kubotacres
Gold Member
well in that case I can't help considering I don't have a FEL.
L3400 3-point hitch adjustment
- Thread starter Chilly807
- Start date
- Views: 81661
well in that case I can't help considering I don't have a FEL.
LD1
Epic Contributor
I kinda mentioned what is going on above if you can decipher it
Problem with mine with the overlap though is that even RPM changes effect the hitch. So if I have the blade just off the ground an inch or so, simply revving the engine up and down makes the blade move up and back down:confused2:
You are living up to your signature... :thumbsup: ".........there is only one way to find out." "Ok, hold my beer and watch this.........."
Good luck with the plan... Let us know the outcome... The only thing that concerns me with the "really old & jerky" valve... is that they were replaced to cure the jerky hitch. I hope yours can be adjusted to make it "livable".
Good luck with the plan... Let us know the outcome...
The only thing that concerns me with the "really old & jerky" valve... is that they were replaced to cure the jerky hitch. I hope yours can be adjusted to make it "livable".
LD1
Epic Contributor
You are living up to your signature... :thumbsup: ".........there is only one way to find out." "Ok, hold my beer and watch this.........."
Good luck with the plan... Let us know the outcome...
I am thinking it cant be adjusted, but still worth a shot. I noticed in the PDF with the flow breakdown, the newer valves Type 3 and up have changed the main spool design to include a "tapered part" and by their definition this allows "poppet 1 to close gradually to absorb shock".
So I think the newer valves CAN be adjusted to acceptable performance. But mine??????? See signature:laughing::laughing:
LD1
Epic Contributor
OP
Chilly807
Elite Member
What you're thinking is pretty much exactly my thought process as well. I can visualize the flow you're describing and it makes perfect sense to me.
Either we're both wacked or we're both right.
As to the timing of the two valves there might need to be a slight overlap, but I obviously have too much, since my hitch is being held by a dynamic hydraulic balance when it's in neutral as opposed to fluid being mechanically trapped and supporting the weight of hitch and implement. The "in" flow is being countered by the "out" flow, just enough to hold the hitch steady. When you cut off the "in" pressure by either shutting down the engine or diverting pressure to the loader or remotes, that overlap comes into play by dropping the hitch until the poppet closes and supports the cylinder again. When you re-start the engine, or the remote or loader valve closes the pressure to to "in" side is restored and the flow resumes through the PCV as the hitch lifts up once more until the in-out flow is balanced.
I agree that you do have the older valve (type 2), particularly if the shape of the valve body has a rounded corner. The new style are square-ish, and are Type 3 as far as I know. Do you have the parts breakdown for your tractor? The breakdown of which valve is installed by serial number is in the parts list, although how accurate it is is another question. What is your serial number?
My valve went from "overlap" at 0.016", to marginally stable at 0.020", to a very bad hunt at 0.026", to a mild hunt at 0.030", to stable but jerky with no overlap at all at 0.045" (original setting).
I'm hoping to find a compromise at 0.035" to 0.040". If it wasn't for the hunting in the middle, that would definitely be the sweet spot to adjust to.
It'll be interesting to see what yours does in the middle, no-man's land I call it.
Sean
OP
Chilly807
Elite Member
I kinda mentioned what is going on above if you can decipher it
Problem with mine with the overlap though is that even RPM changes effect the hitch. So if I have the blade just off the ground an inch or so, simply revving the engine up and down makes the blade move up and back down:confused2:
Mine does that as well to a small extent, I think a lot depends on how much overlap there is.
Sean
LD1
Epic Contributor
Some different results this time:confused2:
Just put it back together for the 8th or so time. On a positive note, I can have it appart, re-adjusted, and back together enough to test in about 45minutes:thumbsup:
This time I set it up for ZERO overlap. As SOON as the unload poppet starts to open is right when the other poppet is JUST closed. IE: no overlap and no delay. And in fact, when I went back and checkek the clearence with the plate @ 12.5mm, I was right at the spec of .020:thumbsup: But.....
The results were interesting to say the least. The jerkiest hitch I have seen to date. Jerky going up, jerky going down, and jerky in neutral. Infact it seemed like the hitch wasnt sure where it wanted to be. Little inch or two jumps up and back down.
I suspect it may have to do with how the unload poppet works. With a spring seat. It is like it was diverting JUST enough fluid to open momentarily, and start to divert fluid back to case as it is supposed to in N, but the cylinder would settle a tad, the unload poppet would snap closed, and it would raise the cylinder and it was a self perpetuating cycle that didnt end. It could be (now thinking about it) that I had just a TINY bit of overlap in the poppets. and JUST as the unload poppet was opening, the poppet that holds fluid in the cylinder was just starting to open as well.:confused2:
If I have ANY more overlap at all, I am into the dynamic balance you eluded to. And the hitch will once again be effected by RPM change and FEL control.
I think I am going to back the set screw out in tiny increments until I have a "slight" delay in valve timing. Just enough to come out of the problem above. And with a delay, no matter how slight, should cure the dynamic balane problem.
I think the key to these hitchs is minimizing the delay. Because I think the delay is what causes the jerkiness. But an overlap causes the dynamic balance issue. Who knows??
BTW, serial number is 61xxx something?
Just put it back together for the 8th or so time. On a positive note, I can have it appart, re-adjusted, and back together enough to test in about 45minutes:thumbsup:
This time I set it up for ZERO overlap. As SOON as the unload poppet starts to open is right when the other poppet is JUST closed. IE: no overlap and no delay. And in fact, when I went back and checkek the clearence with the plate @ 12.5mm, I was right at the spec of .020:thumbsup: But.....
The results were interesting to say the least. The jerkiest hitch I have seen to date. Jerky going up, jerky going down, and jerky in neutral. Infact it seemed like the hitch wasnt sure where it wanted to be. Little inch or two jumps up and back down.
I suspect it may have to do with how the unload poppet works. With a spring seat. It is like it was diverting JUST enough fluid to open momentarily, and start to divert fluid back to case as it is supposed to in N, but the cylinder would settle a tad, the unload poppet would snap closed, and it would raise the cylinder and it was a self perpetuating cycle that didnt end. It could be (now thinking about it) that I had just a TINY bit of overlap in the poppets. and JUST as the unload poppet was opening, the poppet that holds fluid in the cylinder was just starting to open as well.:confused2:
If I have ANY more overlap at all, I am into the dynamic balance you eluded to. And the hitch will once again be effected by RPM change and FEL control.
I think I am going to back the set screw out in tiny increments until I have a "slight" delay in valve timing. Just enough to come out of the problem above. And with a delay, no matter how slight, should cure the dynamic balane problem.
I think the key to these hitchs is minimizing the delay. Because I think the delay is what causes the jerkiness. But an overlap causes the dynamic balance issue. Who knows??
BTW, serial number is 61xxx something?
LD1
Epic Contributor
well....I'm throwing in the towel.
Kubota won Maybe my valve was never meant to be smooth. (lacking that "taper part" on the spool of the newer PCV's)
From the problems mentioned above, I tried backing off in small increments. ~1/8th turn. First time....same thing. Hitch wouldnt find "home". Oscillated violently. Went another 1/8th turn and BAck to jerky hitch but no ill effects from RPM change or FEL control.
The hitch hasnt been a problem for the 6 years I have had it. Just an annoyance. I had some spare time and thought I'd try to help solve the mystery.
At this point, the only other thing I can think that "may" help would be adjusting the spring pressures on the unload and #1 poppets. But I dont think I want to go there.
Kubota won
Maybe my valve was never meant to be smooth. (lacking that "taper part" on the spool of the newer PCV's)From the problems mentioned above, I tried backing off in small increments. ~1/8th turn. First time....same thing. Hitch wouldnt find "home". Oscillated violently. Went another 1/8th turn and BAck to jerky hitch but no ill effects from RPM change or FEL control.
The hitch hasnt been a problem for the 6 years I have had it. Just an annoyance. I had some spare time and thought I'd try to help solve the mystery.
At this point, the only other thing I can think that "may" help would be adjusting the spring pressures on the unload and #1 poppets. But I dont think I want to go there.
LD1
Epic Contributor
Well, everything is back together now. And I am still the proud owner of a L3400 with a jerky hitch
Not much else I can do without spending $$$ on a new valve.
I do think the design of the new ones with the tapered part on the spool would make it possible to get a smooth hitch. Because I think that is the problem. The poppet that is open to FILL the cyinder, and the unload poppet that bypasses fluid back to the case both snap closed too firmly. The taper on the ""newer" spools would allow for a softer transition from raise to neutral once everything else is adjusted right.
In a last ditch effort though, I firmed up the spring on the unload poppet. Hoping this would cushion the transition a little better by not opening up so quickly.
That made no difference at all
Kubota....you won
Sorry I couldnt help figure this out.
Not much else I can do without spending $$$ on a new valve.
I do think the design of the new ones with the tapered part on the spool would make it possible to get a smooth hitch. Because I think that is the problem. The poppet that is open to FILL the cyinder, and the unload poppet that bypasses fluid back to the case both snap closed too firmly. The taper on the ""newer" spools would allow for a softer transition from raise to neutral once everything else is adjusted right.
In a last ditch effort though, I firmed up the spring on the unload poppet. Hoping this would cushion the transition a little better by not opening up so quickly.
That made no difference at all
Kubota....you won
Sorry I couldnt help figure this out.