Hand-testing Shock Absorbers

"Hand priming" or actuation is effectively worthless as a gauge on the performance of a Shock/Strut Assy. Only when severely damaged or out of service will the activity show any truly noticeable difference. And by priming the shock, you're effectively wasting your time. It will do so on its own. The reason why this "works" is occasionally air or gas may slip into the hydraulic stage of the shock. When you actuate the shock, you move those bubbles that can occur during shipping back into the air/gas stage. The vehicle is perfectly capable of doing this on it's own.

Shocks can be bad and still pass a hand test. What is important is the shock's performance on the vehicle. There are various methods to test shocks, however the best method is thorough road test. Take careful consideration to notice any noises, or nuances in the vehicle's performance on different road surfaces. A "bounce and jounce" test (where you bounce the vehicle's corners while stationary) works to some extent, but will not test the fast stage valving in the shock and you may miss road handling characteristics that may be unfavorable/noisy or otherwise undetectable except during normal operation. Experience with vehicle mechanics, particularly suspension, is certainly worthwhile when it comes to determining if a suspension component is bad or not.

I certainly hope this helps!

Hand Priming Shocks of Various Dampeners/Struts is Urban Legend

This myth has been perpetuated over time and has gained legs and therefore credibility.

Yes, it's true that the gas and oil separate on the shelf lying horizontally. It's also true that they separate on the shelf if stored vertically, piston rod up or down.

But it doesn't matter. These shocks are twin tube shocks. The oil and gas are separated. If you have some gas below the piston it will work it's way to the top upon operation.

Here's an image of a 'twin tube' shock

The 'dead spot' on first operation after a period of time not in operation is normal. You can feel it in steering dampeners, struts, shocks and motorcycle forks. It's just more prominent in feel when there isn't a spring as a component due to the lack of resistance to operate it off the vehicle.

Citation

Here is a write-up from Gabriel (shock manufacturer) declaring that their shocks do not require priming. Which is true, they just fail to state that the competition does not require priming either.

Here's an article from Onallcylinders.com that says, "you can do it but it's not necessary."

As far as my knowledge is concerned and based upon some of the citations I've provided I would call this a Red Herring. I'm sure there are plenty of others who will disagree.

Yes, a loose shock can be hand tested, but the question is what does this test tell you? As there is more than one set of metering holes a hand test will only check those involved in dampening the gentlest movements. So it is only a partial test and its results can be confounded if there is gas in the shock's oil it may only tell you that there is gas in the oil. It still is better than nothing. Bouncing the car manually is better as the forces are greater. Driving over a bump has greater yet forces and is a realistic test.