That's a weird one!

May be a bad booster, but the only time i've seen anything like this it was a bad master cylinder failing to release the pressure in the lines after application. The resultant heat from dragging calipers then causes brake application as the fluid expands.

I would flush the fluid with top quality DOT 4 fluid and verify that all the calipers are working properly, especially the rears -- the temptation to put new pads on old worn out rotors will cause the pads to bind when the contact the anti-rattle spring, and they drag and heat up. That should not cause you problem since the plunger in the master cylinder should be above the fill bore, but if something is wrong there, you could be getting improper release.

Check for correct positioning of the brake pedal and correct installation of the master cyilnder, too.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!