Here’s a pic of the hydrostatic transmission torn apart.

here’s the new pump motors and valve plates cleaned up and ready to go in.

 

I know zip about your mower. What I do know is that the Type U hydro is a transmission for propelling the tractor. It has no provision for powering an implement at the same time beyond lifting and lowering into position.

There is another, and separate, pump involved if the implement is hydraulically driven.

 

Tudor, on this mower the sundstrand u type 15 series hydrostatic pump moves the mower and the same pump drives the power steering and deck lift arms. I have attached a picture of the hydraulic system on my mower.. it has one hydrostatic pump for everything..

 

Jeep, You DO HAVE a seperate pump for your lift & steering. The drive shaft from the engine connects near a flange held on by 2 bolts. Inside this flange is a gerotor pump which produces/supplies oil pressure to your implements and also a flow of oil for lubricating your internal pump & motor that move your mower.

I can't help with too many of your questions, but the 80 psi you found when testing is not good! I know off no area in that system that makes/uses 80 psi. After looking through the Sundstrand manual, I find pics showing a test gage installed on the left side, when facing the input shaft, and reading it's a 1/8" NPT port. You should also have a hex nut in that area, that's your system relief valve and no need to mess with that. On the top, front, center of the hydro is another hex nut. THIS is your implement relief valve and may be an issue. You can remove that inspect for damaged seat and/or broken spring. If everything appears OK, put it back together. I'm suspecting your charge pump is worn out.

You mentioned check valves. If you're referring to the 2 valves on top of your hydro with pins, maybe 1/8" dia., sticking up, they're fine. If your tractor moves, valves are fine. If it doesn't move (which is not the case) your valves could be an issue.

One last comment. I'm pretty sharp on these units and there're others too, but I know of NO ONE more knowledgeable on the hydros than Tudor! If he should reply and it's not in agreement with someone else, go with Tudor's reply.

And Tudor, if you're following, this a a plain ol' Sundstrand 15 U. Bob

 

Don't know about this specific system, but many hydraulic systems are "open center". This means the pump is always pumping fluid at the same flow rate. That is what pumps do. They generate flow. Pressure comes from resistance to flow, like when you close a valve. In an open center system, when the valve is "off" it still let's fluid flow from the pressure port to the tank return. When in this state, the pressure in the line will be very low. Now when you open the valve, the fluid gets directed to the output port and the tank port is closed. The pump continues to try and move the same amount of fluid. Since fluids don't compress, it will cause the cylinder (or motor) to move. Once the cylinder gets to the end of its stroke, there is no more room for more fluid. But the pump keeps pumping more in. This is what builds pressure. The relief valve will then let go to protect the system and allow the excess fluid to return to the tank. The pump and engine driving it have to work much harder when the pressure is high.

There are also closed center systems, but those require a variable displacement pump. Pretty sure gearator pumps are not variable displacement. If you have one of those, you have an open center system. I would expect at least 800-1000 psi on a tractor that size. My CUT is spec'ed at around 2000, bigger ones go to 3000, really big ones 5000 or more.

 

The separate pump to which Bob (rwmeyer) is referring is the charge pump for the hydro. The charging circuit is the ONLY circuit under constant pressure, and it can be anywhere from 50-170 psi. That is where the 80 psi at the test port is coming from.

The same pump also supplies the implement lift and power steering hydraulics via the outflow from the charge relief valve. That relief valve that doesn't dump directly to tank, but to the implement lift and P/S circuits. The pump has a displacement of 0.3 cu-in and is theoretically capable of flowing about 4.5 gpm less what is required to maintain the hydro (its primary task). The implement relief valve is normally set at about 800-950 psi (maximum rated 1000 psi). That pressure combined with the approximately 3 gpm flow available after maintaining the hydro calculates out to about 2 hp. That is not enough to feed the mower.

There is no provision to take hydraulic power off of the hydro pump itself since it would be worthless to operate a continuous duty attachment such as a mower deck while changing speeds and direction of travel for the tractor. Any attachment connected would change speed and direction in lock step with the tractor.

