Bobcat 863 right side drive problem

[Who]

Hi guys. I have been searching online for help with this problem and I'm hoping that someone on this forum can help me. I have some experience with backhoes and recently bought my first skidsteer with plans to restore it. I have the Bobcat on jack stands with the engine idling and the problem that I am having is that the right side wheels operate perfectly for about 30-60 seconds after starting the bobcat and actually works better in reverse than the left side wheels but after that it gradually gets slower (within 1 minute) until the drive lever no longer operates the wheels. The wheels continues to creep in reverse since it needs neutral adjustment but that should not be related to the complete lack of response from the drive levers. If I shut off the engine for about a minute and restart it, the wheel would work again for a short while. I don't hear any strange noises and the engine does not sound loaded when the wheels stop responding. If I run the Bobcat on the ground it will work fine forward, backward and up and down a steep grade and will turn properly for a short while until the right lever becomes unresponsive. In the following video I had gotten the wheel to move forward and backwards a few times before I started recording - http://youtu.be/0t4uQXa5ch4 This is a Bobcat 863 with cable steering linkages and I have verified that the linkages are operating the spool valves as they should. Currently the cab is removed and there are no electrical sensors attached and the traction lock system has been removed. I am activating the fuel solenoid directly from the battery and I'm starting the engine by activating the starter also directly from the battery. All filters and oil have be replaced and I have cleaned the case drain filters. When I was cleaning the right side case drain filter I did find a piece of hydraulic hose in the canister so I am not sure if that could be related to the problem. I have also removed and disassembled the right drive motor and everything in there looks fine. The manual says that the relief valve on the motor should have shims that the factory uses to to set the relief pressure but I did not find any shims so I'm not sure if it just didn't need shims or if they were missing. I removed the replenishing valves from the hydrostatic pumps and did not find anything strange. The manual says to replace the valves if they are damaged but I don't see how those can be damaged...what should I be looking for?

I am hoping that this is just a simple problem of something becoming clogged after the oil begins to flow. Would a clogged case drain filter cause drive problems? Your help with this problem would be greatly appreciated.

 

[OldMachinist]

In your video both sides seem to be slow to respond to the lever movement. I'd start by checking the charge pressure. Put a 500 psi pressure gauge in the port where the charge pressure sending unit screws in and see what it says.
Yes a clogged case drain filter would cause the motors to stop but it would also be screaming.

 

[Who]

In your video both sides seem to be slow to respond to the lever movement. I'd start by checking the charge pressure. Put a 500 psi pressure gauge in the port where the charge pressure sending unit screws in and see what it says.
Yes a clogged case drain filter would cause the motors to stop but it would also be screaming.

Well the engine is running at idling speed so I'm not sure if that is why it seems slow to respond. If it was a charge pump problem, wouldn't it affect both sides equally? I will try to get my hands on a pressure gauge but I am still open to other suggestions. I really want to avoid having to swap left and right motors but I guess that might be the only way to help isolate the problem.

 

[Tazza]

Well the engine is running at idling speed so I'm not sure if that is why it seems slow to respond. If it was a charge pump problem, wouldn't it affect both sides equally? I will try to get my hands on a pressure gauge but I am still open to other suggestions. I really want to avoid having to swap left and right motors but I guess that might be the only way to help isolate the problem.

I'm with OM on this one. The response should be MUCH faster than that. Every time you move the lever, even at idle, the wheels should almost instantly start turning. When you let the sticks go, they should stop instantly. They should never keep rolling like they are in your video.
Check/replace the hydrailic filter. Check the oil level and check the charge pressure.
I have never seen wheels roll like that, even when i pulled the engine and pump out of my 753 and did pump work and re-installed it. There was loads of air in the system after that and it was still fast to respond.

 

[Who]

I'm with OM on this one. The response should be MUCH faster than that. Every time you move the lever, even at idle, the wheels should almost instantly start turning. When you let the sticks go, they should stop instantly. They should never keep rolling like they are in your video.
Check/replace the hydrailic filter. Check the oil level and check the charge pressure.
I have never seen wheels roll like that, even when i pulled the engine and pump out of my 753 and did pump work and re-installed it. There was loads of air in the system after that and it was still fast to respond.

Well it is my first skid steer so I really appreciate the feedback from you guys. I know the right side is extremely slow to respond after it runs for a while which is the problem but I thought the left side was working as it should when not on the ground. At this point I would be happy if I could at least get the right side to run as well as the left. Sigh, now I'm regretting not removing and servicing the pumps before re-installing the fan and reservoir especially since I knew the right side had drive problems when I bought the machine. I just replaced the filters and hydraulic oil so that shouldn't be the problem. You said that there was air in your system but does that automatically bleed out with use like in a backhoe's hydraulics or is there some special way of removing air from the Bobcat system?

