Final Drive Motor on One Side Bogging Down Engine - Cat 304cr

Good day
Cheking the pressure on those small lines one should have pressure at second speed selection the other should at the moment of travel selection (Brake release)
Kind regards
Uffex

These two SysOp documents may be of some interest.

Nige said:

See the hydraulic schematic I posted above. The two small external lines are for travel motor case drain and two-speed. There is no travel motor brake the way we understand it. Same comment still applies though - are the two lines somehow mixed up.?

I found another thread where the OP was asking about the location of the case drain & 2-speed lines at the swivel. I suggest that before going anywhere near the main hydraulic control valve the connections of those two lines between the swivel and the travel motor that is not performing need to be investigated. Also this comment in Post #2 from the OP above - "Also, two-speed does not seem to be working." It could be that a single cause is at the root of both problems.
https://www.heavyequipmentforums.co...dentifying-drive-motor-hydraulic-lines.95929/

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I've followed the case drain line and the 2-speed line from the drive motor to the swivel, and they appear to be connected in the correct places. They mirror the connections of the drive that is working correctly. The 2-speed line isn't getting pressure (on either side) because the 2-speed is not working. At this point, I'm not sure if it's the foot switch you step on or something more involved. I'll try to dig into that today.

Just for clarification, this machine does NOT have a standalone brake line on the drive motors. The drives do have brakes, but they're released as pressure builds in the forward/reverse drive lines. When the drive lines get pressure, the brake is released and the drive starts turning all in one action. This is according to the service manual. I don't believe the issue is with the brake since the drive works fine on the other side of the machine.

I disconnected the case drain line from the problem drive and ran it forward/reverse to see what would happen. I do get some fluid coming out of the case drain port on the drive. Nothing crazy, just think of pouring out a 12-ounce can of Coke. That's as the drive is slowly turning and the machine is bogged down. The place I bought the drive from suggested blowing compressed air into the case drain line to clear any blockages, but I don't see how that could be the issue.

With the drive getting 3,800 psi but the machine struggling to turn it, could this be a flow issue versus a pressure issue? In other words, the drive is getting enough pressure, but not enough flow. Maybe a blockage or a valve that is not opening fully? I've just about hit the limits of my knowledge of hydraulic systems.

Regarding the case drain line and the 2-speed line being switched or mixed up, when I disconnect the 2-speed line AND the case drain line from either drive motor, the drive motors behave the same way. A little fluid comes out of the case drain port, but otherwise, the drive on the left works fine, and the one on the right still bogs the machine down. Wouldn't that eliminate the case drain and the 2-speed as possible causes?

Another question: Does the blade function work correctly.?

Nige said:

Another question: Does the blade function work correctly.?

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The blade is working fine. No issues.

Howey Matt said:

With the drive getting 3,800 psi but the machine struggling to turn it, could this be a flow issue versus a pressure issue? In other words, the drive is getting enough pressure, but not enough flow.

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Could be. Pressure gives you hydraulic power, flow gives you speed.

You said earlier that you had identified the sections of the main control valve that supplies Fwd/Rev oil flow for the LH & RH travel motors. According to this illustration #5 (blue arrow) is LH travel and #7 (red) is RH. This is looking down from above.
Is there any way that you can switch the two hoses that are currently connected to valve #5 to valve #7 and vice versa.? If you can make that switch does the problem stay on the LH side or does it move to the RH side.?

Nige said:

Could be. Pressure gives you hydraulic power, flow gives you speed.

You said earlier that you had identified the sections of the main control valve that supplies Fwd/Rev oil flow for the LH & RH travel motors. According to this illustration #5 (blue arrow) is LH travel and #7 (red) is RH. This is looking down from above.
Is there any way that you can switch the two hoses that are currently connected to valve #5 to valve #7 and vice versa.? If you can make that switch does the problem stay on the LH side or does it move to the RH side.?

View attachment 265812

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I think you're on to something, @Nige. I switched the RH and LH at the main control valve and the problem DID switch sides. Exactly the same issue, but now on the left instead of the right. So, it does appear the section of the main control valve that controls the right drive motor could be faulty. Any ideas on how to test it further? Could it be a pilot line not providing enough pressure to the valve for it to open fully?

Howey Matt said:

Could it be a pilot line not providing enough pressure to the valve for it to open fully?

