773 with drive problems

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Hay Farmer

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Oct 10, 2008
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I have a 1996 773 bobcat loader the drive on the left side works when first started but as the loader warms up it begins act as if somethings is slipping the left side jerks and makes a noise as if one of the chains were slipping but all the inner workings seem to be fine any sugestions as to where to look next would be greatly appriciated Thanks
 

OldMachinist

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I don't how hard it is to do but I would try switching the drive motors from side to side. If it follows the motor then you'll know its the motor. If the left side still has problems then its in the pump.
 
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Hay Farmer

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I don't how hard it is to do but I would try switching the drive motors from side to side. If it follows the motor then you'll know its the motor. If the left side still has problems then its in the pump.
Thanks I don't think it would be to hard to switch the motors looks like only 3 hoses and a few bolts is it possible it could be the pump with everthing else working properly?
 

OldMachinist

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Thanks I don't think it would be to hard to switch the motors looks like only 3 hoses and a few bolts is it possible it could be the pump with everthing else working properly?
There is a hydraulic pump for the lift, tilt, aux and charge pressure and a hydrastatic pump for each drive side.
 
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Hay Farmer

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There is a hydraulic pump for the lift, tilt, aux and charge pressure and a hydrastatic pump for each drive side.
Ok thanks I am not as familiar with the hydraulic drive components I have been into the chain case before but this is my first time dealing with the pump and motors thanks for the help
 
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Hay Farmer

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Ok thanks I am not as familiar with the hydraulic drive components I have been into the chain case before but this is my first time dealing with the pump and motors thanks for the help
Is there anyway to test the motors or the pump for proper flow and is there any possibility that the shaft is worn causing slippage and the nosie I am hearing
 

OldMachinist

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Is there anyway to test the motors or the pump for proper flow and is there any possibility that the shaft is worn causing slippage and the nosie I am hearing
Just from the description in you first post that it works fine until it warms up I have to think its not something mechanical. If a sprocket was slipping on an axle or motor shaft it would likely do it warm or cold. I sure with special equipment there is a way to test the hydrostatic pumps and motors but the service manuals don't have anything about testing them just disassembly and inspection.
 
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Hay Farmer

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Just from the description in you first post that it works fine until it warms up I have to think its not something mechanical. If a sprocket was slipping on an axle or motor shaft it would likely do it warm or cold. I sure with special equipment there is a way to test the hydrostatic pumps and motors but the service manuals don't have anything about testing them just disassembly and inspection.
Ok thanks I will get started on the motor swap monday evening I will let you know how difficult it is thanks for the info
 
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Hay Farmer

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Ok thanks I will get started on the motor swap monday evening I will let you know how difficult it is thanks for the info
Guess this is gonna sound like a dumb question finally go time to start removing the motor and I need to know if I need to drain the chain case or does the motor have a shaft that slides into a socket that seals it from the chain oil sometimes its better to ask than to experiment and then wish you had ask thanks guys
 

Tazza

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Guess this is gonna sound like a dumb question finally go time to start removing the motor and I need to know if I need to drain the chain case or does the motor have a shaft that slides into a socket that seals it from the chain oil sometimes its better to ask than to experiment and then wish you had ask thanks guys
The chain case oil will stay in the chain case.
There should be an O ring that seals the motor to the carrier on the chain case and the main shaft inside the carrier that drives the chains has a seal as well to keep the chain case oil in there and the hydrostatic oil out.
 
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Guess this is gonna sound like a dumb question finally go time to start removing the motor and I need to know if I need to drain the chain case or does the motor have a shaft that slides into a socket that seals it from the chain oil sometimes its better to ask than to experiment and then wish you had ask thanks guys
Did you get a chance to switch the drive motors. I am working on a friend's Bobcat that has virtually the same problem. My plan is to try to switch the hydraulic motors around to see if hte problem switches sides, but I am hoping to hear a success story before I do so. Thanks.
 
