The Stovebolt Site Forums The Parking Lot Big Bolts 1949 2 ton won't dump

I was dumping a large load of wood and a chunk fell off the top. I heard the crash but couldn't see anything. I lowered the bed to see if it was empty and then it wouldn't raise again. A small round had fallen down into the control rods and they were bent. I could pull back on the lever and activate the pump but they did not unhook the bed from the chassis. Thus the pump was pumping against a steel hook. By the time I finally figured this out I think I blew the pump. Now, I straightened the rods, made the hook so it will unhook, but no matter how I shift the control lever for the valve on the pump it doesn't raise or lower the bed.
So, can I fix this without pulling the whole 300# pump out from under the truck?

I got your e-mail and it sounds as though you may have run the pump too long in an attempt to raise the bed while hooked down. You didn't say what sort of pump it is but from the heavyweight description it's probably a cast iron gear pump. Running it as I have described would burn the wear plates (bronze faced steel plates on the sides of the gears) and allow oil slippage past the gears. No choice except to rebuild it. It could (?) also be a piston pump but they are not that heavy. They will not withstand high RPM (anything over 1K) at which point they become worthless.

The pump is likely old as the hills and was shot anyway. Look at it that way so you won't feel too guilty. :>)

Send me some photos of it and perhaps I can help you with parts.

So I'm looking at pulling the whole unit(pump, control valve and lift cylinder) or should I just take the back off the pump and try to fix it in there? I'm wondering how to get that thing out of there.

There is no reason to remove the cylinder at this point. Remove the pump to take it down and see what damage it may have. This cannot be done properly while on the truck. The pump should be bolted to the hoist base manifold or if a separate unit it will have hose connections and be mounted to brackets, etc. to the frame.

I could not read the name of the manufacturer in your photos. Could you provide better pictures?
Thank you.

OK here's pics of the label as best as I can. It looks like St. Paul Hydraulics Hoist Company. I go the pump off and it actually looks OK to me. No melted bronze. Some scars. Can I just dress the faces?
http://picasaweb.google.com/schmidt.danj/Hydraulics#
I'm wondering if the control valve is off with the bent rods. How do I figure this out?
Thanks for any help.

OK, if the wear plates are good then put it back together exactly as it came apart, i.e., the plates on the same side and the exact thickness of gasket(s) on the side covers. It should turn freely with the aid of a wrench but not by hand. Make sure the valve will push in and out it's full travel and has no obstructions. Reinstall to the manifold and if you can put a tee into the connection to a pressure gauge. It should make about 1000-1200 psi or so. If it does then the pump passes. Straighten the valve linkage so it operates freely. Do not use any teflon tape on the fittings as it comes off and screws things up.

St Paul Hydraulics became part of the old GarWood company. Unfortunately the only parts your likely to find will be at the bone yard. If the pump is hot then it must be replaced with a modern gear pump of about 12-15 GPM @1000 RPM size.

OK, here's the skinny. The pump was great but after all the years the pressure relief valve was just all gummed up. Had to pull the pump and parts and clean it out. Now she dumps great. Hope for another 60 years.

All of the old underbody hoists I've had apart were a simple recirculating system and had no relief valve or a need for one. Are you sure that is what it is? I'm thinking check valve.