JD 420c Crawler Hydraulic System

[Hank420]

Hello, I am new to this forum, but I’m hopeful that someone here has some expertise that they are willing to share with me. I have a 1956 420c Crawler with a backhoe attachment. However, the hydraulic pressure is not enough to make the backhoe a very useful tool. Can the pressure be increased and is the original system able to withstand double the current pressure?
Any information anyone may have would be most appreciated.

Thanks,
Hank

[Jim B]

Welcome to the boards.

There is not a yes or no answer to your question, as such. Do you have a blade, loader, or neither in addition to the backhoe? What is the backhoe? Do you know the recommended pressure and flow for the backhoe? Have you done a pressure test to know what the current system relief setting is? What does your crawler have for a hydraulic pump supplying the backhoe? The camshaft driven pump, or does it have a pump mounted under the radiator driven by a shaft from the crankshaft?

If your crawler only has the camshaft driven pump (located on the front of the engine about behind the generator) the manual says set the main relief at 900 to 950 psi. Normal operating pressure is stated as 800 psi with 8.2 gallons per minute flow. Trying to up the pressure much above that is just asking for trouble, like splitting the pump housing.

If you have a crank driven pump (often used with loaders), it might be able to be set up, however a test to document what the current relief setting is and info on the pump and related hydraulic system will need to be looked at.

A 420C with a backhoe operating off the camshaft pump is better than a hand shovel but will never be a production machine.

[Lavoy]

Probably not enough info to give a real accurate answer, would need more info on factory or jobber hoe. But the short answer is if it is already at correct operating pressure, increasing it will just break things. If capacity is not enough, then you need a larger hoe, not more pressure.
Lavoy

[Hank420]

Thanks for your response Jim and Lavoy.
The Crawler does have a blade. I would add a picture of my “Backdozer” (- or “Bullhoe”) if I knew how to. - The hydraulic pump is located just behind the rad at the front of dozer. The pressure is about 1,000 psi which is not enough to effectively use the backhoe. I will probably not be able to use the existing pump/system and will look into getting a separate electric pump to run the attachment rather then trying to use the original hydraulic system beyond what it was designed for.

Thanks again for your input!
Hank

[Jim B]

To post pictures you need to use a third-party hosting site like Imgur or Postimage. Those are both free as far as I know, and there are others.

From your description of, the pump is right behind the radiator, that sounds like what is the referred to as the camshaft driven pump. It works fine for the blades and remote cylinders, which are fairly large bore, designed for use with low pressure. When loaders were installed a separate pump capable of higher pressures and volumes than the cam pump, that is what you need to run a backhoe. You might be able to find used parts to do that.

When you say you are looking at a separate electric pump, I am interested in what you are thinking of for an electric pump. I envision a pump unit like is used on a snowplow or dump trailer. Neither of those would be satisfactory to power a backhoe. They might develop enough pressure but will lack the flow volume needed. Reservoir size and duty cycle of the motor will be other issues. I would look at a small engine driven pump and engine set up, like used on a wood splitter, but having larger flow volume, that could be carried on the blade and removed when the hoe was not in use. Not a best case scenario any way you look at it.

Another thing to consider is that backhoes are generally hard on crawler final drives. Your backhoe may be small so less of a load however you need to remember the crawler was not designed to carry a load on the rear full time.

Good luck.

[Lavoy]

I would GUESS that your setup would be at 1500PSI which if I am correct would explain the lack of power. Flow is another factor, you may be down on flow and pressure both.
Lavoy

[Hank420]

Thanks again guys for your advice. I probably should have consulted with you folks before I started this project, however, since I’ve come this far with it, I hope to tinker with it a bit more before I give up.

I’ll try posting some photos and/or video when it’s done if anyone would be interested.

Hank

[gus]

Always interested in projects and photos!

[dtoots1]

Hank,

It always helps if you add location to your profile..someone may be nearby if help needed...profile is accessed in the drop down box where you login