C50 dump truck information

[olyeller]

Where can I find information about the hydraulic system on the C50 dump trucks? The service manual doesn't say anything about it, so maybe they were fitted after the factory? Anyway, the hoist doesn't start lifting until about 5-15 seconds after you engage the PTO. Maybe this is normal as the pressure is building up. Wasn't sure if that meant a worn pump or not. Seems to lift at the same speed regardless of load. I know the pump is a Chelsea but I don't know how everything fits together (there's a driveshaft running from the pump mounted on the transmission to the hydraulic reservoir, not sure what does what). It's also leaking pretty bad. Pump is mounted on the transmission, so that turns the PTO shaft, but does that thing also run the hydraulic oil through it? I pretty much know the answer already, but how does it work?

Thanks

[morpheusmac]

If it is leaking that's a good sign that there is an issue with the pump. Try and find why/where the leak is coming from, it could be something as simple as a loose fitting, then you can refill and bleed the system to get the air out. Mine lifts almost immediately after engaging the PTO and the lift controls.

[greywuuf]

My assumption is that you are slightly confused in your description. Chelsea is Not know for making hydraulic equipment, they are known for making PTO transmissions.
It seems to me that normally a PTO (Power Take Off) unit is fitted to a transmission and provided with a means to connect either a chain or a drive shaft. That chain or drive shaft Then goes to turn some other piece of equipment...in your case it sounds as though your transmission has a Chelsea PTO bolted on the side (quite common) and a drive shaft running to a remote mounted hydraulic pump (also fairly common).

[mrolds88]

I have a similar setup, less the leakage. First, since its got a leak, have you checked the fluid level? Second, where is it leaking? There are basically 4 places it can leak. 1. Cylinder, 2. pump, 3. lines, or 4. tank. Let us know and we can go from there.

[1976gmc20]

Originally Posted by olyeller

Where can I find information about the hydraulic system on the C50 dump trucks? The service manual doesn't say anything about it, so maybe they were fitted after the factory? Anyway, the hoist doesn't start lifting until about 5-15 seconds after you engage the PTO. Maybe this is normal as the pressure is building up. Wasn't sure if that meant a worn pump or not. Seems to lift at the same speed regardless of load. I know the pump is a Chelsea but I don't know how everything fits together (there's a driveshaft running from the pump mounted on the transmission to the hydraulic reservoir, not sure what does what). It's also leaking pretty bad. Pump is mounted on the transmission, so that turns the PTO shaft, but does that thing also run the hydraulic oil through it? I pretty much know the answer already, but how does it work?

Thanks

Your pump must be self contained inside the reservoir.

Pumps don't run shafts - shafts run pumps

The PTO unit bolts onto the side of the transmission (replacing a factory plate) and has a little gear that slides into a transmission gear that always turns even in neutral. Should be a cable or lever running up to your cab.

Your system is probably low on hydraulic fluid and or has an internal leak. Or maybe your cylinder is leaking and it takes a few seconds for the pump to fill up the cylinder before it starts to extend.

I never had a dump truck myself, but I did set up a log loader with PTO driven pump on my C50. Got the PTO unit from a junkyard, the pump from Northern Hydraulics (Tool, now), and fabricated everything else myself from scrap pieces including an old pole lamp for part of the shaft

[olyeller]

Thanks for the replies everyone. Yes, the remote pump driven via PTO all makes sense to me, but I have a leak coming from the Chelsea PTO; what would that be? The flywheel should be dry and I figured it was hooked up to the transmission just like the starter is. Is it enclosed away from the transmission and full of gear oil?

I topped off the hydraulic fluid and it wasn't low at all, so I guess the reservoir isn't leaking.. I was a bit (completely) confused from the outset, and I figured the fluid would be low since it was taking a while to lift.

It does lift, though! 550 bushels or so on it, it lifts right up.

Other problem is it burns a huge amount of oil (~1qt per 50 miles), people we bought it from said recently overhauled, apparently we're suckers or they aren't very good at making cylinders round.

