Problems with crawler power on a Pel-Job TB 650 S mini excavator

[Kjeles]

My old Pel-Job TB 650 S mini excavator has poor crawler power. After a few minutes of use and after the hydraulic fluid has warmed up, the excavator will barely make turns or move uphill.
I replaced the o-rings on the swivel joint last year, but to no avail.
A hissing sound from the control valve block when operating the crawler levers suggests that there is an internal leak in the valves.
I have taken out the control valve block and inspected the spools of the crawler valves. They seem ok. No apparent wear or leaks. The control levers and the control valve block have been modified before I bought the excavator, so the machine is clearly not in its original condition.
Using pressurised air, I'm surprised (I'm an amateur) to see that there is direct open connection between the input port 'A' (see photo) and the return port 'Return A&B'. It seems to me that the crawler motors cannot get high fluid pressure when the fluid flows unrestrictedly to the output port. Is this normal?
Similarly, there is direct connection from the 'B Input' port to the 'B5' port, which is connected to the return flow by a hose. The free flow through the valves puzzles me although the bucket, booms and swing work ok. However, the swing (rotation) – with the last valve before the return port – has rather low power.
Is the valve block ok?
Any suggestions on how to proceed to improve the fluid pressure to the crawlers?

 

[V8Druid]

My old Pel-Job TB 650 S mini excavator has poor crawler power. After a few minutes of use and after the hydraulic fluid has warmed up, the excavator will barely make turns or move uphill.
I replaced the o-rings on the swivel joint last year, but to no avail.
A hissing sound from the control valve block when operating the crawler levers suggests that there is an internal leak in the valves.
I have taken out the control valve block and inspected the spools of the crawler valves. They seem ok. No apparent wear or leaks. The control levers and the control valve block have been modified before I bought the excavator, so the machine is clearly not in its original condition.
Using pressurised air, I'm surprised (I'm an amateur) to see that there is direct open connection between the input port 'A' (see photo) and the return port 'Return A&B'. It seems to me that the crawler motors cannot get high fluid pressure when the fluid flows unrestrictedly to the output port. Is this normal?
Similarly, there is direct connection from the 'B Input' port to the 'B5' port, which is connected to the return flow by a hose. The free flow through the valves puzzles me although the bucket, booms and swing work ok. However, the swing (rotation) – with the last valve before the return port – has rather low power.
Is the valve block ok?
Any suggestions on how to proceed to improve the fluid pressure to the crawlers?

View attachment 16583

pressure relief valve stuck open some where?

 

[craig]

If the control leavers have been modified, are they opening the valves fully?

 

[CPS]

Using pressurised air, I'm surprised (I'm an amateur) to see that there is direct open connection between the input port 'A' (see photo) and the return port 'Return A&B'. It seems to me that the crawler motors cannot get high fluid pressure when the fluid flows unrestrictedly to the output port. Is this normal?
Similarly, there is direct connection from the 'B Input' port to the 'B5' port, which is connected to the return flow by a hose. The free flow through the valves puzzles me although the bucket, booms and swing work ok. However, the swing (rotation) – with the last valve before the return port – has rather low power.
Is the valve block ok?
Any suggestions on how to proceed to improve the fluid pressure to the crawlers?

Its an open centre valve block so the free flow is correct, im guessing that it is fed via gear pumps.
Both left and right track are on the same block, which would suggest to me its the pump that is worn, bypassing internally when it warms up.

You could refit the valves and swap input a and b around which would supply the tracks from the good/better puml to see if you get an improvement....... I'm pretty sure you will

 

[jd6820]

Its an open centre valve block so the free flow is correct, im guessing that it is fed via gear pumps.
Both left and right track are on the same block, which would suggest to me its the pump that is worn, bypassing internally when it warms up.

You could refit the valves and swap input a and b around which would supply the tracks from the good/better puml to see if you get an improvement....... I'm pretty sure you will

Yep I'd go with this. Valve block is likely open centre and is operating correctly. The pumps do wear as do the track motors, i'd say a pressure check would be worth while and checking the case drains on track motors to get and idea of where to look next.

 

[Kjeles]

Thanks a lot for useful information. I'll swap the input hoses to check if the main pump is the problem. Good idea!
Is the main pump serviceable if it is worn?
What are the "case drains" of the track motors, and how do I check them?
Can the track motors be serviced?