732 Hydraulic mystery problem

[Hotrod1830]

no way to get the cover off without basically tearing the whole machine down and then reassembling without the cover in place to test, way more work there than what it would be worth good idea to tee in a gauge there, I think I will try that if I dont find anything in the wheel motors, Im going to clean them up and pull them apart to inspect them and replace the O-rings since I have them off anyway. thanks

One last thought.... If you have a smart phone, they sell bore scope attachments pretty cheap. You would only need a hole about the size of a dime to get in there and take a peek.

 

[schmelvy]

One last thought.... If you have a smart phone, they sell bore scope attachments pretty cheap. You would only need a hole about the size of a dime to get in there and take a peek.

Maybe found something... was going to take the motors apart so I took a closer look at the exploded view drawing. there is a (double sided) poppet valve in the motor on the relief circuit. One side of the poppet can be reached by pulling a plug on the outside of the motor. I pulled the plug on both motors, one looked good and clean, the other had some debris in it, so I pulled that motor apart to get at the other side, the inside portion of the poppet valve had more debris including a small rock. I'm guessing that the poppet being stuck open due to debris most likely wouldn't cause any serious problem, however, my hope is that the rock and other debris was preventing the poppet from opening to relieve the pressure in the cavity and causing the problem. assembling today. hope this fixes it. thanks again for the responses.

 

[schmelvy]

Maybe found something... was going to take the motors apart so I took a closer look at the exploded view drawing. there is a (double sided) poppet valve in the motor on the relief circuit. One side of the poppet can be reached by pulling a plug on the outside of the motor. I pulled the plug on both motors, one looked good and clean, the other had some debris in it, so I pulled that motor apart to get at the other side, the inside portion of the poppet valve had more debris including a small rock. I'm guessing that the poppet being stuck open due to debris most likely wouldn't cause any serious problem, however, my hope is that the rock and other debris was preventing the poppet from opening to relieve the pressure in the cavity and causing the problem. assembling today. hope this fixes it. thanks again for the responses.

the mystery continues... reassembled today, pulled the machine out of the shop and turned it around, it stopped moving before i could pull it back into the shop. all the hydraulic oil is in the chaincase again. why??? the seals are good. the return/relief lines are clear. the motors check out ok. no explanation in sight. thinking about just cutting my losses and sending it to the scrapyard.

 

[Hotrod1830]

the mystery continues... reassembled today, pulled the machine out of the shop and turned it around, it stopped moving before i could pull it back into the shop. all the hydraulic oil is in the chaincase again. why??? the seals are good. the return/relief lines are clear. the motors check out ok. no explanation in sight. thinking about just cutting my losses and sending it to the scrapyard.

Did you ever measure the case drain pressure?
Tell us more about the "debri". I honestly doubt a rock made it into your drive motor. More than likely you have a failure in that motor,and found debri from said failure. Did you completely disassemble that motor?
The seals will only hold back so much pressure. If you have a motor failure, it will create too much pressure for the seals to handle.
Dont give up yet.

 

[schmelvy]

Did you ever measure the case drain pressure?
Tell us more about the "debri". I honestly doubt a rock made it into your drive motor. More than likely you have a failure in that motor,and found debri from said failure. Did you completely disassemble that motor?
The seals will only hold back so much pressure. If you have a motor failure, it will create too much pressure for the seals to handle.
Dont give up yet.

The debris for the most part looked like small bits and pieces of rubber O ring. I replaced all the o rings in the control valve a while back, the o rings were really chewed up and i'm guessing what I found was remnants of that. there was definitely a tiny rock in there, probably made it in there during assembly or disassembly of the many, times I have had it apart. I didn't completely disassemble the motor, just the back half to get at the relief poppet valve. I am going to try to find a gauge to measure the pressure, but I have tested the return circuit and found it is working, so with a working return circuit, I cant see how it could be building that much pressure. I will update when I have results from the pressure test.

 

[schmelvy]

The debris for the most part looked like small bits and pieces of rubber O ring. I replaced all the o rings in the control valve a while back, the o rings were really chewed up and i'm guessing what I found was remnants of that. there was definitely a tiny rock in there, probably made it in there during assembly or disassembly of the many, times I have had it apart. I didn't completely disassemble the motor, just the back half to get at the relief poppet valve. I am going to try to find a gauge to measure the pressure, but I have tested the return circuit and found it is working, so with a working return circuit, I cant see how it could be building that much pressure. I will update when I have results from the pressure test.

