I want to delete the servo from a braking system.

When it comes to calculating the new push-rod length, is it simply a case of subtracting the length of the servo unit from the original?

Cheers.

Assuming you have a servo + mcyl assy (otherwise known as a "duplex" ), the mcyl is mounted onto the servo front face. When you delete/remove the servo, the mcyl should then mount onto the face previously occupied by the servo. For practicality, I would recommend using a threaded input rod, with a suitably threaded clevis plus & lock nut. That way, you'll be able to adjust the connection to your pedal to suit the installation.

BUT - using a previously servo-boosted mcyl in a non-boosted manner, will give rise to increased pedal "feel" (i.e. increased pedal loads). You might have to change the mcyl bore size.

[Edited on 7/11/16 by Dick Axtell]

[Edited on 7/11/16 by Dick Axtell]