763 HYDRALIC PROBLEMS FILLING CHAIN CASE FULL

[TNHOTROD]

I have a 763 that is filling the chain case full of oil in about 10-15 mins. I have removed both drive motors and looked at both carrriers and seals but do not see a problem with them. Complete carriers were replaced not long ago on both sides. After inspecting both sides i pulled both sides of the drive motor hoses up were i could connect the drive motors while laying on the frame. so now i have both motors connected but where i can watch the motors actually run. When i start the machine one of the motors at the small hose that attaches to the motor is pushing fluid out , the other motor at the small hose is not doing this.. I'm thinking that the oil that is coming down the small hose is building pressure in the carrier and blowing by the seal into the chain case. I have been told that the small hose going to the drive motors are to return the fluid that has leaked from the drive motors.. ANY HELP WOULD BE GREATLY APPRECIATED... THANKS CHRIS

 

[Fishfiles]

Sounds like You got it figured out , I'd change seal kits in both drive motors , even if only one is leaking the other will probally be right behind

 

[jeffs873]

Sounds like You got it figured out , I'd change seal kits in both drive motors , even if only one is leaking the other will probally be right behind

It sounds to me like your case drain filters are plugged. Take the small lines off after the filter and check for flow.If no flow... clean the filter....Blow out the line after the filter to assure no restriction back to the tank

 

[TNHOTROD]

It sounds to me like your case drain filters are plugged. Take the small lines off after the filter and check for flow.If no flow... clean the filter....Blow out the line after the filter to assure no restriction back to the tank

SHOULD BOTH DRIVE MOTORS ON THE SMALL LINE GOING TO THEM HAVE FLUID COMING OUT OF THEM? HOW MANY CASE FILTERS ARE THERE ON A 763?

 

[sterlclan]

SHOULD BOTH DRIVE MOTORS ON THE SMALL LINE GOING TO THEM HAVE FLUID COMING OUT OF THEM? HOW MANY CASE FILTERS ARE THERE ON A 763?

yes both motors should have similar leakage (not too much) and I dont know about the filters I would assume there is two....unless the two lines tee into one and are filtered there Jeff

 

[TNHOTROD]

yes both motors should have similar leakage (not too much) and I dont know about the filters I would assume there is two....unless the two lines tee into one and are filtered there Jeff

IS THE SMALL AMOUNT OF LEAKAGE YOU ARE REFERRING TO COMING FROM THE SMALL HOSE OR FROM WHERE?

 

[Tazza]

IS THE SMALL AMOUNT OF LEAKAGE YOU ARE REFERRING TO COMING FROM THE SMALL HOSE OR FROM WHERE?

The small connector is the case drain line BUT on one motor its plumbed back to the pump, the other goes direct to the oil reserve, both via case drain filters as previously mentioned. There is no reason for the oil to get back to the chain case unless your carrier seals are shot or the plug is missing from inside the shaft that the carrier seal runs on, excessove case drain pressure could do it too, but i'd suspect that would destroy the seals and you should be able to see that. Look in the end of the shaft where the splines engage on the motor and ensure the allen head plug is indeed tight. If its not, you will get case drain oil pushing past and into the chain case. With the motors off the carriers you see where the shaft comes out of the motor, this area will all have internal leakage and you will get oil coming out of here, thats why the carriers have seals on the shafts.

 

[TNHOTROD]

The small connector is the case drain line BUT on one motor its plumbed back to the pump, the other goes direct to the oil reserve, both via case drain filters as previously mentioned. There is no reason for the oil to get back to the chain case unless your carrier seals are shot or the plug is missing from inside the shaft that the carrier seal runs on, excessove case drain pressure could do it too, but i'd suspect that would destroy the seals and you should be able to see that. Look in the end of the shaft where the splines engage on the motor and ensure the allen head plug is indeed tight. If its not, you will get case drain oil pushing past and into the chain case. With the motors off the carriers you see where the shaft comes out of the motor, this area will all have internal leakage and you will get oil coming out of here, thats why the carriers have seals on the shafts.

ok so i have now taken the motor apart and all the seals,geroller look like new. I can take the small hose off the motor and start the machine and hose will start to poor fluid . i have been told that the small hose is to pull the fluid back to tank that the drive motor has leaked into the carrier cavity. So my question is why does my small hose have fluid coming down it if it suppose to to be returning fluid. Any help or advice would be APPRECIATED THANKS CHRIS

 

