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jratajczek

720 Hydraulic Questions

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jratajczek
Hello Everyone, I have some general questions about the hydraulic capabilities of my 720. The hydraulics have never seemed very strong to me. I have changed the fluid and filter recently and that has helped tremendously, but it still seems week especially after it warms up. Is there anything that I can do to increase the lifting capacity of the system? Is the hydro pump the main cause of this lack of power? If I repower the tractor with a new engine of similiar HP or better will the Hydraulic system be stronger or act the same? Can I find a new Hydro pump for this model yet and does anyone have an idea of cost? Sorry for the ramblings. Any advice would be appreciated. Jamie

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acjohn
Jamie, I'm no hydraulics expert, but unless the engine bogs down when you are using the lift, or other part of the hydaulic system, a repower will do nothing for you. If your engine is maintaining speed, and the hydraulics are weak, it is very likely due to a worn pump. If you have enough engine power, and the pump is strong, exceeding the load capacity of the system should put it into bypass mode.

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Dutch
Jamie, I don't know anything about the 720 tractor specifically, but here's what I would do to diagnose the hydraulic problem. The hydraulics should perform satisfactorily with the OEM engine. Make sure the engine RPM is set properly. If the engine "bogs down" when trying to lift a normal load, that would indicate the hydraulics are working but the engine lacks power (tune the engine). If the engine does not "bog down", that would indicate a problem in the hydraulic system. The problems I would check are: 1) Hydraulic pump pressure (PSI) and flow (GPM). If you noticed an improvement after changing the fluid & filter, dirt may have entered the system and damaged the pump. 2) Pressure relief valve setting. Relief valves go out of adjustment over time, and relief valve springs can become weak. An improperly adjusted relief valve will never let a perfectly good pump produce high pressure. 3) Flow can be checked with a watch and a bucket. If the pump's flow is under spec, the pump could be worn or there could be a restriction in the system (check for internally collapsed hoses, partially closed valves & sludge). 4) Cavitation. If the fluid level is low or there is a restriction or leak on the suction side, the pump will try to pump more fluid than is available and will cavitate (pump air). Air will compress (fluid will not), the result will be a spongyness in the cylinders. 5) If the pump's pressure and flow are up to spec, check the control valves and linkage to make sure they are opening fully. Check for internallt collapsed hoses. Check the cylinders for internal leaking. Make sure to use an accurate guage and start at the begining. The engine must turn the pump at the specified RPM, the pump must produce the specified PSI & GPM. Unless you have that, the rest of the system will never work properly.

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powermax_paul
Jamie, I expect also, that your problem lies in the pump. The Sunstrand Series 15 is not a complicated pump, but because of the closeness of its surroundings in a powermax tractor, It is difficult to troubleshoot. Here are a few things to check: 1. Do you have freeplay in the clutch? Wheen the clutch is pressed in, you will lose all hydraulic pressure. The clutch releases the belts that run the pump, and if they are slipping, you may not be getting full power and rpm to the pump. 2. Purge the air out of the pump. Remove both plug wires and the + wire to the coil. Remove the cover plate between the seat and steering column to expose the pump. On the front-left-top of the pump near the hydraulic return line hose connection is a pipe plug. Remove this pipe plug and turn the engine over until only clear oil flows out of the port. Once there is no foam or bubbles in the oil, the air is purged. 3. With tractor shut down, operate the hydrostatic lever and watch the input shaft on the hydro unit. If there's any lateral movement at all, you may have bad bearings on the input trunion shaft. That will affect Hydrostatic drive power, but not hydraulic lift power. 4. With the tractor running at, say, half throttle and in high (3rd range on the range shift lever) range. Drive the tractor on a level surface and operate the 3point hitch at the same time. If operating the hydraulics affects the ground speed of the tractor, then you may have excessive internal leakage in the pump. This may be caused by scratched pump or motor valve plates. Hope that helps, let us know what you find. Paul

Paul Kjorlie, The Norwegian

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jratajczek
Thanks everyone for the advice. I will dig into it this weekend and get back to you with results. If I do have a bad Hydro pump, does anyone know the best source to get one and any idea on cost? Thanks

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JP
So... Wil that be MasterCard or Visa? LOL I would think finding one from a parts tractor would be the hot setup. I also think (usually) rebuilding Sundstrands can go from 3-700. You don't want to ask what a new one costs. My question would be, what are you trying to do? Is the tractor moving properly? I think what you're running into is why most loaders have their own pumps. Just another 2 cents......... JP

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thedaddycat
This might be getting a little too close to splitting hairs, but loosing suction(trying to pump air) is not the same as cavitation. Cavitation is the condition where the fluid actually flashes to a vapor state, then the vapor bubbles collapse. This usually occurs at the pump suction due to that being the area of lowest pressure, and is the reason for head tanks on large industrial systems. It is also a concern for submarines going to higher bells(shaft RPM) due to noise/stealth concerns. You can cavitate a screw(propeller) at depth by jumping the speed up too fast, even though the whole ship is under hundreds of psi.

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powermax_paul
Jamie, If you do need to rebuild the hydro, it isn't that hard to do yourself. The parts are the most expensive, but you may not need to replace everything. In fact, I doubt if you'd have to replace the Piston/Cylinder Block assemblies. You probably only need to Restore or replace the pump and/or motor valve plates. Bill Klein of Sandy Lake Imp. was very helpful in getting me used and new hydro parts and giving me advice on lapping the pump and motor valve plates. I think when all was said and done, I had $180 bucks invested in parts and the hydro's been running perfectly for over a year now. It is in a different tractor now,(I have three) because of a necessary swap, but this hydro works 10X better now than it had for the first five years I had it in its original tractor. If you do send it out, I wouldn't recommend the "average" Simplicity dealer as most of them haven't seen one of these for quite some time. You may be better off taking it to a Ransome dealer or some other company that still uses this unit. Otherwise, find an authorized Sauer/Sunstrand service center. Paul

Paul Kjorlie, The Norwegian

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