Models with ABS should be used with care, the battery should not be disconnected before any of the hydraulic unions of the braking system are removed and it should not be reconnected until the hydraulic system is reconnected and the fluid tank is filled up otherwise air may get into the hydraulic unit and the hydraulic unit will then need to use special Audi/VAG test equipment to bleed it. Prior to the commencement of working, know the risks of hydraulic fluid. To reduce the loss of fluid during the refilling of any pipe or hose, initially take off the master cylinder reservoir cap and cover it with polythene or brake hose clamp is to be used in case of flexible hose, however, metal brake pipe unions must be filled with a cap or plug as soon as it is disconnected. Where any union is disconnected a rag is placed to receive the spilled fluid. To remove a flexible hose, unscrew the union nut of the brake pipe then take off the spring clip holding the hose. One should employ a brake pipe spanner the right size when unscrewing union nuts; when none is available a close fitting open ended spanner might work but it should be used carefully not to round off the nuts. A self-locking wrench might be required in some stubborn unions, and nut and pipes which have been damaged need replacement on re-assembly. Clean the union and immediate surroundings before disconnection and always make good notes on connection in case this is not the only union. To renew a brake pipe it could be obtained via Audi/AAG dealers and cut to length with union nuts and end flares fitted and then bent to run in the same direction as the original. Alternatively, motor accessories stores are able to produce brake pipes using kits, but they have to measure the original really carefully. When refitting, make sure that union nuts are not tightened too hard since a good joint does not need to be tightened hard. Properly route the pipes and hoses without bending them, clamp them in the given clips or brackets, and, when it is completed, take out the polythene cover on the reservoir, bleed the hydraulic system, rinse off the spilled fluid and verify that there are no leaks.