It may become apparent when removing shocks from a vehicle that aftermarket parts from OE suppliers can occasionally look different to the original equipment parts they’re replacing. This often leads to technicians questioning whether there’s a fault with the replacement. In reality, the reason for its difference is the opposite; they’re purposely engineered as a way to improve and optimise comfort and safety.
KYB piston rods can occasionally look shorter than the OE equivalent, making it look like the incorrect shock absorber for the job.
This is due to the fact that many KYB shock absorbers are fitted with a rebound spring; this a small spring made from alloyed steel, placed around the base of the piston rod inside the body of a shock absorber. Designed to protect against potential damage to the piston rod, the spring essentially acts as a cushion to prevent the bottom of the piston rod from hitting the top of the cylinder during full extension. Not only does this prevent damage to the piston rod – therefore increasing the life-span and longevity of a shock absorber – it plays a direct role in ride comfort and safety, working to add smoothness and stability during movements of heightened body roll.
Some vehicle manufacturers have been known to remove this rebound spring after models have been on the market for a while. If the rebound spring is missing, it means the piston rod can extend longer (sometimes up to 50mm) compared to a KYB unit which will still have the rebound spring inside.
Did you know? There are tools specifically designed to assist with fitting shock absorbers that have a rebound spring. Given the shorter length of the piston rod, there may be a need to raise the axle or suspension slightly to be able to attach the shock absorber mountings on select vehicles. These tools compress the internal rebound spring sufficiently to be able to extend the piston rod to the required length to be able to thread the top nut correctly.