This is a heads up for all ABS equipped A6 C4 Avant owners. This is a properly dangerous fault.

For a reason I have yet to discover, these cars are fitted with flow restrictors in the rear brake lines, between the caliper flexi-hose and the hardline on the trailing arm. This is a small part, hidden in the pipe retaining clip and usually caked in mud.

The scary thing is that it is made of aluminium. It is also right by the wheel, so it gets splashed by mud and road salt and eventually dissolves away to nothing. Because it's small and well hidden you are unlikely to notice any problem with it, unless it's already leaking. Neither is your MoT man.

When it fails (not if!), your brakes stop working. I was very lucky as mine somehow failed on the drive overnight and I was warned of low fluid by the car check. At that point I had no hydraulic brakes at all in spite of the fluid reservoir not being completely empty and one of the two brake circuits still being intact (just!). Not good - especially if you are moving at the time of discovery!

This is where the offending object hides. Under the mud in the centre of the brake pipe clip. This is the one than was still holding.



However, I was able to snap it off easily with finger and thumb producing this



The failed one was pouring out fluid and fell part at a single finger touch. The exposed alumium parts had literally dissolved. Just some white power amongst the mud.

My car now has 4 new flexihoses on the rear and no restrictors. The restrictors are available new from Audi only. They are still made from aluminium and fiercely expensive. No-one seems to know what they are for. The saloons don't have them. If any one knows what they are supposed to do I like to know so I can decide whether not having them is (even) more dangerous than having them!

If you follow this link you'll see mine is not the only case
http://www.audifans.net/ftopict-34187.html

Get them checked - could easily be fatal.

Nick