873 Left Side Only Engages When Joystick is Maxed Out

[zghorner]

I bought a used bobcat 873C a few weeks ago with 2400 hours and it has had this problem since I got it home. It only seems to do this after you try to work the machine under load, When it first starts up and even up to operating temp it moves around as it should but after you go try to move some dirt or what have you, the left side stops working for the most part. What its doing: The right side works like it should, but the left side joystick doesn't move the wheels until it is pushed all the way forward then the wheels engage and peel out/move at full speed. When it is malfunctioning sometimes when you move the left joystick to the rear, the machine want to move forwards slightly. I opened up the cab and all of the linkage looks good, both sides engage everything more or less the same. Has anyone else dealt with this issue before? This is my first skid steer so I don't even know where to begin to fix the issue. Any advice will really be appreciated.

 

[bobbie-g]

Let me take a shot at this. With the cab up and looking at the left linkage, you should see where the linkage goes from the front of the machine back toward the engine, then connects with a bell crank. It'll be very hard to see, under a horizontal plate. The plate moves side to side as the joysticks/bell cranks are moved. The plate's purpose is to hold both right and left bell cranks in a neutral position when the joysticks are released. Looking at the center of either bell crank, you will see the top of a square shaft. That shaft is vertical, and runs down into the valving on the end of the hydraulic pump. As the valve shaft turns, hydro oil/pressure is applied to the drive motors (one on each side between the wheels). Each bell crank is aluminum, sad to say, and clamps onto the square shaft via a locking bolt/nut which when tightened, pinches the shaft with the aluminum bell crank as I recall. I think the aluminum is prone to deform and not grip the shaft securely, allowing for some really disconcerting wheel motion. BTW, this is much easier to understand by moving the joystick (engine off!) while watching what happens. I think the right square shaft is easier to see. So check for perhaps looseness between the shaft and the alum bell crank. Pse let us know what you find. More details here if you need them (like how to get that plate out of the way without draining all the hydro oil). Also, don't disassemble the plate/bell cranks without checking back here first. There be monsters out there......! ---Bobbie-G

 

[zghorner]

Let me take a shot at this. With the cab up and looking at the left linkage, you should see where the linkage goes from the front of the machine back toward the engine, then connects with a bell crank. It'll be very hard to see, under a horizontal plate. The plate moves side to side as the joysticks/bell cranks are moved. The plate's purpose is to hold both right and left bell cranks in a neutral position when the joysticks are released. Looking at the center of either bell crank, you will see the top of a square shaft. That shaft is vertical, and runs down into the valving on the end of the hydraulic pump. As the valve shaft turns, hydro oil/pressure is applied to the drive motors (one on each side between the wheels). Each bell crank is aluminum, sad to say, and clamps onto the square shaft via a locking bolt/nut which when tightened, pinches the shaft with the aluminum bell crank as I recall. I think the aluminum is prone to deform and not grip the shaft securely, allowing for some really disconcerting wheel motion. BTW, this is much easier to understand by moving the joystick (engine off!) while watching what happens. I think the right square shaft is easier to see. So check for perhaps looseness between the shaft and the alum bell crank. Pse let us know what you find. More details here if you need them (like how to get that plate out of the way without draining all the hydro oil). Also, don't disassemble the plate/bell cranks without checking back here first. There be monsters out there......! ---Bobbie-G

Wow, thank you for the detailed instructions. I will check it out today and post back what I find.

 

[zghorner]

Wow, thank you for the detailed instructions. I will check it out today and post back what I find.

one thing I should clarify, I am calling the left side as you sit in the machine to operate it. I looked it over and their doesn't appear to be any looseness or deformities in the bell crank. However, The right side has a rubber spacer on the bolt that connects the linkage to the bell crank...and the left side it is missing and the bolt is loose and allows the bell crank to move up and down slightly along that bolt. Probably ought to fix that while I'm at it but I highly doubt that will solve this problem. Is it odd thing is it only does this after it has been worked.

 

[bobbie-g]

one thing I should clarify, I am calling the left side as you sit in the machine to operate it. I looked it over and their doesn't appear to be any looseness or deformities in the bell crank. However, The right side has a rubber spacer on the bolt that connects the linkage to the bell crank...and the left side it is missing and the bolt is loose and allows the bell crank to move up and down slightly along that bolt. Probably ought to fix that while I'm at it but I highly doubt that will solve this problem. Is it odd thing is it only does this after it has been worked.

