You're most likely to be OK so long as the fluid level in the reservoir didn't get too low. But if you are already working on the rear (for whatever reason) and you haven't touched the front brakes recently I'd advocate giving them a bit of a bleed too if only to make sure that everything is fine and dandy there too.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!