 to the newer piston type. There's a note about the VIN cut-over during '89 in that same service bulletin.

jon928se

You could have just rung me up LOL. It was in the back of my mind that it wasn't quite as clear cut as rasied letters or not.

Do you have the front X member out yet ?