[Fishfiles]

ok so i have now taken the motor apart and all the seals,geroller look like new. I can take the small hose off the motor and start the machine and hose will start to poor fluid . i have been told that the small hose is to pull the fluid back to tank that the drive motor has leaked into the carrier cavity. So my question is why does my small hose have fluid coming down it if it suppose to to be returning fluid. Any help or advice would be APPRECIATED THANKS CHRIS

That small hose is a return line , it hooks to other lines in the system and there will some oil returning to the tank thru it , in some cases that hose may route right to the bottom of the hydraulic tank so it will drain also , but it's a small amount of pressure , it is called back pressure , and is usually lower than 100 psi max , it does pull the oil back to the tank it flows to it , that travel motor has some by pass of oil and it returns thru that hose , if the amount is excessive it will build up pressure adjust the rock filter and leak thru the seal at the shaft of the travel motor thru the carrier seals and into the chain case , the carrier seals seldom need changing , it is the seal in the motor that lets the oil build up too much pressure on the drain line

 

[TNHOTROD]

That small hose is a return line , it hooks to other lines in the system and there will some oil returning to the tank thru it , in some cases that hose may route right to the bottom of the hydraulic tank so it will drain also , but it's a small amount of pressure , it is called back pressure , and is usually lower than 100 psi max , it does pull the oil back to the tank it flows to it , that travel motor has some by pass of oil and it returns thru that hose , if the amount is excessive it will build up pressure adjust the rock filter and leak thru the seal at the shaft of the travel motor thru the carrier seals and into the chain case , the carrier seals seldom need changing , it is the seal in the motor that lets the oil build up too much pressure on the drain line

What is the rock filter?

 

[Tazza]

What is the rock filter?

Look on your case drain hoses from the motor to the pump and reserve tank, look for an alloy cylinder, there is a filter inside here made of bronze.
Leakage from the hoses is totally normal.

 

[TNHOTROD]

Look on your case drain hoses from the motor to the pump and reserve tank, look for an alloy cylinder, there is a filter inside here made of bronze.
Leakage from the hoses is totally normal.

my question now is should both sides have flow at the small lines going to the drive motors.. because on mine right now (which is F**% upright now) one side has fluid coming out of it and the other side has nothing coming out of it. I am going to check the case drain filters 1st thing in the morning though. I have heard a couple people talk about some filter behind the battery is this filter also on the 763??? Thanks for all the help

 

[jeffs873]

yes both motors should have similar leakage (not too much) and I dont know about the filters I would assume there is two....unless the two lines tee into one and are filtered there Jeff

There are two case drain filters, one for each drive motor. Good luck, they are tough to get to.

 

[Ersok]

There are two case drain filters, one for each drive motor. Good luck, they are tough to get to.

You stated that the motor carriers had been replaced, how long ago? if you are building pressure on the case drain of the motor it will compress the seal and is almost always obvious. I have seen the case drain line on the right side put in the wrong location many times but normally when the control valve has been repaired and that would explain the amount of oil you are getting out of the line. not all case drain lines go directly back to tank some connect to a port on the control valve first, without a serial number I dont know the loaction your case drain line should be but verify that the oil does indeed make it's way back to the case drain in the bottom of the tank. Just a thought.......Ernie

 

[TNHOTROD]

You stated that the motor carriers had been replaced, how long ago? if you are building pressure on the case drain of the motor it will compress the seal and is almost always obvious. I have seen the case drain line on the right side put in the wrong location many times but normally when the control valve has been repaired and that would explain the amount of oil you are getting out of the line. not all case drain lines go directly back to tank some connect to a port on the control valve first, without a serial number I dont know the loaction your case drain line should be but verify that the oil does indeed make it's way back to the case drain in the bottom of the tank. Just a thought.......Ernie

Both carriers have less than 100 hrs on them. they were bought as complete units from bobcat.. I do know that one of the small lines is going to the control valve assy. and the other is going to the hydralic pump . I'm not 100% positive that they are in the right place or not..

 

[Tazza]

Both carriers have less than 100 hrs on them. they were bought as complete units from bobcat.. I do know that one of the small lines is going to the control valve assy. and the other is going to the hydralic pump . I'm not 100% positive that they are in the right place or not..

