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Take the drums off again..give the linings a good sanding with 60 grit aluminimum oxide sandpaper.Take off some material.Take some cleaner..that evaporates..NOT varsol!,clean the drums and give them a light sanding with some light sandpaper..220 is ok.
This failing providing everything else is ok..turn the druns/replace the linings.
What PROBABLLY..almost guaranteed happenned..is that the egy' brake was left on..(probablly got "stuck" on because the adjuster was rusted)..the shoes dragged on the drum.Shoes are designed to work better when warmed up..the friction of the metal/lining creates the heat..BUT!!! they also have to cool too.With the linings dragging..they just get hotter and hotter..can't cool..and BEFORE they get a chance to wear much ..they glaze/harden..LOL..they ain't gonna wear much now.
Next question..OK THEN..why do the brakes work ok..just the emergency doesn't work eh?
1..The contact area is MUCH less when applying the egy for starters.
2.. This area being considerablly less doesn't rely on some heat build up for friction aid.It relys on the smaller contact area.This area in PARTICULAR could be glazed.
3.An understanding of the egy. brake mechanism shows that in NORMAL braking the shoes are pushed out from a central solid,HIGHLY leverged point..the wheel cylinders..with the egy almost ALWAYS 1 shoe is pushed out my a central mechanical lever..the OTHER shoe is pushed out WHEN the first shoe hits the drum..and is pushed back.
4 There is also a good chance that when the drums overheated they warped slightly.
LOL..I have been through this scenario PLENTY! of times..pretty baffling isn't it??..EVERYTHING looks ok..BUT the linings are simply heat hardened..in spots.Depending on how deep the hardening goes/is.I have fixed some with 2 seconds of sandpaper.Others..at the other end..new linings,drums.
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