601 htdraulic issue

Hi All, helping my dad with his 601. TPH wont lift (all the time). I've spent hours looking at archives here and watching videos on pump rebuilds, etc, but they have only helped so much. TPH started lifting intermittently after it sat a while. Once it started working, it worked fine and was "strong". Ultimately, it wouldn't lift at all despite manually lifting TPH, cycling control lever, etc. Dad drained oil (it was pretty bad shape), flushed everything clean and added new oil. He removed cover plate and cleaned up the easy-to-get-to items. Main cylinder is tight - no leaks. O-rings where vertical tubes meet cover are good. Control valve, and check valves removed and cleaned and reinstalled - work freely. Primed pump and restarted with no luck. TPH wont lift - doesn't even budge. Pulled PTO lever cover off and watched inside for leaks when attempting to lift TPH - no leaks. Could see some minor movement of fluid down toward front right corner of bottom. Pulled cover back off. Removed control valve / spring. Looked well and moved free. Removed check valve and pilot/spring and ball. Seemed clean - moved freely. Did NOT pull the backpressure valve out as nothing handy to pull the bushing. Did move the valve back and forth with screwdriver. Moved freely. Valve would push in and spring back freely on its own. I know there is an o-ring back in there also. Unsure of its exact function. Could see the ID of it all the way around and looked ok, but unsure of its actual condition. Pulled the unloader valve and it looked decent, but seemed to stick somewhat at extreme travel positions. Moved very freely in between. Polished bore and valve some and reassembled with similar sticking at extremes. Unsure if this is an issue. Was able to put air to cover ports and use control valve to cycled unloader back / forth. With cover off, started tractor and got nice fountain of flow up out of vertical supply tube. Put back together and nothing. TPH never budged. Looking through side hole, no leaks, just minor movement of fluid in bottom. Played with control level and lifted TPH up/ down manually and banged things around a bit and saw TPH budge a little. Then, on next control lever cycle, TPH worked perfect. Very strong and smooth. This lasts about half dozen cycles and then just quit in the down position. Never got it to budge again despite more "mechanical agitation" / cycling, etc. Shut tractor off and checked pump prime - fluid was at very top when took plug out, so don't think any issues with pump. Prior to this, the TPH was always very strong and smooth with no issues. Also, when it worked those few times, it lifted me on hitch effortlessly. So, don't think any pump issues. The fact that it lifted me those few time, don't believe and issues with pressure RV or with piping holes in tranny. Think I have a valve sticking. ?.. Which one would do that? Can I test pump pressure with port under seat if valves are not working? Thanks for any insight - this should be enough to get us started. Dale
 
(quoted from post at 14:16:36 08/04/18) Hi All, helping my dad with his 601. TPH wont lift (all the time). I've spent hours looking at archives here and watching videos on pump rebuilds, etc, but they have only helped so much. TPH started lifting intermittently after it sat a while. Once it started working, it worked fine and was "strong". Ultimately, it wouldn't lift at all despite manually lifting TPH, cycling control lever, etc. Dad drained oil (it was pretty bad shape), flushed everything clean and added new oil. He removed cover plate and cleaned up the easy-to-get-to items. Main cylinder is tight - no leaks. O-rings where vertical tubes meet cover are good. Control valve, and check valves removed and cleaned and reinstalled - work freely. Primed pump and restarted with no luck. TPH wont lift - doesn't even budge. Pulled PTO lever cover off and watched inside for leaks when attempting to lift TPH - no leaks. Could see some minor movement of fluid down toward front right corner of bottom. Pulled cover back off. Removed control valve / spring. Looked well and moved free. Removed check valve and pilot/spring and ball. Seemed clean - moved freely. Did NOT pull the backpressure valve out as nothing handy to pull the bushing. Did move the valve back and forth with screwdriver. Moved freely. Valve would push in and spring back freely on its own. I know there is an o-ring back in there also. Unsure of its exact function. Could see the ID of it all the way around and looked ok, but unsure of its actual condition. Pulled the unloader valve and it looked decent, but seemed to stick somewhat at extreme travel positions. Moved very freely in between. Polished bore and valve some and reassembled with similar sticking at extremes. Unsure if this is an issue. Was able to put air to cover ports and use control valve to cycled unloader back / forth. With cover off, started tractor and got nice fountain of flow up out of vertical supply tube. Put back together and nothing. TPH never budged. Looking through side hole, no leaks, just minor movement of fluid in bottom. Played with control level and lifted TPH up/ down manually and banged things around a bit and saw TPH budge a little. Then, on next control lever cycle, TPH worked perfect. Very strong and smooth. This lasts about half dozen cycles and then just quit in the down position. Never got it to budge again despite more "mechanical agitation" / cycling, etc. Shut tractor off and checked pump prime - fluid was at very top when took plug out, so don't think any issues with pump. Prior to this, the TPH was always very strong and smooth with no issues. Also, when it worked those few times, it lifted me on hitch effortlessly. So, don't think any pump issues. The fact that it lifted me those few time, don't believe and issues with pressure RV or with piping holes in tranny. Think I have a valve sticking. ?.. Which one would do that? Can I test pump pressure with port under seat if valves are not working? Thanks for any insight - this should be enough to get us started. Dale
' Can I test pump pressure with port under seat if valves are not working?" Only if you block the tube that you had gusher from earlier. Take off accessory plate under seat and bolt it back on with two bolts and it positioned such that it covers and blocks the tube in question.
 

