B200 Hydrostatic Issues - sluggish/no movement forward or back when warm.

[gjb012]

I have a Bobcat 2003 B200 (EF200) with 670 hrs on it, and it has been left unused for long times (hence low hours), but runs well.
The oil and hyd fluid/filter have been changed at 500 hrs and in general the tractor has not been worked hard and has been well maintained.
I recently checked the hyd filter and it was clean as new, with no metal debris or really much of any debris in it at all.
There was some small blue rubber pieces in the bottom, which looked like a seal of some sort in the system that may have degraded.
For someone with in-depth knowledge of the internals of the system - these blue pieces could be an important clue to my problem.

The tractor will move forward and backward sluggishly and without much force when cold, but after running the backhoe/loader/tractor for 5-10 minutes the movement decreases to basically no movement at all. After 30 minutes of use the tractor will not budge in either direction. Allowing it to cool for an hour will get some movement out of it, but very limited, in the morning it will move sluggishly along for a few minutes.

The tractor was working fine until over the course of one day of constant back-hoe use, this forward/reverse degradation of movement happened. It got quickly very bad to the point where the tractor was unusable. I assume it will not move at all soon, cold or hot. I want to use the last bits of life in whatever component is failing to either diagnose the problem or get it on its trailer and off to someone who can fix it.

The hydraulics (loader/backhoe) and steering work perfectly, as does the hydraulic fluid cooler.
The drive safety button to work well - i.e. tractor will not move until it is pressed and once pressed, will move, or at least attempt to move.
The hydraulic brake seems to work, regardless of operating temp, i.e. even of the tractor will not move under its own power, when the pedal is not depressed it still seems to be in brake mode, i.e. will not roll. (I will have to check this again to be absolutely sure this is the case).

The last clue in the scenario is that the backhoe arm piston rod snapped off internally about 4-6 operational hours before this problem started to occur. It was repaired and put back in service. The next day or two this hydrostatic problem started to happen. Perhaps these issues are related in that the cracking of the piston rod may have left metal fragments in the oil...which could have passed through the pump or motor and done it in.

I have the owners, parts and service manuals and have read these and all the threads and advice on this site concerning various failures of the hydrostatic systems. I feel relatively well informed on the workings of the systems having done all this reading, but...

I cannot pin-point the problem after doing some diagnostics. The local Bobcat dealers do not have much experience with this model tractor and I am concerned to bring my issue to them un-diagnosed, and rack of $$ in diagnostics time without a solution. I would prefer to diagnose the problem (if possible) and point them at it; or better yet, just fix it myself. I have done extensive mechanic work in my life and am not worried about the work here....though I would like to diagnose the problem correctly, and not just replace one expensive part after another until the problem is fixed!

My assumptions/understandings are (please correct as I am sure some of these are incorrect):
There are 3 hydraulic pumps: Hydrostatic (31), Charge Pump (21) and Gear Pump (34) (# refer to numbers on schematic)
The hydrostatic pump supplies the power to the drive motor
The Charge pump runs the controls relays and drive pedal for the hydrostatic transmission system
The Gear pump runs the steering motor and the hydraulics (loader/backhoe)

If this was a drive motor shuttle valve (25) or Relief valve (20, 23, 24, 29) it would not be affected so dramatically by the temperature of the fluid nor would it be the same exact behavior in forward and reverse. I am assuming the valves/solenoids would either work or not, i.e. go or not go, and not degrade in both directions with temp.

If the Charge Pump failed, it would affect more than just the forward/backward motion of the tractor - as I assume it does something else than just this control function.

I assume the foot control valves are working well - as this problem is exactly the same in forward and reverse, as I assume if the foot control failed it would work better in one direction than the other.

I am assuming (dreading) it is the drive motor and/or hydrostatic pump - both of which are very expensive and near impossible to get, or even get repair kits for.

My questions are:
1) What do the above symptoms point to as the likely suspect?

2) Are my gross assumptions about ruling out the control valves, solenoids, charge pump valid or should I do more detailed diagnostics on these smaller components?

