Erratic Hydraulics

[TRH]

I have a Ford 1900 tractor with a Ford 771 loader on the front. In the 6 weeks I've owned it I have thoroughly cleaned and then lubed the whole machine. I changed the engine oil and the hydraulic fluid, cleaned the hydraulic filter and changed the fuel and oil filters. I think that the fluid changes were way overdue. I've put about 40 hours on the engine, equally divided between the loader and the backhoe. Both use the same hydraulic fluid reservoir and pump.

My problem is that the loader bucket is erratic in when it works. Sometimes when I am tipping (dumping) the bucket and stop tipping to raise it, it will not continue to dump. If I either raise it more or lower it, it normally works. Similar problem with raising the bucket. Sometimes if I stop raising, dump, and try to continue to raise, it will not raise. It always will go down (gravity?), but not always tip downward. Eventually it will work on both the dump and lift modes. So far, when I raise the bucket to the max, the dump function has always started to work again. It appears that there are no leaks in any of the hoses or cylinders.

I've had no problems with the operation of the backhoe, other than operator errors.

Any ideas?

Tom

 

[mmurphy]

My thought would be before thinking hydraulic problem, make sure pins are not binding in bucket. Take them out clean and grease. Make sure holes are not all wore out also. I have seen cylinders bend because of siezed pins.

 

[Jbrink64]

TRH, by any chance do you have these problems when the engine is below 1000 rpm?

 

[J_J]

I think if you install a hyd gage in the system, you will find your problem, just by doing some logical trouble shooting

 

[Gary Sweat]

Sounds similar to the problem I have with my bucket dumping. If I let it dump too fast, it will take a couple of seconds to continue moving once the load has emptied from the bucket. Determined that the pump is not keeping up with the cylinders. I think this is caused by the loader valve being to big and lets the oil move through the system faster than the pump can supply oil back to the opposite side of the cylinders.

I will either have to put flow control valves in the lines or go to a smaller loader valve gpm to correct it. This may not be your problem but it sounds similar.

Currently I have a 10gpm valve on a 4gpm pump and 3/8" lines.

 

[AKKAMAAN]

If I let it dump too fast, it will take a couple of seconds to continue moving once the load has emptied from the bucket. Determined that the pump is not keeping up with the cylinders.

Thats right, gravity dumps flow faster than the pump flow can refill....creates temporary vacuum or air get sucked in.

I think this is caused by the loader valve being to big and lets the oil move through the system faster than the pump can supply oil back to the opposite side of the cylinders.

Size of loader valve is basically not your primary problem, it is a pumpflow vs gravity flow problem.....Try to speed up pump rpm (throttle) while dumping, and it will show less of this "slack"....You can also slow down dump cycle with a one way restriction, but then you lose the benefit of quick dump cycle....usually a regen function is used to cure this problem.....

Currently I have a 10gpm valve on a 4gpm pump and 3/8" lines.

3/8" is perfect size...
10gpm valve is a little over sized, and will make it hard to feather functions...it will take almost full lever movement to build enough pressure to lift loads, and almost no lever movement to lower gravity loads.....

 

[Gary Sweat]

Thats right, gravity dumps flow faster than the pump flow can refill....creates temporary vacuum or air get sucked in.

Size of loader valve is basically not your primary problem, it is a pumpflow vs gravity flow problem.....Try to speed up pump rpm (throttle) while dumping, and it will show less of this "slack"....You can also slow down dump cycle with a one way restriction, but then you lose the benefit of quick dump cycle....usually a regen function is used to cure this problem.....




3/8" is perfect size...
10gpm valve is a little over sized, and will make it hard to feather functions...it will take almost full lever movement to build enough pressure to lift loads, and almost no lever movement to lower gravity loads.....

Thanks, what you have said is pretty much what I have going on. I wasn't trying to hijack the thread just putting out another possibility to what might be going on with his system. I'm going to replace the loader valve with one that has regen to see if that cures the problem.

 

[kjung17]

Deere uses a regen circuit for this same problem. There is usually a valve to bypass when not needed. You'll still have a short hesitation, but not nearly as bad as without the regen.

 

[J_J]

Thanks, what you have said is pretty much what I have going on. I wasn't trying to hijack the thread just putting out another possibility to what might be going on with his system. I'm going to replace the loader valve with one that has regen to see if that cures the problem.

With regen, it should dump about 50 % faster. It may be to fast for you. Just pull it back out of regen.

 

[Gary Sweat]

With regen, it should dump about 50 % faster. It may be to fast for you. Just pull it back out of regen.

It will dump pretty fast as it is but then just like TRH is saying, it takes a few seconds before I can continue with any dump movement. If I pull it back up a little then I get dump control again. I need someway to get the discharge oil from the cylinders routed into the pressure side of the cylinders during the dump cycle so it will fill the cylinder faster. I am hoping regen does that.

