Servicing hyd on 71 Chevy dump truck

AlanB · Mar 22, 2009

My current internet connection is poor (wildblue) and cannot usually upload pictures.

I have bought a 71 Chevrolet C60 dump truck with a Galion / Hercules dump bed.

It has a Pto box off the xmsn, driving a driveshaft back to the pump, and a seperate control knob to engage the pump.

Everything on this truck leaks, and I need to service the cylinder.

There is no resovoir to service, the lines from the pump go direct to the large lift cylinder.

I believe I feel an access port (I am guessing 1/2" pipe) on the top highest point of the cylinder, which would be the highest point on the system.

I am thinking I need to fill that port to the top in the collapsed state and that would be the correct fill level. Unfortunately I cannot acces that plug from the bottom.

Current thought is to cut an access door in the bed of the dump and fill from there, but I am certain there is a better way of doing it as this thing must have been serviced many times in it's life.

I also thought about taking the hoe, lifting the bed halfway, and servicing it half full and trying that.

Anyone familiar enough with this type system from my probably inadequate description to lend me some guidance before I do something stupid?

Thanks

Diamondpilot · Mar 22, 2009

What ever you do secure the bed with cribbing if lifting it half way and servicing.

Have you thought about a pump? I have one that goes on the top of a 5 gallon pale and I use it to pump out 80W90 gear oil into diffs and things like that. It has a 6' hose and I have adapted it down to about 3/8" outside dia to fit small plug holes.

Really cant help you much. I do maintain a Ford F-700 dump truck for a neighbor in exchange for using it but never had to service the hydro system. Not even sure what brand it is. All I care is that it works.

Chris.

mattman · Mar 22, 2009

Thats a very important thing the cribbing that is. I have not seen a dump bed that did not have a hydraulic fluid tank somewhere's on the truck. It takes a good bit of fluid to fill the cylinder at full lift. I have not seen a cylinder with a built in tank for the extra fluid needed. I guess there could be a way without a tank, but I would trace the hoses going into and out of the pump to look for a tank.

Someone will chime in with more knowledge than I have.

kennyd · Mar 22, 2009

mattman said:
Thats a very important thing the cribbing that is. I have not seen a dump bed that did not have a hydraulic fluid tank somewhere's on the truck. It takes a good bit of fluid to fill the cylinder at full lift. I have not seen a cylinder with a built in tank for the extra fluid needed. I guess there could be a way without a tank, but I would trace the hoses going into and out of the pump to look for a tank.

Someone will chime in with more knowledge than I have.

I agree, sounds very strange to me also. I bet the "fitting" at the top of the cylinder is a vent, not a fill port.

Wis Bang · Mar 22, 2009

mattman said:
Thats a very important thing the cribbing that is. I have not seen a dump bed that did not have a hydraulic fluid tank somewhere's on the truck. It takes a good bit of fluid to fill the cylinder at full lift. I have not seen a cylinder with a built in tank for the extra fluid needed. I guess there could be a way without a tank, but I would trace the hoses going into and out of the pump to look for a tank.

Someone will chime in with more knowledge than I have.

Small, single stage, dump cylinders don't have a tank, at least the one we had & the ones dad's workplace had didn't. The cylinder housing is oversize to act as the reserve. Follow the hoses, there should only be two going to and from the PTO mounted pump. You add the fluid where OP indicated.

Multi-stage units like those on a ten wheeler +/or a dump trailer need alot more fluid.

A track jack or porto-power will raise an MT body and WILL be a dangerous place so use a few 4x4's to support the raised body. Opening the plug on the cylinder jacket will vent the system so there will be zero resistence to even slow down the falling dump body...you can't have enough support.

Stimw · Mar 22, 2009

IIRC some used the cylinder to lift the bed and used the back side of the cylinder for the reservoir. In which case you can fill it in the up position. Is there a hose coming off the top side of the cylinder? Does it go to the input on the pump?
As stated ALWAYS block the bed when in the up position. I met a guy once with only one leg. He said he climbed up on the frame of a dump truck to get to the rear end and the bed fell severing his leg! The worst part was the bed had been up all weekend and when he climbed up it was monday morning.

DANOCHEESE · Mar 22, 2009

like above make sure the box is cribbed. Lower it on the cribbing to make sure it will hold. Think of it like a leg hold trap and you are the prey. The box always wants to get the guy who makes it go up and down.

EddieWalker · Mar 22, 2009

Hey Alan,

Here's a picture of mine. Is it similar?

I have the PTO pump that powers the cylinder that lifts the bed. It is a single action cylinder that when engaged, lifts the bed. Then when the pressure is released, the bed comes down by gravity.

The cylinder area above the piston is your storage area for fluid. There is no need for it to be full, and if you make the same mistake that I did and fill it up, the bed won't come all the way down. Basically, when the cylinder is pushing the bed up, the fluid comes from the other end of the piston, through the hose, into the pump and then pushes the piston up. When released, the fluid flows the opposite direction.

I add to mine with the bed up and blocked with 2x6's to keep it up. Then the screws comes off with a philips head screwdriver. I use a plastic, disposable cup, and pour in one cup full at a time. When I get it right, the bed will raise all the way. I then add two more cups and call it a day.

Do you have the same triangle shaped brackets? Be sure to grease them real good. I've broke the ends off of mine twice. The first time, I had a local guy weld it back together and it was a simple job. The second time, it twisted the heck out of the metal and I had to take it to a machine shop to weld it up and align it. That was $500 and two days of pain to get it apart and back together. MISERABLE PAIN!!!!

Eddie

AlanB · Mar 24, 2009

Thanks guys,

Yes, it is very much like your's Eddie, but I have never seen it up so I am not positive on the triangles but I must have something similar.

Spoke with an old timer master mechanic yesterday and he went through the servicing, he suggested lifting it with a forklift (of course I had the forklift at the house yesterday, on my way to his shop where I was dropping it off

)

He said that you get it about halfway up, then get it pumping, and then keep adding fluid till it will go up to full travel, then close it up. That as it leaks you will see the bed will not go all the way up and that is the time to service it. He also suggested cribbing for safety.

Call me a weenie, but I think I am just going to cut a floor in the bed and make a little slide in / bolt in plate to go in there with a beveled edge. Then I can pull the plate and service it from above. I have a feeling as leaky as this thing is, servicing it will be a fairly regular occupation and being between the frame and doing it, with or without cribbing just makes me uncomfortable.

If my plate hangs a bunch of stuff I can always weld a flush plate back in and service it the "normal" way.

EddieWalker · Mar 24, 2009

Alan,

I like the plate idea, but once you get fluid in there, that's a done deal. You'll find the leaks quickly enough since there is only one hose. But over the long term, you will have to grease those pins. mine has four pins per side, plus the main pivot rod that holds all the weight of the dump bed. You will have to figure out a way to get under the lifted bed and grease those fittings.

I tried to lift my bed with my loader, but didn't have much luck. I didn't have the forks for it then, so you might be able to do it with the forklift where I wasn't able to with just a bucket. When I broke mine, I lifted it with a bottle jack and allot of blocks of wood. Back and forth, with bracing in three places on both sides. It's slow, tedious and painful, but it works.

I found that the rings on my piston were very much like a piston on a car. They were also all lined up so that fluid could flow right through the ends of the rings. I kept the same rings in there, bu turned them so that the ends were staggered. Now my bed stays up when I'm not using it. It will bleed down over night, but it's way too slow to see. Before, you could see it coming down and had to keep pumping fluid into it to keep it up with a load.

Good Luck,
Eddie