3) Could it be that a piece of fragment of metal from the backhoe arm piston would NOT be filtered out before it got into the motor or pump? i.e. would returning oil from the arm piston get to the drive motor or hydrostatic pump BEFORE it passed through the filter?

4) if the hyd oil was contaminated could I realistically be looking at a pump AND motor failure or does the fact that the other hyd systems work well indicated the hydrostatic pump is still OK? i.e. does the hydrostatic pump only operate the drive motor or does it operate some other system on the tractor all of which are working?

5) I am assuming (dreading) that the drive motor has failed and have started to investigate getting it rebuilt or replaced:

a) the part/tag number on it (780-0280-170-000) makes no sense to Bobcat or Parker dealer/distributor. No one seems to be able to cross ref this tag number on the German made motor to a current Parker number. I am sure this is a Parker TF/TG/TH series motor but the specs are so exact, without the cross reference to this number, I would be guessing to get the right replacement. Bobcat has said they MAY be able to get the motor for $1800 and 4 weeks delivery time - but no guarantees! Long story short - can anyone help provide a cross reference to a current Parker Model number, i.e. TF 0170 E W 26 0 XXXX?

b) is there some trick to getting the drive motor out, as I have removed all the obvious bolts (6) and hoses and the motor will not budge. I have tried to persuade it out with a mallet and brass hammer, I have even gotten it to rotate IN the casing but it will not come out! Is there a press fit, or worse, a clip or nut on the shaft inside the transmission that prevents it from coming out? I am pulling my hair out trying to remove the motor so I can at least take it to a hyd motor specialist to see if they can test it or cross reference it.

c) is the best way to test the hydrostatic pump by just testing the pressure as detailed in the repair manual on page 30-50-1 - or can we assume it is working because some other system (loader/steering/etc) is working?

Sorry for the long explanation - but I thought it best to give a comprehensive summary for best way to get the best advice on the way forward.

Thanks, Greg

 

[SSdoxie]

If I was testing this here is what I would do:
1. Remove the Tow Valve spool and inspect it closely making sure the O-ring & backup ring are fine plus tip of the valve is not scratched. Tow valve is the smaller of the 2 hex plugs on top of the pump next to Charge Pressure adjustment screw. Tow valve must be screwed down tight for good drive power.
this is not likely the problem, but eliminate the easy first.
2. Go through the pump adjustment/test procedures step by step starting with Charge Pressure first then test Flushing Spool adjustment even if Charge Pressure was at spec. Note: If Flushing Spool is adjusted, go back and redo Charge Pressure and continue to go back and forth on these 2 until both stay in spec. Then test/adjust Torque Limiter. If Torque Limiter is adjusted, go back to Charge pressure and retest everything.
Another note: You could disconnect the pressure out lines to the drive motor and plug the pump outlet ports with steel caps/plugs. Be sure to use caps/plugs capable of withstanding the high pressure. After ALL pump adjustments are complete and verified pump outlet is able to create 3600 psi. reconnect drive motor. If drive loss it still there, drive motor is the problem.

It has been a number of years since I worked on 1 of these, but some of those EF200 and early B200 did require readjustment of the pump after a few hundred hours. What you are describing usually was an excessive pressure drop in Flushing Spool and/or Limiter adjustment.

And yes, the drive motor is supposed to slide out. No internal clips in differential.

 

[SSdoxie]

Debris can get past the filter from the loader or backhoe valve if the filter by-pass check ball is stuck open. Might want to inspect that too.

What fluid did you use when changed? Book says OK to use motor oil, but hydraulic/hydrostatic fluid works better especially when system is hot.

Another question I just thought of. Where is the oil cooler? Is it up in front of radiator or back by the pump? If by the pump, move up front and mount it in front of the radiator. This was one of the changes Bobcat made after inheriting this product and encountering some loss of drive due to heat. You can still use the electric fan on it, just run long hoses and wires to front of radiator.

