631 right drive problem

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alexvbugman

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Hello, I have an older Bobcat 631 with very little right steer. it just moans. Everything was fine till I topped off the hydraulic fluid, the reason I topped it off is because when the unit sits for long periods, it leaks into the bottom of the case, so I opened the drain and threw it back in the tank. any info would really help, I'm new at this. Thanks
 

Tazza

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Opened the drain?
Where did the oil come from? not from the bung at the front of the chain case below the bobtach? This is your chain case not your main oil reserve. If your hydraulic oil is going down and your chain case is getting over full you need to replace 2 O rings on the hydrostatic motors, fairly simple to do.
It could be a blocked filter in the port block or a pump or motor problem.
Give me a little more info and i can give you more info. I had a 731 that was essentially the same machine but a little bigger. Same pumps and motors.
 

alexvbugman

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Opened the drain?
Where did the oil come from? not from the bung at the front of the chain case below the bobtach? This is your chain case not your main oil reserve. If your hydraulic oil is going down and your chain case is getting over full you need to replace 2 O rings on the hydrostatic motors, fairly simple to do.
It could be a blocked filter in the port block or a pump or motor problem.
Give me a little more info and i can give you more info. I had a 731 that was essentially the same machine but a little bigger. Same pumps and motors.
Yes, there is a drain plug on the face of the case right behind the bucket. the guy I bought it from told me to drain the oil and dump it back in the hydaulic tank. thats what we did, then I lost the right side steering, and the bucket seems alot slower. Thanks for any help.
 

alexvbugman

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Yes, there is a drain plug on the face of the case right behind the bucket. the guy I bought it from told me to drain the oil and dump it back in the hydaulic tank. thats what we did, then I lost the right side steering, and the bucket seems alot slower. Thanks for any help.
How easy is it to get access to the hydrostatic motors? I would like to replace the two orings you mentioned. Thanks
 

sterlclan

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How easy is it to get access to the hydrostatic motors? I would like to replace the two orings you mentioned. Thanks
they arent too bad remove the seat, and you can see them bolted to both sides of the chain case tazza knows more about the seals than me if you need I can help with some scans of the service manual I have a 630 Good luck, Jeff
 

Tazza

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they arent too bad remove the seat, and you can see them bolted to both sides of the chain case tazza knows more about the seals than me if you need I can help with some scans of the service manual I have a 630 Good luck, Jeff
That is a real bad idea, the chaincase can get water inside it pretty easy and runs chains and sprockets so you get metal shavings. The oil in here is not filtered either, please never use oil out of there in your hydraulic/hydrostatic system. Removing the motors is fairly simple, you may need to remove a hose or 2 off the motor and un-do the 4 bolts. Simply pull the motor ourwards and it will come free. There is an O ring inside a bronze bush on the end of the motor and one large one on the outside of the motor. The inside one is the critical one, the outer one has no real pressure on it but it seals the chain case.
Best to remove the wheels on that side of the machine and block it to give better access.
This won't fix your drive problem but it will fix the oil leaking to the chain case.
There is a hidden filter that hopefully is the cause of your lack of drive. Remove the seat and look at the top of the hydraulic pump, there should be a square block. 3 hoses enter the left side, remove the middle one and the nut that goes into the block, its a larger nut than the other 2. Behind here is a bronze filter. Replace or clean it and *hopefully* your problem will be fixed.
It would be a good idea to change your hydraulic oil and filter too, with all that oil from the chaincase you may have water contamination.
If anything is un-clear just let me know!!!
 

alexvbugman

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That is a real bad idea, the chaincase can get water inside it pretty easy and runs chains and sprockets so you get metal shavings. The oil in here is not filtered either, please never use oil out of there in your hydraulic/hydrostatic system. Removing the motors is fairly simple, you may need to remove a hose or 2 off the motor and un-do the 4 bolts. Simply pull the motor ourwards and it will come free. There is an O ring inside a bronze bush on the end of the motor and one large one on the outside of the motor. The inside one is the critical one, the outer one has no real pressure on it but it seals the chain case.
Best to remove the wheels on that side of the machine and block it to give better access.
This won't fix your drive problem but it will fix the oil leaking to the chain case.
There is a hidden filter that hopefully is the cause of your lack of drive. Remove the seat and look at the top of the hydraulic pump, there should be a square block. 3 hoses enter the left side, remove the middle one and the nut that goes into the block, its a larger nut than the other 2. Behind here is a bronze filter. Replace or clean it and *hopefully* your problem will be fixed.
It would be a good idea to change your hydraulic oil and filter too, with all that oil from the chaincase you may have water contamination.
If anything is un-clear just let me know!!!
You guys are great giving all this info, I'm going to work on it this week and let you know. Thank You very much.
 

Tazza

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You guys are great giving all this info, I'm going to work on it this week and let you know. Thank You very much.
If you are un-sure about anything just yell, i knew my 731 pretty well inside and out.
 

skidboy

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If you are un-sure about anything just yell, i knew my 731 pretty well inside and out.
If only a 631 was as easy as a 731.The drive motor on a 631 has the drive gear attached,which means that you have to let a front chain go then move the motor rearwards to drop the back chain off,then remove the motor.You then have to remove the tapered drive gear off the motor shaft.The seals in the motor will need to be replaced.It may be better to get a hydraulic guy to do this.A 731 is very simple as the motor bolts to a reduction drive.
 

Tazza

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If only a 631 was as easy as a 731.The drive motor on a 631 has the drive gear attached,which means that you have to let a front chain go then move the motor rearwards to drop the back chain off,then remove the motor.You then have to remove the tapered drive gear off the motor shaft.The seals in the motor will need to be replaced.It may be better to get a hydraulic guy to do this.A 731 is very simple as the motor bolts to a reduction drive.
I thought the drive motors were attached the same...... Well that makes the job a little harder.
 

alexvbugman

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I thought the drive motors were attached the same...... Well that makes the job a little harder.
I pulled the seat and cleaned the bronze filter, is there a trick to filling the hydraulic tank. I lost about 3 gallons or so. Do I have to bleed the system?
 

Tazza

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I pulled the seat and cleaned the bronze filter, is there a trick to filling the hydraulic tank. I lost about 3 gallons or so. Do I have to bleed the system?
No tricks, it will bleed its self.
Just top up the reserve tank.
Use 10W30 or 10W40 engine oil. Run the machine a bit and it should bleed its self. Hopefully that will restore your drive. It may growl a bit as the air is removed but shouldn't take much. I think mine ran perfect after i cleaned the filter. Replaced it and ran really well, no waiting for the system to bleed.
 

alexvbugman

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No tricks, it will bleed its self.
Just top up the reserve tank.
Use 10W30 or 10W40 engine oil. Run the machine a bit and it should bleed its self. Hopefully that will restore your drive. It may growl a bit as the air is removed but shouldn't take much. I think mine ran perfect after i cleaned the filter. Replaced it and ran really well, no waiting for the system to bleed.
I cleaned the bronze filter and still no right drive side. I pulled the wheels off and cracked open an allen screw on the motor and had alot of pressure coming out. I think I'll try pulling the motor out. Can I pull the outside bolts out or do I have to pull the whole motor out?
 

alexvbugman

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I cleaned the bronze filter and still no right drive side. I pulled the wheels off and cracked open an allen screw on the motor and had alot of pressure coming out. I think I'll try pulling the motor out. Can I pull the outside bolts out or do I have to pull the whole motor out?
I pulled the 4 outer bolts out and pulled the motor right out, (pretty easy) but I don't understand what can go wrong with these. Other than 2 o-rings. The motor was just growling before I pulled it apart. Please help. Thanks
 

sterlclan

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I pulled the 4 outer bolts out and pulled the motor right out, (pretty easy) but I don't understand what can go wrong with these. Other than 2 o-rings. The motor was just growling before I pulled it apart. Please help. Thanks
is the end of the shaft splined or keyed my machine lost a nut on the right side and munched the shaft I also had no drive the sprocket in the chain case can be a bugger to put together .Take the covers between your feet off and have a look that nut (if you have it)and sprocket are probably laying in there. let us know. .Jeff
 

sterlclan

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is the end of the shaft splined or keyed my machine lost a nut on the right side and munched the shaft I also had no drive the sprocket in the chain case can be a bugger to put together .Take the covers between your feet off and have a look that nut (if you have it)and sprocket are probably laying in there. let us know. .Jeff
Almost forgot this guy has parts for your/my machine http://stores.ebay.com/skidloader-hydraulic-parts-source_Bobcat-Parts_W0QQcolZ4QQdirZ1QQfsubZ9685124QQftidZ2QQtZkm
 

Tazza

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I pulled the 4 outer bolts out and pulled the motor right out, (pretty easy) but I don't understand what can go wrong with these. Other than 2 o-rings. The motor was just growling before I pulled it apart. Please help. Thanks
There is a fair bit of stuff inside the motor its self.
The O rings you will need to replace are the big one that goes around the outside and there is a smaller one that is inside where the gear hangs out the motor. You can still access it without pulling the motor down, look inside where the gear pokes out, you'll see it.
If the motors are that easy to remove, can you swap the motors over? this way you can confirm if its a motor or pump problem. If the problem switches sides you know its a motor. If not, you will have to pull the pump. I would leave the O ring replacing till you sort the drive problem out as you may be removing the motors again for repair.
I have details of whats inside both the motors and the pump so when you work out what is the problem i can give you the needed info.
 

alexvbugman

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There is a fair bit of stuff inside the motor its self.
The O rings you will need to replace are the big one that goes around the outside and there is a smaller one that is inside where the gear hangs out the motor. You can still access it without pulling the motor down, look inside where the gear pokes out, you'll see it.
If the motors are that easy to remove, can you swap the motors over? this way you can confirm if its a motor or pump problem. If the problem switches sides you know its a motor. If not, you will have to pull the pump. I would leave the O ring replacing till you sort the drive problem out as you may be removing the motors again for repair.
I have details of whats inside both the motors and the pump so when you work out what is the problem i can give you the needed info.
I took the motor apart and there are round pieces of stock with a star that fits in between them, but they don't fit perfectly. I can't spin the gear when its in? wierd.
 

alexvbugman

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I took the motor apart and there are round pieces of stock with a star that fits in between them, but they don't fit perfectly. I can't spin the gear when its in? wierd.
If my left side drive works fine but the right don't, does it mean my pump is good?
 
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