Bobcat 853 movement and hydraulics go extremely weak, seemingly at random

[mark.s]

Having an issue with a skid steer I bought a while back. I expected to have to do some maintenance and repairs on it since it is a pretty old beast (2622 hours now). I recently repaired a leaky left side lift and tilt cylinder and those no longer go down over time.

Ever since I've owned the machine, it has made a funky whirring noise when rotating around the axis (full forward right, full back left - and vice versa). After making the repairs to the hydraulic cylinders, I've used it a bit, but have noticed that I would lose power in the tilt/lift/aux hydraulics as well as on the left and right wheels intermittently. I have not yet been able to identify which conditions bog it down. The engine seems to be running totally fine when this happens, and revving it higher does not help. When I noticed it, I hopped out and topped off the fluid, in hopes that I was a bit low. That did not seem to help, although after letting the machine sit for a few minutes, things worked well enough that I was able to drive back to where I park the machine. I had to go up a somewhat steep slope on the way and bogged down to a standstill, dropping the revs and edging my way up allowed me to continue up the hill. Engine did not seem to have trouble even at low revs.

Any thoughts on what this may be? A quick google search revealed that it may be a hydraulic filter/hydrostatic pump issue. I wonder if I introduced some contamination when rebuilding the cylinders that might have blocked up the filters - I thought I worked pretty cleanly.

Thanks

 

[brdgbldr]

Are you sure that you are not accidentally engaging the auxiliary hydraulics?

If you accidentally push the right stick all the way to the right it will engage the detent that holds the auxiliaries on. This will cause the relief valve to open and slow down all of the other functions.

 

[mark.s]

I would think I would notice the auxiliary hydraulics moving if that were the case. I have a grapple bucket on there right now so it would be quite visible. I don't think they were maxed one way or the other. I will run out and check that right now. Did not know my 853 had that functionality.

Appreciate the reply.

 

[worktruck]

I don't know what this pushing the right stick all the way is about... Don't you have to push a button to turn on auxiliary hydraulics in the 853, and then press it again to enable the locking feature for the toggle switch on the right drive stick?

 

[Jim A]

In hydraulic tank there is a suction screen which feeds charge pump and all fluid required for all operations .
Few people ever check clean this screen on main supply inlet pipe.
I have found many partially clogged restricted plastic bag fragments sludge on them .
In cold weather or high rpm pump starves makes buzzing noises cavitation low slow power etc .
I would check it.

 

[Jim A]

In hydraulic tank there is a suction screen which feeds charge pump and all fluid required for all operations .
Few people ever check clean this screen on main supply inlet pipe.
I have found many partially clogged restricted plastic bag fragments sludge on them .
In cold weather or high rpm pump starves makes buzzing noises cavitation low slow power etc .
I would check it.

 

[Jim A]

In hydraulic tank there is a suction screen which feeds charge pump and all fluid required for all operations .
Few people ever check clean this screen on main supply inlet pipe.
I have found many partially clogged restricted plastic bag fragments sludge on them .
In cold weather or high rpm pump starves makes buzzing noises cavitation low slow power etc .
I would check it.

 

[Jim A]

In hydraulic tank there is a suction screen which feeds charge pump and all fluid required for all operations .
Few people ever check clean this screen on main supply inlet pipe.
I have found many partially clogged restricted plastic bag fragments sludge on them .
In cold weather or high rpm pump starves makes buzzing noises cavitation low slow power etc .
I would check it.

 

[Jim A]

Check hydraulic suction screen in tank clean it off.
Then check main drive belt tension which drives main pumps .
Check charge pressure while operating.

 

[mark.s]

Check hydraulic suction screen in tank clean it off.
Then check main drive belt tension which drives main pumps .
Check charge pressure while operating.

Thanks for pointing me to this. Got a chance to take a look today at the tank and I could not find any hydraulic suction screen near the bottom of the tank. I do not see that in the diagram here either, but I suppose it could be built in. Maybe I should look in there with a borescope or something.

Image of parts schematic

I did discover that part number nine in that schematic, the filter screen for pouring oil, was missing its bottom half. My assumption is that is somewhere in the hydraulic tank or down the line further. I am betting that is blocking flow somewhere in the hydraulics. I will try taking it apart tomorrow and seeing if I can find it. Filters are also incoming, those do not look like they have been changed for a while.

