My '84 does the same thing.  The brakes work fine in normal situations, but I have twice bottomed out the brake pedal on fast downhill stops.  This situation is helped by proper adjustment of the rear brakes (do the automatic adjusters ever work?), but even right after adjusting, the brakes seem a bit "iffy".  I have wondered if the pushrod on the master cylinder is mis-adjusted, but I have never been able to see (or even touch) it to check.  Bentley says to adjust this before installing the master cylinder.

Bill

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 My 1982 Westfalia's brakes have always traveled about 1/3 to 1/2 down
 before feeling meaty, but they work perfectly well (30k of driving over
 mountains, etc.). They've been bled a number of times, and had shoes
 replaced, etc.  Do other people's brakes actuate higher up on the pedal
 swing?