Hydraulic PTO issues ..... flow divider???

[Mechanos]

Sorry, this a long one....

I have a problem with my PTO that so far I have not been able to figure out. The PTO uses a hydraulic clutch/brake to engage. Here's the background:

I hitched up my 5' rotary cutter and headed out to a field that needed to be cut. I engaged the PTO, lowered the cutter and began cutting. After about 50ft., the cutter began slowing down. After another 50ft. or so, the cutter quit turning altogether. I could not get the PTO to engage even with the cutter in the raised position. I took the tractor back to the barn, dropped cutter off and took the tractor inside. I could not even get the PTO engage with nothing attached to the output shaft.

Per the service manual, I installed a pressure gauge in the PTO test port, ran the engine at the specified RPM and was reading 80psi. It should be reading at least 120psi and the maunal states that if the pressure reading is low, add shim(s) to the PTO Delay Relive Valve. I decided to just rebuild the DRV instead of shimming it. Rebuilding it basically consists of replacing the springs and O-rings.

After rebuilding the valve, I was still getting only about 80psi. I was thinking that maybe the valve was not getting enough flow to develope the pressure necessary to engage the clutch. I decided to drain the oil, check/clean the strainer and replace the hydro filter. After refilling it with oil, I noticed that now I am getting 140 psi and the PTO engages just fine. Thinking all is good, I hitch up the cutter and try it again.... this time I left the gauge installed and routed it to a location that I could watch while cutting. As I began cutting, I noticed the pressure steadily dropping until once again the PTO clutch would disengage.

It dawned on me then that everything is fine when the hydro oil is cold. As the oil warms up, the pressure in the PTO circuit decreases.... again making me think that the circuit is not getting enough flow. The implement pump is plumbed to a flow divider that sends 70% of the flow to SCV's then onto the rockshaft and then back to the tank. The remaining 30% of flow is plumbed to the steering valve then onto the PTO circuit. When the PTO valve is off, the flow is dumped back to the tank. When the PTO valve is on, it directs fluid to the Delay Relief Valve that is designed to build the required pressure to release the brake and engage the clutch in approximately 2 seconds.

So now, I'm wondering if maybe my problem lies in a malfunctioning flow divider? At this point, I feel like I am just throwing darts at this thing trying to "hit" the problem. If anyone has some insight or suggestions, I would love to hear them.

 

[glastron23]

are the rest of the hydraulics working fine?? normally if the pressure drops when the units oil heats up it's related to pump wear, as the pump wears and the tolerances between the gears/pistons/pump body increase and as the oil heats up and gets thinner, then the will oil bypasses inside the pump as you increase the demand on it and it will decrease the pressure and flow that it's rated for. do you have excess to a flow meter? this will tell you if its the pump or not. the flow divider will normally give priority to steering/brakes and bleed the rest to the other conponents, and if the unit uses 120psi a pressure reducer on this circuit. Jim

 

[yankeerider]

If the problem is in the flow divider, and the PTO is on the same side of the flow divider as the power steering, how is the steering reacting when you lose pressure to the PTO valve?

 

[AKKAMAAN]

If the problem is in the flow divider, and the PTO is on the same side of the flow divider as the power steering, how is the steering reacting when you lose pressure to the PTO valve?

I don't think the power steering is not sharing flow with anything else.. ..for its safety...

 

[Mechanos]

are the rest of the hydraulics working fine?? normally if the pressure drops when the units oil heats up it's related to pump wear, as the pump wears and the tolerances between the gears/pistons/pump body increase and as the oil heats up and gets thinner, then the will oil bypasses inside the pump as you increase the demand on it and it will decrease the pressure and flow that it's rated for. do you have excess to a flow meter? this will tell you if its the pump or not. the flow divider will normally give priority to steering/brakes and bleed the rest to the other conponents, and if the unit uses 120psi a pressure reducer on this circuit. Jim

The implement pump is 2500psi/7gpm. Pressure readings at the SCV ports does not fall off when the oil warms up, so I'm thinking the pump is fine. This unit uses mechanically activated wet brakes, so they are out of the equation. Unfortunately, I do not have access to a flow meter.

If the problem is in the flow divider, and the PTO is on the same side of the flow divider as the power steering, how is the steering reacting when you lose pressure to the PTO valve?

