Importance of Priming Shocks & Struts Before Installation

Issue: New Shocks & Struts Misdiagnosed as Damaged

Designed to function in a vertical position, Monroe shocks and struts may rest on their sides during shipping and storage. This can cause the gas charging withing a shock or strut to mix with the hydraulic fluid causing the unit’s damping characteristics to seem irregular. This can cause the shock or strut to perform erratically which may cause the installer to deem the unit defective. However, this is normal and not a defect with the shock or strut.

Solution: Prime Shocks & Struts Prior to Installation

When a shock or strut appears to be damaged right out of the box, it may be necessary to prime the unit before installation to counteract any adverse effects from being shipped and stored in a horizontal position. Priming a shock takes the gas from the working chamber and moves it back into the reservoir. Designed to avoid loss performance and noise issues, priming a shock can be completed in 3 simple steps.

How to Prime Shocks or Struts

These steps can be used for priming or checking the rod reaction on twin-tube shocks or struts. Monotube shocks don’t need to be primed since their single-tube construction comes with a high-pressure nitrogen gas charge.

1. Make sure the unit is at room temperature.
2. With the rod facing up, cycle the unit from full extension to full compression two to three times.
3. Fully compress the unit and allow the rod to extend on its own. This should require less than 45 seconds on a unit with normal gas pressure and up to two minutes for a low-gas unit. To avoid damaging the valving, avoid using excessive force to compress the unit.

After priming the unit, there should be no lag in control or dead spots while cycling through the complete stroke. Once the shock extends to these specs, it is ready to be installed on the vehicle. Please note that non-gas units won’t extend and that it is not uncommon for two like units to extend at different speeds until it is broken in.

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The content in this article is for informational purposes only. You should consult with a certified technician or mechanic if you have questions relating to any of the topics covered herein. Tenneco will not be liable for any loss or damage caused by your reliance on any content.