This page: How to check and replace a tyre's or inner tube's valve core.
Tyre valve cores.
How to check and replace in the event of a slow puncture.
Please note: All advice on Old Classic Car is just that, advice. If you have any doubts about your own abilities when it comes to working on your car, I'd recommend getting hands-on advice & help from someone who is used to working on old cars. I can't accept any responsibility for mistakes you make, or things being damaged as a result of your working on a car after having read articles on this site. If in doubt, check with a marque expert first. You can find contacts for owners clubs in the club directory (see homepage).
From time to time, a tyre (tire) on an old car of mine might develop a slow puncture - in other words, it loses air over the course of several days. Air leaks can be caused by a number of issues. Perhaps the most common is the simple puncture, where a sharp object such as a nail, or a piece of glass, has punctured the carcass of the tyre, and - if applicable - the inner tube within. Tubes can often be repaired or replaced at home, using no more than suitable tyre levers and strength. Where a tyre that doesn't have an inner tube is punctured, this repair is best left to a tyre repair shop.
Over the years I've also found that many tyres that lose pressure over time, do so as a result of the valve core - ie the assembly within the valve - developing a leak. Fortunately, they can be straightforward to test and replace. All you need are a few spare valve cores (for example the Schrader type) and a suitable tool to remove the core from the valve. Obviously a footpump, or tyre inflator, will be required afterwards to re-inflate the tyre once the valve core has been swapped.
I put the following video together to show how I checked and replaced a couple of the tyre valve cores on my old Volvo, I hope it proves to be of use. If you have any comments to add to the video, please post them direct to the Youtube video below, thanks.