Mechanic said we probably don't want to rev it over 3000 because he doesn't know whether it's a 366 or 396 (some mixed pieces maybe), but both of those can get up to 5000... I know they have a long stroke but still. Course he put in a new carb (he said the Holley 4 barrel was "just old;" I told him to give me the Holley because a rebuild kit is only $50) and it doesn't have the vacuum governor.

EDIT: I just realized I put "I pretty much know how it works" at the wrong place; I don't know how any of the pumps or PTO works, I meant I already know what the answer is to fixing the leaking... or something. Who knows what I was trying to say.

[1976gmc20]

Originally Posted by olyeller

Thanks for the replies everyone. Yes, the remote pump driven via PTO all makes sense to me, but I have a leak coming from the Chelsea PTO; what would that be? The flywheel should be dry and I figured it was hooked up to the transmission just like the starter is. Is it enclosed away from the transmission and full of gear oil?

I topped off the hydraulic fluid and it wasn't low at all, so I guess the reservoir isn't leaking.. I was a bit (completely) confused from the outset, and I figured the fluid would be low since it was taking a while to lift.

It does lift, though! 550 bushels or so on it, it lifts right up.

That would be transmission oil.

Yes, the transmission comes with a plate that you can remove to install a PTO that can engage a transmission gear that turns in neutral. So it's running in the same gearbox and oil as the transmission.

Totally different than a starter.

[olyeller]

Originally Posted by 1976gmc20

That would be transmission oil.

Yes, the transmission comes with a plate that you can remove to install a PTO that can engage a transmission gear that turns in neutral. So it's running in the same gearbox and oil as the transmission.

Totally different than a starter.

Oh, thanks! Sorry for the dumb questions, harvest just started and of course we waited until a day before to make sure the truck was working so I don't have much time to think or poke around underneath. I guess it would be hard to engage something directly from the flywheel while the engine was running.

[1976gmc20]

Originally Posted by olyeller

Oh, thanks! Sorry for the dumb questions, harvest just started and of course we waited until a day before to make sure the truck was working so I don't have much time to think or poke around underneath. I guess it would be hard to engage something directly from the flywheel while the engine was running.

Is the PTO leaking from the shaft seal(s) or from the mounting gasket?

Did you check the oil level in the transmission ???????


If you're in the middle of harvest then just make sure the fluids are kept topped off and keep going.


I suspect there is some sort of internal leak in your hydraulic system and the oil is leaking down from the lift cylinder to the reservoir - hence the pump has to refill the cylinder before it starts going up.

I've never worked on one of those pump in tank systems, just the separate pump, hoses, tank, valve(s), and cylinder(s). I've set them up from scratch so I know a wee bit about the basics, anyway

[mrolds88]

Might be the best thing if you could post some pics. Will get us headed in the right direction.

[olyeller]

Originally Posted by mrolds88

Might be the best thing if you could post some pics. Will get us headed in the right direction.

Good idea, I'll take some tomorrow morning if I can. I like looking at old trucks anyway, I imagine you guys do too

[greywuuf]

also , pumps wear out, I have four that were given to my by a logging outfit as they were removed and replaced... they did not want the hassle of rebuilding or having them rebuilt.

most are gearrotor pumps ( like your engine oil pump) and if there is not a GOOD filter in the system they can become scored and worn .... pressure suffers as does system speed and response time. hydraulic systems should be rather self bleeding, but a spot of air trapped at the top of a ram will impart a slight delay ( the air will compress some before anything happens ) DO NOT try to bleed the system under pressure.... hydraulic fluid cuts like a LASER from a minor leak ( at least not by 'cracking" fittings,if there is a bleed port it my be designed to use under pressure....that is an unknown on my part ) I have a thread going about my PTO and I have a couple of pictures in it that may help you visualize what a PTO is and how they work .... http://67-72chevytrucks.com/vboard/s...d.php?t=674960

good luck with the harvest!