Case/Davis trencher backhoe

[Spike188]

@Eugen how close are the speck of Princess Auto cylinder to the Davis?

[Eugen]

@Eugen how close are the speck of Princess Auto cylinder to the Davis?

Very close. I got what they call the screw head utility cylinder 3-18. Both PA and Davis are pin to pin 26", bore 3", stroke 18". The Davis rod is 1.5 whereas the PA is 1.25. The outer diameter is 3.5 for the PA and a little less than 3.5 for the Davis. Pin hole is 1-1/8 for Davis and 1" for the PA, so I made new 1" pins. Pressure rating for the PA cylinder is 3000 psi. It has #8 orb ports.

As far as I'm concerned it's an almost perfect replacement. Even having to buy this new cylinder I cannot be upset.

[JSinMO]

Great job! I’m glad the function test was all positive!

[RoamingGnome]

Great to see it all coming together... can't wait to see a video of it digging!

[Eugen]

Thanks guys, I'll shoot a video if I get it to run something resembling normal. I've tried to cover the hole using the backhoe. The 15HP engine is clearly struggling at times.

Question to you guys who have the D100 on your tractors: how does it behave when you get to the end of the stroke? Mine tends to bog down the engine, and if I move the backhoe fast and get to the end of a cylinder stroke the engine just stops, the relief valve doesn't kick in. The manual states main relief at 2000 psi. I find it hard to believe that this 15HP can't push through a relief valve at 2000 psi.

Sure, real answer I'd get if I measure the pressure. Hoping that you guys with backhoes would give me some indication on what normal operation is like.

Edit: some thoughts I've had about this issue since I wrote this above. There are clear signs that the main previous owner was someone conducting a business with this device. Also clear modifications and departures from the original build. The backhoe boom and dipper has many reinforcements, welded patches. The hoses it came with were all custom made and not with the original Davis routing. I wouldn't be surprised if the relief valves have been "adjusted" to death. From a practical standpoint, given that the current engine may be somewhat underpowered for the d100, I think I'll just adjust down the main relief valve by ear.

[JSinMO]

My engine bogs down at the end of travel but it has never died as a result. I’d guess your thought on the relief valve being adjusted way beyond where it should be is probably correct.

[Eugen]

My engine bogs down at the end of travel but it has never died as a result. I’d guess your thought on the relief valve being adjusted way beyond where it should be is probably correct.

Thank you Jeff! Do you remember if you hear the relief valve "squealing" somewhat? There is a certain different sound when the relief valve opens up, am wondering if you noticed that, at the end of travel, if you try and push further.

[JSinMO]

My engine bogs down at the end of travel but it has never died as a result. I’d guess your thought on the relief valve being adjusted way beyond where it should be is probably correct.

Thank you Jeff! Do you remember if you hear the relief valve "squealing" somewhat? There is a certain different sound when the relief valve opens up, am wondering if you noticed that, at the end of travel, if you try and push further.

Sorry I should have said that. Yes I can hear the relief valve.

[Eugen]

Sorry I should have said that. Yes I can hear the relief valve.

This is very helpful and it confirms my suspicion!

[Eugen]

The owner manual for the D100 that put in the technical library section had some interesting details about the relief valves. Together with the service manual for the hydraulics on the 600 series lbh it gave me a good idea that one is not supposed to mess around with the relief valves. The relief valves for the dipper and boom are straightforward to adjust. They are like a big bolt and the valve is in it, you can tighten or loosen a mid positioned screw. I'll post a picture next time I take it out.

The main relief valve though, is more complicated. Once it was out it was clear someone's been there before. At the vertically bottom there's a steel mesh screen held in place by an internal snap ring/circlip. One eyelet on the circlip was broken.


Of course I did not have a 1/2" internal snap ring on hand, so I practice some patience. The little adjustment did nothing though.

Seeing that somebody has already disassembled it, I did too. It too has an inner element with a screw and a spring, making me think that's the only way to adjust it.