Gradall G3WD Bizarre Hydraulics Modifications

[CraneInnovation]

I have been working on rebuilding a 1988 Gradall G3WD and have made a few puzzling discoveries on the hydraulics system. I have a thread going in the Shop Talk forum about the rebuilding project:

https://www.heavyequipmentforums.com/showthread.php?38100-The-Great-Gradall-Project

..but I wanted to get some thoughts from the Excavator forum about what I found.

On the factory machines, one output from the tandem pump on the G3WD goes straight to the center pin while the other goes to a valve on the frame that powers the remote travel motor (to allow carrier driving from the excavator cab). If the fluid is not used by that valve, it goes through a power beyond port and joins the other line at the center pin. All parts and service manuals agree that this is the ONLY circuit that Gradall ever put on these machines after the main pump. The main pump is mounted to the torque converter just behind the engine.

I have the 4x4 version where the transmission is mounted at mid-ship and is not supposed to have anything connected to its PTO.

Here's what I've found on my machine.

Our first discovery was two high pressure filters near the main pump.

One is currently bypassed:



The other one is plumbed just after the second main pump output:



We haven't traced the lines in full, but it doesn't appear that that second filter output goes to the remote travel valve. The first pump output goes directly to the center pin through a hose that is zip-tied to the frame. So yeah, someone's been busy making it "better".

The other thing we discovered this weekend was a total surprise. There is a second single stage hydraulic pump on the transmission PTO:





It appears (without confirmation, we discovered it at 9pm on Saturday after replacing the TC charge pump) that this pump comes directly after the smaller high pressure filter. This would mean that it comes AFTER the main pump. Huh???

The G3WD is a low pressure machine (~2000psi and the last one Gradall built before going high pressure on the 4100) and a booster pump might make sense? I don't know enough about hydraulic system modifications to know if that is ever "done". I am new to hydraulics servicing and the only thing I'm sure of is that this is all after-market (Gradall has confirmed none of this was shipped with any of their machines). Granted, there IS a PTO on the transmission so its not a bad idea...

In summary, my question to everyone is this: Has anyone ever seen these kinds of after-market modifications before? If so, what was their purpose? Is there any value in keeping them or should I restore the machine to its original configuration?

(We are completely disassembling and rebuilding all hydraulics....so I am wondering if it is worthwhile to include this stuff in the rebuild or to remove it?)

Thanks so much for any pointers. Like I said, this is a new ball of wax for me!

 

[dirthog]

That is not a pump on the rear of the transmission that is the motor for remote drive. Now on the pressure filters there were a few machines that had those installed on them in fact the dealership I work for had a couple of them which we put on. It was done because they were having trouble with pumps.

 

[CraneInnovation]

<looks back over the parts manuals>

Wow, I missed that. I had assumed the motor-looking thing on the torque converter was the propelling motor, but no, its the power steering pump. I figured I was missing something.

Now, see, I thought those high pressure filters looked awfully well installed to be someone's after market project. However, Gradall told us they hadn't ever put them on and had no info about them. I guess they're wrong (understandable, the thing is 25 years old) Do you know where I could look to find information about them?

I wish they hadn't been bypassed by the previous user. We're disassembling and cleaning the entire system for exactly the reason you mention....pump is chewed up and metal was all over the filter magnet. There was also water in the fluid.

Thanks dirthog, I figured someone would see those pictures and set me straight.

 

[dirthog]

I don't have anything here at work will look at home in some of the old service stuff I have but I don't think I keep any of it they did not work as well as we hoped at the time and the elements were a bit pricey too. The main thing is get it clean to start with and keep the filters changed.

 

[GregD1]

Somehow I remember there being a sliding collar on that trans mounted pump to engage it. We had two of them years ago on a deal with Gradall. They were the first two off the assembly line and we actually had more time on them than the prototype did. Two machines side by side and they were like night and day as far as electrical.
Don`t remember which one it was but there was a diode in the harness somewhere that if/ when it went bad, it would upshift the trans if you blew the horn.

 

[CraneInnovation]

Haha, I'd believe it! The electrical on these machines is absolutely baffling. We're fairly certain that a good portion of the things that don't work are due to electrical problems.

Our machine had a smashed windshield due to the bucket hitting the cab whenever you accelerated (the pump PTO got munched and the lines weren't pressurized). This means the dash and electronics underneath spent at least a year getting rain on them.

Its a heck of a project right now. We're making progress though. PTO is replaced and the transmission fluid is no longer chunky chocolate milk. We have a new roof on the driver's cab. Another weekend of fabrication and we'll be making a glass order. It's fun though

 

[dirthog]

Sorry but I can't find anything on the aux filters. You need to look at the AMP connectors under the cab they had a habit of comming loose and the locking rings were prone to break also most of them you will see were held together with zip ties. The other problem area was the center pin and brass rigs that carried electrial functions form the lower to the upper. Also the controller for the older machines was no longer serviced but Gradall did have a update which I installed on a couple of machines which seemed to work well.

 

[CraneInnovation]

Sorry but I can't find anything on the aux filters. You need to look at the AMP connectors under the cab they had a habit of comming loose and the locking rings were prone to break also most of them you will see were held together with zip ties. The other problem area was the center pin and brass rigs that carried electrial functions form the lower to the upper. Also the controller for the older machines was no longer serviced but Gradall did have a update which I installed on a couple of machines which seemed to work well.

Thanks dirthog, I'll look at the centerpin too. Its completely coated in oil and dirt, which makes me fear it was leaking before we got it. That would make the fouling you mention on the rings very likely. We haven't had the system pressurized yet to tell if it is leaking. I'm starting to come to peace with the fact that I may have to rebuild the entire swivel because its probably never been done before....

Our machine does have the shift controller retrofit, thankfully! I've heard that's an expensive operation. We do have a shift problem (1st, 3rd, 5th) don't work, but we think its the #6 solenoid. Not a major problem.

And yup, the AMP connectors are all zip-tied! We are probably just going to replace them all, they aren't too expensive.

 

[dirthog]

Trouble is they still will not stay even brand new machines the rings would be broken or break off very quickly they are not expensive for a reason LOL. What usually happened to the center pin is the chrome on both pins would wear where the slipper rings ride if you have a VERY good hydraulic shop they could rechrome them just make sure you put both pins in the housings with the new seals before tightening the bolts tht hold the two halfs together. Snug them up and turn the inside several times to make sure it is centered then torque them up. On the bottom brass all you can do with that is replace it which is the air side and some of the pilot oil. then it is just a matter of cleaning up the electrial contacts. Oh almost for got you HAVE to either cut the wires to disassamble the centerpin or if it has been taken apart before remove the connectors.