Telescopic Jack
A telescopic jack is a jack structure that provides a much longer stroke than its closed length by means of nested body stages. The more stages there are, the greater the extension, but lateral flex also increases because of the clearance between stages. It is preferred on vehicles with limited ground clearance.
In the closed position, the length of the jack cannot exceed the free height under the chassis. On a single-piece jack the stroke is limited by this length. In a telescopic design, since the inner stage comes out of the outer stage, total extension can reach several times the closed length.
- Advantage: it takes up little space in the travel position and can be used on vehicles with low ground clearance.
- Cost: every stage transition means a certain amount of clearance; lateral sway increases at full extension.
- Sealing: water, sand and salt getting between the stages are the main causes of corrosion and seizing.
The choice starts with a simple measurement: on the ground you park on, compare the distance under the chassis with the closed length of the jack and the required stroke. If the stroke is not enough, rather than raising the vehicle afterwards with blocks, you should move to a jack design with a longer stroke. In maintenance, keeping the stage surfaces clean and wiping the muddy part before retracting prevents most seizing faults.
Context in which this term is used: How to choose levelling jack capacity