make sure it's not the rear brakes hanging up, see if they feel hot, if you have drum brakes on the back a wheel cylinder could be hanging up.
poop
If a calliper is "hanging", it could be causing the brake pads to press against the rotor and overheat the brakes. You may want to see if the calliper is dragging.
Friction from excessive braking causes heat, thus the lubricant on brakes release this burnt smell.
The clutch is slipping and needs replaced.
I advise you to perform a careful examination of your car's brake system.
Like Rubber
if you are talking about brake as in like fourwheeler brakes or car brakes the rubber part would be called the brake pad
like a condom or rain coat
when changing the oil sometimes oil can be spilled on the engine block. as your engine heats up it causes this smell. it is completely normal
The burning rubber smell in the tranmisson breaking apart inside.
sounds like your A.C. compressor clutch is locking up
tire store