Jinma 254 tractor hydraulic question

[sporta]

Hey all,
As the title says, we have a Jinma 254 tractor that has a hydraulic issue. We are the 2nd owners of the tractor and it has a few issues related to the hydraulics, the biggest is the previous owner bypassed the hard lines for the backhoe attachment and instead has split the line on the front end loader to power the hoe attachment. The hard lines that run back to the 3 point hitch (where the hoe would normally hook up to) are still there but are not being used. The rear 3 point hitch is extremely slow to activate when first getting going. The system seems to be leaking the hydraulic fluid out the rear of the tractor under the seat (seepage, I'll try to get a picture of what I'm talking about in the next few days). When fluid levels are full (after cycling the front end loader and rear 3 point hitch to ensure that there is no air in the system) it seems to work ok for a while.

Whew, long winded backstory completed...now for the questions.
1. There a way to see if something is blocking the lines that are supposed to feed the rear hydraulic system (backhoe or whatever)?
2. Would a internal (ram) seal for the 3 point attachment allow leak down and seepage of hydraulic fluid?
3. If the system is torn down, can the hard lines for the rear attachments be cleaned/inspected (kinda goes along with #1)?

Thanks in advance,

Steve

 

[piper184]

Hi Sporta, Welcome to the forum.

My tractor is a 2006 Jinma 284 with Jinma FEL and Jinma Backhoe so my comments will be based on that. They should be just about the same tractor. YOu didn't say if you have Jinma FEL and BH or some other brand. Also if the BH is a frame mount or 3 point mount, that may make some difference.

For the FEL the hydraulics tap into the tractor lines with quick disconnects. The fluid flows from the tank to the pump to the FEL and back to the tractor. At this point it goes through a diverter valve which gives priority flow to the power steering. From there it flows back to the 3 point control valve and eventually the tank.

In the FEL valve there is a pressure relief valve that dumps fluid back to the tractor when a cylinder bottoms out. This prevents damage to the pump. There is another relief valve inside the 3 point control that dumps fluid back into tank internally. This is to protect the pump when the 3 point hits the top of the stroke or is overloaded. This is needed because the fluid has already left the FEL or there is no FEL.

The 3 point only has power lift (one way cylinder). When you move the lever to let it down all it is doing is dumping fluid from the cylinder through the control valve (knob under the front of the seat) and back into the tank directly. The knob controls how fast the 3 point goes down, but not up. If you screw that knob in all the way the 3 point will not come down.

The remote connectors on the back of the tractor: One has pressure when the 3 point lever is lifted and the ram has traveled all the way to the top. The other connector just is a fluid return directly to the tank. If you follow the lines you can see which is which. In theory you can pull the 3 point lever up and it will supply flow out to the remote couplers to run something like a log splitter or a BH that have their own control valves. I have never used mine that way but I do have a dirt scraper with a single acting cylinder that I can connect to the remote pressure output. It then operates in tandem with the 3 point.

That's the basics of how things are intended to work. More on the BH in the next post.

 

[piper184]

You didn't say where the previous owner T'd into the FEL lines for the BH or how the BH return line is connected. On my factory setup BH, it has it's own hydraulic system that is completely separate from the tractor. It has a tank that holds ~8 gallons and a pump that bolts onto the tractor. There is a plate just above the PTO shaft. Remove the plate and install the pump. The pump has a tang that connects to the PTO intermediate shaft inside the tractor. To operate the BH you put the PTO speed selector in neutral so the shaft doesn't spin and then engage the PTO lever. This makes a solid connection from the engine to the pump which is much closer to the BH.

I think that trying to use pump at the front of the engine is less than ideal for a BH for a couple of reasons and tapping a line to the FEL makes it even less desirable.

First up is pump flow capacity. The pump on my BH moves quite a lot more fluid than the pump designed mostly for power steering and 3PT. Driving the FEL with this pump is about all the additional capacity it has. Sure the BH will move and eventually gain the power it needs, but it will operate significantly slower than using a larger pump that is connected with shorter hoses.

Second is tank capacity. The tank under the seat holds less than 3 gal. of fluid while the one on the BH holds more than twice that. This is important for heat dissipation. Heat is the enemy of fluid but even more so of seals and valves that are less than commercial quality.

Even with the factory plumbing, and working off of the remote connectors the BH is not going to perform optimally. Who knows what compromises were made when connecting to the FEL on your tractor.

Speaking of which, the factory FEL valve is not set up to run any other hydraulics. Many aftermarket valves have a place to install a part that is called "power beyond". This allows the user to run additional hydraulics like a grapple fork or other attachments that require hydraulics. Some hay balers or log splitters or maybe even a hydraulic top link for the 3PT.

I'll get to the 3PT next.

 

[piper184]

3PT issues.