Since there is no other pump, you're missing a drive shaft that connects to the splined shaft on the front of the hydro via a clutching mechanism. In studying the pic that I found of your tractor, there appears to be a drive shaft coming from under the footrest to the mower.

I suspect that the auxiliary lines noted in the pictorial at the front of the tractor are for the chute control for a snow blower attachment since they originate at the same valve set as the implement lift hydraulics.

 

Tudor, if the deck lift hydraulics and the power steering has stopped working, but forward/reverse is still working, were is the most likely of the hydraulic loss?

 

Implement relief valve.

If the charge pump is lost, the hydro goes down for lack of fluid.

The free wheeling valves are a defeat setting for the charge relief check valves and have nothing to do with the auxiliary hydraulic circuits unless the engine is running. If the engine is running, why would the freewheel valves be activated? The charge pressure should be enough to reset them if they're stuck so that the springs alone can't pop them up.

Jeepsarebuilt, implement lift pressures are normally tested with the cylinder dead headed, as in at the end of stroke while the control valve is activated.

With an open circuit hydraulic system, the fluid has a free flow path from the pump to the tank when the valves are centered. As previously noted, the charge circuit is a special case where the flow from the charge relief valve goes to the auxiliary (implement lift) circuits where it has a free flow path back to tank. You are checking the pressure on the pump side of the charge relief valve.

The same port can be used to check the implement relief pressure as described above. With the control valve actuated, there is no free flow back to tank path available until after the implement relief valve, but the indicated pressure goes all the way back to the pump, including the charge relief circuit.

Check your implement control valve body for an integral relief valve that may be a contributor to your problem. From the pictorial that you posted with the work circuit ports on the bottom of the valve body, any integral relief valve will be on the tractor left of the valve body beside the left hand spool. JD has a tendency to not use the implement relief valve provision available on the Sundstrand and instead uses one in the valve set. The same max pressure rating of 1000 psi applies since that is the rating for the pump.

You may find it beneficial to come back and reread some of my posts that seem indecipherable at first read as I tend to pack a lot of technical information in some of them that takes time to digest. I've gotten bogged down myself on a couple of them over the years and had to do extensive re-wrights to simplify things a bit, especially for those new to the topic. Don't be afraid to ask questions when you don't understand. I'm here to help, not confuse.

 

Charge pump on very front of hydro or implement relief valve, also on front of hydro between free-wheeling valves.

 

Thanks for the replies, I appreciate the inputs. I'm not a expert on hydraulics and this is the first time I've really worked on a hydraulic system. So, all your comments help me understand things more.

Tudor, there is another driveshaft coming from the engine, and that one goes to the PTO, and goes to the mower deck gearbox that turns the blades. That part is working fine, the mower blades will turn on and mow the grass. I just can't lift the mower deck, which is lifted by hydraulic rams, and those are powered by the sundstrand correct ?

rwmeyer, I replaced my charge pump, and I get 150 psi at idle and almost 300 psi at full engine speed - so that is good correct ? I am thinking maybe my implement relief valve has worn out and just isn't working - is that possible ? The spring is not broken, and the valve visually looks fine. Also, what does "also of hydro between free-wheeling valves" mean, can you explain more what that is ?

Heres a picture of me testing the sundstrand at the implement pressure, Is this the correct test port ? I have a 5,000 psi gauge, but the test port will not move it, so I used the 300 psi gauge. The Sundstrand manual shows to test on the left side port, but I would have to remove a bolt that bolts the caee halves together. I can snap another picture of this...

 

Jeep, "also on front of hydro between free-wheeling valves." is the location of the implement relief valve. Bob

 

I pulled the Relief valves out of the sundstrand today, and here's a couple pics of them, The implement relief valve has a shorter but stiffer spring - dose this look correct ? Also the implement relief valve has a wear ring that looks like it wore a shiny spot from where it seats in the bore.

