DUMP TRUCK PROBLEMS

Priming here

https://www.justanswer.com/medium-and-heavy-truck/i1m0k-manual-fuel-pump-primer-5-9l-cummins.html

More here

https://www.google.com/search?q=1999+Ford+F600+prime+lift+pump

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They are a fine US company, phone their Support Department. Doesn't the pump go into reverse to lower the bed?

https://loadtrail.com/contact-us-2/

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Amber,

Since your dump bed is not a dealer installed option, it could be anything.....Do you know who installed the dump bed? From your post,....it sounds like you experienced a hydraulic fluid leak as motors don't have any fluid in them. You need to take it to someone who can check out the hydraulic system and troubleshoot the drive motor if it isn't working...also I would bet money that you hydraulic system is empty of fluid! Shops that work on large trucks (ie garbage, dump, or other trucks with wet systems...wet meaning hydraulic systems that do something on the truck) should be able to diagnose and fix your problem. good luck

Your hyd system has manually operated bleed valve that will allow you to retract the cylinders. Opening this bleed or dump valve will allow the oil to return to the tank as the springs pull the the jacks up. The dump valve will be opened electorally when you normally raise the jacks. This dump valve may be leaking by or the manual valve on it may not be completely closed. You did not mention whether all jacks affected or just one. If only same jack affected, problem may be with just that jack. These are one way pressure cylinders; so if jack cylinder seal is leaking, there should be oil visible on the ground or on jack cylinder. If you have additional problems contact the HWH service center for troubleshooting. They are very helpful and back there product exceptionally well.

You need to have the hydraulic control valve checked.

http://www.saltdogg.com/Support/

Well, if you are not leaking fluid everywhere it can only be 2 things, either the cylinder is not holding pressure internally or the pump is not making enough pressure. I would start by getting the cylinder rebuilt, this is common and usually cheaper than having the pump rebuilt.

I'm guessing this is a power up, gravity down system (pump runs to raise the trailer, and doesn't when it's let down). Should be a check valve on the pressure side, and a solenoidal actuated return valve on the fluid dump side that lets fluid back into the tank from the hydraulic cylinder. It could be a bad check valve, or a bad seat in the return valve.

I'd avoid tapping into the vehicles electrical system or it can mess with computers. Take power directly from the battery. use either a three way switch, using the center as "neutral". This can be wired with "normal" gauge wire. Run a larger diameter power wire to a pair of relays, each connected to the switch. Attach the "up" power lead from the pump motor to one relay, the down to the other. Attach ground wire to the chassis.
You also have the option of using two independent push buttons instead of a three way switch...each would then serve one relay.
If you want to get fancy, you could put fuses or breakers in the power lines as well.

you either have a pump problem or a relief valve not working right. if your relief valve is integral with the pump you will have to tear the pump apart and either clean the trash out or rebuild valve. same for the pump if bad.