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Hay Farmer

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Did you get a chance to switch the drive motors. I am working on a friend's Bobcat that has virtually the same problem. My plan is to try to switch the hydraulic motors around to see if hte problem switches sides, but I am hoping to hear a success story before I do so. Thanks.
I am working on it unfortunatly I only get to work on it in my spare time which is not much lately I will let you know soon as I can
 
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Hay Farmer

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I am working on it unfortunatly I only get to work on it in my spare time which is not much lately I will let you know soon as I can
Ok seems to be the motor same problems now on the right side how difficult is rebuilding one of these motors and are there any special tools needed
 

Tazza

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Ok seems to be the motor same problems now on the right side how difficult is rebuilding one of these motors and are there any special tools needed
If its the same a 751 or 763 motors they are very simple. Just ensure you keep it all clean and that ALL the parts go back in the same place. I'd pull it down and check the seals on the back section where the oil comes in. There are a few O rings and backup rings here that hold back the 5000 PSI that the pump generates. I have pulled a motor down that 1/4 of one O ring was gone, it turned to dust. The other 2 had cracked backup rings.
Seal kits are available from your dealer and i'm sure http://www.skidloaderpumps.com has them too.
No special tools are required, use lots of oil when re-assembling it.
 
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If its the same a 751 or 763 motors they are very simple. Just ensure you keep it all clean and that ALL the parts go back in the same place. I'd pull it down and check the seals on the back section where the oil comes in. There are a few O rings and backup rings here that hold back the 5000 PSI that the pump generates. I have pulled a motor down that 1/4 of one O ring was gone, it turned to dust. The other 2 had cracked backup rings.
Seal kits are available from your dealer and i'm sure http://www.skidloaderpumps.com has them too.
No special tools are required, use lots of oil when re-assembling it.
Thanks guys. Your sucess Haymaker convinced me to switch my motors from side to side and the problem followed the move. I will more than likely just put a new motor on it since it has been down for so long, and I need to get it back in use as soon as possible. I might tear the motor down afterward to see what makes it tick though. Thanks again.
 

Tazza

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Thanks guys. Your sucess Haymaker convinced me to switch my motors from side to side and the problem followed the move. I will more than likely just put a new motor on it since it has been down for so long, and I need to get it back in use as soon as possible. I might tear the motor down afterward to see what makes it tick though. Thanks again.
Honestly look into seals first, a new motor is NOT cheap! Or even try www.skidloaderpumps.com and see what Levi has available, he may be able to do a reman motor or even a new one. He may even be able to re-kit your old one. I had a motor that said it was stuffed, a new one would have cost me over $2,000 to replace i spent $7.50 in new O rings, good as new!
But of course, its your choice :) i hope you get it up and running soon, at least its not a pump issue, they are a little more expensive and far more work.
 

danman

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Nov 1, 2006
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I have a 642b that had this problem. It would work under a small load as soon you would put the motor under more load it woud feel like it kicked out of gear. It did make a noise as if oil was bypassing. Anyway I ordered a new seal kit it was around 40.00 and that solved the problem.I also found a broken spring inside the motor. It was not hard to replace parts . just keep everything clean. hope this helps
 

Fishfiles

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Feb 8, 2007
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I have a 642b that had this problem. It would work under a small load as soon you would put the motor under more load it woud feel like it kicked out of gear. It did make a noise as if oil was bypassing. Anyway I ordered a new seal kit it was around 40.00 and that solved the problem.I also found a broken spring inside the motor. It was not hard to replace parts . just keep everything clean. hope this helps
This is an easy fix , as Tazza said and I would have to agree it's the same problem you have , the o ring and back up ring at the very end of the motor is deteriated and half or all gone , it is very common , it causes a delay in travel and then a sudden jump ,when cold it's not as bad as whn oil heats up , once the oil is hot it sometimes won't move at all , mark the alignment of the sections with a cener punch such as 1dot-1dot and so on , 2-2 , 3-3 , , the whole job should take 2 hours and cost about $50 , a new motor will set you back probally in the $800 range
 
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