Most all 3 points (and other hydraulics) have some leak down factor. Seepage in a valve or a hose or fitting can all add up. I consider some leak down as normal and only start troubleshooting when it gets to be more than just a slight nuisance. The 3PT cylinder is completely enclosed in the tank, it is part of the casting. For it to leak down it has to let fluid out past either the piston seals or back through the control valve. Unless of course there is other internal damage like a crack or casting flaw.

Any leaking you see on the outside of the tractor is coming from some other source. Most likely is the rocker shaft seals that keep the fluid in the tank from coming out. I have a leak in this area but it only shows up when I over fill the tank. Second most likely place is the breather vent which is probably in filler cap. If you over fill, operate with the front higher than the back (pushing snow up in large piles) excess fluid runs out the breather and makes a mess all over the back of the tractor. Remember the tank was designed with enough capacity for power steering and 3PT. Adding the FEL takes more fluid and unless you over fill, pushing up piles can cause the suction line to open up and you basically run out of fluid until you back up to a more level spot. This happens to me a lot and I have a tendency to run the tank over-full.

Another thing that can cause the vent to spit fluid is if you are getting air in the system. Most likely place for that to happen is in the suction line from the tank to the pump. The fluid foams up and overflows. Occasional momentary sucking of air is mostly inconvenient but if you have a persistent air leak it is hard on the pump. Air bubbles in the tank usually dissipate overnight.

Other leak points are hose and pipe connections and the control valves themselves or the gaskets between them and the tank. Just last winter after 15 years. one of the bolts that holds the 3PT valve to the tank worked loose. That let the gasket blow out and spit fluid everywhere! Fortunately it was above 0 out and I was able to take it off and make a new gasket in the shop. Stuff happens...

Slow hydraulics can be due to a lot of things but most likely is a plugged pickup screen in the tank, or external spin on filter. Check and clean the screen often. This can be done without draining the tank. It also give you a chance to look inside at least a little. A spin on filter is a nice feature if you have it. Keep a spare filter on hand and spin it on at the first sign of trouble.

A sluggish 3PT until it warms up is a problem for me too. In the summer I have 3PT lift at start up, but as the temps drop I have to wait longer and longer for it to work. In really cold temps (-20F or more) I have to let the tractor run quite a while to get things warmed up enough to even lift the back blade off the ground. I find that continually working the FEL hydraulics helps speed up the warm up process. I even installed a heating element in the tank so I can plug it in for a while before start up.

I've never been able to figure out the exact cause of this. Changing to lower viscosity fluid helps some but does not eliminate the issue. It might be that the pump just doesn't work very well when cold or it could be any of the valves in the system or it could be that the 3PT cylinder casting shrinks enough to make the piston a tight fit and it has to be warm up and expand enough to release it. After many years of operation and observation, I think the last part is most likely as the pre-heat has most positive effect. There is a lot of mass to go from -20 to +40!

Hopefully all of this will help you out in some way. Please post questions and pictures if you need more info.

 

[Jimmy254]

Hi Piper, The gold mine of information you have provided in this thread is going to come in very handy as I try and understand the hydraulic system. I too have the slow 3PT until the tractor warms up but I haven't changed the fluids or filter yet. Will let you know how it goes.

I have often looked at and thought about those rear connectors.

Do you have a pic of how your 'dirt scraper with a single acting cylinder' is hooked up, how it works etc. What do you mean by operated in tandem with the 3PT?

 

[piper184]

Of the two remote couplers on my tractor the bottom one is just a pipe connected to the tank with a banjo bolt. No pressure available there, just a return.

The upper one has a pipe that goes forward and connects to the 3 point lowering control block. The one with the knob just below the seat. I am not exactly sure how the passageways are drilled in that block but from experimentation I found that it provides pressure to the coupler while raising the 3 point and drops that pressure when lowering the 3 point. It is probably nothing more than a tap into the pressure line for the internal 3 point cylinder. It has been several years since it was last used and I don't remember if I had to close the knob or open it all the way up. There is a lock screw on the face of that valve and if it is tight you can't turn the knob.

To use the scraper you have to lift the 3 point up until the arms top out then wait for the pressure to travel to the scraper. When you want to drop the scraper you lower the 3 point control and the scraper will drop, after it is down, if you keep holding the lever to "down" the 3 point arms will lower too. Sometimes they will go down at the same time.

My scraper is a strange little device. It has two one way cylinders that lift the machine up under pressure and the weight of the unit pushes them back the other way when the pressure is released and the fluid allowed to flow out. There is only one hydraulic hose that makes this happen. The front apron and floor with the cutting edge are all operated off of some levers and slots connected to the tub.

Like I said it has been years since I have used it and I hope my memory is correct on this.

I have a male quick coupler with a pressure gauge screwed into it. It lets me plug into a port and operate controls to figure out what is going on.

I think the intent of the remotes is to have the 3 point valve send fluid out the top port and then you plumb in a second control valve for whatever equipment you are using. Then the return to tank outlet of that valve is supposed to be connected to the lower coupler.