Originally Posted by
tq_danpatterson
You wouldn't think it would happen because the oil inside can obviously go through the piston holes, but an overfilled shock will actually be nearly impossible to completely compress.
The issue is that the shock shaft is displacing volume.
Take a top fill shock and remove the cap and bladder. Push the piston almost to the top but still below the oil and note the level. Now pull the shaft down and you'll notice that the oil level decreases as well.
Bladders help, but you have to get the initial fill correct. The bladder usually doesn't displace the same amount as the shaft.
Some shocks when built correctly but without springs, will be easy to fully compress and expand, but will slightly come back out on their own on the compression, AND slightly pull the shafts in when fully extended.