One of our 2 HM300-3 (SN:3040) trucks has started dropping the bed extremely fast when you press the lever forward into the lower position. I was watching them make round when I first saw it happen so I climbed in to see what was happening. When the bed is loaded if you raise the bed up and then try to lower back down if you just barley inch the lever ahead it will go down slowly but a little too much and its almost as though it goes into float or something along those lines and just free falls down causing a shock load situation. Anyone delt with this? I looked up the control and its an electric over hydraulic setup. Could we have a bad control in the cab that is no longer able to sense the position of the lever? The other HM300 we have will allow the bed to drop but at about the last 15-20% it hits a soft stop and eases it on down. This truck isn't doing anything like that. Below are from the parts book showing the lever and the only solenoid (Part #6) I could find so far after looking around for one on the hoist system. My guess is that its one or the other or possibly a bad spring (?) in the hoist valve? What do you think?
May not be related but this thread might give you some ideas. HM400 Box Control I got a call this morning from a friend troubled about a scary occurrence on his HM400-1 articulated haul truck. It seems a couple of weeks ago his operator was on a haul when the box started going up on its own. People saw it going up and through a lot of wild gestures and such, got the... HeavyEquipmentForums
Check the dump body position sensor for loose or binding linkage. The sensor and linkage are located very near the right side dump body hinge pin at rear of machine. If linkage looks OK I would perform the dump body calibration procedure, might get lucky.
Thank you Nige. I’ll give it a look
This is worth a shot. I’ll be on the project Wednesday and will try this procedure and check the linkage