 

[Who]

Well it is my first skid steer so I really appreciate the feedback from you guys. I know the right side is extremely slow to respond after it runs for a while which is the problem but I thought the left side was working as it should when not on the ground. At this point I would be happy if I could at least get the right side to run as well as the left. Sigh, now I'm regretting not removing and servicing the pumps before re-installing the fan and reservoir especially since I knew the right side had drive problems when I bought the machine. I just replaced the filters and hydraulic oil so that shouldn't be the problem. You said that there was air in your system but does that automatically bleed out with use like in a backhoe's hydraulics or is there some special way of removing air from the Bobcat system?

I opened up the case drain filter today and there was a little black muck in there but not enough to clog it. I washed it out and re-installed it. I did some more testing on the Bobcat and I realized that the right wheels only stop working if I move the lever suddenly. Like if I push it back and forward quickly or push it forward and just release it. If I gradually move the lever it will continue to operate the wheels and I tested it by pushing into a heap of gravel. It pushed into to it and the wheels were skidding when it couldn't push anymore. I did notice a bit of screaming noise from the right side when the engine was at high rpms though so I'm not sure if that is normal. I'm getting a pressure gauge for $42US in my country but I'm considering ordering a $19 gauge that I found on Amazon. Any suggestions on where to order testing equipment?

 

[Tazza]

I opened up the case drain filter today and there was a little black muck in there but not enough to clog it. I washed it out and re-installed it. I did some more testing on the Bobcat and I realized that the right wheels only stop working if I move the lever suddenly. Like if I push it back and forward quickly or push it forward and just release it. If I gradually move the lever it will continue to operate the wheels and I tested it by pushing into a heap of gravel. It pushed into to it and the wheels were skidding when it couldn't push anymore. I did notice a bit of screaming noise from the right side when the engine was at high rpms though so I'm not sure if that is normal. I'm getting a pressure gauge for $42US in my country but I'm considering ordering a $19 gauge that I found on Amazon. Any suggestions on where to order testing equipment?

I can't see the case drain filters being the issue. The main hydraulic one should be changed if you haven't done that already.
You have some good power, but i still think the charge pressure needs checking.
The cheapie gauge from amazon should be ok, as long as it will fit into the charge pressure sender port.

 

[Who]

I can't see the case drain filters being the issue. The main hydraulic one should be changed if you haven't done that already.
You have some good power, but i still think the charge pressure needs checking.
The cheapie gauge from amazon should be ok, as long as it will fit into the charge pressure sender port.

The main filter has been changed. I realized that I only have good power when the machine has just been started but after a while it seems to lose power. Initially, it will drive at idle speed but when it warms up I have to increase the rpms to get it to move. I am guessing maybe when the oil heats up the pumps don't work as well anymore. I am waiting on the pressure gauge but it looks like I will have to be pulling out the pumps...sigh. Is there a way to pull the pumps without removing the whole engine? Also what is the easiest way to save all the new oil I just put in the machine. Thanks for the help guys.

 

[Tazza]

The main filter has been changed. I realized that I only have good power when the machine has just been started but after a while it seems to lose power. Initially, it will drive at idle speed but when it warms up I have to increase the rpms to get it to move. I am guessing maybe when the oil heats up the pumps don't work as well anymore. I am waiting on the pressure gauge but it looks like I will have to be pulling out the pumps...sigh. Is there a way to pull the pumps without removing the whole engine? Also what is the easiest way to save all the new oil I just put in the machine. Thanks for the help guys.

Some don't lik my way of saving the oil, but what i do is running the machine at idle and pump it out the aux connector. When it starts to spit, shut it down.
Pulling the pump and engine isn't as bad as you may think. It comes out as one unit. I'm not sure how hard it is to pull just the pump out, or if it is even possible to do.
See what the gauge tells you, work from there.

 

[Who]

Some don't lik my way of saving the oil, but what i do is running the machine at idle and pump it out the aux connector. When it starts to spit, shut it down.
Pulling the pump and engine isn't as bad as you may think. It comes out as one unit. I'm not sure how hard it is to pull just the pump out, or if it is even possible to do.
See what the gauge tells you, work from there.

Pumping out the oil through the aux seems like a good idea but would that also remove the oil in the motor and motor lines? Yeah I guess I will be waiting on the gauge before I decide what to do.

 

[Tazza]

Pumping out the oil through the aux seems like a good idea but would that also remove the oil in the motor and motor lines? Yeah I guess I will be waiting on the gauge before I decide what to do.

It will only remove oil from the pump to the coupler. It will never get it all, there will be residue so the pump won't be running dry.