 

[worktruck]

Thanks for pointing me to this. Got a chance to take a look today at the tank and I could not find any hydraulic suction screen near the bottom of the tank. I do not see that in the diagram here either, but I suppose it could be built in. Maybe I should look in there with a borescope or something.

Image of parts schematic

I did discover that part number nine in that schematic, the filter screen for pouring oil, was missing its bottom half. My assumption is that is somewhere in the hydraulic tank or down the line further. I am betting that is blocking flow somewhere in the hydraulics. I will try taking it apart tomorrow and seeing if I can find it. Filters are also incoming, those do not look like they have been changed for a while.

There should be three of them in your 853... One on the bottom of the hydraulic reservoir and then one for each drive motor below the cab... Not sure why they're unlisted in many diagrams.

6661807 replacement element for in-line case drain filter, 6661022. (17 in diagram)

Hydraulic screen fits in the film mouth of the tank..(9 in diagram).. It often gets busted off and sinks to the bottom of the tank

 

[Old_853]

My early 853 does not have case drain filters. His might not either. Making sure the tank is debris free and changing main/case drain filters will hopefully fix the problem.

 

[mark.s]

Yes, it looks like my screen for filling has been busted off.

Under the cab

It looks like I do have that in-line case drain filter. It does not appear to be listed as a replacement part for my machine on the service decal on the back door. What is the purpose of that filter? I was under the impression that it was part of the return system, is it only used when draining?

 

[worktruck]

My early 853 does not have case drain filters. His might not either. Making sure the tank is debris free and changing main/case drain filters will hopefully fix the problem.

Do you have filters for the drive motors? Did the factory not actually install them or were they removed by people after the fact?

 

[Old_853]

It takes the excess from the drive motor back to the tank. It's a good idea to have them. Mine does not have any, but it's like the 30th 853 ever made. It has a bunch of weird stuff compared to most of them. Still runs good though, almost 4000 hours on it.

 

[worktruck]

Yes, it looks like my screen for filling has been busted off.

Under the cab

It looks like I do have that in-line case drain filter. It does not appear to be listed as a replacement part for my machine on the service decal on the back door. What is the purpose of that filter? I was under the impression that it was part of the return system, is it only used when draining?

It's an inline filter that's supposed to collect particles.. it should be an item that should be serviced if you haven't for a while you can buy the replacement elements on Amazon/eBay cheaply. You should be able to locate two more that are for your drive motors.

I think Jim was suggesting that pour filter you said was missing can fall to the bottom of the reservoir and jam up the intake

 

[mark.s]

Alright, pour filter was indeed swimming around at the bottom of the tank, may have been restricting the flow there when it got sucked into the outlet there.

Also, I got the chance to remove one hydraulic filter and tear it apart. I confess I don't really know how to diagnose blockage in these. I used an angle grinder to get the case off so I left a ton of aluminum shavings on there, if anyone has a better way to do this let me know (I still have to do the second one). Attached are pics of the pour filter (longer than I expected!) and the hydraulic filter.

Hydraulic filter teardown + pour screen

 

[mark.s]

It takes the excess from the drive motor back to the tank. It's a good idea to have them. Mine does not have any, but it's like the 30th 853 ever made. It has a bunch of weird stuff compared to most of them. Still runs good though, almost 4000 hours on it.

My tank only has two ports, one (larger) seems to be going back to the hydraulic pump near the back-center of the machine, the other one is coming up from the case drain filter. Does the case drain filter also pass fluid from the rest of the hydraulics? Or do those not return to the tank in the same way?

 

[worktruck]

I used an angle grinder to get the case off so I left a ton of aluminum shavings on there, if anyone has a better way to do this let me know (I still have to do the second one). Attached are pics of the pour filter (longer than I expected!) and the hydraulic filter.

Hydraulic filter teardown + pour screen

I thought you were talking about cutting open the inline filters which unscrew and have replaceable elements for a moment and got worried!

 

[mark.s]

I thought you were talking about cutting open the inline filters which unscrew and have replaceable elements for a moment and got worried!

I wouldn't put it past myself, but thankfully this time I didn't screw up that bad!

After changing all hydraulic filters and removing obstructions, the issue persisted. Finally found that the drive belt was loose and tightening it up solved all of my power issues. Probably should've checked that first. Thank you everybody for the wealth of knowledge!