[geoffbaltz]

Can anyone educate me on what the numbers on the brake proportioning valve mean?

From the 944/Turbo Factory Manual:

A braking-force booster is installed for the rear-axle braking circuit of the 944 S and 944 Turbo.

The changeover pressure differs.
944S: 33/5
944S2/944 turbo: 18/5
924S and 944 are not fitted with braking-force regulators.

Identification
Changeover pressure and reduction factor stamped on regulator.
33 or 18 = changeover pressure in bar 5 = reduction factor 0.46
(check correct correlation).

Notes on Assembly
It is essential to ensure that correlation is correct. Under no circumstances may braking-force regulators with a different reduction factor (e.g. 3 = 0.3) be installed.

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I have been told to go with the 33/5 on my turbo instead of the 18/5 for more breaking to the rear of the car.

What does the changeover pressure and the reduction factor mean?

Thanks!

-g