“Hey, I bought some new shocks from you, but one of them doesn’t seem to work.”
“This new shock only has hydraulic action in one direction.”
These are common concerns the shock experts at KYB hear from customers after they buy new shocks. According to the KYB guys, it can take some convincing to assure the customers there’s nothing wrong with the new shock. The truth is the shock has probably been just “laying around” too long.
Here’s the deal:
More than 85 percent of all vehicles are equipped with twin tube style shocks and struts. Twin tubes have an open space inside so that the hydraulic fluid has someplace to go during operation. That space is pressurized with nitrogen gas to reduce foaming as the fluid is agitated.
Since there’s a top and bottom to these shocks, they’re designed to work vertically. During shipment, or while the new part is lying sideways on an inventory shelf, the nitrogen gas within the shock will have a tendency to push its way into the hydraulic working area. When that happens, the first few strokes are going to feel like the shock isn’t working.
The fix is simple. As the new shock is exercised, the nitrogen gas will be pushed back into the reservoir and the hydraulic fluid will stay where it belongs as long as it continues to stay vertical.
Although not required, the shock can be “primed” before installation: Hold the shock vertical (normal installation position) and then stroke the shock to fully compress it and then fully extended it several times.
The first movement or two may feel like the shock isn’t working due to its low nitrogen gas pressure that sometimes seeps into the hydraulic area during extended horizontal storage. If this procedure is not performed prior to installation, noisy operation and loss of performance can occur for a short time. The shock however, will begin working normally after several strokes or as the vehicle begins driving.
Again, shock priming is not required, but it’s quick and easy and can help reduce any “break-in period” for your new shocks.