Stupid hydraulic machines!

[Cord]

I have a Gehl 6635. When I bought it the machine had 28xx hours on it. Now just rolled over 2900. When I bought the machine the left control didn't feel correct. Seller assured me that it was just an adjustment. Turns out the left drive pump was dying. $1,500 for the part and we stabbed it in our selves. It was a 8 hour job. I changed the oil and filter and stuck a bunch of neodymium magnets on the filter. Last week the loader arms started dropping on me. The problem came in real quick and hasn't gotten any better or worse. At first I was thinking I had a lift ram that had gone bad. Then I noticed that the arms wouldn't drop if the engine was shut off. Talked to the dealer and he felt the check valve had some dirt in it. When the engine is shut off there is a solenoid that will lock the arms for safety. If the ram was bad, the arms would continue to drop. I bought a replacement check (only $12) and was going to set about replacing it. When I went to move the machine I noticed the left side was ghosting if I didn't have my hands on the controls. I mean, the left wheels would start to turn on their own. To replace the check valve, I need to drain out the hydraulic fluid. When I was dumping the oil out of my pan, I noticed a dozen metal flakes. A magnet confirmed they were steel. These flakes are big, easily 1/8" across. Subsequent oil pans revealed maybe 8 more flakes. The oil is clear with no suspended debris. Best I can tell, that drive pump that I just replaced is failing and the check valve is jammed open from a metal flake. The pump is still under warranty, but of course, labor isn't included.

I guess there isn't much for the board to do, I was just looking to vent.

 

[oldnslo]

Cord,
ghosting could be a control issue on the drive pump Vs a complete pump failure. Do you have the brand name and or model code of the pump you installed. I suspect it has a hydro-mechanical control head on it that also could have a small piece of contamination holding it partially in the drive mode.

Metal flakes the size you are describing would indicate some thing major is failing. Again depending on the make and model of pump it could be the drive pump or motor failing or the auxiliary lift circuit. Typically with that many large flakes from the drive circuit you would have noticed some degradation of performance.

 

[Harry in Ky]

Funny thing with hydrostats - when a pump fails, it usually takes the drive motor with it(and vise/versa). If you had a bad pump, replaced it and did nothing to/for the drive motor, you shouldn't be surprised at more failures coming. I know this is not what you want to hear, but there you are.

 

[wdchyd]

Funny thing with hydrostats - when a pump fails, it usually takes the drive motor with it(and vise/versa). If you had a bad pump, replaced it and did nothing to/for the drive motor, you shouldn't be surprised at more failures coming. I know this is not what you want to hear, but there you are.

Exactly......hydrostat drive systems are not ...."Just a pump or Just a motor"......they all work together sharing the load, oil, heat, contamination, ect.....when repairing/replacing one component it leads to more troubles if the unit is not torn down further to find causes

 

[Cord]

Cord,
ghosting could be a control issue on the drive pump Vs a complete pump failure. Do you have the brand name and or model code of the pump you installed. I suspect it has a hydro-mechanical control head on it that also could have a small piece of contamination holding it partially in the drive mode.

Metal flakes the size you are describing would indicate some thing major is failing. Again depending on the make and model of pump it could be the drive pump or motor failing or the auxiliary lift circuit. Typically with that many large flakes from the drive circuit you would have noticed some degradation of performance.

The pump is a tandem Eaton 72400. This unit has a built-in servo. I'm figuring a flake is what is holding the check valve open. So could a flake could also be causing the servo to malfunction? I was never told what actually failed on the pump, but I've been told that the earlier version of these pumps had a defective snap ring that would be prone to breakage. Supposedly Eaton has a update kit to address the issue. I have no clue where the snap ring is located or what it does. This repair shop seems to be very conservative so I'm having a tough time filtering good advice from cya advice.

This machine has two hydraulic pumps, two drive pumps and two drive motors. The one drive pump that I had rebuilt costed me $1,500 for the part alone. Since the entire system is contaminated, theoretically I would need to rebuild all of those components. This means I could easily spend $7,000 on sympathetic inspections. At what point do you cut it off? My dealer says to just replace the pump and then run the machine on the filter rack. The hydraulic shop says that they'll "work with me" to just reseal the components. A reseal is about half the cost of a rebuild. However, these guys are conservative, so I know that once they crack the case open, we'll be rebuilding it.

I've been here before "Yea, that part was good. But now that we have it apart, it's not good enough to put back together. We're going to have to rebuild and that will cost..."

 

[ovrszd]

I sympathize. We have a Bobcat T300 with 2500 hrs. The left track hydraulic motor just ate a bearing. It's being rebuilt, don't know the cost yet. Already told my Brother to expect more fallout from this failure. The warning of the failure was when the hydraulic filter light came on and the buzzer sounded. So we know the system is full of debris. Good luck with yours. I'll post again when we get ours going again.

 

[Midniteoyl]

Are you sure this isnt just contamination from the prior failure? How good to you flush the fluid out before putting in new?

 

[Cord]

Are you sure this isnt just contamination from the prior failure? How good to you flush the fluid out before putting in new?

