UrS6 Brake Master Cylinder

[waveydavey]

My A6 has HP2 struts and brakes fitted and the brakes have never been that great since the conversion. Now the brake pedal continues to sink when pressed so I'm thinking the master cylinder is probably a bit tired after 200k miles and could do with replacement.

Rather than just replace with a new standard cylinder I'm wondering whether an urS6 one, with it's larger bore and being the right one for the front calipers, would be a straightforward plug and play swap. Can anyone confirm this and suggest a supplier as I'm struggling to find one through the usual sources.

Cheers

David

[A1QSHIP]

Some of the later S6 brake master cylinders have a larger pipe fitting than the earlier S4 brake master cylinders. Do not know how that works with an A6. Watch your vehicle production dates for the correct part.
HTH, Chris

[waveydavey]

Strangely a search for a master cylinder for an urS4 brings up a couple of results with the 25.4mm bore. My car is a 95 with the two ports the same size so I think I should be OK with the S4 cylinder if it is a straight swap.

[popdemonic]

It's normal if you upgraded the larger calipers whilst retain the stock MC.you'll end up having longer pedal travel.
A6 has smaller MC than UrS6. It pedal was sinking whilst depressing it's something leaky or airlock in the system.

[recurveandy]

I upgraded to HP2 brakes and retained the standard MC
Can't say I noticed any more travel in the pedal, however I swapped the reservoir and gave the system a full flush, including pulsing the ABS whilst bleeding
How old is your fluid? Mine came out black

[waveydavey]

My brake fluid has been changed quite a few times over the years so it's still pretty clean.

I'm intrigued by the ABS pulsing you mention. How do you do that?

[recurveandy]

You need to run the return pump, V39
Unplug the connector to the ABS unit and hook up a spare battery to pin 11 (I think) and run the pump for no more than 60 seconds
Alternatively, find a quite slippery road, gravel track, playing field etc and give the ABS a good work out.