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Leave the lines you swapped before where they are for now, then swap the pilot lines from #5 to #7 and vice versa. Does the problem switch sides again or stay where it is.?

Nige said:

Leave the lines you swapped before where they are for now, then swap the pilot lines from #5 to #7 and vice versa. Does the problem switch sides again or stay where it is.?

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I just finished swapping the pilot lines and the problem stayed. So, I guess I need to tear into this valve and see what’s going on… Must be debris, bad seals, or maybe even corrosion. This machine had a lot of water in the hydraulic fluid when I got it.

All signs point to the valve, right?

Also, the 2-speed isn’t working because the foot switch isn’t connected to anything. I still haven’t found the other connector, but I’m hoping I can just plug it back it and have 2-speed.

Howey Matt said:

All signs point to the valve, right?

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They seem to. If it was a pilot problem the symptoms would have changed sides for a second time when you switched the pilot lines over.

I removed the problem valve and inspected it. I don’t see anything obviously wrong. No debris, corrosion, or anything else. The springs look like they’re in good shape. Maybe a piece of debris fell out and I didn’t notice… I guess the plan is to clean it up the best I can and reinstall. I’m not sure what else to do with it.

Did you remove the spool from the centre bore.? Was it a smooth sliding fit in the bore.?
While you have it disassembled it might be an idea to put a seal kit in it. Seal kit for the LH travel valve is Part Number is 200-4938.
Specifically there are 2 seals #7 in the kit that seal each end of the spool. Disassembly instructions for the control valve attached.

Nige said:

Did you remove the spool from the centre bore.? Was it a smooth sliding fit in the bore.?
While you have it disassembled it might be an idea to put a seal kit in it. Seal kit for the LH travel valve is Part Number is 200-4938.
Specifically there are 2 seals #7 in the kit that seal each end of the spool. Disassembly instructions for the control valve attached.
View attachment 265980

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Yes, I removed the spool. It was a tight fit, but I’d say it was smooth. I didn’t have to fight with it to get it out.

Howey Matt said:

Yes, I removed the spool. It was a tight fit, but I’d say it was smooth. I didn’t have to fight with it to get it out.

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Honestly I expected the spool to be at least difficult, if not impossible, to get out by hand. Apart from having the end covers off and removing the spool, what else did you do to that section of the control valve.?
I wonder if there is a blocked port or passage inside it.?

Good day
It appears that you have isolated the issue to the valve slice, I suggest while you may have achieved full pressure on the main lines speed is dependent on flow.
Attached information how to check out spool movement.
Looking at previous posts, there is no mention of why those motors were replaced, could it be something is floating around in that crawler slice.
Kind regards
Uffex

uffex said:

Looking at previous posts, there is no mention of why those motors were replaced,

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According to the original post, one final drive was failed mechanically but makes no mention of why two final drives were actually replaced. "I just replaced both final drives on this machine. It solved my issue on one side (caused by a failed final drive) but I'm still having a problem with the other side."

Also it is not 100% clear to me at least whether the mechanically-failed FD was on the side that is still not working (RH side) or on the LH side that is now operating normally. I'd wager on a "floater" stuck somewhere in a passage or port in the valve section.

uffex said:

Good day
It appears that you have isolated the issue to the valve slice, I suggest while you may have achieved full pressure on the main lines speed is dependent on flow.
Attached information how to check out spool movement.
Looking at previous posts, there is no mention of why those motors were replaced, could it be something is floating around in that crawler slice.
Kind regards
Uffex

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The LH drive was replaced because it failed mechanically (grinding internally and leaking). I replaced the RH drive (subject of this thread) at the same time because I was having this issue and thought the RH drive was bad as well. There very well could be a piece of the LH drive floating around and causing problems. I haven't found it yet unless it came out of the valve with some of the fluid and I didn't notice it.

Nige said:

Honestly I expected the spool to be at least difficult, if not impossible, to get out by hand. Apart from having the end covers off and removing the spool, what else did you do to that section of the control valve.?
I wonder if there is a blocked port or passage inside it.?

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I'm out this week on vacation, but I'm going to inspect the valve, spool, and springs a lot more carefully when I get back. I'll also clean the valve passages thoroughly and replace the seals for good measure. I've been reading up on these valves, and it seems like the slightest imperfection in the spool or the valve body can cause big problems. I didn't notice anything at first glance, but I was headed out the door for vacation and I wasn't looking with such tight tolerances in mind.