The previous failure produced a very fine flake that was suspended in the oil. This time the oil is free of debris. The flakes were in the reservoir and I found then when I drained the tank. You are absolutely right in that I don't know if they are new or old. I just know that the servo is acting up and so is the check valve.

As for flushing, I unfortunately don't own a filter rack. I filled the tank with about 10 gallons of oil and a new filter. I then used the machine for a few hours and then changed the oil and filter. I have about 6 neodymium magnets on the filter, so I can't figure out how the flakes would have got past the magnets. The only thing that I can come up with is that the filter is clogged and the bypass is open. There is a indicator on the filter, but I don't know how to read it.

 

[Cord]

Over the weekend I got the check valve replaced. Didn't see any debris in the old valve and the ports appeared to be clear. Didn't have the time to get the oil hot (that's when the arms fall the fastest), but there didn't seem to be a significant difference when cold. I'll see if I can run it long enough on Tuesday to get the oil hotter.

I did change the oil filter, but don't have a oil filter cutter. I've since learned how to open them with a tin snips so I'll do that tonight and I'll post the results. I did check the flow gauge and there is no difference after changing the filter.

The servo for the left motor seems to be getting worse because now it'll pull hard enough to stall the engine at idle.

 

[wdchyd]

Your rotating groups (pistons, shoes, valve plates and barrels) are going into catastrophic failure

 

[CJONE]

Your rotating groups (pistons, shoes, valve plates and barrels) are going into catastrophic failure

+1 1 pump runs 1 side of the machine the other runs the other side. The pump and both drive motors need to be inspected and repaired as required per side. The hoses on the high pressure side need to be cleaned at a minimum or replaced. You either do it right or you will never fix it. Both pumps and all 4 motors do not need to be repaired [unless everthing is shot] just the side that is giving you fits. The creeping is either a adjustment or zero is not set correct on the hystat. Your other functions run off of a gear pump and control valves in another location in the machine. Almost every hydrostatic system either has a suction filter or a medium pressure filter on the discharge side of the charge pump to keep crap from the reservior out of the high pressure loop. CJ

 

[Cord]

+1 1 pump runs 1 side of the machine the other runs the other side. The pump and both drive motors need to be inspected and repaired as required per side. The hoses on the high pressure side need to be cleaned at a minimum or replaced. You either do it right or you will never fix it. Both pumps and all 4 motors do not need to be repaired [unless everthing is shot] just the side that is giving you fits. The creeping is either a adjustment or zero is not set correct on the hystat. Your other functions run off of a gear pump and control valves in another location in the machine. Almost every hydrostatic system either has a suction filter or a medium pressure filter on the discharge side of the charge pump to keep crap from the reservior out of the high pressure loop. CJ

That machine has a common reservoir. The debris will not stop at just a loop between the pump and motor but would be found throughout the entire system. Only one central filter. Looks like the return from the drive pump/motors is not filtered. That would explain why the filter is not catching the flakes. The charge pump is inside the drive pump. I don't see where the reservoir supply is connected to the drive pump, but the hard line connecting the two pumps is shown.

View attachment SL5635 & SL6635 Series II Parts Manual.pdfView attachment SL5635 & SL6635 Series II Parts Manual1.pdf

 

[CJONE]

That machine has a common reservoir. The debris will not stop at just a loop between the pump and motor but would be found throughout the entire system. Only one central filter. View attachment 340736

Really? According to your print and every correctly designed hydrostatic system the suction for the charge pump is filtered, so this means that the only dirt that can enter the system has to be generated by the HP side of the system or by the charge pump itself. Some systems have a filter on the discharge side of the charge pump but that allows the charge pump to be unprotected [read dumb] I have only seen 1 charge pump failure to where it blew particles into the system and that is because someone adjusted the chargepump relief to high not knowing what they were doing. So yes the debris will not cross contaminate 2 high pressure loops. The dirt, metal will find it's way into the low pressure system for the gear pump side. But hey what do I know! CJ

 

[Cord]

Well, heard from the dealer this morning; both lift cylinders have gone bad. Severely galled cylinders are the diagnosis. $900 to rebuild the pair of them. It's so expensive because they are replacing one rod, two pistons, two glands and both cylinders. Frankly, I don't know they are saving with that parts list! However, he says this is way cheaper than buying a replacement cylinder. Ironically, I just had a bucket cylinder rebuilt and they said that one was just as bad. I asked him if this was a sympathetic failure and he wasn't sure. At the end of the conversation, we agreed that he would continue with the diagnosis and see what else he can find...

 

[aczlan]

Well, heard from the dealer this morning; both lift cylinders have gone bad. Severely galled cylinders are the diagnosis. $900 to rebuild the pair of them. It's so expensive because they are replacing one rod, two pistons, two glands and both cylinders. Frankly, I don't know they are saving with that parts list! However, he says this is way cheaper than buying a replacement cylinder. Ironically, I just had a bucket cylinder rebuilt and they said that one was just as bad. I asked him if this was a sympathetic failure and he wasn't sure. At the end of the conversation, we agreed that he would continue with the diagnosis and see what else he can find...

Ouch, I might look at Surplus Center and see if you could find a set on there for less...

Aaron Z