Spent some quality time with ETKA, found the following part numbers and applications for "Brake Pressure Regulators", what we are calling proportioning valves. 533 612 151 cabby, from 15-E-011 291 (84.5 up??), same for 'rocco, 8V 533 612 151 A for 16V 'rocco Both part numbers screw directly into the master cylinder in line with the rear brake lines. 179 612 151 cabby, up to 15-E-011 290 (up to 84.5??) is the load sensitive valve, bolts to the body, a spring connects it's lever to the rear beam. It is adjustable. Cryptic spec numbers for A1 master cylinders------ Cabriolet; 171 611 019 N, up to 15-E-011 291 (up to 84.5??) Remarks, 20, 64-16/14 191 611 019, 15-E-011 291 (84.5) to 15-L-015 000* (up to '90??) Remarks, 20, 64-16/14 357 611 019, 15-L-015 000* ('90 and up??) Remarks, 20, 64X16/18 Scirocco: Same three part numbers, production numbers are 'rocco relevant, similar to Cabby, one additional master cylinder, 533 611 016, for 16V applications, Remarks, 22, 2-17/15. (note the asterisks above, typed as found in ETKA, no explanation readily apparent.) (Also note the change in "Remarks" notation style from "20, 64-16/14" to "20, 64X16/18", again, no explanation as to the significance of these figures nor the difference in notation style.) The "20" is most certainly the cylinder inner diameter. My best guess is the other numbers refer to mounting flange dimensions. Then I read the 16V 'rocco Remarks, now Remarks make less sense........ '93 A3 uses a 23.81mm master cylinder with an adjustable, rear mounted proportioning valve, some models with ABS as well. Front rotors; A1 8V, 239mm A1 16V, 256mm A3, 239mm, 256mm, 280mm, 288mm, (last two are 5 lug) Rear rotors; A1, 226mm, 4 lug only A3, 226mm, available both 4 and 5 lug. 8V drum brake park brake cables, 171 609 721 C, quantity, 2, no lefts or rights shown, assume same side to side. 16V Scirocco disc brake park brake cables: 533 609 721, quantity, 2, no lefts or rights shown, assume same side to side. Front calipers; with 239mm rotors 171 615 123 B, left 171 615 124 B, right with 256mm rotors 357 615 123 AV (or suffix "AX", "X" for exchange??), left. 357 615 124 AV (or suffix "AX", "X" for exchange??), right. (16V Scirocco, Audi 4000 also used on some models) Spent some less quality time in A1 and A3 Bentleys, found A1 rear drums are 180mm (approx 7.1") diameter. A3 drums are 200mm (approx 7.9") diameter. A1 shoe width from ETKA is 30mm, A3 shoe width is 40mm. ___________________ Thread Swapping to 200mm A3 rear drums should logically present the same brake balance problems as swapping to rear discs [b]IF[/b] the stock 239mm front brakes are retained. A3 drums will also be heavier adding both rotational inertia and unsprung weight. Rear rotors should be lighter than even the stock 180mm drums, decreasing rotational inertia, although the weight of the complete rear disc conversion may be greater than stock, if so, unsprung weight will increase. Anyone that has experienced drum brake fade during spirited mountain driving will appreciate rear discs, as will those that have gotten nervous waiting triple the distance for drums to dry enough to be effective during a long freeway drive in heavy rain. ALL wheel cylinders will eventually leak with normal use unless they get replaced prior to this eventuality. Frozen wheel cylinders are extremely rare, I've seen maybe 6 frozen wheel,cylinders in a 37 year career. Calipers seize more commonly, rare here in the snow free West. Caliper park brake levers seize no matter where, probably VERY common where there is real Winter and salt on the roads. Caliper leaks are very uncommon, about like frozen wheel cylinders, again, maybe 6 in 37 years. Park brake cables shouldn't even be a problematic issue, on cars 13 years old and older they are likely stretched considerably and ought to be replaced anyway, drum or discs. If either A3 rear drums or rear discs are swapped in, suggest also swapping fronts to 256mm rotors and matching calipers along with 'rocco proportioning valves.