The power steering remains easy to turn, but since there is not much weight on the front end of this tractor, I'm not sure I could tell any difference if the power steering was also loosing pressure. There is also no place to insert a gauge into this circuit (other than the PTO test port) without cutting a line.

Below are the hydraulic schematics and the PTO circuits theory of operation:

View attachment PTO theory.pdf View attachment Hydro schematic.pdf

 

[Mechanos]

As expected... when I went out to the tractor today with the oil cooled off from sitting all night, the PTO circuit has 140psi and all works as expected.... until the oil warms up. Then the pressure in the PTO circuit falls off to a point where it will not engage the clutch. This one has me stumped.

 

[mmurphy]

I would see what pump pressure is doing when cold to warm also.
After rereading I see you did that.

 

[RickB]

It could just as easily be a failed seal in the PTO clutch assembly, or a small leak anywhere between the PTO valve & clutch.

 

[oldnslo]

It could just as easily be a failed seal in the PTO clutch assembly, or a small leak anywhere between the PTO valve & clutch.

+1 on this. If the main system is building pressure properly the problem lies in the PTO side of the circuit.

 

[Mechanos]

It could just as easily be a failed seal in the PTO clutch assembly, or a small leak anywhere between the PTO valve & clutch.

Shhh.... don't say that too loud. My tractor might hear you!! :laughing:

Yes, that is a distinct possibility, but I sure hope that is not the case. There is an O-ring on the clutch piston and two more fiber seals on the PTO clutch shaft. Both of those require the removal of the shaft which requires the removal of the transaxle from the tractor which requires...... well you get the point. Hours and hours of labor to replace a $0.50 part.

I am doing my best to eliminate all the other "easy" things it could be before I resort to pulling the transaxle.

 

[Stonehaller]

If pressure is dropping in the PTO circuit when the oil warms up, then there is probably a leak in the circuit as others have said. It could be that the Delay Relief (item 47 in the schematic) is leaking. I do not know if you have access to this valve without splitting the tractor, but if you do, I would check it. This valve controls the PTO pressure and relies on circuit pressure on the back side of the relief spring to boost the circuit pressure. The valve may be leaking internally to where pressure is not maintained on the back of the relief spring and will gradually feed on it self and lower the circuit pressure.

 

[Mechanos]

Thanks Stonehaller... I know there was a lot of info to digest in the first post, but rebuilding the Delay Relief Valve was the first thing I tried. I even pulled the DRV out of another tractor and put it in this one and got the exact same results... so, I think I've ruled out the DRV.

Since it will only cost me a few dollars to rebuild the flow divider, I think that is going to be the next dart I toss at this problem.

I did talk to a Service Tech at my local dealer today on the phone. He kept going back the electrical system and about the 4th time of politely explaining to him that I've mechanically bypassed all the electrical safety interlocks for diagnostic purposes, he finally settled in to looking at the hydro/mechanical side of the issue. We got to a point where he needed some information that I didn't have, so I will have to run a few more tests for him and get the info back to him. Maybe I can convince him to call the Dealer Assistance Tech Center if he can't figure it out.

 

[oldnslo]

Is there any line exposed where you could hook in a flow meter in the PTO circuit? My guess is all of the connections are internal in the tranny so checking flow from the flow divider is very difficult.

Option: can you install a flow divider in the FEL line and see if that flow changes significantly when the PTO is operating? Might give some direction or diagnostic help.


good luck

Roy

 

[Mechanos]

Is there any line exposed where you could hook in a flow meter in the PTO circuit? My guess is all of the connections are internal in the tranny so checking flow from the flow divider is very difficult.

Option: can you install a flow divider in the FEL line and see if that flow changes significantly when the PTO is operating? Might give some direction or diagnostic help.


good luck

Roy

Yes, there is an external line from the steering valve to the PTO circuit in the transaxle. Unforturnately, I do not have or have access to a flow meter (wish I did). Probably a very expensive tool to have sitting around....

 

[Mechanos]

Just share a little more info I obtained last night...... I had a few minutes to kill, so I hopped on the tractor and fired it up. Engaged the PTO and was reading 140psi on the circuit. Decided to leave the PTO running and drive around the yard to warm the oil up and see how long it took for the pressure to drop. While tooling around the yard in high gear at about half speed, I punched the go pedal all the way down (sure has more pep after the fluid/filter change). Under "hard acceleration", could pull the PTO circuit pressure down to about 60 psi, but after the initial load... the circuit would rebuild pressure. Did this a couple of times, but by then the oil was warm and pressure would not rebuild in the PTO circuit.