Yup, left side is to your left as you are sitting in the seat. That bell crank shouldn't move up and down. It should be solidly clamped to the square head on the shaft that goes downward into the large pump/valve assembly. Were you able to put eyes on the square headed shaft? As I said, I think last time I tried to check for looseness during routine maint, I could not see the left shaft, only the right. Once I get back home early next week, I can try to snap a pix and post it here. Rubber grommets: at other places in the linkage, those are fabricated as a unit with an outside metal bushing, rubber insert, and inside bushing. If the left rubber is gone, it may be this is a large source of your issue. Unsure why this would only manifest after warmup. ---Bobbie-G

 

[zghorner]

Yup, left side is to your left as you are sitting in the seat. That bell crank shouldn't move up and down. It should be solidly clamped to the square head on the shaft that goes downward into the large pump/valve assembly. Were you able to put eyes on the square headed shaft? As I said, I think last time I tried to check for looseness during routine maint, I could not see the left shaft, only the right. Once I get back home early next week, I can try to snap a pix and post it here. Rubber grommets: at other places in the linkage, those are fabricated as a unit with an outside metal bushing, rubber insert, and inside bushing. If the left rubber is gone, it may be this is a large source of your issue. Unsure why this would only manifest after warmup. ---Bobbie-G

yea I could see the square shaft decent enough. Just laid on my belly with my head up in there as far as I can. The bell crank wasn't rounded at all and felt and looked very tight while moving it. The other side of the bell crank that attaches to the joystick linkage is loose as a goose and looks to be missing something. Here is a link to a picture of my steering components, Bolt (num 24) seems to be missing the bushing (num 29). http://imgur.com/17JrJZ4

 

[bobbie-g]

yea I could see the square shaft decent enough. Just laid on my belly with my head up in there as far as I can. The bell crank wasn't rounded at all and felt and looked very tight while moving it. The other side of the bell crank that attaches to the joystick linkage is loose as a goose and looks to be missing something. Here is a link to a picture of my steering components, Bolt (num 24) seems to be missing the bushing (num 29). http://imgur.com/17JrJZ4

Glad the square shaft is solid in the bellcrank. == OK, there is a really good chance that the missing rubber bushing is your issue. Here's an abbrev description of how the joysticks control the square-headed shafts: The spring-loaded plate (12 in your parts layout) has two bars (19) that attach underneath. With no hand pressure on the joysticks ("neutral" position), the pair of rollers (44) at the end of each bell crank are against the bars (19), which holds the bellcranks in their neutral positions (note: adjusting those bars will change the bellcrank position, which then will result in wheel creep or worse when the joysticks are in neutral, so don't adjust the bars casually!). Once either joystick is moved, the plate shifts sideways (because the rollers (44) bear on the bar and cause the plate to shift) against spring pressure, and the joystick that was moved causes the corresponding wheels to turn. But at the same time, the bar (19) has now moved away from the other set of rollers (44), so that bellcrank is no longer held in the neutral position and becomes very easy to move. Much easier to see, than to grasp this process from this description. At any rate, once a bellcrank is not held in neutral by the rollers/bar, that side of the machine is very prone to run fwd or back without positive joystick control. You machine doesn't have good joystick control due to being missing that rubber bushing, which puts lots of slop in that linkage. Once you move the right side joystick, the left bell crank is no longer held in neutral. And since it has no good linkage to the joystick, it sort of moves where it pleases and the left wheels jerk around without good control. Whew, this may have you even more confused! Sorry for the longwinded monolog. ---Bobbie-G

 

[zghorner]

