the hydraulic control levers on a tow truck cause the following
complaints: the equipment moves too slowly when you depress the
lever, the equipment doesn't move at all or the control lever stays in the
on position upon release instead of returning to center.
Occasionally I see a tow truck where you have to manipulate two levers at
once to get one function to work.
First, check the easy-to-see
parts. Are the pins loose in the linkage rods? Are the pins
missing? Are the linkage rods broken? Do the linkage rods need
adjustment? All the linkage and linkage rods need to be reasonably
tight and intact, because if the linkage train contains very much play,
the control levers will hit the end of the hole in the control panel when
you depress them before they get to actuate the hydraulic valve body and
make the equipment work. Control levers that don't all line up in
the released position may need adjustment of the linkage rods. If an
individual control levers works fine one way but not the other (works up,
for example, but not down), adjust the linkage rod.
You've fixed all the above
easy-to-see parts, but the control levers still don't work properly?
Get underneath the control panel and check the axle shaft the control
levers turn on. If the axle shaft is bent, broken or held loosely,
the control levers won't work properly. When you depress the control
lever, the axle shaft will be displaced sideways and the hydraulic valve
body won't be actuated.
Damaged axle shafts are easy to
miss because they're usually covered up by the deck of the tow truck
bed. How do axle shafts become damaged? Blown-out tires, wheel
lifts that have broken loose from the truck, subframes that have broken in
half, slings that rest on top of the axle shafts, and errant flatbed
hose-track asssemblies all have the ability to damage axle shafts.
When you have to operate two levers at once to make one function work,
suspect axle shaft problems. Check for axle shaft disorders by
manually trying to displace the shaft sideways. A good shaft will
not move sideways at all.
Solve axle shaft problems by
installing new axle shafts to replace bent or broken ones, and by making
sure the axle shaft holder keeps the shaft firmly in place. It's not
enough to make sure that the linkage rods and pins are tight and adjusted
properly; in order for the control levers to work properly, the axle
shafts also have to be whole, straight, and held firmly in