Dump Truck Stalls

[Village Idiot]

Geez this site is addictive.

I bought a '94 GMC 3500 with a dump bed. The dump hydraulics are run by an electric motor (not PTO) and even when the bed is empty the truck nearly stalls when lifting (hey it was cheap!). If I rev the engine the lift works fine. Since I've never had an electric hydraulic pump I'm not sure if this is normal or indicates a problem with the pump/alternator.

At first I figured it was just a bad (or undersized) alternator but after reading a different thread on dump trucks I'm starting to think it may be the pump itself. Part of me wants to ignore it until something breaks and then fix what's wrong, but the other part of me wants to fix it before I have 3 yards of crushed rock in the back with no way to lift it.

Any wisdom on how I should tackle this?

 

[Dmace]

I would test the battery and alternator, if it is an electric hydraulic system then those should be the only affected items on the truck.

 

[Treemonkey1000]

Take and clean up any and all connections to the pump motor. That thing is going to want some good current to drive it. Any corrosion on the connections can affect it. Especially if it has been splashed with road salt. Is there a fluid filter for it? Check that if there is one. Unloading that by hand would be a drag if you had a nice dump bed that was supposed to be working. I want a dump bed for when I have a load of wood chips after doing a tree job...

 

[kenstrac]

Check to see that the wire is heavy enough going to the motor from the battery and you have a good connection if the ground side uses the chaise run a heavy wire from the pump to the battery as over time you loose the ground.I use 00 welding wire, also check the condition of the bushings in the lift I had a unit that would not lift until the body was lifted up a few inches then it would lift fine made new bushings and it worked like it should.
I would also put a gauge between the pump and the piston and check pressure.

 

[J_J]

Letting the truck run at idle, is not putting a lot of juice in the battery. If the hyd pump motor runs good above, then do so. Have you measured current draw on the hyd pump motor, and is the alternator putting out 13.5 to 14.2 v when charging? How old is the battery. Do the cables to the motor get hot?

 

[Village Idiot]

Jeez you guys are great!

I'll start with the wiring, and work back from there. So far everyone seems to be suggesting electrical issues "upstream" from the pump. Give me a week or so to run some trials.

Thanks again.

JC

 

[Treemonkey1000]

Jeez you guys are great!

I'll start with the wiring, and work back from there. So far everyone seems to be suggesting electrical issues "upstream" from the pump. Give me a week or so to run some trials.

Thanks again.

JC

A week! We can't wait that long! I do have to add that you said when you start to lift the bed it starts to stall the engine. That might indicate the electric motor is gritted up and pulling a lot of current. If it has brushes you might check those. Also clean and lubricate bearings or bushings. If you can uncouple the motor from the pump then see if it still pulls down your engine. That would help to isolate the hydraulic side.

 

[Village Idiot]

Just a quick follow-up here.

I checked the wiring and nothing was corroded. Jumping the ground with a jumper cable made no difference. I couldn't find a hydraulic filter (although it may be tucked away somewhere I didn't see).

I have found that once the hydraulic fluid gets warm it is MUCH easier to lift the bed up. It still needs a little gas, but my foot is barely on the pedal. It really struggles when I have a few tons of rock in the back, so now I run it up and down empty once before I take my first load of the day. I have found that I just can't haul as much rock as I thought.

Thanks for all the suggestions.

 

[kenstrac]

I don't know what you have for oil in it, But I sold and installed a few and they came from the factory with ATF,and that is what the manual specified.

 

[J_J]

It is hard to see where a 12 v motor would stall a large truck. I think there is some wiring problem, or the 12 v motor is drawing to much current. How hot does the motor get after raising and lowering several times? Have you checked the pressure on the pump?