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. Basically, when I engage the final drive on that side, the engine bogs down and the hydraulic pump whines like it's under strain. The final drive does turn, but not as fast as the other side. It's a brand new final drive, and the old final drive did the same thing, so I'm wondering what to look at to figure this out. I have a parts manual, owner's manual, and service manual - I'm just not sure where to start. Any troubleshooting steps or help would be greatly appreciated. It's a 2004 Cat 304cr (NAD00987). Thanks!
Some additional info... This happens with the tracks off, so zero load on the drive motor. Also, two-speed does not seem to be working.
I don't have my computer near me to look up specifics but it sounds like the brake isn't releasing. I would imagine both sides are teed together but have seen them separate in the rotary manifold before
Good day A couple of possibilities - binding brake - failing bearing in the transmission, if one side required replacement there is a good chance the remaining drive is not far behind. Drain some lube for evidence of impending failure. Kind regards Uffex
It looks like they each connect to different ports on the rotary manifold - no tees. I'm wondering if it's a valve or something since the drive motor is brand new. I'm thinking I can do a pressure test on the hoses at the drive to see if the drive is getting adequate pressure or not. That would tell me if the problem is with the drive or something else.
If there is a brake release hose and a 2 speed hose is there a chance you have them mixed up on the final drive motor? Did the final drive come with the motor and brake as a unit ?
Everything came as a unit - just bolt on and connect the hoses. I thought maybe I hooked the hoses up incorrectly, but I followed the instructions exactly (I even verified the case drain and two-speed lines). I installed both drives the same way and one of them is working. Also, the old drive had the same issue, so that would mean that one was installed incorrectly as well. I'm pretty sure it was the original drive.
If there are separate brake ports on the rotary manifold you could have a blockage there. Try to put a gauge on that brake line somewhere and see what kind of pressure you are at.
Which line are you referring to when you say brake line? I have two large drive lines and two smaller hoses which are the case drain and the two speed. I thought the brake on these smaller machines was released when the pressure in the drive line increased. So, I'm assuming I need to test the pressure on the drive lines? If the drive is getting pressure and not releasing, it's the drive. If the drive is not getting pressure, it's something further up the line.
I ordered a pressure test kit. I'm leaning towards an issue with the swivel valve since both the drives are new. Any idea how to test the swivel valve? I went through the service manual but I don't see anything. I guess I'll just see if the swivel valve is getting pressure but not sending it to the drive. Would bad seals in the swivel valve cause this issue?
I will do my best to remember to grab my computer from the shop tomorrow and can do some more digging. Since it is loading up the engine you have a restriction somewhere. Could be any number of things but does not sound like a rotary manifold issue. Usually that leads to problems with both tracks not just one.
Time for a public service announcement Final drives have oil They need it It's very important Change regularly That will be all
Is it possible to swap the main forward/reverse hydraulic connections of the LH & RH motors somewhere in the upper frame of the machine (before the swivel in other words) and see whether the problem changes sides.? The 2-speed and case drain lines at the swivel are common.
I'm getting around 3,800 psi on each of the large hoses (forward and reverse) at the drive motor. That should be adequate according to the service manual. Must be a problem with the brand new drive... I'm going to call the place I bought it from tomorrow. I really didn't think it would be an issue with the drive since it's brand new, but I would be the guy to get the defective one.
Good day Compliments on a sensible approach to troublee shooting. Kind regards Uffex
UPDATE The place I bought the drive motor from swears there's nothing wrong with the drive. They're saying they tested it before it was shipped and everything checked out. I wasn't sure what else to do, so I removed the problem drive and hooked it to the hydraulic lines on the other side of the machine, and it works perfectly fine! So, the drive is getting 3,800 psi and it works fine on the other side of the machine, but it barely turns and strains the hydraulic pump and engine on the side where it belongs. Any ideas as to what could be causing this? When I say it strains the engine/pump, I mean it sounds like the hydraulic line is capped and the drive spins very slowly.
Sounds like a main control valve problem. What failed on your original final? The hydraulic or mechanical side?
The drive on the other side failed mechanically. I decided to replace the drive on this side as well since it was having this problem. So, I guess one side mechanical, the other side hydraulic. I’ve been going over the service manual and I located the port on the main control valve that controls the right drive motor. Any idea how to go about testing it?
Good day I suggest check the brake release pressure at the motor although its strange to release one side and not the other. Be sure that the case drain and brake release lines are not switched over. Kind regards Uffex
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. HeavyEquipmentForums
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.
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.?
The blade is working fine. No issues.
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.?
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?
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.?
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.
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.
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.
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
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.
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.
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.
You mentioned that "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" On a machine the size of yours IMO the spool should literally be able to be pushed out of the tunnel in the valve body with no more than finger pressure. It does not sound like yours was that loose.? When you can try posting some good-quality photos of the spool.
Good day The spool is of a hard steel billet whilst the slice is of a softer cast material, a small scratch on the spool can as a rule of thumb be ignored whilst a damaged slice will result in problems. Look hard at the main filters could give you some clue to what may have been going on. Spools of this type will only shift a small distance less than i/2" see attached. Kind regards Uffex
Here are some photos.
Now that it’s clean and dry, it does push through with one finger. It stays in just enough to not fall out when I turn the slice sideways. It falls out when I shake it. It came out fairly easily as well - I just had to twist it a bit. I’m wondering if there was some debris in there that got washed out when the fluid came out. I don’t see any issues with the spool or the slice. No damage, not even a little as far as I can tell.
Good day According to the shematicc you have two main pumps No.1 & No.2 Number one provides fluid & pressure for right side crawler - Arm & Option. Pump number two provides fluid & pressure for left side crawler - Boom & Bucket. From a distance Im asking do those remaining circuits for the troublesome side perform correctly? From your post and the photo's I cannot see so much wrong with the spool & slice. Kind regards Uffex
Everything else is working correctly. Boom, bucket, blade, stick, etc. I haven't tested the aux hydraulics because I don't have a thumb yet.
Good day The symptoms are very strange, I suggest you measure the return line pressure when the motor is active. Your post describes a loading of the hydraulics when the motor is running, as I have interpreted the issue it is a question of loading and lack of speed. Question has the spool been removed from the slice installed the wrong way around ? Kind regards Uffex
See attached photo. I’m fairly certain it came out like this, which looks correct according to the diagrams I can find. I could be mistaken about how it came out, but I think I remember the ring around the end as I pulled it out. I’m going to pull the slices around this slice (one of them is the LH travel) and get everything cleaned up and reinstalled correctly. I’m hoping that fixes it.
UPDATE I got everything put back together and PROBLEM SOLVED! The only problem then was a pretty good leak between the slices. So, I removed the entire main control valve this time, and I'm going to replace the 11 o-rings between the slices. Should have done it the first time around! It's only time and busted knuckles... Thanks for everyone's help! I really appreciate it.
Does anyone know how to get the air out of the hydraulic system after a job like this? My controls are spongy and the machine has very little power. I’ve worked the controls back and forth for a while now, and I unscrewed the plug on top of the main pump to let the air out per the service manual. Nothing seems to be working. The blade is so weak it won’t even pick the machine up. Any ideas?