Hi, my name is Dawn. My husband has an older Northwestern Skid steer that has sundstrand motor/transmission. He blew out a hose on the machine a while back, so he replaced the hose and drained the fluid and put new fluid in it. When he ran it after that, it keeps making a winding noise in it. Someone suggested that possibly a gear broke in the pump but there is no gear broken. He thought that maybe the pressure release valve was stuck, he found it on the front side, which it was not stuck, but cannot find one for the right side. He switched the hoses, and then the other side was doing the winding. It does not want to go when you apply pressure to the one side. Does anyone have any ideas? I have been on the internet three days looking for help. There is not one place unless you are taking it out and sending it to them. It is an older machine we use on the farm for cleaning out the barn. Honestly, we could not afford to replace it. I have tried looking for a schematic or a way to find out if there is a rebuild kit for the pump. ANY info would be so greatly appreciated. Thank you so much, Dawn

I would inspect the new hose to see if it is faulty. I have seen hose assemblies that were put together with the Inner Liner out of place and causing a restriction, therefore the hose switch causing the change in the sympton.

The hose was replaced for the forward and there is a separate hose for forward and reverse, and it doesnt want to go either way. Any idea? Thank you so much for the time. Dawn

Dawn;

My background is Industrial and I have only worked on a few Hydr-Static drives.

My thouhts on trouble shooting always start at what was changed when the prolem occurred. Often the problem lies in what was done to fix the the original problem.

Other than that I don't have other suggestions except for you to try to get help on other Fluid Power forums.

http://www.ifps.org/phpBB2/viewforum.php?f=1&sid=c4837c...261ee47c42bcb97edb3c

http://www.patchn.com/forum1/

Usually about the same posters at both places but you could get a better answer at one of these.

As a sauer danfoss specialist i dont think that your fault is the hose.
check again fluid level and filters
after the hose failed is the engine steel run?
when you replace the hose did you keep cleanliness?
i think there is a damage in the pump you should the best way is to take the pump to service shop.

When the hose blew, he replaced the hose and drained the fluid and replaced it with new. The machine always ran. It never stopped it just has a winding sound when you try to turn it to the left. There is a front transmission and a back. When he switched the hoses around, it did it on the right side and then the left side worked fine, so he assumes the pump was fine there. Then he put the hoses back the right way and it returned to the left side. There is a pressure release valve on the front one that wasnt stuck(someone suggested it could be stuck) but he cant find one on the back trans. pump/ I just wondered if someone knows where to find that one to check to see if it was stuck. Thanks so much for the reply. Dawn

It's possible when changing the hose that it gets air in the system.

Although it's a long shot being the hose, I tend to look at the last thing changed, especially when its the easiest and cheapest to investigate. I assume you do not have any flowmeters or pressure gauges.

When you say switched hoses, do you mean
a. moved the hose completely over to the other sides drive, but right pump still driving right motor,
b. or did you switch hoses at pump such that right pump now drives left motor?

If b., continue the same process by flip flopping components further downt the line. Instead of crossing hoses at the pumps, do it at motors. You are looking for a place that changes or not changes the problem from left to right side.


If a. (you kept pump & motor same, but moved hose compltetely to the other side drive) can you leave the hose on the same pump but turn it end for end? Motor fitting now to pump, pump fitting now to motor?

Also, if that is the case, try removing hose, drining fluid, and reinstall right back. See if air causes the effect you are seeing, without changing hoses around.


I am cureently chasing an issue with HydroGear BDL type mini hst pump/motor package on a LEsco Zero Turn lawnmower. One wheel lsporadically weak, not respond to full stick.Changed oil and filter, now both sides are sporadically weak. I think it is sucking air somewhere, just can't find it.

kcj

We did B. It wont barely go on the left side. We took the two hydraulic lines from the right side drive motor and put them on the left side that wont go, and it worked and then the right side wont go. When he switched he assumes this meant the drive motors were not the problem. when the first initial hose broke for the left hand side, it looked like the line busted because it was rubbing the hose on the motor and it busted where it was rubbing. He then put on a new hose and checked there is no obstruction in the hose.Then when he used it it ran for about three days fine and then it began with the probem, it will not go forward or reverse on the left side. When you push the lever to go forward or pull it to go back, it makes a very loud winding sound like if a valve was stuck open. Someone told him that possibly there is a release valve that may have a piece of dirt or the rubber from the old hose stuck in the pressure release valve. On the two transmissions there the first one on the front has a release valve right in the bottom of it. Which he took out and was fine. That one is for the right side. On the second transmission, he cannot find a release valve on that transmission. Someone said that it could be possibly inside one of the hose fittings. We stopped right there. Is it a possibility that the second transmission has to have a release valve? That is why I was looking for a schematic for the sundstrand ...thank you for any information you can give us.