First off, you do know there are 3 oil compartments on that tractor yes? Tranny, hydraulic reservoir and rear end. Make sure all three are full to specs.
It sounds like you have been pretty thorough which is better than most.
I would hook a hose barb into the bleed port on the side of the pump and run a clear hose back to the oil fill hole on the hyd reservoir.
Then start the tractor and look for a good bubble free flow of oil in the hose.
You might not be getting a good prime to the pump and looking at the oil in that bleed hole won't tell you much.
If you are not getting a good bubble free flow of oil in your hose it could be the manifold from the transmission to the pump is damaged or loose. Maybe someone hit a stump? Tighten the manifold bolts first and see if they are loose. Or pull the manifold off (drain reservoir first) and replace the orings on both ends. I always use the square cut orings from the dealer on those manifolds.
 
it wouldn't lift at all despite manually lifting TPH

Lifting the 3 point arms does nothing at all to the piston or the valves inside. All it does is potentially move the connecting rod out of its proper position. It should be pinned in place at the rockshaft end, but if it isn't then that end could drop out of position. If it pulls out of the piston at the other end then it could damage the piston once things do start working.
 
I spite of the fact that the unloading valve is seldom the problem, (my theory) I would go to your New Holland dealer and get the right O ring for the unloading valve, as per you description. I believe, NCA 836 C
 
Thanks All. Yea - I apologize for the book - should have broken it up a bit.

Yes - I'm aware of the three compartments. All fluid levels were / are correct and none had been changing level prior to or during any of this.

Connection at bottom of pump is bone dry and always has been, so doubt having any seepage / air in leakage there.

Good suggestion on the clear tube from pump bieed back to reservoir to check for bubbles. I have some tygon and can do so.

Yes, I know lifting the TPH does not really move anything inside - was just looking to see if removing all resistance would let system "work".

I can also swap that plate around and check on my pressure as suggested.

Does anyone know the specific function of the o-ring furthest in on the check valve seat and back pressure valve? I may have to order me one and get it swapped just so I can positively rule that item out.

Thoughts on pressure relief valve? Would I have had the "gusher" of flow out the top of the tube if that RV were stuck open?

Appreciate any other suggestions. Thanks All. Dale
 
Without O-ring, oil could just leak around the check valve. Gusher? Path of least resistance.
 
Hi All, just wanted to follow up with what I ultimately found as the cause of my issue (No lift on TPH). In short, pump and relief valve were good. Check and Back Press valves were good. The Unloader was my issue. The value itself and the bushing it slides in were fine. The o-ring was the issue. Appearance wise, it looked perfect. But when you "shuttled" the valve back and forth in its port by hand, it would be "stuck" in place - where ever it was setting - and took a decent force of the thumb to break it loose. Once moving, it slid fine. Once stopped it would be stuck again. Seemed as though the oring had swelled or something and was just too tight. So - the oring on the unloader valve was my culprit. Unloader was stuck in the "unload" position.

A side question. My dad had replaced his hydraulic fluid (after doing a clean / flush) with "Mobile DTE Heavy Medium" oil. No idea why he did not take time to look for proper oil. Guess old age..... Anyways, does anyone have some "oil knowledge" as to whether that oil is acceptable in that 601 tractor?

Thanks All.

P.S. I had found an awesome thread on hydraulics that had led me to find the solution to my problem. It was Authored by Overland on June 7, 2015 and was titled 601 wont lift, blows relief valve - or similar... Anyways, it had some pics in it and great discussions on how the components work in different modes. JMOR and John in la had worked with Overland to figure out his issue. Their discussions helped me - a thanks to you guys!! Took a bit to digest it all, but led me straight to cause.
 

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