holds pressure for using the brakes when the motor isn't running
The brakes in these cars have a hydraulic assist system, instead of the normal vacuum booster type. therefore, if the engine is not running, the hydraulic pump is not running, and there would be no brake assist (say, if the car died on the highway and you still needed to stop). The bomb accumulates pressure while the motor is running, and uses that pressure so you can still have full brake assist with the motor off. It also slightly improved brake feel when I changed it on my car.
1997 Audi S6 - Tornado Red on Ecru
RS2 with MTM Chipset
Porsche 928 GTS "big blacks" with 2 piece 993tt rotors
S6+ euro sport springs and Boge shocks
e-code xenons with range control motors
1990 Audi 90q 20V - The Back-up
1991 Alpina B10 BiTurbo - The Hobby Car
1992 VW Passat Wagon Syncro - The Wife's
It also effects the braking while the engine is running.
Tim - Fishers, IN
I don't own an Audi anymore, but stop by semi-annually. 07.Cooper S, with stuff 05.Subie Outback XT 55.****** CJ5 94.UrS4 - with stuff (sold..sniff) 99.A6Aq - (sold) 88.80 - The Duke (sold)