They make plenty of air till the diaphram tears. There's no warning, just won't be air all of a sudden. Definitely a good idea to keep rebuild kits on hand....... Rebuilding is really simple, as long as you don't have to wait for a kit.
I've just been redoing mine once a year and no longer worry about them leaving me airless. Was averaging 13-15 months/rebuild.
Thanks for the info.
I'll be ordering a rebuild kit this week.
Plus, I still have my power sucker I can use in an emergency.
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