Back in the days, when Time Capsule was full, it automatically deleted old back ups to make space for the new ones. Recently, it just doesnt do that anymore, ...
Indeed.. it is a problem.. Mainly due to annual OS upgrades and large patches.. we can no longer delete enough to allow TM to work so it just packs it in.
Like, it just stops at say 8/16 GB and doesnt back up any further. What to do?
Like. this is confusing because you used like too many times.
If you did an erase of the TC and you cannot backup your computer beyond 16GB before it stalls.. then either the disk of the TC is actually bad.. or your computer drive is bad.. or you have some strange issues going on with network.
To go through each in turn..
1. Tell me what OS you are now running?
2. Do you connect to the TC with wireless or ethernet? Let me strongly recommend ethernet as wireless on a gen3 or earlier TC is slow.
3. How much capacity is used on the Mac internal drive?
4. Do a proper test of the Mac disk
You cannot properly test a disk that is your boot drive.. so it is best to boot to recovery on the Mac and run first aid from disk utility across your disk. Fix any errors. I would certainly be careful with this if the computer is old laptop, the drives become pretty poor and you might be well advised to do a different sort of backup first.
ie buy a suitably sized USB drive and use a backup software like Carbon Copy Cloner.. and create a bootable clone of your Mac.. this is before you scan the drive. Test the clone by booting from it to ensure it works..
If you have multiple Macs you will need multiple boot drives.. but if they are all similar era they all might boot from the same one.
5. do a one pass erase of the TC..
This will check the actual TC disk.
Mostly your TC is now too old .. It could be Gen1 or 2 or 3.. The hard disk in the TC Gen3 is a samsung spinpoint and they are not great drives.. even the WD in the Gen2 was not great.. the Hitachi in the Gen1 was the pick of the bunch.. but that is 9 years old now.
Honestly it is time to upgrade your backup hardware. If you want a backup you can trust.. buy a couple of self-powered USB drives.. one for each computer and use that..