 

[Who]

It will only remove oil from the pump to the coupler. It will never get it all, there will be residue so the pump won't be running dry.

Ok so I installed the gauge to test the charge pressure but the gauge is a 4000 psi gauge and the increments are every 100psi. At idle the gauge shows zero but at 10-20% throttle it reaches 100psi and after that, even if I increase the throttle to maximum, it would only go up to approximately 120psi. Is this normal? Is the pressure relief valve limiting the pressure to 120 psi or is the pump worn and this is the highest pressure that it can achieve? The manual has information about the pressure sender unit mapping pressure to ohms in a table and the highest pressure value in the table is 150psi so I'm not sure if that is the maximum charge pressure. I also noticed that when I operate the drive levers, the pressure drops back to basically zero while the wheels are skidding on the ground. Is that normal?

 

[Tazza]

Ok so I installed the gauge to test the charge pressure but the gauge is a 4000 psi gauge and the increments are every 100psi. At idle the gauge shows zero but at 10-20% throttle it reaches 100psi and after that, even if I increase the throttle to maximum, it would only go up to approximately 120psi. Is this normal? Is the pressure relief valve limiting the pressure to 120 psi or is the pump worn and this is the highest pressure that it can achieve? The manual has information about the pressure sender unit mapping pressure to ohms in a table and the highest pressure value in the table is 150psi so I'm not sure if that is the maximum charge pressure. I also noticed that when I operate the drive levers, the pressure drops back to basically zero while the wheels are skidding on the ground. Is that normal?

120 psi of charge pressure at mid to high speed is good, this is regulated by a relief valve. I just don't know what this figure shoul be when driving/spinning the wheels. I dont' believe it should hit zero, it will lower but not drop out totally.
I'd like to think it's a drive motor issue leaking internally.
Hopefully Bobcatdan will pop his nose in, but the next thing i'd try would be to remove the two large hoses to the drive motors and cap them with metal plugs. Start the machine and slowly push the lever forward and backward. This should strain or even stall the engine. There should be very little lag with the levers pushing back at you. You shouldn't have to push the lever forward and wait like the video showed, it should be almost instant.

 

[Bobcatdan]

120 psi of charge pressure at mid to high speed is good, this is regulated by a relief valve. I just don't know what this figure shoul be when driving/spinning the wheels. I dont' believe it should hit zero, it will lower but not drop out totally.
I'd like to think it's a drive motor issue leaking internally.
Hopefully Bobcatdan will pop his nose in, but the next thing i'd try would be to remove the two large hoses to the drive motors and cap them with metal plugs. Start the machine and slowly push the lever forward and backward. This should strain or even stall the engine. There should be very little lag with the levers pushing back at you. You shouldn't have to push the lever forward and wait like the video showed, it should be almost instant.

I bet the drive motor has blown orings. Common on 863 and 873.

 

[Who]

I bet the drive motor has blown orings. Common on 863 and 873.

I had pulled the right side motor and the orings seemed fine. There were some scuff marks on the valve plate but nothing that I could feel with my fingers. I would post images but it seems that this forum doesn't allow images? There was a lot of crap in the case drain filter, including a little piece of hose, when I first cleaned it so I'm wondering if some of that is still stuck in the pump. That still would not explain why both sides loses power over time though. Would a badly calibrated shuttle relief valve cause the same symptoms as internal leakage in the motor? How would I cap the hoses on the drive motor? Are there special plugs for those or would I have to construct something to cap them?

 

[Tazza]

I had pulled the right side motor and the orings seemed fine. There were some scuff marks on the valve plate but nothing that I could feel with my fingers. I would post images but it seems that this forum doesn't allow images? There was a lot of crap in the case drain filter, including a little piece of hose, when I first cleaned it so I'm wondering if some of that is still stuck in the pump. That still would not explain why both sides loses power over time though. Would a badly calibrated shuttle relief valve cause the same symptoms as internal leakage in the motor? How would I cap the hoses on the drive motor? Are there special plugs for those or would I have to construct something to cap them?

I'd have thought if the valves were stuck, you'd just have lower power to the drive motors.
The caps should be standard JIC or ORFS, not sure when they all went ORFS, sorry, not sure about the size that it would be.

 

[Who]

I'd have thought if the valves were stuck, you'd just have lower power to the drive motors.
The caps should be standard JIC or ORFS, not sure when they all went ORFS, sorry, not sure about the size that it would be.

Well I'm almost sure the valves are not sticking but they could be missing shims that are required for setting the relief pressure. It's ORFS so I will looks for some caps to do the test. I think I will also check the charge pressure after the machine warms up to see if it drops off. Thanks again for all the help/suggestions.