At 04:42 PM 3/26/2009, Blake Heinlein wrote:
>   1. Axle is bent

No opinion except not likely.  Don't know enough.

>    2. Hub (part with the wheel studs) is bent

Ditto

>    3. Something wrong with wheel bearings

Ditto

>    4. Something wrong with proportioning valve to rear wheel

Strongly believe not -- opinion, not authoritative.

>    5. The axle nut is not torqued correctly

That can wreck your splines, but I don't believe it would cause this.

>    6. Brake pads don't seat properly in the drums (i.e. the
>    curvature radius  is different)

If radius too small they'll just seat on the high spot.  If too
large, they'll seat on the ends.  In either case I can't see them
tripping on the rotating drum, which they'd need to to make them jump.

Three thoughts:
a) Look for a bur or foreign material stuck to the hub/drum mating surfaces.
b) Check runout and wobble on the hub using a dial gauge and magnetic
stand.  Compare with other side.  For cheap substitute for dial
gauge, use a piece of chalk on a stand and compare length of
marks.  Measure wobble at same radius on hub, of course, near the
edge.  For runout, clean rust off the edge or if necessary measure
against a shim held at the base of each stud.  You'd need the gauge for that.
c) Swap drums left to right to isolate problem.

d) (bonus) I've had a set of drums wrecked by shop that turned
them.  Shop owner (an acquaintance) suggested that VW drums with thin
inner rim don't mate very reliably with American drum lathes. I have
no opinion on this opinion.
d1) It's perfectly possible to get a bad new part.

  --
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'89 Po' White Star "Scamp"