What side was leaking?
If it was plumbed incorrectly the right side is the only one that would get excessive pressure, the left goes into the hydro pump. If excessive pressure was the cause, you would see the lip of the seal being pushed inwards or even torn apart.
I know the line you are talking about on the control block, the one to release pressure from the lift curcuit with the lever or the lockout solenoid.
Ensure you ckeck that the plug is installed in the carrier shaft, its a small allan head plug. If its not there oil will go into the chain case.
If it was me, after checking the plug and seal lips i'd install a T piece on the case drain lines and install a small pressure gauge, say 300 PSI and see if it gives me a reading. If it shows more than your charge pressure, about 200 PSI you know there is a problem.
With the motor you pulled down, did you chack the shuttle valve? if its damaged it will allow high pressure to enter the case drain section if i remember correctly. I'm not 100% sure on where they are located though, i have 2 pulled down but need to get to putting them back together.

 

[thetool]

What side was leaking?
If it was plumbed incorrectly the right side is the only one that would get excessive pressure, the left goes into the hydro pump. If excessive pressure was the cause, you would see the lip of the seal being pushed inwards or even torn apart.
I know the line you are talking about on the control block, the one to release pressure from the lift curcuit with the lever or the lockout solenoid.
Ensure you ckeck that the plug is installed in the carrier shaft, its a small allan head plug. If its not there oil will go into the chain case.
If it was me, after checking the plug and seal lips i'd install a T piece on the case drain lines and install a small pressure gauge, say 300 PSI and see if it gives me a reading. If it shows more than your charge pressure, about 200 PSI you know there is a problem.
With the motor you pulled down, did you chack the shuttle valve? if its damaged it will allow high pressure to enter the case drain section if i remember correctly. I'm not 100% sure on where they are located though, i have 2 pulled down but need to get to putting them back together.

Trying to put it all together here.......=).
You've got one of two set-ups. Easiest way to ID is hydraulic tank behind the seat, or down on the left side of the frame.
If your tank is behind the seat, your left motor case drain plumbs into the hydrostatic pump drain port, which goes directly to tank. If you disconnect this hose at the motor with the engine off, it will leak toward the motor, because it's draining the tank. The filter is in-line. If it's plugged, it will back-pressure when running and take out your carrier seal. As Tazza said, it is normal for either case drain line to leak away from the motor when the engine is running. The flow should be about the same left and right, away from the motor. But this test requires that the removed lines be plugged so it dosen't drain the tank at the same time.
If your tank is on the left frame, the line goes directly to tank, but the filter and leakage applies as above.
One the right motor, with either set-up, the case drain tees into return lines at the valve, and there is a filter in-line. Same thing about leakeage applies as above.
Now, apparently it was your carrier seal pushed back, and you've got the chaincase-filling issue resolved, BUT.....
If the case drain filter was back-pressuring, or you even have the slightest restriction as stated by another poster, after the filter, this could cause just enough pressure against your seal to push it back without obviously smashing it, and it will “look okay“ but still leak.
So, even though you fixed your carrier seal, make sure to check your filters to reduce the chance of recurrence.

 

[TNHOTROD]

Trying to put it all together here.......=).
You've got one of two set-ups. Easiest way to ID is hydraulic tank behind the seat, or down on the left side of the frame.
If your tank is behind the seat, your left motor case drain plumbs into the hydrostatic pump drain port, which goes directly to tank. If you disconnect this hose at the motor with the engine off, it will leak toward the motor, because it's draining the tank. The filter is in-line. If it's plugged, it will back-pressure when running and take out your carrier seal. As Tazza said, it is normal for either case drain line to leak away from the motor when the engine is running. The flow should be about the same left and right, away from the motor. But this test requires that the removed lines be plugged so it dosen't drain the tank at the same time.
If your tank is on the left frame, the line goes directly to tank, but the filter and leakage applies as above.
One the right motor, with either set-up, the case drain tees into return lines at the valve, and there is a filter in-line. Same thing about leakeage applies as above.
Now, apparently it was your carrier seal pushed back, and you've got the chaincase-filling issue resolved, BUT.....
If the case drain filter was back-pressuring, or you even have the slightest restriction as stated by another poster, after the filter, this could cause just enough pressure against your seal to push it back without obviously smashing it, and it will “look okay“ but still leak.
So, even though you fixed your carrier seal, make sure to check your filters to reduce the chance of recurrence.

filters are new ..now just the lift arm problem.. lift arms dropping when you let off the pedal..cylinders already rebuilt by bobcat . i'm think im gonna have to remove the control valve .. any suggestions??? tank is behind the seat thanks