Then, just for fun, I decided to just jab the go pedal from a near standstill and see how far it would pull the pressure down..... that when I figured out that I could come close to pulling the front wheels off the ground and dig a couple of nice holes with the Goodyear Dyna Torque II's. :laughing: Those few extra hp and extra torque under the hood are just begging to get out and play! (original 33hp engine was replaced with a 37hp engine).

 

[oldnslo]

Yes, there is an external line from the steering valve to the PTO circuit in the transaxle. Unforturnately, I do not have or have access to a flow meter (wish I did). Probably a very expensive tool to have sitting around....

In-line flow meters from Hedland or Lake monitors should not be that expensive in the flow range you are talking about. Aluminum versions are good for 3,000 PSI.

I have attached the cut sheet for Hedland so that you have some idea of the style I am talking about.

Roy

 

[oldnslo]

Just share a little more info I obtained last night...... I had a few minutes to kill, so I hopped on the tractor and fired it up. Engaged the PTO and was reading 140psi on the circuit. Decided to leave the PTO running and drive around the yard to warm the oil up and see how long it took for the pressure to drop. While tooling around the yard in high gear at about half speed, I punched the go pedal all the way down (sure has more pep after the fluid/filter change). Under "hard acceleration", could pull the PTO circuit pressure down to about 60 psi, but after the initial load... the circuit would rebuild pressure. Did this a couple of times, but by then the oil was warm and pressure would not rebuild in the PTO circuit.

Then, just for fun, I decided to just jab the go pedal from a near standstill and see how far it would pull the pressure down..... that when I figured out that I could come close to pulling the front wheels off the ground and dig a couple of nice holes with the Goodyear Dyna Torque II's. :laughing: Those few extra hp and extra torque under the hood are just begging to get out and play! (original 33hp engine was replaced with a 37hp engine).

Reading this makes me wonder if the PTO is being powered by the "charge" pump on your tractor. Loosing pressure at high speeds sounds like it is taking all the flow to drive and starving the PTO circuit. Do you by chance have a hydraulic schematic for this machine? If you do can you post it. Could help with diagnosing possible components and potentially eliminate others.

Roy

 

[kennyd]

Do you by chance have a hydraulic schematic for this machine? If you do can you post it. Could help with diagnosing possible components and potentially eliminate others.

Roy

He did, in post #5.

 

[Stonehaller]

Thanks Stonehaller... I know there was a lot of info to digest in the first post, but rebuilding the Delay Relief Valve was the first thing I tried.

Oops! My mistake in not reviewing the posts after looking at the schematic.

Under "hard acceleration", could pull the PTO circuit pressure down to about 60 psi, but after the initial load... the circuit would rebuild pressure.

Hydro demand should not affect your hydraulic circuits as they have separate pumps, unless it was really a drop in engine RPM due to your stomping on the peddle. However, the hydraulic and hydro charge pump share a common suction filter screen. You did say you cleaned the strainer, but could there be a suction leak? Does your oil foam when it gets hot?

Also, I don't know how well the sump is designed in that tractor, but the rapid acceleration could slosh the oil away from the suction port causing a momentary lose of pressure as well.

Since it will only cost me a few dollars to rebuild the flow divider, I think that is going to be the next dart I toss at this problem.

If the flow divider was the issue, then I suspect that you would see a noticeable decrease in power steering performance. You could compare steering performance by making rapid slow speed turns cold vs. hot. But, as you implied, it may be best just to rebuild it to make sure.

 

[oldnslo]

Sorry, I missed the schematic on post #5. In looking at that there is also the "Lube Relief" (Item 49) which is down stream of the delay relief. Assuming the schematic is drawn correctly this would also have some influence on PTO engagement pressure. I am not sure which one would have the most influence on actual operating pressure but I do know the company I work for sells lube reliefs in the 90 - 120 PSI range for ag and construction equipment. Some are even in 300 PSI range for larger high HP equipment.

I believe the best way to start eliminating possibilities is check the flow. If flow doesn't change and the pressure drops then you have a leak somewhere in the PTO circuit. If flow drops then you have a supply issue, pump, priority flow control or the flow divider, etc could be faulty. I believe the pump has been ruled out since you have pressure for your FEL etc.

Roy