I also decided to take apart my steering valve, I discovered broken springs inside - not sure if that's the problem all along or not... but I guess I will fix this part and then try again.

 

Sundstrand Series 15 and Series 70 technical manual.

http://www.wfmfiles.com/download/Sauer_Danfoss_(Sunstrand)_Technical_Information_Series_70_15_Pumps_Motors_Transmissions(BLN-10006_RevB_Jan93).pdf

The link is in the stickies of the Hydraulics Forum, along with the service manual. Loads of really interesting information. Enjoy the read.

 

I finally got my spring kit from JD to repair the steering column yesterday. I got it installed and back together this evening and fired it up.. And I still have the same problem - no power steering or lift to the deck. I have gone though the entire hydraulic system now.. I am pretty stuck. Im not sure what to do now, except to try replacing the relief valves ? JD only sells them as a kit for about $194 each.. can I get the relief valve cone by them selves from sundstrand for less ?

 

Can you measure pressure before the relief valve, then measure after it?

 

condone - I have hooked up a gauge at the test ports on the sundstrand at the 1/8" npt ports. I did not get any high pressure measurements. The manuals I have are not clear which port is the correct test port for measuring. I assume its "before the relief valve" but would it matter ? if the relief valve controls the pressure by opening/closing wouldn't the pressure be the same before it reaches the relief valve and after the relief valve ?

Tudor - I have re-read your post several times - thanks for your input. I am now wondering about the control valve - does it have a "relief valve" in it ? I reviewed the diagram for it and I see a "poppet and a spring"

I also see you said JD tends to not use the sundstrand relief valve available, but on my machine they used it.. but on the newer f935 mowers, they moved it to the steering valve.

 

The poppet and spring are indeed a relief valve, but it is a relief for the specific work port that it is installed for, not for the system.

The gauge port on the transmission is between the charge pump and the charge pump relief valve, schematically speaking. From that position, all aspects of pressure at and above the charge pressure can be read.

Okay, just reviewed the diagram of the line configuration. Relief valves are bullet proof unless a spring breaks or debris prevents the poppet from seating. The charge relief is functioning correctly as indicated by the pressure. The implement relief reveals no mechanical faults (broken spring or debris preventing the poppet from closing). The orbit p/s valve has been overhauled, which rings a bell for me.

In my reading of the many hydraulic issues on MTF, there have been very few issues presented by these valves. Since I have never had the opportunity to disassemble one, I tend to read the rare posts on the topic with some interest and to note where problems have occurred. From my reading, reassembling these valves is very exacting. If the directions are not followed precisely, they won't work.

I note on the line drawing that there are five lines on that valve, one from the hydro, two to the power steering cylinder, one back towards the control valve, and one that goes??? I can't tell if it is going back into the reservoir or somewhere else, but I assume the reservoir. If there is something amiss with the p/s valve, it may be bypassing all of the flow directly to the reservoir leaving none for the implement lift.

If you have a couple of spare hoses and a clean bucket, you can prove/disprove flow to the correct location by removing a hose from the p/s valve and subbing in a hose that goes into the bucket. If the port that should flow back to the control valve comes up dry, and the other port that MAYBE goes to the reservoir shows full flow, you've found your culprit. It should only take a few seconds at engine idle to find out.

Note that this assumes that the hoses were connected to the proper ports in the first place. It's too darn easy to mess up the connections when they are grouped that close together! Been there, done that!

 

Regarding my previous post, Testing pressures before and after a component in a circuit is how you troubleshoot and determine where the problem is. You tested the pressure from the pump and saw 80psi. The pressurized fluid goes to several different components. 80psi is your baseline. that's dead head pressure. Put your gauge after the implement relief valve, do you still have 80psi? If the answer is yes, then the valve is letting pump pressure through. Its probably not the problem.

 

If the circuit is open after the charge relief valve, the pressure should be that which is required to push the fluid back to tank against the resistance of the lines, usually less than 50 psi.

