Power Take-off (PTO) to Hydraulic Pump Connection - Out of Sight, Out of Mind

One of the most important (and most often neglected) components of crane operation and maintenance is the connection between the power take-off (PTO) and the hydraulic pump.

While you are swinging trusses with your National Crane 8100, an impressive 23 ton capacity, 60,000# GVW machine, or lifting a co-worker in a basket on the end of your National 1300H, be aware - the entire crane operation is utterly dependent on a rather simple looking, 7/8" - 1 1/4" thick, 18 inch long piece of machined steel with 1/4 inch splines; humming along under the truck engaged with it's transmission.

If the humming stops. So does your crane.

Most machines in use today use a direct mounted pump which eliminates the need for a drive shaft between the pump and the PTO. While this does provide a nice clean installation, it is not maintenance free. Pumps today require 200 - 450 horsepower to run your machine and this conversion of power to crane operation is accomplished through that 7/8" - 1 1/4" diameter "splined shaft".














New shaft and splines on top, well worn shaft and splines below.


To make matters more interesting, the connection is NOT lubricated by the PTO or the pump at their connection area. This critical connection must be manually lubricated and it requires hi-temp grease. Hydraulic systems can run 100 degrees over air temperature - a point that is sure to melt out standard chassis grease. Some PTO's do have a greaseable shaft, but most of the time there is no zerk or aperture to get to this connection. The only alternative is partial removal of the pump in order to get the lubricant to the point of contact.

Proper inspection and servicing of the splines on that shaft will greatly reduce the possibility of spline failure which WILL result in a complete loss of crane/outrigger operation - certainly at the worst possible time in the middle of a job. The splines are subject to wear under the extreme pressures and temps in which they work and at some point, with enough wear, the splines will be unable to mesh or may distort and thin to the point of snapping off. If the splines happen to give while your crane is open and working, you will not be closing it without help from a crane service company - most towing companies are not experienced or equipped to handle crane recovery.

Most manufacturers recommend inspecting and servicing the splines twice a year. Our shop technicians provide this service and we recommend it to our customers when they come in for their annual crane inspection. Our experience has taught us (and we highly recommend) shaft replacement at 80% + wear on those splines

If you don't know or can't remember the last time your splines were checked, get the maintenance scheduled for safety sake and to head off a sizeable repair bill. Crane repair, after-the-fact is always costly.