Telescopic dump cylinders: what wears them out and how to make them last
The cylinder under a dump body takes a beating on every load. Most of the damage comes from a handful of habits that are easy to change.
A telescopic cylinder is a set of tubes nested inside each other. When you dump, the biggest stage comes out first and the smallest one last. When you lower the bed, they go back in the opposite order. As long as they move in that sequence and stay lined up, the cylinder lasts a long time. Most of the trouble starts when one of those two things stops being true.
Dumping on uneven ground
This is the big one. With the bed up and the cylinder at full extension, any side load goes straight into the stages and their seals. Dump on a slope, or with one side of the truck sitting lower, and you're pushing the thinnest, most extended part of the cylinder sideways. That's how you get bent stages, torn seals and, in the worst case, a truck on its side. Level ground first, every time.
Dirt on the chrome
Every stage has its own wiper and seals, and all of them wipe the chrome on the way back in. Dried mud, concrete splatter, asphalt and sand get dragged into the seals and score the stages. Hosing off the extended stages after a dirty job does more for this cylinder than most people think.
Driving with the bed not all the way down
If the bed isn't fully seated, the cylinder carries the load over every pothole instead of the frame. Make sure it's all the way down before you pull away.
Oil, mounts and grease
- Check the hydraulic oil level with the cylinder retracted, and keep up with the filter.
- Grease the top and bottom mounts. A dry pivot side-loads the cylinder every time the bed moves.
- When the stages are out, look for rust or pitting. A pit on any stage will eventually take out that stage's seal.
Signs it needs a look
- Stages coming out of order, or one stage hesitating or jumping.
- Oil weeping at one of the stage seals.
- The bed creeping down on its own while loaded.
- Chatter or shudder as it extends.
A telescopic cylinder takes longer to rebuild than a simple one, because every stage gets taken apart, inspected and resealed. If yours is showing any of these signs, it's better to plan the repair than to have it fail with the bed full. This is how we handle hydraulic cylinder repair in Denver, and if you want a quote, this is what to send us.