 

[kjung17]

Yes. Regen opens a passage from the rod end to the piston end of the cylinders.

 

[J_J]

Ever how fast it is now, the regen is going to shove a lot more fluid in there. A smaller valve may solve your problem. Do you really care about fast dump?

 

[kjung17]

It's not so much about fast dump as it is plain old gravity. When dumping the bucket, as the load comes past the center of gravity, the rod side of the cylinder, which was low pressure return oil, becomes pressurized by the weight of the load. The hydraulic system cannot keep up with this sudden change in "demand" and a vacuum forms in the piston end of the cylinder. The regen function allows the cylinder to refill itself, avoiding the delay experienced when the system has to refill the piston end. Yes, if you take great care and go slow, you will almost never have this problem. You can also throttle the maximum dump speed by installing a restriction orifice in the return line.

 

[Gary Sweat]

Ever how fast it is now, the regen is going to shove a lot more fluid in there. A smaller valve may solve your problem. Do you really care about fast dump?

I like the fast dump but not the possibility that I am creating a vacuum in the cylinder or having to wait for it to catch up. If regen corrects or helps to eliminate that then that is what I am looking for. It might also solve TRH's symptoms. For now I just have to feather the valve and wait for it to finally dump.

I've been watching the pressure gauge and if I dump it fast, the pressure is zero. It stays at zero for a few seconds until the pump catches up. If I feather it, I can keep about 5 lbs on the gauge so I know I am not creating a vacuum. It's either a regen or a larger gpm pump and so far I have not found a way to put a bigger pump on the tractor.

Sorry TRH, I didn't mean to jump in with my problem but I do appreciate the advice from everyone.

 

[Jbrink64]

I think we're missing the point.

The original post stated there was an issue dumping, stoping, then not able to continue dumping. Similar issue with the loader raise circuit. It's really not a regen issue.

I would be more inclined to think there is a flow or intermittent flow issue.

A 1900 has a steering priority valve on the hydraulic pump. At 1000 rpm and below, almost all hydraulic flow goes to the steering.

 

[Gary Sweat]

I think we're missing the point.

The original post stated there was an issue dumping, stoping, then not able to continue dumping. Similar issue with the loader raise circuit. It's really not a regen issue.

I would be more inclined to think there is a flow or intermittent flow issue.

A 1900 has a steering priority valve on the hydraulic pump. At 1000 rpm and below, almost all hydraulic flow goes to the steering.

Wouldn't that only apply if he is turning the wheels while using the loader? I don't fully understand the priority valve but without steering movement how would any oil be flowing to the steering?

 

[Jbrink64]

Wouldn't that only apply if he is turning the wheels while using the loader? I don't fully understand the priority valve but without steering movement how would any oil be flowing to the steering?

On this setup, the priority valve always sends the first 2-2.5 gpm to the steering gear, regardless of steering or not. The "excess" flow then goes to the main hydraulic system. When the engine idles down, pump flow decreases to the point all flow goes to the steering. This was always a problem with these models, when releasing the throttle pedal while dumping or lifting, usually in a tight spot, or inching up to a truck.

 

[Hooked_on_HP]

Since the backhoe works fine the hyd. system is working properly. I would check the quick disconects for the loader hyd. hoses first. Un hook and inspect and reconnect if they look ok. Check the position of your TPH lever. On my 1900 with the backhoe on the tph lever needs to be all the way down. As others have stated make sure you don't have frozen pins on the bucket.
Bill

 

[RickB]

I think we're missing the point.

The original post stated there was an issue dumping, stoping, then not able to continue dumping. Similar issue with the loader raise circuit. It's really not a regen issue.

I would be more inclined to think there is a flow or intermittent flow issue.

A 1900 has a steering priority valve on the hydraulic pump. At 1000 rpm and below, almost all hydraulic flow goes to the steering.

The OP also mentioned that the original hyd oil was contaminated and the suction screen needed cleaning. It would not be out of the realm of possibility to think that the screen was plugged a second time from garbage not flushed from the transmission and rear axle during the first drain/fill cycle.

 

[AKKAMAAN]

Wouldn't that only apply if he is turning the wheels while using the loader? I don't fully understand the priority valve but without steering movement how would any oil be flowing to the steering?

A priority valve "secures" a certain max flow to steering independently if pump is delivering a higher flow. Power steering is supposed to be designed to work normal at lowest possible pump flow (engine at low idling rpm).

So if power steering is designed to work with a "normal" speed at a flow of 4gpm, pump must be able to deliver that flow at idling, 600rpm. This is a safety requirement for power steering on tractors. Accordingly pump flow at 1800rpm will be 12gpm...