853 will not move

[Railmech]

Hello all, I have an 853 that I acquired from a friend whose husband passed from cancer a little over a year ago. What I have is a skidsteer that runs great, tilt and lift work but no movement any direction either side. Here is what I have done, put in a missing/bypassed charge filter housing and new filter, filled completely with new hyd fluid. At the tee where the sensor is located on the charge pump fitting, I took a pressure reading and at idle it is somewhere around 20psi, at high idle it goes up to around 70 psi. The PO claimed to have removed the hydrostat, split it and inspected the charge pump and pin, said it was all good with minimal wear. Last evening, I removed the belt cover, although the belt seems tight, it has split and apparently threw one groove worth of belt off some point in its life. Would a bad/slipping drive belt be enough to run the hydraulic pump but not enough to build charge pressure? I pulled the relief out and I did not see the shim listed in the manual but the spring seemed good and the seat area seemed fine. I'm always reluctant to give VIN's or s/n on the internet but it is a 5128-21xxx. Thanks in advance

 

[Tazza]

That charge pressure is quite low, I'd still expect it to move, but make noise. Does it bog down when you try and move? I wonder if the brake is stuck on causing this issue?
Minimal wear is still wear. A piston pump relies on really fine tolerances to work correctly. If you can feeel the wear with a fingernail, it's too much.

 

[Railmech]

That charge pressure is quite low, I'd still expect it to move, but make noise. Does it bog down when you try and move? I wonder if the brake is stuck on causing this issue?
Minimal wear is still wear. A piston pump relies on really fine tolerances to work correctly. If you can feeel the wear with a fingernail, it's too much.

No it does not bog, if you move the levers there is nothing as it would act if the machine were turned off. My understanding of the charge pump on this one is located between the hydro pumps and is a geroller type unlike the swashplate piston setup of the hydrostats. On the brake interlock, all the components are gone aside from the solenoid itself. It is my understanding there needs to be charge pressure to unlock the hydraulic brake. (Orange pedal on floor)

 

[Railmech]

That charge pressure is quite low, I'd still expect it to move, but make noise. Does it bog down when you try and move? I wonder if the brake is stuck on causing this issue?
Minimal wear is still wear. A piston pump relies on really fine tolerances to work correctly. If you can feeel the wear with a fingernail, it's too much.

One thing I know from the P.O. wife is that the machine was started in the winter, engine sounded like it was struggling/bogging then smoothed out and wouldn’t move after that

 

[Tazza]

One thing I know from the P.O. wife is that the machine was started in the winter, engine sounded like it was struggling/bogging then smoothed out and wouldn’t move after that

The drive pump setup will be two piston pumps back to back that power the motors, there will be a hydraulic pump/charge pump at the end, so 3 pumps all linked together.
The brake is disengaged with an electric solenoid, no fluid is required to unlock it, tracked machines do have a hydraulic brake though.
The bogging down in winter could have just been because the engine was cold and the fuel possibly was gelling, reducing the amount of fuel getting to the pump.

 

[Railmech]

The drive pump setup will be two piston pumps back to back that power the motors, there will be a hydraulic pump/charge pump at the end, so 3 pumps all linked together.
The brake is disengaged with an electric solenoid, no fluid is required to unlock it, tracked machines do have a hydraulic brake though.
The bogging down in winter could have just been because the engine was cold and the fuel possibly was gelling, reducing the amount of fuel getting to the pump.

Okay, thanks, I will look at that when I get back in town. I just thought it was between the two hydrostats because my lines from cooler and to charge filter are in the center of the two. In my parts manual it shows a rotor assy in between the two hydrostats, so that’s why I thought it was a charge pump.

 

[Tazza]

Okay, thanks, I will look at that when I get back in town. I just thought it was between the two hydrostats because my lines from cooler and to charge filter are in the center of the two. In my parts manual it shows a rotor assy in between the two hydrostats, so that’s why I thought it was a charge pump.

The image in the manual might have been a picture of a rorating group. Round thing with a bunch of pistons that run inside it to generate pressure for the drive motors.
Ideally, the best way to go on an unknown machine that has been sitting is to pull the pump and tear it down and inspect for wear, then you know that part is good, if the problem still exists, you move on to the drive motors.
Did you change the filter too? just in case it's something simple.

 

[Railmech]

The image in the manual might have been a picture of a rorating group. Round thing with a bunch of pistons that run inside it to generate pressure for the drive motors.
Ideally, the best way to go on an unknown machine that has been sitting is to pull the pump and tear it down and inspect for wear, then you know that part is good, if the problem still exists, you move on to the drive motors.
Did you change the filter too? just in case it's something simple.