Glad the square shaft is solid in the bellcrank. == OK, there is a really good chance that the missing rubber bushing is your issue. Here's an abbrev description of how the joysticks control the square-headed shafts: The spring-loaded plate (12 in your parts layout) has two bars (19) that attach underneath. With no hand pressure on the joysticks ("neutral" position), the pair of rollers (44) at the end of each bell crank are against the bars (19), which holds the bellcranks in their neutral positions (note: adjusting those bars will change the bellcrank position, which then will result in wheel creep or worse when the joysticks are in neutral, so don't adjust the bars casually!). Once either joystick is moved, the plate shifts sideways (because the rollers (44) bear on the bar and cause the plate to shift) against spring pressure, and the joystick that was moved causes the corresponding wheels to turn. But at the same time, the bar (19) has now moved away from the other set of rollers (44), so that bellcrank is no longer held in the neutral position and becomes very easy to move. Much easier to see, than to grasp this process from this description. At any rate, once a bellcrank is not held in neutral by the rollers/bar, that side of the machine is very prone to run fwd or back without positive joystick control. You machine doesn't have good joystick control due to being missing that rubber bushing, which puts lots of slop in that linkage. Once you move the right side joystick, the left bell crank is no longer held in neutral. And since it has no good linkage to the joystick, it sort of moves where it pleases and the left wheels jerk around without good control. Whew, this may have you even more confused! Sorry for the longwinded monolog. ---Bobbie-G

That makes sense to me, you are very good at describing how these machines work. I will call the local bobcat dealer I the morning to see if they stock that part. I will let you know how it goes after I get it installed.

 

[zghorner]

Glad the square shaft is solid in the bellcrank. == OK, there is a really good chance that the missing rubber bushing is your issue. Here's an abbrev description of how the joysticks control the square-headed shafts: The spring-loaded plate (12 in your parts layout) has two bars (19) that attach underneath. With no hand pressure on the joysticks ("neutral" position), the pair of rollers (44) at the end of each bell crank are against the bars (19), which holds the bellcranks in their neutral positions (note: adjusting those bars will change the bellcrank position, which then will result in wheel creep or worse when the joysticks are in neutral, so don't adjust the bars casually!). Once either joystick is moved, the plate shifts sideways (because the rollers (44) bear on the bar and cause the plate to shift) against spring pressure, and the joystick that was moved causes the corresponding wheels to turn. But at the same time, the bar (19) has now moved away from the other set of rollers (44), so that bellcrank is no longer held in the neutral position and becomes very easy to move. Much easier to see, than to grasp this process from this description. At any rate, once a bellcrank is not held in neutral by the rollers/bar, that side of the machine is very prone to run fwd or back without positive joystick control. You machine doesn't have good joystick control due to being missing that rubber bushing, which puts lots of slop in that linkage. Once you move the right side joystick, the left bell crank is no longer held in neutral. And since it has no good linkage to the joystick, it sort of moves where it pleases and the left wheels jerk around without good control. Whew, this may have you even more confused! Sorry for the longwinded monolog. ---Bobbie-G

Went to remove the bolt that I thought was missing the bushing and turns out it is in there. Seems to be a press fit because I cant get the bolt or bushing to budge a bit with the nut off. Their is slop on both sides and after messing with it for a while I looks to be by design probably to prevent wear on the aluminum T-shaped lever. Maybe I'm wrong about that, just looks that way to me. I missed seeing it on the first examination because the right side bushing is sagging a bit and more easily visible. I think their is something else going on, doesn't make sense that linkage is the problem if this only happens after the machine gets hot. One thing I should have mentioned earlier is I replaced a small hydraulic hose on the left side arm early last week. I have worked all of the hydraulics several times through their range of motion on several occasions in fear that it was air in the system causing this issue. But like usual everything works like it should until I go to work it and the left side goes to crap.

 

[bobbie-g]

Went to remove the bolt that I thought was missing the bushing and turns out it is in there. Seems to be a press fit because I cant get the bolt or bushing to budge a bit with the nut off. Their is slop on both sides and after messing with it for a while I looks to be by design probably to prevent wear on the aluminum T-shaped lever. Maybe I'm wrong about that, just looks that way to me. I missed seeing it on the first examination because the right side bushing is sagging a bit and more easily visible. I think their is something else going on, doesn't make sense that linkage is the problem if this only happens after the machine gets hot. One thing I should have mentioned earlier is I replaced a small hydraulic hose on the left side arm early last week. I have worked all of the hydraulics several times through their range of motion on several occasions in fear that it was air in the system causing this issue. But like usual everything works like it should until I go to work it and the left side goes to crap.

Well, sounds like the linkage isn't your problem after all. I would try one more thing: with the engine turned off, lift the cab and watch the aluminum T-shaped lever as you move only the left joystick. The stick should move the alum lever very evenly and reliably, throughout the full range of motion of the stick, with very minimal slop. You said you already verified that the square shaft was secure to the alum T-shaped lever. The rubber inserts in the end of the alum lever can get worn out and that will add to the slop, but still the joysticks should control things nicely. If the stick moves the alum lever evenly with good control throughout the range of motion, then it appears that's not your issue. As far as one of the drive motors being a bit flakey (or the control valve at the end of the main pump), I have no experience with that. Perhaps one of the more knowledgeable folks here will jump in. Many thanks for sharing what you've found so far, and all of us would like to hear about the next chapter. The 873 is a great machine and you'll love it. And don't forget about the timing belt. Bobcat recommends changing it every 1000 hrs or 5 years. I gotta figure out how to do mine pretty soon now. ---Bobbie-G

 

[bobbie-g]

Well, sounds like the linkage isn't your problem after all. I would try one more thing: with the engine turned off, lift the cab and watch the aluminum T-shaped lever as you move only the left joystick. The stick should move the alum lever very evenly and reliably, throughout the full range of motion of the stick, with very minimal slop. You said you already verified that the square shaft was secure to the alum T-shaped lever. The rubber inserts in the end of the alum lever can get worn out and that will add to the slop, but still the joysticks should control things nicely. If the stick moves the alum lever evenly with good control throughout the range of motion, then it appears that's not your issue. As far as one of the drive motors being a bit flakey (or the control valve at the end of the main pump), I have no experience with that. Perhaps one of the more knowledgeable folks here will jump in. Many thanks for sharing what you've found so far, and all of us would like to hear about the next chapter. The 873 is a great machine and you'll love it. And don't forget about the timing belt. Bobcat recommends changing it every 1000 hrs or 5 years. I gotta figure out how to do mine pretty soon now. ---Bobbie-G

Oops, my Bobcat manual says 3000 hrs or 5 years, not 1000 hrs. ---Bobbie-G

 

[Adam A]

Oops, my Bobcat manual says 3000 hrs or 5 years, not 1000 hrs. ---Bobbie-G

The drive motor may need a seal kit. I seems to be something that fixes jerky movement. Mine is doing something similar but not to the extent yours is and I have a kit that I'm going to change it next week so I'll let you know how it goes. Cheers. Adam.

 

[zghorner]

The drive motor may need a seal kit. I seems to be something that fixes jerky movement. Mine is doing something similar but not to the extent yours is and I have a kit that I'm going to change it next week so I'll let you know how it goes. Cheers. Adam.

Did it again just now when moving a project truck from my house to my storage (maybe 1/4 mile). Seems once the machine got up to 180 degrees the left side gave out...does not work in reverse at all and forward does not work until the joystick is all the way forward and then it peels out at full power. I lifted the cab to check the linkage and it moves like it should. I doubt this is unusual but one of the lines going to the hydraulic oil filter was quite a bit hotter than the others. I am going to replace the filters since I have no clue when that was last done and cut them open to check for debris. it has NAPA gold filters on it now, will that be okay to replace them with or should I use a bobcat brand filter?

 

[Tazza]

Did it again just now when moving a project truck from my house to my storage (maybe 1/4 mile). Seems once the machine got up to 180 degrees the left side gave out...does not work in reverse at all and forward does not work until the joystick is all the way forward and then it peels out at full power. I lifted the cab to check the linkage and it moves like it should. I doubt this is unusual but one of the lines going to the hydraulic oil filter was quite a bit hotter than the others. I am going to replace the filters since I have no clue when that was last done and cut them open to check for debris. it has NAPA gold filters on it now, will that be okay to replace them with or should I use a bobcat brand filter?

If you are talking about the aluminium cans on the case drain lines, disassemble the ones on there and clean with solvent and compressed air.
It almost sounds like your shuttle valve in the drive motor is sticking. It moves from side to side as you change direction.
If you swap drive motors from side to side, you can see if the problem moves, if it does, the drive motor is the cause, not the pump.