 

[cheaptubes]

I have a B250 & a similar issue. Its always had the problem of overheating after 20-30min and getting sluggish but I could work with that. 2 winters ago it decided it wouldn't drive fwd or bk. I had a diesel mechanic pick it up and he look at a lot of things and it was back to normal self but when he brought it back it failed within 20 min. He fixed it again for free but said he didn't know what was wrong other than he thinks its electrical. He said he checked the connections and coil relays and showed me where they were so I could do the same. It then worked for me all winter for up to 45 min at a time & i thought it was fixed so I started working on a project. I did get stuck & unstuck and the problem immediately reappeared. Its slightly different now in that before it wouldn't move period. Now if I keep my foot on the pedal in either direction it will crawl after about a minute. Today I cleaned the coils/relays he showed me and added some dielectric grease. When I started it it drove perfectly for 10 seconds until I tried to go fwd, then the delay again. I'm trying to level a site for a pool for my son. I do depend on this machine in our yard and to push snow banks so I need to fix it. It has 523 hrs. any thoughts? I also suspect the green buttow/switch or the relays themselves. I did find a burnt wire under dash but it went to the fuel gauge so I fixed it but wasn't to concerned. Also the problem initially started when mice made a house under the dash panel. I've got the floor off and the dash apart trying to figure it out. I'm trying to mess with 1 thing at a time & test so if it does come alive again I will know what I did to fix and can hone in on the ultimate cure. Please help if you can. Bobcat tried selling me a new hydro pump for $3500 or a wire harness for $1700. I don't think its the pump & neither does the mechanic. He did turn up the pressure a bit and it ran great from Oct till now.

 

[gjb012]

Thanks for the replies and I will post the solution when found.

Thank you SSdoxie as I have read many of your posts and I was hoping you would reply. You are clearly very knowledgeable of these systems and machines and greatly appreciate you taking the time to reply. I will go through the steps you advised and it would be great if this can fix the issue; fingers crossed.

To answer your questions (and ask a few more):
- Hyd oil changed with Bobcat Hydrostatic oil and is super clean and I really doubt the issue is the oil contamination - but it is always a concern to consider.

- The oil cooler is under the seat and it is a good suggestion to move it - and I will do that; though is not the main problem now, though is probably a contributing factor. I am concerned at the temp the hyd oil becomes when it is running, it is very very hot. The whole storage tank becomes so hot that one cannot even hold a hand to it. This seems not right, but not sure as this is the first time I have worked the tractor a lot in the hot weather. The fan runs for a while (10-15 minutes) after the machine is shut off, so obviously it is working and cools the oil, but I can see the fan not being able to keep up with the heat of the machine while working it hard. It is curious that both myself and 'cheaptubes' did not have problems until the hot weather came this year, i.e. worked fine in the cooler/colder weather.

- can you advise if the "filter by-pass check ball" is located inside the oil tank/filter component, or is it external? I think it is at the bottom of the filter element, in the black plastic housing, but not sure. This is where I found the blue rubber fragments - but once cleaned it all seemed to work OK, though could have been held open by some of this rubber debris and allowed some debris to get into the system...but I will investigate this further when/if the advised adjustments do not rectify the issues and I am considering a failed pump/motor again.

- if you get a chance and it is not too much trouble, can you verify my summary of the roles of the three pumps, i..e charge, gear and hydrostatic. Clarifying this for me would allow me to know exactly what each does for further problems down the road. I am also looking to replace the gear pump if possible for a slightly higher volume to that I can get more GPM to the third valve to run more attachments on the front. I am not looking for high-flow, but upping the gear pump from 12GPM ->16 GPM would give the tractor more usability for me....though this is just a wish-list at this point.

- one last question - in the manual it says to test all the pressures at 150 degrees F oil temp. How accurate do I need to be with this aspect, i.e. do I need to get a thermometer as well as I am not sure the one on the storage tank is that accurate.

Again - greatly appreciate your time and I will post the results of the investigation - as these are great machines that give a great service with perhaps a bit more TLC and attention to detail tuning than most.

Thanks, Greg

 

[SSdoxie]

Thanks for the replies and I will post the solution when found.

Thank you SSdoxie as I have read many of your posts and I was hoping you would reply. You are clearly very knowledgeable of these systems and machines and greatly appreciate you taking the time to reply. I will go through the steps you advised and it would be great if this can fix the issue; fingers crossed.