Pulled both motors apart. One looks good. One does not. The geroler looks chewed up and the end plate is worn. I still can't imagine it bypassing fluid at the rate i am losing it but it is at least something. Now I need to try to find parts to fix it.

 

[schmelvy]

Pulled both motors apart. One looks good. One does not. The geroler looks chewed up and the end plate is worn. I still can't imagine it bypassing fluid at the rate i am losing it but it is at least something. Now I need to try to find parts to fix it.

Arrgh! I lost the stupid tag off the motor that had one. anyone know who manufactured these or where to source parts? I cant find much except for a used one on ASAP

 

[Hotrod1830]

Arrgh! I lost the stupid tag off the motor that had one. anyone know who manufactured these or where to source parts? I cant find much except for a used one on ASAP

loader parts source would be a good place to look. They may be able to tell you what brand motor you have. Just looked, they stock a motor for it.

 

[schmelvy]

loader parts source would be a good place to look. They may be able to tell you what brand motor you have. Just looked, they stock a motor for it.

Thanks, I am going to see whether it will be cheaper to repair the motor or replace it with a used one. I took time to clean shop until I found the tag. Eaton/Char Lynn 111-1021-004 No luck so far finding a geroler for it. Bobcat dealer cant get one. Hydraulic shop is checking on availability and supposed to be getting back to me.

 

[Hotrod1830]

If they tell you you cant get parts for it, dont give up just yet. It is possible they used those motors in other makes of equipment and other dealers may stock it. Usually hydro shops do a good job of researching parts availability, but a couple emails or phone calls wont cost alot of time.
fwiw, Pretty sure I used central hydraulics in El paso, Il when I was looking for pump parts for my 1830, that everybody told me I couldnt get. been a few years though.

 

[flyerdan]

If they tell you you cant get parts for it, dont give up just yet. It is possible they used those motors in other makes of equipment and other dealers may stock it. Usually hydro shops do a good job of researching parts availability, but a couple emails or phone calls wont cost alot of time.
fwiw, Pretty sure I used central hydraulics in El paso, Il when I was looking for pump parts for my 1830, that everybody told me I couldnt get. been a few years though.

That number gets a few hits for motors for sale, one place will rebuild yours, and there is
one here that has it listed for avialable parts, might want to fill out the contact section and see if they have what you need.

 

[schmelvy]

That number gets a few hits for motors for sale, one place will rebuild yours, and there is
one here that has it listed for avialable parts, might want to fill out the contact section and see if they have what you need.

The saga continues. finally was able to get a new geroler for the wheel motor. (long wait, I think they actually built one for my order.) disassembled and reassembled both motors, (looks good) 1 with new geroler and installed on the machine thinking I have finally got it. I was wrong. The machine still emptys the hydraulic resivoir into the chaincase in a matter of seconds of use. Does anyone know if there is another interconnection between the hydrostatic system where high pressure fluid can be pushed into the chaincase? I simply do not know how this is happening and have exhausted every option I can think of. frustrated and tired of throwing away good money on a bad machine.

 

[schmelvy]

The saga continues. finally was able to get a new geroler for the wheel motor. (long wait, I think they actually built one for my order.) disassembled and reassembled both motors, (looks good) 1 with new geroler and installed on the machine thinking I have finally got it. I was wrong. The machine still emptys the hydraulic resivoir into the chaincase in a matter of seconds of use. Does anyone know if there is another interconnection between the hydrostatic system where high pressure fluid can be pushed into the chaincase? I simply do not know how this is happening and have exhausted every option I can think of. frustrated and tired of throwing away good money on a bad machine.

responding to my own post seems odd, but a penny for anyone's thoughts- I am beginning to wonder if there could be a one-way valve somewhere in the system that hung up or stuck open which would allow high-pressure fluid to push into the return line of the wheel motor and into the chaincase. logically that couldn't happen because it should just vent back to the tank though and I have already established that the vent lines are open and vent back to the tank. ugh, I'm just thinking in circles here.

 

[Tazza]

responding to my own post seems odd, but a penny for anyone's thoughts- I am beginning to wonder if there could be a one-way valve somewhere in the system that hung up or stuck open which would allow high-pressure fluid to push into the return line of the wheel motor and into the chaincase. logically that couldn't happen because it should just vent back to the tank though and I have already established that the vent lines are open and vent back to the tank. ugh, I'm just thinking in circles here.

Is the case drain line that runs back to the tank un-restricted?
Even if you remove the line at the motor and attach a hose from it to a bucket to collect the oil. When not under load, you shoudl get very little fluid coming out.

 

[spitzair]

Is the case drain line that runs back to the tank un-restricted?
Even if you remove the line at the motor and attach a hose from it to a bucket to collect the oil. When not under load, you shoudl get very little fluid coming out.

I’ll take a look at the hydraulic schematic and physically at my machine to see if there’s any other way for hydraulic fluid to possibly get into the chaincase. Might be a few days before I can get to it but I’ll do my best. We’ll get this figured out one way or another!

 

[schmelvy]

I’ll take a look at the hydraulic schematic and physically at my machine to see if there’s any other way for hydraulic fluid to possibly get into the chaincase. Might be a few days before I can get to it but I’ll do my best. We’ll get this figured out one way or another!

I pulled the return lines off both motors today and started the machine to see what is going on, whith the machine at idle, no load, there is just a dribble of hydraulic fluid running out of the return/relief port on the motor. No fliud coming from the return lines so that rules that out. with a load applied to each motor, the volume of fluid coming out of the return/relief port increases, but dosent appear to be under an exreme amount of pressure, and the amount is similar on both motors. I (again) verified the return lines vent back to the resivoir with compressed air, both checked out ok. spitzair- I think that maybe there is some other point of interconnection between the systems where the problem is. I am going to look through the diagrams again. thanks for the help

 

[schmelvy]

I pulled the return lines off both motors today and started the machine to see what is going on, whith the machine at idle, no load, there is just a dribble of hydraulic fluid running out of the return/relief port on the motor. No fliud coming from the return lines so that rules that out. with a load applied to each motor, the volume of fluid coming out of the return/relief port increases, but dosent appear to be under an exreme amount of pressure, and the amount is similar on both motors. I (again) verified the return lines vent back to the resivoir with compressed air, both checked out ok. spitzair- I think that maybe there is some other point of interconnection between the systems where the problem is. I am going to look through the diagrams again. thanks for the help

Having run out of ideas, I spoke with the service manager at the local Bobcat dealer. He was helpful, but unsure what might be causing the problem, he believes there is something restricting the return which is causing the fluid to blow past the seals. I printed the hydrostatic diagrams from the bobcat and started to map the flow for the return lines from the wheel motors, it looks like it ends up getting back to the tank via the connection block that is on top of the vane pump. I was wondering if anyone had a picture or diagram of that block (bobcat part number 6558359) I cant seem to find anything. I am going to try to tee an oil pressure guage into the return line today to see what the return pressure actually is at the motor. The seals between the motors and the chaincase are only rated at 10 psi, so if its more than that, I will have to investigate the return circuit in detail.

 

[schmelvy]

Having run out of ideas, I spoke with the service manager at the local Bobcat dealer. He was helpful, but unsure what might be causing the problem, he believes there is something restricting the return which is causing the fluid to blow past the seals. I printed the hydrostatic diagrams from the bobcat and started to map the flow for the return lines from the wheel motors, it looks like it ends up getting back to the tank via the connection block that is on top of the vane pump. I was wondering if anyone had a picture or diagram of that block (bobcat part number 6558359) I cant seem to find anything. I am going to try to tee an oil pressure guage into the return line today to see what the return pressure actually is at the motor. The seals between the motors and the chaincase are only rated at 10 psi, so if its more than that, I will have to investigate the return circuit in detail.

I scrounged up enough fittings to tee in an oil pressure gauge on the return line from the wheel motor. it sits close to zero with no load but applying a load to the motor instantly pegged the gauge (100psi) I dont have any spec on the return pressure, but with a 10 psi seal, there is no question why its blowing through there. now, If I could just find out: is the oem bobcat seal capable of holding back much, much more pressure than the aftermarket seal I installed? OR, is the return pressure much, much higher than is ahould be? I am guessing the latter, but I think I will try to find out for sure before I tear it apart, again. If anyone has a return pressure spec or information on the rating of the OEM bobcat seal, that would be very helpful and greatly appreciated.

