Are you bleeding the rear calipers? If so make sure there's fluid in the rear reservoir by filling the master cylinder with as much fluid as it'll take and keeping the fluid level close to that while bleeding. The way the master cylinder is designed is that you need to fill it up all the way to the top to make the fluid overflow to the rear reservoir.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL