hydr drive motor

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Sx200

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hi all espc Tazza, thanks for all your help. http://www.skidsteerforum.com/DesktopDefault.aspx?tabid=54&frmView=ShowPost&PostID=1341 my last post concerned oil leaking into crank case which was fixed with a seal kit costing $10. i used the bobcat qutie alot since but recently the drive motor that i stripped seems to be slipping.it judders a bit like the chain is slipping on the cogs, its not as violent as that, and i know its coming from the drive motor but thats sort if how it feels. hope this makes sense?????? so when it gets warm the left hand side hardly moves, just judders? any ideas whats wrong?? its a 632 skid steer
 

sterlclan

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this is the motor you took apart right? my machine a 630 has similar issues groans and right hand side weak when hot I will be keeping an eye on this thread for possible solutilns for my issues as well I assume youve checked all filters and hoses? sounds like a weak drive motor or pump you kept it all clean during reassembly I know that tolerances in drive/hydrostatic pumps is tight and dirt is bad keep us informed Jeff
 

Sx200

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this is the motor you took apart right? my machine a 630 has similar issues groans and right hand side weak when hot I will be keeping an eye on this thread for possible solutilns for my issues as well I assume youve checked all filters and hoses? sounds like a weak drive motor or pump you kept it all clean during reassembly I know that tolerances in drive/hydrostatic pumps is tight and dirt is bad keep us informed Jeff
thanks sterlclan, yeah it is the motor i pulled out. i did keep everything clean, and yep checked hoses and all. it had a groan b4 i pulled it out but now as soon as it gets warm it just judders.......
 

Tazza

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thanks sterlclan, yeah it is the motor i pulled out. i did keep everything clean, and yep checked hoses and all. it had a groan b4 i pulled it out but now as soon as it gets warm it just judders.......
Does this machine have any case drain filters or a port block filter?
Sorry, i can't remember the model you have was a little while ago now :/
My 731 when i got it had a drive problem with it got warm, it would refuse to do any work and would squeel like a stuck pig. The problem was the bronze filter in the port block was full of gunk, it looked like it was never changed (the machine was abour 25 years old at the time).
Its somewhere to start looking, as you said it made noises before the motor re-build.
If there were no parts broken off the motor i think you are safe if you kept the re-assembly clean. I have heard stories of people having a drive motor spit its guts out, they changed the motor but dodn't change the oil or purge the pump and hoses!. All those metal fragments would go floating around the pump and brand new motor.
As its a problem when the machine warms up makes me really suspect a filter.
 

Sx200

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Does this machine have any case drain filters or a port block filter?
Sorry, i can't remember the model you have was a little while ago now :/
My 731 when i got it had a drive problem with it got warm, it would refuse to do any work and would squeel like a stuck pig. The problem was the bronze filter in the port block was full of gunk, it looked like it was never changed (the machine was abour 25 years old at the time).
Its somewhere to start looking, as you said it made noises before the motor re-build.
If there were no parts broken off the motor i think you are safe if you kept the re-assembly clean. I have heard stories of people having a drive motor spit its guts out, they changed the motor but dodn't change the oil or purge the pump and hoses!. All those metal fragments would go floating around the pump and brand new motor.
As its a problem when the machine warms up makes me really suspect a filter.
hi tazza thanks for ur reply, yes it does have a bronze filter, the model is 632 or 642? noone has been able to identify it yet lol. it has struggled to lift recentley is that got somethin to do with it? i clean the filter regularly.
 

Tazza

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hi tazza thanks for ur reply, yes it does have a bronze filter, the model is 632 or 642? noone has been able to identify it yet lol. it has struggled to lift recentley is that got somethin to do with it? i clean the filter regularly.
Well other than that i have no idea....
The hydro motors and hydraulics are seperate systems, its almost like your hydraulic pump may have a problem. As it provides charge pressure to the hydrostatic pump... It could also be cavetation which will reduce your lifting and driving power.
There are so many valves and poppets in the system too, it could be a piece of crap stuck in one.
As you describe the problem, it seems to be linked. It may be an idea to check your charge pressure to start off with. Remove your hydraulic pressure switch and put a pressure gauge in. I can't remember the pressure off the top of my head, but should be around the 90PSI mark
Sorry i can't be of more use..
 

Sx200

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Well other than that i have no idea....
The hydro motors and hydraulics are seperate systems, its almost like your hydraulic pump may have a problem. As it provides charge pressure to the hydrostatic pump... It could also be cavetation which will reduce your lifting and driving power.
There are so many valves and poppets in the system too, it could be a piece of crap stuck in one.
As you describe the problem, it seems to be linked. It may be an idea to check your charge pressure to start off with. Remove your hydraulic pressure switch and put a pressure gauge in. I can't remember the pressure off the top of my head, but should be around the 90PSI mark
Sorry i can't be of more use..
the pressure seems erratic, and under load drops quite significant? is that normal?
 

Tazza

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another thing is its only one side that judders, the other side works great?
Under load its normal to slow down a bit, but it shouldn't fall really badly. It should still be able to lift even with a good load on it. I would suspect it to drop sharply if it was such a big load that the engine was about to stall.
As for one side being affected and not the other it really does seem like the hydrostatic pump not the hydraulic/charge pump. You could try swapping motors over and see if its the motor. If it doesn't change, try removing the high pressure relief valves on the hydrostatic pump, cleaning and re-installing. Also do the cold weather by-pass ones. Basically the 4 bolts on the pump near where the hoses go down to the motors. There should be 2 either side. If thats not it, you may need to take the machine to your dealer for a flow and pressure test to check the state of your pump. I would leave this as an absolute last resort as i bet it won't be cheap.
Remember the drive and hydraulic systems are seperate, what affects one shouldn't do anything to the other. I still think there is something there with your description of lack of lifting power. I take it the engine seems to be running well? and running at a good speed?
Good luck on this one.
Keep us informed.
 

Sx200

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Under load its normal to slow down a bit, but it shouldn't fall really badly. It should still be able to lift even with a good load on it. I would suspect it to drop sharply if it was such a big load that the engine was about to stall.
As for one side being affected and not the other it really does seem like the hydrostatic pump not the hydraulic/charge pump. You could try swapping motors over and see if its the motor. If it doesn't change, try removing the high pressure relief valves on the hydrostatic pump, cleaning and re-installing. Also do the cold weather by-pass ones. Basically the 4 bolts on the pump near where the hoses go down to the motors. There should be 2 either side. If thats not it, you may need to take the machine to your dealer for a flow and pressure test to check the state of your pump. I would leave this as an absolute last resort as i bet it won't be cheap.
Remember the drive and hydraulic systems are seperate, what affects one shouldn't do anything to the other. I still think there is something there with your description of lack of lifting power. I take it the engine seems to be running well? and running at a good speed?
Good luck on this one.
Keep us informed.
i havent had a lot of time this week to check out my problems but i went to start it up today and it felt like the left hand lever had come off. i checked trhe linkages and they were fine so started it up and after a few seconds the steering was fine.... pressure back up worked ok till it got warm then started juddering again? why woukld it be like that? driving me nuts!!!!!
 

Tazza

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i havent had a lot of time this week to check out my problems but i went to start it up today and it felt like the left hand lever had come off. i checked trhe linkages and they were fine so started it up and after a few seconds the steering was fine.... pressure back up worked ok till it got warm then started juddering again? why woukld it be like that? driving me nuts!!!!!
That really sounds like a blocked filter.
Can you see where your charge port is on your pump? there is usually a pressure switch there. Get some clear tubing, remove the pressure switch and attach a vavle with the clear tubing on the other end. Run this tube back to your tank. Run the machine and when it starts doing this again, block the machine and open the vavle, move the levers around a bit and see if there are any bubbles. If there are, there is a restriction causing the oil to foam. My 731 did this to me, i striped it for painting and re-assembled it and it refused to drive properly. I just couldn't get the air out, i then cleaned the bronze filter AGAIN and it worked just fine, all the bubbles went away.
My 731 did this when i bought it too, it would work fine for 10-15 mins then it would howl and refused to move. Cleaned the filter and it was great. The only other thing it could be is your oil, it may be too thin? when it heats up its just too thin and causes it to cavetate?
You could always harass your local bobcat dealer and pick their brains on what the cause could be.
Let us know how you go.
 

Sx200

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That really sounds like a blocked filter.
Can you see where your charge port is on your pump? there is usually a pressure switch there. Get some clear tubing, remove the pressure switch and attach a vavle with the clear tubing on the other end. Run this tube back to your tank. Run the machine and when it starts doing this again, block the machine and open the vavle, move the levers around a bit and see if there are any bubbles. If there are, there is a restriction causing the oil to foam. My 731 did this to me, i striped it for painting and re-assembled it and it refused to drive properly. I just couldn't get the air out, i then cleaned the bronze filter AGAIN and it worked just fine, all the bubbles went away.
My 731 did this when i bought it too, it would work fine for 10-15 mins then it would howl and refused to move. Cleaned the filter and it was great. The only other thing it could be is your oil, it may be too thin? when it heats up its just too thin and causes it to cavetate?
You could always harass your local bobcat dealer and pick their brains on what the cause could be.
Let us know how you go.
ok tazza i connected a clear tube as you suggested and ran it for a while, the oil did seem a little foamy but hard to tell lol. i noticed a leak in the hydraulic control valve. could this be somethin to do with it? it still judders its gettin worse........ at the end of the line with it now..... the right hand side seems fine its just the left, having said that it does groan alot, never been beat before with loads of car repair jobs, this is my first bobcat and im losing faith, never been as low.........
 

Tazza

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ok tazza i connected a clear tube as you suggested and ran it for a while, the oil did seem a little foamy but hard to tell lol. i noticed a leak in the hydraulic control valve. could this be somethin to do with it? it still judders its gettin worse........ at the end of the line with it now..... the right hand side seems fine its just the left, having said that it does groan alot, never been beat before with loads of car repair jobs, this is my first bobcat and im losing faith, never been as low.........
The control block leak will have nothing to do with the problem. All the fluid there is at charge or higher pressure. It will not draw air in from there.
The only thing i can think of is the poppets in the pump. Have a look where the 4 high pressure hoses come out of it that go to the motors (2 per side) there should be two bolts on each side. Behind these are poppets and springs. All i can think is there may be something holding one of them open...... I would remove all 4, one at a time and inspect them for wear and replace. Be sure to replace the O ring, as 2 of these are at very high pressure, you don't need for it to leak. If thats not the problem, it could only be the motor or that section of the pump.
You will sort it out, never fear!!! it hasn't beaten you yet.
 

Sx200

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The control block leak will have nothing to do with the problem. All the fluid there is at charge or higher pressure. It will not draw air in from there.
The only thing i can think of is the poppets in the pump. Have a look where the 4 high pressure hoses come out of it that go to the motors (2 per side) there should be two bolts on each side. Behind these are poppets and springs. All i can think is there may be something holding one of them open...... I would remove all 4, one at a time and inspect them for wear and replace. Be sure to replace the O ring, as 2 of these are at very high pressure, you don't need for it to leak. If thats not the problem, it could only be the motor or that section of the pump.
You will sort it out, never fear!!! it hasn't beaten you yet.
ok thanks tazza had a break and now ready for the challange again lol!!! took the poppets out today all seemed ok, still judderin? just left hand side? is is worth takin the motor back off and lookin for somethin else?
 

Tazza

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ok thanks tazza had a break and now ready for the challange again lol!!! took the poppets out today all seemed ok, still judderin? just left hand side? is is worth takin the motor back off and lookin for somethin else?
Can you try moving the motor to the other side? this way you know if its the motor or the pump. You will need to rotate your fittings to join back to the hoses. It will most probably leak a bit of oil, but for the time being let it leak a little untill you have it all sorted out and you can replace the O rings.
I re-read your post and noticed you said the steering lever felt like it wasn't connected. My 731 when cold going down hills at high speed sometimes does this. Pushing the levers forward then going to stop by pulling the levers back the machine swings to the right and the left hand lever feels like nothing. I push it back forward then pull back and it works. This is ONLY when cold, it warms up and works 100%. It could be a problem with your rotating group in the pump if the motor swap doesn't work. Keep this to a last resort, do the easier things first, the inside of the pumps are quite simple, but the parts are very expensive.
Have you tried pestering your local dealer? It may pay to get them to do a flow and pressure test on your hydrostats, then you will know what the state of your pump is. Just a thought, never hurts to get a price.
*if* you have to remove the pump, i found the easiest way is to remove and plug the hoses to the motors at the motor end. Remove the hoses to the super charge port on the pump and any others that need to go. Remove the pump with the 4 hydro motor hoses still attached. They are a swine to un-do at the pump end.
Let me know how it all goes!
 

Sx200

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Can you try moving the motor to the other side? this way you know if its the motor or the pump. You will need to rotate your fittings to join back to the hoses. It will most probably leak a bit of oil, but for the time being let it leak a little untill you have it all sorted out and you can replace the O rings.
I re-read your post and noticed you said the steering lever felt like it wasn't connected. My 731 when cold going down hills at high speed sometimes does this. Pushing the levers forward then going to stop by pulling the levers back the machine swings to the right and the left hand lever feels like nothing. I push it back forward then pull back and it works. This is ONLY when cold, it warms up and works 100%. It could be a problem with your rotating group in the pump if the motor swap doesn't work. Keep this to a last resort, do the easier things first, the inside of the pumps are quite simple, but the parts are very expensive.
Have you tried pestering your local dealer? It may pay to get them to do a flow and pressure test on your hydrostats, then you will know what the state of your pump is. Just a thought, never hurts to get a price.
*if* you have to remove the pump, i found the easiest way is to remove and plug the hoses to the motors at the motor end. Remove the hoses to the super charge port on the pump and any others that need to go. Remove the pump with the 4 hydro motor hoses still attached. They are a swine to un-do at the pump end.
Let me know how it all goes!
the steering feels loose when its been stood a while and the engine is not running when i start up the pressure comes back into the steering.............. i noticed using it today it judders when under load or up hill, when its not under any strain it runs ok?....... if the only alternative is to swap motors over ill have to do it but its a bugger of a job....:-(
 

Tazza

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the steering feels loose when its been stood a while and the engine is not running when i start up the pressure comes back into the steering.............. i noticed using it today it judders when under load or up hill, when its not under any strain it runs ok?....... if the only alternative is to swap motors over ill have to do it but its a bugger of a job....:-(
Did you check the charge pressure at all? it plays a very important part of the hydrostatic pump, it needs the pressure there to hold the pistons in the rotating group backwards on the yoke (the part that the steering levers are attached to). Without the pressure, the shoe of the postons will not make contact to the yoke and it will feel like the steering linkage is broken. It will also not produce any pressure. Is there any noise when its trying to move? maybee like a hammering noise of the pistons onto the yoke? this should cause a fair amount ot vibration in the lever.
Remove the charge pressure switch and install a pressure gauge from memory it should be around the 60-120 PSI mark, but every machine is different.
I hope you get it all sorted out!
 

Tazza

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Did you check the charge pressure at all? it plays a very important part of the hydrostatic pump, it needs the pressure there to hold the pistons in the rotating group backwards on the yoke (the part that the steering levers are attached to). Without the pressure, the shoe of the postons will not make contact to the yoke and it will feel like the steering linkage is broken. It will also not produce any pressure. Is there any noise when its trying to move? maybee like a hammering noise of the pistons onto the yoke? this should cause a fair amount ot vibration in the lever.
Remove the charge pressure switch and install a pressure gauge from memory it should be around the 60-120 PSI mark, but every machine is different.
I hope you get it all sorted out!
Just to show you what i meant about a rotating group:
This is what they look like. I'm sure you didn't need to know, but i was quite amazed at how clever the person that invented them was. So simple, i'd never think of it!
group.jpg
 

Sx200

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Just to show you what i meant about a rotating group:
This is what they look like. I'm sure you didn't need to know, but i was quite amazed at how clever the person that invented them was. So simple, i'd never think of it!
thats maybe what the juddering is?...... sounds and feels like using a hammer drill lol???? i got a car oil pressure guage to attach is that ok?
 
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