3-Point Hitch L-series Jerky 3PH - Jeff's homebrew repair.

[J252]

*** I will return to this thread and fill in this post with a great more details as I get the chance.***

For now, you can watch this Youtube video and read the extended description.

Kubota L3400 - 3PH Action @ 2000 RPM - YouTube

Quick summary:

L3400 with extremely jerky 3PH (violent) with old YR909-00100 PCV. We bought the tractor used this winter, and were quickly and thoroughly disgusted by this fundamental problem. I dismantled and studied the PCV system and made the mods early this spring. Have been using the tractor like this all summer and am very happy with the result.

1. Disassembled the PCV and chamfered the spool control edges by ~200 um. This increased PCV response and reduced the violent jumps from 1" down to less than 1/4".

2. Added an external pressure compensated flow control valve ($~90 + lines and fittings). This reduced the flow to the 3PH system and took the violence out of the 3PH motion. It also reduced the lift speed though this is now adjustable. It did not affect the 3PH lift capacity or the FEL in any way.

I will fill in the blanks, and explain much more thoroughly later as well as show photo's and a part list of the install.

Cheers,
Jeff

 

[J252]

Reserved for OP's upcoming pictures.

 

[J252]

Reserved for OP's upcoming pictures #2.

 

[TheGoose]

subscribed.

 

[LD1]

subscribed.

me too

 

[k0ua]

me three

 

[moored4]

ME 4 also!

 

[canoetrpr]

Brilliant!

 

[teg]

Reserved for OP's upcoming pictures.

Looking forward to seeing what you did!!!

FYI... You only have 24 hours that you can edit the post... no problem with posting them later if you didn't get to it in time...

 

[J252]

Mini Rant

The closed loop 3PH position control system on this tractor is just plain and simply badly designed. Its not just badly executed, its also fundamentally flawed. The YR909-00100 position control valve is effectively offering only ON-OFF closed loop control in the up direction. The way the spool valve and unloader poppet are designed, it is not really capable of providing much (if any) proportional response - its output flow is really pretty much either on or off.

Now ON-OFF control would be a legitimate (albeit simple) method of closed loop control, provided the system is relatively slow changing (high capacitance). Your home thermostat does a pretty good job with on-off control of holding your room near the set point - it is a nice slow changing system. Our 3PH system are not slow moving; the cylinder is too small or the flow rate is too high (whichever way you want to look at it). ON-OFF is not going to work under those conditions. I have a bit more ranting to do that I'll save for a later post.

I wanted to see what it would take to make the existing system work. Since I couldn't increase the size of the cylinder, I tried a few different ways of reducing the flow into the cylinder thereby slowing its response. Inline restrictions (after the PCV but before the cylinder) did work but introduced some new problems. The pressure compensated flow control valve was the cleanest way to get the job done.

***I'll discuss the YR909-00100 PCV and the mods I made to it in a later post****

For now, what I will say is that for those with YR909-00100 PCV's like mine, I expect just reducing the flow to the 3PH by using the flow control valve will smooth out the motion, but will not get away from the fact that the handle has to be moved 1" before the 3PH hitch responds with its discrete 1" lift. (The reason it is 1" is a result of the PCV spool to housing dimensional relation (either by design or tolerance)). For many that is not a big deal, and can live with it if the hitch is no longer jerking.

Maybe some of later L-series owners can speak to this, but I have heard that those, though still jerky, are better resolution and have smaller (1/4") jumps. In that case, just adding the flow control would be all you'd want to do anyhow.


Installing the pressure compensated flow control valve

To reduce the flow to the three point hitch system, I used a pressure compensated flow controller. This valve works as an adjustable flow divider, which divides the flow between the controlled flow (CF) port (leading to the 3PH system) and the exhaust port (back to sump). The pressure compensating spool inside ensure that the flow rates through the controlled flow port doesnt vary due to load changes. The valve I bought was a 16 GPM unit from my local Princess Auto (Princess Auto Flow Control Valve) though Surplus Center has a nice 8GPM Prince unit that is better sized for the flow rate of the system (Surplus Center - SAE 8 HYD FLOW CONTROL VALVE RD108-8) and probably better quality.

Mounting

I mounted the valve on the underside of the loader control valve. It fits there like its meant to be.

I used two of the 4 existing mounting holes on the loader valve and made a bracket to mount. The location is nicely out of the way, doesnt interfere with anything, and is still accessible (bracket dimensions in mm).

Plumbing

1. 1. I removed the hose from the BY port on loader valve and turned the fitting 90 degree to the outside.
   
2. 2. With a new hose, the BY (power beyond) on loader valve was routed to Flow control valve inlet (IN).
   
3. 3. The hose to 3PH (formerly connected to loader BY port) was connected to CF port on flow control valve.
   
4. 4. EX port on flow control valve gets teed into EX line on loader valve via a new hose and a tee. This flow goes back to tank (sump).