To answer your questions (and ask a few more):
- Hyd oil changed with Bobcat Hydrostatic oil and is super clean and I really doubt the issue is the oil contamination - but it is always a concern to consider.

- The oil cooler is under the seat and it is a good suggestion to move it - and I will do that; though is not the main problem now, though is probably a contributing factor. I am concerned at the temp the hyd oil becomes when it is running, it is very very hot. The whole storage tank becomes so hot that one cannot even hold a hand to it. This seems not right, but not sure as this is the first time I have worked the tractor a lot in the hot weather. The fan runs for a while (10-15 minutes) after the machine is shut off, so obviously it is working and cools the oil, but I can see the fan not being able to keep up with the heat of the machine while working it hard. It is curious that both myself and 'cheaptubes' did not have problems until the hot weather came this year, i.e. worked fine in the cooler/colder weather.

- can you advise if the "filter by-pass check ball" is located inside the oil tank/filter component, or is it external? I think it is at the bottom of the filter element, in the black plastic housing, but not sure. This is where I found the blue rubber fragments - but once cleaned it all seemed to work OK, though could have been held open by some of this rubber debris and allowed some debris to get into the system...but I will investigate this further when/if the advised adjustments do not rectify the issues and I am considering a failed pump/motor again.

- if you get a chance and it is not too much trouble, can you verify my summary of the roles of the three pumps, i..e charge, gear and hydrostatic. Clarifying this for me would allow me to know exactly what each does for further problems down the road. I am also looking to replace the gear pump if possible for a slightly higher volume to that I can get more GPM to the third valve to run more attachments on the front. I am not looking for high-flow, but upping the gear pump from 12GPM ->16 GPM would give the tractor more usability for me....though this is just a wish-list at this point.

- one last question - in the manual it says to test all the pressures at 150 degrees F oil temp. How accurate do I need to be with this aspect, i.e. do I need to get a thermometer as well as I am not sure the one on the storage tank is that accurate.

Again - greatly appreciate your time and I will post the results of the investigation - as these are great machines that give a great service with perhaps a bit more TLC and attention to detail tuning than most.

Thanks, Greg

Definitely move the oil cooler up front. This was a major contributor to hot oil & weak drive when cooler was under the floor. Just not enough fresh air circulation and too close the pumps. Bobcat did enlarge the cooler when it was moved, you could simply add an extra transmission cooler in-line when it is moved.

I believe you are correct in location of the filter by-pass in bottom of the filter.

The hydrostatic pump (variable piston pump) is the ground drive feeding oil to the drive motor. Charge pump supplies pilot oil to the travel pedals and moves the swashplate in the piston pump, charge oil is also getting fed into the lower pressure side of the hydrostatic pump to replenish case drain oil from pump and motor. This pressure on the low side (return from motor) also creates pressure to keep tractor from free-wheeling (coasting) when you release travel pedal to neutral. If you cannot build or maintain charge pressure when hydro pump is under load means oil is escaping to tank via worn pump or motor parts. Gear pump supplies oil to steering through Priority valve and to loader & backhoe functions then through cooler and filter back to tank.

Pump test do need to be done with warm oil 150 - 200 is OK. Use an infra-red temp gun checking it at inlet to charge pump or gear pump would be close enough. Better to test oil a little on hot side than cool since it drives now with cold oil.

 

[gjb012]

Dennis,

thanks again for the reply. On moving the oil cooler, I am considering leaving the original in there, and putting an additional decent sized one in front of the radiator with electric fan, and plumbing it in series with the one under the seat. My thinking is I would rather have too much cooling capability than too little.

My questions on this are:
- I assume putting the coolers in series with the one on the radiator being primary and the original under the seat being secondary, with the fan on both actuated from the one sensor in the original one. Any issues you can see with this?

- you wouldn't remember which direction the oil flows in the cooler (i.e. which fitting is inlet and which outlet), as ideally I would like to make the one under the seat the second in the series of the two.