Keep in mind that the system is pushing up to 4.5 gpm at WOT through a 1/4" diameter hose or 0.281" diameter steel tube. The necessary pressure to accomplish that will be added to the charge relief pressure.

Per Sundstrand, the normal charge relief pressure is 120 psi. How come the OP is getting 300 psi at WOT? That's 120 psi to pop the charge relief and another 180 psi to push the fluid through the resistance of 3 components and about 8' of line. Open center valve porting doesn't normally add a whole lot of resistance to flow.

Working this particular logic path, the only component that had broken parts was the p/s valve. It was also the only component serviced and therefore the first suspect. The spool valve will have an exterior indication that there is a malfunction. One handle will be sloppy or out of place compared to the other handle because a spool would have to be broken partly shifted in order to increase the resistance to flow. I'm unsure of the purpose of the weight shifting valve, or it's design. Oil coolers by nature reduce the pressure within themselves by offering several paths for the fluid to flow, or by offering a larger than normal pathway. Slower moving fluid allows more time for the cooler to extract heat.

 

Tudor - regarding where the flow goes after the lift control valve you were asking.. system pressure goes from lift control valve to weight transfer valve, then exits weight transfer valve to a tee, though the cooler and back into the pump.

Here is a explanation of how the weight transfer valve works from my manual. I don't quite understand it myself..

Heres the manual saying charge pressure should be 90-180 psi at idle.. and normal to raise to 500psi at full speed.

I will do the hose test you described.. and that would determine if the steering valve is causing the lift control valve to not operate, correct ?

 

Another name for the weight transfer valve is counterbalance valve and by that name, I understand the principal. Basically it takes some of the weight off of the mower deck wheels by applying some pressure to the lifting end of the lift cylinders via the float position of the spool valve normally used to raise and lower the mower deck.

That's a really simplified version.

Doing the hose test as described will tell us where the fluid is going. If it isn't going to the control valves, the steering valve is where the problem lies.

 

Doing the hose test as described will tell us where the fluid is going. If it isn't going to the control valves, the steering valve is where the problem lies.

Wouldn't it be easier to just bypass the steering valve altogether by coupling the input and output hoses together. Then you aren't running the risk of running out of fluid or are you trying to test for something else?

I could go with the theory steering valve broke and there was another problem introduced trying to find it.

 

You are correct, it would be easier, but bypassing the steering valve would not prove the condition of said valve, The steering valve is on the list of features that are currently not working. More importantly, it is also the first component after the pump to get fluid. Besides, most people do not have the necessary fitting in their tool box that is needed to connect the two hoses together, but they will have the necessary wrenches in their tool box for disconnecting the hoses in the first place.

As to running out of fluid, at idle the charge pump will flow about 1.5 gpm. Some of that goes directly to the hydro as make-up fluid that compensates for internal leakage which should leave about 1 gpm for testing purposes. The final drive contains.at least 5 quarts of fluid and the hydro will function quite nicely with as much as 2 quarts removed when on level ground. At a flow rate of 1 gpm, you have 30 seconds to observe whether there is fluid coming out of the end of the hoses or not before there is risk to anything in the system.

It should only take a couple of seconds for the active part of the test, or about a half cup of fluid. As long as the observer doesn't get mesmerized by the flow, it should all be good.

Optionally, if you are unsure as to how fast the flow will be, or how much volume is available to dump into a bucket, disconnect the spark plugs and turn the pump with the engine starter motor.

 

Ok, I did the flow test today.. this is exiting the steering valve, where it would go to the lift control valve(I traced the line back to it). I took a video while I did it so I could review the time and show it to you guys. I ran it for 10-11 seconds it looks like, the tube went into a empty 1 gallon container with quart measurements on the side. It measured approximately 1 1/4 quarts of fluid that came out in 10 seconds.

Heres the video.. I started the engine right at the 10 second mark of the video..

So I don't know if this rules out the steering valve being the problem.. but there's flow to the control valve.

I found in my F935 manual a charge pump flow test. It sounded kinda similar to what I just did, but with a meter. Specs on this page says 3.6 gpm min at full idle I think. I have a F935, and that's the diesel version of this mower.. the f932 is a gas mower.

 

Okay. Fluid flow to the valves has now been established. The ability of that flow to develop pressure to lift the mower has not.

There is also something hinky with the specs that needs to be sorted out, but more on that later.

New test. Same procedure but with the line going to the reservoir from the p/s valve. This is a two part procedure.

• First part is identical to the previous test. (No flow is what we want.)
• Second part requires that the valve for the mower lift be placed in the raise position. (No flow is the desired result. If flow results and the mower does not raise, the relief valve or some other aspect in the p/s valve is suspect.)

The specs.

There are 3 optional charge pumps for the Sundstrand hydros, 0.19, 0.30, and 0.33 cu in displacement. Some of the gross fluid flow is for replenishing fluid loss in the hydro due to normal internal leakage. That loss should be consistent with all of the optional pumps, ie. if there is a loss to the hydro of 1.24 gpm with one pump, the others should have a similar loss of flow.

- 0.19 cid @ 3700 rpm (gas) = 3.04 gpm minus 1.24 gpm to the hydro = 1.8 gpm flow for the p/s and implement lift circuits.

- 0.30 cid @ 3650 rpm (diesel) = 4.74 gpm minus 1.24 gpm to the hydro = 3.5 gpm for the p/s and the implement lift.

Close enough for the resulting flow rates, but my question is why the two different pumps for the same operations in what are basically the same machines? Engine type doesn't matter. All the pump cares about is the rpm that it has to work with, and that is within 1.36% for both engines. In addition, most tractors with power steering dedicate at least 2 gpm for p/s.

I know, nit picking at its worst, but that 1.8 gpm flow rate just jumped off of the page for me. Sad to say, but that's how my mind works.

 

I did the 2nd flow test today.. and the results were that I had flow while the lift control valve in neutral and pulling up in raise position, also deck did not raise. I ran it for about 12 seconds, and I caught nearly 2 quarts of fluid.

Heres the video..

I guess I should take my steering valve back apart or replace it ? One problem is that I don't have the correct manual for my f935.. the manual I have covers 90 and up f935's and I have a 86. I think most of the stuff is the same, but there is a small difference in the steering valve, My steering valve dose not have a built in pressure relief valve like the newer f935's have.

Also I believe I have the .30 cid charge pump. I have a early f935 and they used part number AM104733 which is a .30 according to the JD parts catalog. I also saw they listed a .50 cid charge pump for f935's with serial numbers 360361-475000, that's part number AM105015.

I did replace my charge pump with a used Ebay one, my old one was worn out and the bearing was failing. The Ebay one I got looked pretty good. The Ebay seller claimed it was a AM104733, but is it possible it was a 0.19 cid pump and I wouldn't know it ? If it was.. would that matter ?

I also noticed the 1.8 gym flow spec for the gas version, and I thought it was strange it was different than the diesel. I did find a few errors in this tech manual, so maybe it is a error ?

 

Is that the same port where the first test was done? If it wasn't, there is definitely a problem with the p/s valve. There shouldn't be flow from both ports at the same time.

Five ports on the valve indicates that it has a relief valve. The fifth port is the return to tank for the relieved flow should the relief valve pop.

I believe that the charge pump gears are all the same diameter. It's the width that changes for the different displacements. If the gears are a different width, the housing should also be different or the gears will have too much or not enough side clearance.

I didn't know about the 0.50 cid pump. If it were readily available, it would save some of the members a lot of money that they wouldn't have to spend for an auxilliary hydraulic system for their GT loaders.

To the best of my knowledge, most Type U hydros in GT service came with the 0.30 cid charge pump, and the Inline type usually got the 0.33 cid pump. There were many different applications for the Sundstrand hydros, not all of which required auxiliary hydraulics, such as Cushman golf carts, where the 0.19 cid charge pump could be utilized..

You're right. I'm thinking misprint for that low flow rate too.