Master Cylinder Swap, Euro-S to S4

Master Cylinder Swap, Euro-S to S4

For anyone who is interested. I finally have the information I was looking for to hook up the S4 brakes and S4 MC to my 80 EuroS track car. I took a careful look at the 928 Workshop Manual and found out the following information. Up to 1983 the 928 used a diagonal braking system with two bias valves and a single bore MC with a 23.81mm dia.

Starting 1984 the system went to a conventional front/rear braking system. ABS was an option integrated into the conventional system. The MC changed to a dual bore. 23.81mm/19.05mm with a single bias valve screwed into the front port for the rear brakes.

Starting with S4 brakes and also with GTS brakes - a MC with a dual bore of 23.81mm/20.64mm with ABS standard from 87 on.

So the correct hook up will be to install the S4 MC and hook both front calipers to the rear port of the MC which is 23.81mm. Hook both rear brake calipers along with a bias valve to the front port which is 20.64mm

John Veninger
1990 928GT
1980 EuroS (losing weight!)

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