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Does manually hand-testing shock absorbers have any validity for checking if a shock is good or bad? Does hand-priming shock absorbers help?


I usually hand-prime shock absorbers that I feel are acting inconsistently or behaving not as it should. Usually they are shocks that have been sitting on the shelf for a long time, usually sideways, so it causes issues with the fluids in the shock.

Shock manufacturer I contacted states that it does not have any validity as to the status of the shock, nor does it help the shock in any way (i.e. for "priming" before installation) due to the forces it sees (or doesnt see) when hand-priming.
Basically was told that the only way to see if a shock is good or bad is to check for any leaks or to install the shocks on the vehicle and check for noise during operation.

I see installers have videos showing how to manually cycle or prime the shock absorbers before installation. I assume this means that they can see a benefit of some kind.
Also lots of people on forums and whatnot have posted about priming the shocks and reasons as to why and how it helps the shock absorber.

My Experiences:

I have personally tried hand-priming shocks absorbers and:

  • Noticed significant changes to behavior in my hand-tests among most of the shocks I hand-primed. Most of the time, they become much more firm and consistent.
  • Minimal or no changes in ones I suspect were faulty. They had "dead zones" and behaved inconsistently before installation and even after riding on them for a while.

Example: I take off a pair of shocks that are the same product/model from a vehicle that has been riding on them for a while and hand-test them. The 1st is extremely firm and very consistent/smooth while the 2nd doesn't provide nearly as much resistance, is very inconsistent, is not smooth (has dead-zones).
Ignoring how it performed on the vehicle for this example, does the hand-test have any validity here?

I understand that hand-testing is not nearly as effective as a test on the vehicle or a shock dyno. But that is not what I am asking. I am only asking about the validity of hand-tests on its own merits, and not about hand-tests in relation to other tests or anything else.

Feel free to edit my question to make it better or make suggestions.


  • By hand, not really, the vehicle will test them far beyond what your muscles can provide. By hand one might feel better than the other but is not a real world test, A better test is to mount them on the vehicle and bounce that corner of the vehicle up and down several times as hard as you can, let go of the corner and see how fast it comes to rest. By the way after a shock is mounted and put in service it will self bleed all on its own. – Moab Apr 28 '16 at 0:41
  • @Moab I understand that the vehicle will "test" them much more effectively AND that it will self-prime more effectively, but my question is more about whether or not the hand-test can give indications that the shock is bad or not at all, as opposed to whether or not hand-testing is a good way to test shocks or if it is an effective way to test shocks. this is particularly in relation to my situation where I took off a pair of shocks that should behave the same, but hand-testing them showed drastic differences in consistency, forces, and noise. – agent provocateur Apr 28 '16 at 17:08
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"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!

  • Thanks for that. However, I wanted to know more about how a hand test can give indications of whether a shock is good or bad, not whether a shock that is bad can pass a hand test. I already understand that the hand test is not nearly as effective as a on-vehicle test of any kind. But does that necessarily mean that hand-tests are completely ineffective and unable to give any indications of failed shocks in any situation? – agent provocateur Apr 28 '16 at 17:08
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    Clearly a shock that fails a hand test is trash. Any shock that's leaking oil is also trash. So yeah the hand test has at least some validity, but as jeepCherokeeRS states, its not a very comprehensive test.. – zipzit Apr 28 '16 at 17:52
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    As Zipzit has stated, a failure of the hand test in most cases is almost always a positive failure of the shock. – Jeep Cherokee Rescue Society May 3 '16 at 12:42
  • @zipzit I would agree that if a shock "fails" a hand test, it is probably trash, but the manufacturing company's engineer (i believe he was an applications engineer) strongly disagreed with me, saying no matter what results you find from a hand test, it does not have any correlation to the shock being good or bad overall. In the end, I still disagreed with him and I warrantied the one I thought was "bad". The new one worked like the ones I thought were "good" both on vehicle and off the vehicle (hand test). – agent provocateur Feb 22 at 22:28
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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

enter image description here

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.

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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.

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