First, I appreciate your time helping me. I did change the charge filter but not the hyd filter. I am familiar with how piston/variable displacement pumps work off swashplates. This link shows the hydrostat exploded parts view. Number 55 is the part I was referring to as the charge pump. I looked at mine again tonight and on the end I just see one hydraulic gear pump with two lines coming out, nothing piggybacked on it. https://gpim-media.dibhids.net/ipc/b20369.gif

 

[Tazza]

First, I appreciate your time helping me. I did change the charge filter but not the hyd filter. I am familiar with how piston/variable displacement pumps work off swashplates. This link shows the hydrostat exploded parts view. Number 55 is the part I was referring to as the charge pump. I looked at mine again tonight and on the end I just see one hydraulic gear pump with two lines coming out, nothing piggybacked on it. https://gpim-media.dibhids.net/ipc/b20369.gif

The image does look a bit like a geroler star, but i'm not fully convinced it is. The parts manual i have for this machine has the images, but no list of what the numbers are.... So not a whole lot of use really....
The way i understand how the charge pressure is generated is, oil from the hydraulic pump goes to the control block, then through the outlet of the control block, through the oil cooler, through the filter through the drive pump where the charge pressure relief is located, then back to a tee where it goes to the oil tank or the hydraulic pump depending on demand on the system.
This way no dedicated charge pump is required and why charge pressure changes when you lift and lower the lift arms.

 

[Railmech]

The image does look a bit like a geroler star, but i'm not fully convinced it is. The parts manual i have for this machine has the images, but no list of what the numbers are.... So not a whole lot of use really....
The way i understand how the charge pressure is generated is, oil from the hydraulic pump goes to the control block, then through the outlet of the control block, through the oil cooler, through the filter through the drive pump where the charge pressure relief is located, then back to a tee where it goes to the oil tank or the hydraulic pump depending on demand on the system.
This way no dedicated charge pump is required and why charge pressure changes when you lift and lower the lift arms.

Okay, I understand your verbal schematic. I’lll be out of town for a week or so, but when I get back I will try and follow that flow pattern you mentioned and let you know what I found if anything. Thanks again

 

[Railmech]

The image does look a bit like a geroler star, but i'm not fully convinced it is. The parts manual i have for this machine has the images, but no list of what the numbers are.... So not a whole lot of use really....
The way i understand how the charge pressure is generated is, oil from the hydraulic pump goes to the control block, then through the outlet of the control block, through the oil cooler, through the filter through the drive pump where the charge pressure relief is located, then back to a tee where it goes to the oil tank or the hydraulic pump depending on demand on the system.
This way no dedicated charge pump is required and why charge pressure changes when you lift and lower the lift arms.

It’s been over a year but I started back on my 853. To recap, runs great, tilt, lift worked great. But no movement forward or reverse. At high idle only had 100psi charge pressure, manual states it should be around 300-ish. I pulled the tandem hydrostat, split it and pulled out the gerotor.. I have nothing that tells me how much wear is acceptable. The charge relief looked fine. There is scoring on the inside of the gerotor aluminum housing.

 

[cwjohndeere]

It’s been over a year but I started back on my 853. To recap, runs great, tilt, lift worked great. But no movement forward or reverse. At high idle only had 100psi charge pressure, manual states it should be around 300-ish. I pulled the tandem hydrostat, split it and pulled out the gerotor.. I have nothing that tells me how much wear is acceptable. The charge relief looked fine. There is scoring on the inside of the gerotor aluminum housing.

The 853's do have a dedicated charge pump for the hydrostatic system in between the drive pumps, this is also why there are two separate hydraulic filters. One for the gear pump for boom bucket and auxillaries and another filter for the hydrostatic system. Also on the 853's there is no direct connection between the steering levers and the swash plates. The steering levers operate some valve spools which direct charge pressure to either side of a piston that actually does move the swashplates. This is why the steering feels very light and mushy on these machines but if there is not sufficient charge pressure to actuate the pistons that move the swashplates the machine will not move. Ive got the pumps and motors out of my 853 out getting rebuilt at present, be prepared as parts are expensive and hard to find.

 

[Railmech]

The 853's do have a dedicated charge pump for the hydrostatic system in between the drive pumps, this is also why there are two separate hydraulic filters. One for the gear pump for boom bucket and auxillaries and another filter for the hydrostatic system. Also on the 853's there is no direct connection between the steering levers and the swash plates. The steering levers operate some valve spools which direct charge pressure to either side of a piston that actually does move the swashplates. This is why the steering feels very light and mushy on these machines but if there is not sufficient charge pressure to actuate the pistons that move the swashplates the machine will not move. Ive got the pumps and motors out of my 853 out getting rebuilt at present, be prepared as parts are expensive and hard to find.

Thanks for the reply. I don’t think I want to take the chance of replacing the charge pump and sticking this back in since it was such a pain. Maybe I should just take it to bobcat and have them test and quote. Thanks

 

[Tazza]

Thanks for the reply. I don’t think I want to take the chance of replacing the charge pump and sticking this back in since it was such a pain. Maybe I should just take it to bobcat and have them test and quote. Thanks

Not sure Bobcat will have the gear to bench test it, but they may.
Try loader parts source, i know they do have a test jig that they can run your pump up on to check it.

 

[Railmech]

Not sure Bobcat will have the gear to bench test it, but they may.
Try loader parts source, i know they do have a test jig that they can run your pump up on to check it.

Thanks for the info, I’ll give them a shout first, they’d likely be cheaper than the local dealer anyhow.