Did you know? Swing Assembly

The following Did you know Swing Assembly article is a lightly edited reprint of an old Cranes101 blog post from 2015. We hope you will find iit nformative.

Did you know? The swing assembly that is usually buried in the pedestal of a boom truck, bucket truck or digger derrick is often times mounted output shaft up.

When the output shaft is facing up, it has the ability to fill the rotation gearbox with water. Once you have water in the gearbox, it’s just a matter of time before it destroys all the components in the gearbox.  This problem can get quite pricey.

There’s a couple of telltale signs that will help you determine if there’s a possibility of a problem. One sign is if there is gear oil dripping down from the swing motor or maybe even from the swing limit lever shaft. If you see gear oil, then it’s likely that the gearbox has been pressurized by a faulty seal. This could be in either the swing motor or brake. This can affect the output shaft seal and lead to the seal allowing water into the gearbox.

The sooner something like this is fixed, the cheaper it will be.

swing assembly boom truck
This shows a view of the swing motor from the right side of a National boom truck’s pedestal.
swing assembly brake motor gear box
Here is a view of the swing motor, brake and gearbox on the same crane from the left side of the pedestal. It’s carefully hidden behind the hoses.

We’ll be posting more informative Did you know series articles like this one on the swing assembly. If there are any topics you’d like to read more about, email us at info@cranes101.com.

Our classes cover components on heavy equipment like cranes and boom trucks extensively. Check out our Courses page for more information.

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