- do you know what PSI the oil in cooler is pumped at, as this is critical in getting a cooler than can handle the pressure. I was looking at generic ones from Zoro or hydraulicsdirect.com that have a 377 max PSI. Seems a bit low, but I cannot find the spec anywhere for what the max or normal pressure in the cooler is. I am guessing it is not too high, but ~350PSI seems low. Just want to make sure I get the right cooler.

I will post my findings/solution to this problem. Hopefully making the adjustments you suggested to: Charge Pressure, Flushing Spool and Torque Limiter will remove the problem when the system is cold, and adding a cooler will make it never happen again.

Thanks again and hope to not have to bother you anymore ... and fingers crossed, problems will be solved. I need to get this thing back running as I am dead in the middle of a job.

 

[SSdoxie]

Cooler up front shouldn't need an electric fan. Oil is only flowing through it when engine is running so engine/radiator fan will draw air through it. I would put front cooler as second in line, not primary. This way the original cooler can reduce fluid temp some degree then the front cooler and finish cooling it. If the front cooler is primary then the radiator will be exposed to that much hotter air cooler heating up the air that much more.

There is no pressure spec on the return (cooler) line. The only pressure seen is what is caused by resistance inside the cooler plus flow through the filter and the filter has 36 psi. by-pass relief. Match the cooler equal to or greater than the combined flow of gear pump (12 GPM) and Charge Pump (8.2 GPM).

No idea which is in & out of the cooler, need to follow the lines at each connection to see where they go or come from. From the Backhoe valve is In to cooler, line going to filter/reservoir is cooler out.

 

[gjb012]

Sorry for the delayed update - have not had time to investigate this further. Finally yesterday I did.

As per suggestions, checked tow valve - looks fine, so scores, just a little ring where it seats, as I would expect.

Installed test gauges as per the manual, at 1000RPM I was getting ~100PSI at the charge port on initial start-up. This reduced a bit as the hyd fluid warmed to 150F. I am unable to get the charge pressure any higher than this unless I rev to 3000+ RPM. I tried screwing the adjuster all the way in (clockwise) and out and no change. The charge pressure had no change no matter where the adjustment was set. I pulled the charge pressure adjuster out and it looked fine, no scores, nicks, marks, looked perfect. I have a good amount of hyd fluid. If I increase the RMP to 3000 I get more charge pressure but not over 200 PSI and adjuster has no effect on it.

Question: can I adjust the charge pressure while the motor is running, or does it only need to be done when the engine is off? I assume it is just a pin valve that increases/reduces the flow, or is there some mechanism that is set when the engine is off and the charge pressure is set on startup? Just curious as I did it both ways (engine off and engine on) and still got no change, but also wondered if adjusting charge pressure valve while engine is running did some damage.

I am also getting zero pressure on the Swash Plate adjuster gauge at 1000 RPM. The manual says, "note pressure then depress the forward drive and pressure should increase by about 30 PSI". The pressure does increase by about 30 PSI, but the noted pressure at 1000 RMP is zero....which does not seem correct.

Any thoughts? I am getting a sickening feeling the hydrostatic pump is NG. I expect reading through other threads it will be impossible to find....not to mention expensive.

I would like to do further diagnostics to ensure it is the hydrostatic pump before I take it out and start down that path.

Any help is appreciated.

Thanks, Greg

 

[SSdoxie]

Book advises to adjust charge pressure (or any relief valve) with engine off. This is for safety purposes and minimize leaks. When you loosen the locknut it could allow some oil to escape. if the adjustment screw is turn out to far hydraulic could spray out and hit you. All the screw doing during adjustment is apply more tension or reducing tension on a spring that pushes on a poppet against the hydraulic pressure thus increases or decreases pressure.
The hydrostatic pump and drive motor both see charge pressure, if leakage in either one or both is greater than the flow of oil from the charge pump, charge pressure is zero. Sounds like you have leakage than the charge pump can over come, either excess leak in motor or pump or worn charge pump.

To see if motor is the problem, cap off the lines from the pump going to the motor (with good strong steel caps) and repeat tests. If pressure adjustments return then motor is your problem. If they don't then pump is for sure, but motor leakage is still unknown (could also be bad).