CAT 931 Backhoe

[SniperDave]

I have a Cat 931 without the backhoe attachment and I have the backhoe I would like to attach. I am hoping someone can send me pics or tell me where the two hoses attach to the 931 for connecting the lines from the hoe.

 

[Welder Dave]

I have a 931B with a backhoe but I would guess they are similar. I think the loader valve uses a power beyond function and lines come from there to the back of the machine. I think the best thing to do is post your serial number and one of the Cat experts with access to SIS could put up a hydraulic schematic of what's required for the backhoe hydraulics. I know there's a spaghetti arrangement of lines around the loader valve. My machine has the optional higher flow piston pump for the hoe from the factory. One thing that's really important to remember is that the lines for the backhoe always have to be connected together when the engine is running so you don't dead head the pump. When the backhoe is on the oil flows through the control valve and when the backhoe is off the lines are connected together to allow the oil to flow through. You forget this for 10 seconds and your pump could blow up.

 

[SniperDave]

Thanks for the input. The tractor is a 931, Serial Number 78U4491 Arrange. Number 5G0515. The backhoe came from another machine that is not in my area so I can't check it. The two connection hoses on the backhoe have pioneer quick couplers on them. I need to know which ports in the system to plumb into for pressure side and return. I had to replace the main pressure hose from the pump to the valve body so thought n ow would be a good time to attach the hoe.

 

[Welder Dave]

It likely has larger quick couplers than what is normally used to handle the hyd. flow. I started another thread asking if someone could post what is required to run a backhoe on your machine. I don't think it's as simple as just adding a couple hoses but don't know what all is required.

 

[Nige]

Is the backhoe attachment a Cat one..?
Does it have a Serial number..?

Here's the dilemma as far as the 931 range and backhoe installation goes: -
1. There is no hydraulic schematic listed under the machine S/N prefix (78U) that shows the backhoe plumbing. There is only a system Operation document that shows bucket lift, tilt, & a ripper (if installed).
2. The SysOp document DOES show a 3rd section of the control valve for "extra equipment" which I assume would include something like a backhoe. Problem is it's all very basic and does not go into detail.

 

[Welder Dave]

Thanks Nige. It's odd there isn't a schematic because backhoes were made for the 931. If it is a Cat hoe off of a 931, maybe SniperDave can take some pictures and/or buy the hyd. lines and stuff to hook up the backhoe. I think the 3rd section would be for a 4 in 1 bucket or a ripper. I know on my 931B, there is a set up for MP bucket, set up for ripper, set up for ripper and MP bucket and then the backhoe has it's own set up that just flows oil without having to move a lever to get flow. I would think it would have a power beyond set up but maybe they just tee in to the in and out lines to the loader valve?

 

[Nige]

Machines that old it's not unusual. I guess the assumption is that with the basic schematic shown in the SysOp (see below) and the Parts Manual any competent mechanic should be able to figure it out. That's how it worked back then.



Quite a few of us on here have found electrical schematics for older machines were listed in the Parts Manual rather than being separate, but then again they were the type that would fit on the back of a cigarette packet...!!

 

[SniperDave]

I thank you guys for your thoughts on this problem so far. The backhoe is a CAT hoe and came of a different 931 so I am thinking I should be able to make it work somehow. I can't find a serial number on the hoe. The backhoe is the type with hydraulic lift-up downriggers not the horizontally moving ones. The hook ups on the hoe are #16 pioneer type with what looks like #12 hose. My 931 does have the connections for the multi purpose bucket plumbed to the front of the tractor but not hooked up. I was wondering if I could hook the pressure side of the hoe into the T in the line from the pump made fro pressure checking and then not sure where to put the return. Any continues thoughts or information would be greatly appreciated.

 

[Welder Dave]

You're in luck. I looked through some old Cat brochures and found a brochure for the older 931/D3 fixed pivot and side shift backhoes with the rack and pinion swing. I think the Cat dealer gave it to me if I recall. It says the 931 pump will run the backhoe but the D3 requires an optional higher capacity pump (22 GPM, 2500 PSI). Most importantly it says "Connection to machine hydraulics: via power beyond adapter on implement valve for live power to backhoe". Is the other machine dead or still running? Maybe you can get the parts required for the backhoe or swap parts to get what you need. Think about the seat too because yours isn't on a pedestal to allow it to swivel. My machine has a flip over back rest but Cat doesn't offer this seat anymore. You'll also need the mounting brackets on the back. Publication number on the brochure is AEHQ9221 (7-75). Your machine is an early 1979 (931B started later 1979)). If you have a 4 in 1 bucket you'll be OK without additional counterweight but with a standard bucket the machine is really light on the nose. Cat had counterweighted idlers and counterweights to bolt on the inside top of the bucket. Take lots of pictures of the valve and hydraulic lines on both machines. Maybe a parts book would show the optional power beyond adapter for the valve? That's the big thing you need. Lines are usually easier to figure out and don't necessarily have to come from Cat. Try to find out the model of backhoe. Should be a tag riveted on the frame.

 

[Cmark]

Sorry I'm a bit late to the party. Here's some info.
I can only find a basic block diagram, but it looks like the feed to the backhoe is simply taken from the outlet side of the MCV which is item 2 in the diagram. 4 and 13 are the quick disconnects. The return goes to tank via filter 12. Some filters are in-tank, some are external.
From the lines illustration you may be able to figure out what you need.

 

[Welder Dave]

Curious if the power beyond adapter is just taking a plug out to connect the line? Looking at both machines and taking pictures would help a lot.

 

[SniperDave]

The machine that the backhoe was taken from is out of my area and not available for me to look at. I can see on the valve body where #3 from the above picture is. I can hook the pressure/supply side there. So am still trying to determine where to install the return line. I will take some pics of my machine and post them. I am hoping to find a nearby machine with a how I can look at but so far no luck.

 

[Welder Dave]

You may have to add a special power beyond plug but I'm not sure. Can you have pictures sent from the machine showing the control valve? The return tee's into the return line currently on your machine but posting pics. of your valve may not help without seeing what the other valve set up for the backhoe is like or knowing what exactly the power beyond adapter is.

Just did some looking on the net and it looks like the 931 backhoes were 87U and 88U models. I would assume fixed pivot and side shift models. It was a link to SIS parts look up that I couldn't look at but did list a bunch of different hydraulic sections that may list the power beyond kit. Another number shown was UEG0703S. Hopefully this helps to get some more info on the hook up.

https://avspare.com/caterpillar/ueg0703s/?catalog=c00000989