Hmm, I just took the metal line off, including the fitting threaded onto the pump that it screws into. I see no check valve. There is one further up the line near the brake booster, but I think that's not the one you are referring to (and it works anyway). If I peer into the pump I can see what appears to be a flap against the opening. Maybe mine is different and has an internal check valve, or I'm missing the obvious? Anyway, I'll wait a while then will probably proceed with the removal. Thanks for the tip on the length of the wood block, that's helpful.

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1983 CD
1958 Studebaker Packard (being resuscitated)