 

[spitzair]

I scrounged up enough fittings to tee in an oil pressure gauge on the return line from the wheel motor. it sits close to zero with no load but applying a load to the motor instantly pegged the gauge (100psi) I dont have any spec on the return pressure, but with a 10 psi seal, there is no question why its blowing through there. now, If I could just find out: is the oem bobcat seal capable of holding back much, much more pressure than the aftermarket seal I installed? OR, is the return pressure much, much higher than is ahould be? I am guessing the latter, but I think I will try to find out for sure before I tear it apart, again. If anyone has a return pressure spec or information on the rating of the OEM bobcat seal, that would be very helpful and greatly appreciated.

Ok I got some time to look through the hydrostatic system schematic. By return line do you mean one of the big lines going to the motor or the case drain? The way these hydrostatic motors work is they get fed pressure from either of the 2 big lines going into them depending on which way you want to go. The smaller case drain line takes any oil that leaks around the rotating group in the motor and returns it to the hydraulic system upstream of the oil cooler through a check valve. It does not return it directly to the reservoir. The fact that you mention in one of your previous posts that you checked the case drain lines with compressed air and they are clear to the tank has me thinking there is a bad check valve somewhere. I don't know how to post the schematic here but from looking at it the case drain lines could potentially feed fluid back through them to the motors if the check valve is stuck open where it joins up with the oil going to the cooler. Oil will take the path of least resistance and in this case it looks like all the oil coming out of the hydraulic pump is being routed to the cooler. If the valve is stuck open and your oil cooler or hydraulic filter which is downstream of the cooler are even partly plugged up the oil will try to go through the case drain lines through the 10psi seals on the motors and into the chain case as that would be the path of least resistance. So what I would do is check to see if any oil comes out of the case drain hoses coming from the machine when you try to move it. If not then we know that isn't the issue. If there is then we know your motors are likely not the direct culprit and we need to look at the rest of the system. I'll see if I can't figure out how to put the schematic up here or post it someplace else and put a link to it... unfortunately my "genuine new" manual is a black and white photocopy so the schematic coloring is lost but it still gives a very useful diagram of how things are supposed to happen in there.

 

[schmelvy]

Ok I got some time to look through the hydrostatic system schematic. By return line do you mean one of the big lines going to the motor or the case drain? The way these hydrostatic motors work is they get fed pressure from either of the 2 big lines going into them depending on which way you want to go. The smaller case drain line takes any oil that leaks around the rotating group in the motor and returns it to the hydraulic system upstream of the oil cooler through a check valve. It does not return it directly to the reservoir. The fact that you mention in one of your previous posts that you checked the case drain lines with compressed air and they are clear to the tank has me thinking there is a bad check valve somewhere. I don't know how to post the schematic here but from looking at it the case drain lines could potentially feed fluid back through them to the motors if the check valve is stuck open where it joins up with the oil going to the cooler. Oil will take the path of least resistance and in this case it looks like all the oil coming out of the hydraulic pump is being routed to the cooler. If the valve is stuck open and your oil cooler or hydraulic filter which is downstream of the cooler are even partly plugged up the oil will try to go through the case drain lines through the 10psi seals on the motors and into the chain case as that would be the path of least resistance. So what I would do is check to see if any oil comes out of the case drain hoses coming from the machine when you try to move it. If not then we know that isn't the issue. If there is then we know your motors are likely not the direct culprit and we need to look at the rest of the system. I'll see if I can't figure out how to put the schematic up here or post it someplace else and put a link to it... unfortunately my "genuine new" manual is a black and white photocopy so the schematic coloring is lost but it still gives a very useful diagram of how things are supposed to happen in there.

I do have the schematics, I was able to pull off of bobcat online parts. When I said return line, I misspoke, meant case drain. in tracing everything out, I can see it does not return directly to the reservoir but does get back there in a roundabout way. I have run the machine with the case drain lines removed, and no oil comes out from them when the motors have a load on them. oil does come out of the motor itself where the case drain line fitting was removed. as I see it the check valve/poppet (located in the block which both case drain lines connect to) should allow oil to flow away from the motor, so using compressed air would force the poppet open and it work its way through the cooler, filter, and back to the connection block that sits on top of the vane pump, which appears to interconnect with the reservoir tank then bubbling up through the tank. I can only think that for some reason maybe the check valve/poppet is taking a lot more pressure to open than it should. that will come apart for inspection next.