 

[zghorner]

If you are talking about the aluminium cans on the case drain lines, disassemble the ones on there and clean with solvent and compressed air.
It almost sounds like your shuttle valve in the drive motor is sticking. It moves from side to side as you change direction.
If you swap drive motors from side to side, you can see if the problem moves, if it does, the drive motor is the cause, not the pump.

when you lift the cab their are 2 oil filters right in front. Good idea on the drive motors.

 

[zghorner]

when you lift the cab their are 2 oil filters right in front. Good idea on the drive motors.

ding ding ding we have a winner. swapped the drive motors and the problem is now on the opposite side. Thanks a bunch for the idea. I noticed when powerwashing both sides that the good side was much cleaner which leads me to believe the motor had been rebuild previously while the bad side was absolutely covered in junk. Also the rings on the bearing pistons (no clue if that's the right term) seemed to be more worn out on the bad side and popped in and out pretty easily. Its a pretty simple unit and I think I can rebuilt it myself, does anyone know of overhaul kits for these? I will call bobcat tomorrow and check with them just curious if anyone has other sources.

 

[Tazza]

ding ding ding we have a winner. swapped the drive motors and the problem is now on the opposite side. Thanks a bunch for the idea. I noticed when powerwashing both sides that the good side was much cleaner which leads me to believe the motor had been rebuild previously while the bad side was absolutely covered in junk. Also the rings on the bearing pistons (no clue if that's the right term) seemed to be more worn out on the bad side and popped in and out pretty easily. Its a pretty simple unit and I think I can rebuilt it myself, does anyone know of overhaul kits for these? I will call bobcat tomorrow and check with them just curious if anyone has other sources.

Loader parts source will have parts for these motors.
I wonder if the issue is your shuttle valve or just a bad seal. Get it open and then hopefully it will be clear.
Is it a piston motor or geroler style? The geroler will have rollers and a star looking bit in the middle.
If you look up m profile, send me an email, see if i can find a pdf on how to assemble the motors.

 

[zghorner]

Loader parts source will have parts for these motors.
I wonder if the issue is your shuttle valve or just a bad seal. Get it open and then hopefully it will be clear.
Is it a piston motor or geroler style? The geroler will have rollers and a star looking bit in the middle.
If you look up m profile, send me an email, see if i can find a pdf on how to assemble the motors.

just wanted to conclude this issue for anyone searching in the future. I bought a seal kit from bobcat for $110 and put it in the drive motor and it works good as new. If I can do it anyone can, its really not that hard of a job. A shop quoted me $250 just to install the seal kit and that is with me paying for and provided the kit so I decided to give it a go myself and like I said above it was very simple, maybe took 30 minutes and that's with me being super slow. thanks for the help everyone.

 

[kweber]

just wanted to conclude this issue for anyone searching in the future. I bought a seal kit from bobcat for $110 and put it in the drive motor and it works good as new. If I can do it anyone can, its really not that hard of a job. A shop quoted me $250 just to install the seal kit and that is with me paying for and provided the kit so I decided to give it a go myself and like I said above it was very simple, maybe took 30 minutes and that's with me being super slow. thanks for the help everyone.

Ok, so I know this is an old post but hopefully someone can help me. I have an early model 873 with the single speed drive motors. A couple years ago one side started not responding to lever movement and when it did it hit hard and I could kill the engine if I wanted, so I was pretty certain my pump wasn't the issue. Recently the other side started doing the same thing, slow to respond to lever movement in both directions and when it did it hit hard. I changed filters and checked charge pressure and it was in spec. I pulled the case drain filters apart and found tiny black specs almost like pepper only smaller. I suspected an o-ring might be the culprit. So two days age I pulled the right drive motor out and disassembled it. It is a fairly simple motor with rollers that run inside of a ring with cam lobe type configuration on the inside of the ring, all machined surfaces looked brand new. When I removed the center part that distributes the oil, I found the o-rings behind the distributor sealing rings were disintegrating. I called my local Bobcat dealer and we were able to get a seal kit number (6676035) but the bad news is, it's no longer available. Does anyone have any ideas where I could come up with a couple of these seal kits? If not I'm probably looking at a couple of $2000 motors. It seems a shame I would have to replace something that just needs o-rings. Thanks for your help in advance.