I'd wager that the pump needs to be serviced. It was damaged when the hose blew or the new hose took it out.

The system you have is referred to as a closed loop system, commonly used for transmission applications. It literally uses a closed loop of oil that runs from the pump to the motor and back to the pump. The direction of oil flow is controlled by stroking the pump to one side or the other with the magnitude of the stroke controlling the speed.

These circuits utilize a charge pump, sometimes called a replenishment pump, to keep the loop full of oil. By design the loop leaks a small quantity of oil to the case to lubricate and carry heat out of the unit through the case drain. The displacement of this pump is small compared to the main pump. If the main pump leaks more to the case than the charge pump can makeup then the main pump will cavitate and make the whining sound your hearing when you try to load the pump.

There is a plugged port between the two ports that to the motor. It is the charge test port. Depending on model number the pressure will be in the 40-70 PSI range or 135-165 range. Put a 300# gauge in the charge port and start the machine but don't move the lever that makes it go to and fro.

Note the pressure at idle with the pump in neutral, it should be in one of the ranges above. Gently stroke the pump a little and see if it holds charge pressure. If it drops by 20% or more then there is damage in the pump. Your hose failure could cause this in two ways.

If the hose burst and wasn't immediately noticed you could run the loop dry by outrunning the charge flow, causing friction damage to the face of the valve plate. One this damage is done the new hose won't fix it.

The more likely cause is from the hose itself. The loop hoses are very critical of cleanliness. Cutting a piece of hose with a chop saw to fabricate a loop line is almost a guaranteed failure because of the little steel spherules formed by the sparks from the wire braid in the hose. They bounce down the inside of the hose and vulcanize to the liner as they cool. Rinsing or lite scrubbing will not remove them all. Once a few of these pass through the valve plate the damage is done.

It is also easy to introduce other contamination when installing the hose and any contamination that can't be sheared by a brass valve plate will cause damage.

If you do find that it's the pump the motor should be serviced as well. Even if you just take it apart, wash it good and put it back together. Any comtaminates left behind frequently damage newly rebuilt pumps..

Doesnt it have to be in the main transmission since I reversed the hoses and it made it do the winding on the other side/? Do you know where there is a release valve for the second pump? I thought that something could be stuck in there causing it to stay open and release too much fluid. On the first drive pump for the right side there is a release valve that is right next to the feed line that feeds the second transmission, but I cannot find one that releases the fluid on the second transmission. Any idea where that may be found? Is there a kit available from somewhere to rebuild this transmission. I do not know where I can find something like that , I have searched for weeks. I contacted sundstrand and I got no reply from them , and any other place that I contacted, just wants to redo it for me. I can do it myself if I could get a hold of a kit for it. Any idea? Two other companies offered me to take it off and send it to them for 1100.00 and they will rebuild it for me. If they can rebuild it, there must be a kit available if they can rebuild it so that I can rebuild it myself. It is a sundstrand 18 series. Any idea where i could locate a kit or parts? Thank you for the reply. Frank

Reversing the lines does indicate a pump problem but, because it's a closed loop system anything that went through that pump and caused any damage went through the motor too. That doesn't mean that it damaged the motor but the motor could harbor that contamination and redamage the pump if it is rebuilt and reinstalled without inspecting the motor internally.

Sundstrand has parts and you can get them from your local Sauer Danfoss dealer. Call Sauer Danfoss at 515-239-6403 to ask for the name of a dealer in your area. The only kit they offer is a seal kit. Beyond that you have to buy discreet parts and/or recondition any damaged parts. If you don't have the required equipment to recondition the internal parts you will be limited to replacement only. It also requires some experience with these units to know which parts can be reworked vs replacing them.

Your noise is not likely to be the result of a stuck release valve. The whining noise you hear is cavitation in the main pump resulting from internal leakage that exceeds the capacity of the charge pump. FWIW, the high pressure reliefs on these units are just plugs on one of the sides. Under them is a poppet and spring.

If you go to Sauer's site, http://www.sauer-danfoss.com/index.html, go to Literature>>Hydrostatic Propel Products>>Series 18 Pumps and Motors, you can download a service manual that will show you where the valves are that you are looking for.

Thank you all for the replies. The diagram of the 18 series on the Sauer-Danfoss site is exactly what I was looking for. Thank you all for the time you have given. I REALLY appreciate it very much. Dawn

Ok, I am back again. We took the pump apart, and I did find the diagram on the site. The valve plate is cracked. Apparently something did get into it when the hose blew. Anyone know where I can get one? Everywhere I look just repairs them, not sells parts. Any ideas? Dawn

Dawn, we have these in stock. Call me 856-665-4445 ext 158

John, would you also have the gasket-seal kit? You can e mail me directly at Boeracres@msn.com thanks, Dawn