 

[Gordon Gould]

I am not a hydraulic engineer but from your explanation I can understand your fix, and how it works, and why you are criticizing the original design. Thank you very much for taking the time to post this. The thing that bothers me is why Kubota won't take care of this.

 

[Harvest Moon]

Nice! Thank you!

All that's left is put together an after market kit with the valve, bracket, hardware, hoses and instructions and I bet there will be a lot fewer up sells at Kubota! Shame on them for letting it go on this long.

Great tractor, lousy hitch function.

 

[J252]

Nice! Thank you!

All that's left is put together an after market kit with the valve, bracket, hardware, hoses and instructions and I bet there will be a lot fewer up sells at Kubota! Shame on them for letting it go on this long.

In my mind, there's no real need for a kit - Other than the bracket (something suitable can be made with a drills and tap), pretty much everything else is right on the shelf at your local surplus center/princess auto/misc hydraulic store. Should be well within the scope of the average owner.

 

[Chilly807]

This looks like a pretty good fix to me. We had talked about adding a restriction before the 3 point hitch, but the problem was that without giving the excess fluid somewhere to go, it ends up going over the relief valve. This type of valve was discussed, I think, but nobody had taken the plunge and tried it.

Reducing the flow rate to the lift cylinder will certainly help, I've noticed that if the loader is lifted at the same time (feathering it is enough) the hitch is much smoother.

Mine will be a little bit different, since I have the remote valve in between the loader valve and the 3 point valve. There may be enough room to one side of the seat to mount the flow divider.

Mine has a newer version of the PCV, I may try checking the adjustment on that before I go this route, but it sure does look like an improvement over mine.

Thanks, Jeff, for both trying this and also taking the time to show us the results. I assume you're in Canada (Princess Auto), but I don't suppose you're in NS??

Sean

 

[canoetrpr]

I am very much a hydraulic newbie so you will have to explain to me how modifying the flow to the 3PT cylinder does not impact the lift capacity.

Also, do I understand correctly that in order to change the lift increment to being more granular, you had to change the physical linkage of the 3PT control arm in some way?

 

[k0ua]

I am very much a hydraulic newbie so you will have to explain to me how modifying the flow to the 3PT cylinder does not impact the lift capacity.

Also, do I understand correctly that in order to change the lift increment to being more granular, you had to change the physical linkage of the 3PT control arm in some way?

Here let another hydraulic noob, try to help, since the cylinder is still the same, and the relief valve is still set at the same, it will just take a little longer to develop the full pressure in the cylinder as the flow rate is lower. So the 3pt lifts slower but will still have the same ability to lift the same load. I learned about pressure and volume about 40 years ago. from trading for a 200 PSI air pump that ran on 12 volt DC. Yes it will develop 200 PSI, but it would take a minute to do that in just filling up its own little 1 foot hose. let alone a tire. the Volume of air it can compress and deliver to anything is miniscule. On the other end of the spectrum is an air pump designed to inflate toys and air mattress etc. It is very low pressure, (PSI) and high volume (Cubic Foot/ Minute)
hopes this helps.

James K0UA

 

[canoetrpr]

Makes perfect sense.

I will try to get a video of my L3400 3PT before it gets traded in next week. I am one of the lucky few to have gotten it changed to the valve from the L3010 so it is 'relatively' smooth. I would say equivalent to what we saw in this thread.

I'm expecting that the 3PT on my new to be M7040 is gonna be smooth!

 

[J252]

Thanks, Jeff, for both trying this and also taking the time to show us the results. I assume you're in Canada (Princess Auto), but I don't suppose you're in NS??

Sean

No problem, I've been meaning to post this up for months.

I'm in the rainy Fraser Valley in BC.

 

[J252]

I am very much a hydraulic newbie so you will have to explain to me how modifying the flow to the 3PT cylinder does not impact the lift capacity.

So the 3pt lifts slower but will still have the same ability to lift the same load.

Yea, Koua got it. The maximum lift force is limited by the system pressure (which we are not changing). The rate of cylinder extension is determined by the flow rate.

Also, do I understand correctly that in order to change the lift increment to being more granular, you had to change the physical linkage of the 3PT control arm in some way?

Actually, I did look into that, but any changes would have to be made to the error mechanism inside the casting near the control valve, and there wasn't clearance to do it.

What I actually did is took apart the control valve and modified the actual spool slightly. I'll post up what I did there later. That said, its a bit of a hassle, and if one can live with non-jerky but low resolution control, just add the flow control.

 

[Chilly807]

The video you posted was at 2000 rpm, and was pretty smooth. How does the flow divider valve work at lower speeds (and pump flow rates), at idle for example? Does it scale the delivery from the CF port to be the same volume (provided the pump still produces that much flow at the lower speed, of course), or is the lift proportionally slower?

Sean