3-Point Hitch Another L3700 with Jerky lift

[Verticaltrx]

I'm not very familiar with the L series, but do they have an external hydraulic line that runs to the 3pt hitch cylinder like the B-series does? If so, a very simple fix in my mind would be to install an adjustable flow regulator. It could be left in the open position for max flow when doing tasks such as bush hogging or discing where you want a quick lift, then turn it down to a lower flow setting when you want more control, such as box blading. Surplus center sells various types of flow regulators, not very expensive either.

My old Ford NAA has a 3pt hitch that's a little bit jerky as the result of too much flow to the 3pt cylinder. It has a replacement hydraulic pump on it which has a higher GPM than the original pump. Also, the original pump had a little flow restrictor knob right on the pump so you could dial up or down the flow rate depending on the job.

 

[teg]

BTW Kubota Dealers are telling people that the problem was fixed

According to most kubota dealers, there was never a problem in the first place... I was told by a dealer that he never heard of a problem with the valves being jerky, then I went around back to talk to the service mechanic... he told me that he had fixed 3 of the jerky valves, one done within the past week...

I loved this "mystical" comment...
http://www.tractorbynet.com/forums/kubota-buying-pricing/162156-any-info-b3300.html#post1864659

Again... try it before you buy it... my problem is that they sell the tractor as "standard" and it is not a standard... it is uniquely different, IMHO.

 

[johnrex62]

According to most kubota dealers, there has never a problem in the first place... I was told by a dealer that he never heard of a problem with the valves, then I went around back to talk to the service mechanic... he told me that he had fixed 3 of the jerky valves, one done within the past week...

Did he say how he fixed it? A replacement valve or rub it with a rag till it shined and submit a bill?

 

[teg]

They used a valve from a higher priced L series (old thread... long ago). There were suppose to have been changes made to the Newer L3400/L2800 that made that valve no longer fit (at least that the "story" I remember). If someone has access to a parts book, I think there might have been 3 changes for that valve. ...But you should never believe everything you read on the internet...

The only problem I have with my lift is when I use a boom/pole type implement....but that jerking extended out 5-6 feet like a post hole digger is very amplified.

This is what I had a real problem with... since I was close to maximum weight for lifting and had to lift it up to it's max height... One time I had to stop (thinking the top link was going to pull OUT). I had to drive the trailer out from underneath what I was lifting.

 

[InThePines]

Thanks for all the input guys. A Kubota service rep called me today. I had submitted an inquiry to the corporate office and pasted link to this thread. I was worried that my lift was somehow damaged or defective and I may make it worse using it. I did not want to take it back to the dealer now but wanted it noted that there may be an issue that I would like to be consulted about, I like to spend my spare time on the tractor, not pulling it. He was very helpful in talking me through possible issues. I am not proficient on how fluid pumps and hydraulic systems work, but in summary, the L3400/L3700's do not have the same components as the Grand L's and part of those components in the Grand are to allow what he called feathering or shock absorbs ion when making small adjustments to the lift. My comparison was to water hammer where when flows thru pipes abruptly stop, caused a kickback. Sorry I cannot be more technical in my explanation. But he said the higher end models had features to lessen the impact of such changes in force and that what I was describing sounded normal for that model (3700), and yes that does mean there is some bounce to the lift. But it does not rock the tractor. By the way, he did mention that there were some very knowledgeable writers contributing to this link that have a good understanding of what is going on. The more I use the tractor, the more I get used to managing the lift.

 

[Chilly807]

I think I'll have a good look at mine soon. If I can easily plumb in a flow control valve I may try it and see what happens. After all, there is one in the "down" circuit, which is the return to tank.

The linkage to the 3ph valve may bear some inspection as well, I've never really taken a look at how it's set up.

I think part of the trouble is that it's a servo controlled valve in a very simple sense. In other words, all the operator does is shift the position control valve to start the sequence in motion. The valve opens, moving the 3 ph lift arms, then is shut by the feedback linkage once the lift arms reach the desired height. It's possible that the jerky motion is caused more by the feedback linkage abruptly shutting off the flow of oil than anything else. If that's the case, then metering the flow to the valve won't entirely eliminate the problem, though it would improve it somewhat.

It may be possible to "damp" the shutoff action of the feedback linkage, as long as the valve can't continue to try and raise the lift arms once they're fully up.

I'd like to know what the difference is between the 2800/3400 valves and the ones fitted to the Grand L series.

 

[teg]

I'd like to know what the difference is between the 2800/3400 valves and the ones fitted to the Grand L series.

I would *ALMOST* be willing to take mine apart... for research and development ... I think mine is very smooth... this weekend I'll video it (both high and low rpms).

Here is the difference I can tell from the old really jerky valve and the newer one that was used in 2006 until the tractor was "changed" so that the Grand L valves could not be used any more... I would like to see what the Grand L valve looks like, too...

 

[Chilly807]

I had a close look at the feedback linkage tonight, as well as reading Harvest Moon's saga (all 20 pages) from 2009 !

About the only thing I could see that might help is to increase the length of the moment arm (lever) on the valve, which would result in slower closing as the lift arm reaches it's desired position. What that would do to the actual position of the 3ph I'm not sure without actually trying it.

I think it might result in the loss of linear control over the 3ph movement. The feedback link is designed to simply translate the lift arm position into a close signal to the valve, if the lift arm must move further to deliver that signal, you'd have to adjust the length of the link to compensate for that. My concern would be either overtravel of the 3ph, or a "dead zone" at one or both ends.

The only way to know for sure is to try it.

One thing we didn't get into in the thread from 2009 was the internal linkage from the cylinder to the rock shaft. Unless the 3ph has a rotary actuator, which I doubt, there has to be a crank arm or bellcrank of some sort in there to change the linear motion of the cylinder to a rotary output on the rock shaft.

If that setup is biased towards high rotational speed and less lift power, which it seems to be, the motion of the 3 ph is going to be rough unless very fine control is exercised over the fluid flow through the valve and to/from the cylinder.

Sean

 

[e30racer]

I've owned my L3700 for about 3 weeks now and have about 14hrs on it. My tractor definitely has the jerky 3pt lift. It's smooth if you raise it fast but if you try to raise it slowly it is really jerky (with 60" Land Pride rotary mower on the back). I've got a box blade and it'll be interesting to see how the jerky 3pt impacts performance there. I'm guessing that I'll learn to compensate but time will tell.

Steven

 

[johnrex62]

I've owned my L3700 for about 3 weeks now and have about 14hrs on it. My tractor definitely has the jerky 3pt lift. It's smooth if you raise it fast but if you try to raise it slowly it is really jerky (with 60" Land Pride rotary mower on the back). I've got a box blade and it'll be interesting to see how the jerky 3pt impacts performance there. I'm guessing that I'll learn to compensate but time will tell.

Steven

We are in the same boat, Steven. I see you have had a bit more time than me. I have owned mine a week longer, but have only 9 hours on mine. :confused2: