Jinma 354 Steering Problems

[Tim Berframe]

Jinma 354 with one hydraulic pump system. After several go-arounds with replacing the hydraulic pump and installing a pressure relief bypass into the system, I have no power steering.

Observations with front wheels off the ground:

It takes 4 full turns of the steering wheel to move wheels from hard right to hard left and three and a half to go left to right with the engine off. The same with engine running.

Disconnected steering hoses and put in separate buckets. With engine off, one turn of the steering wheel pumps out about 50ml for each direction. With engine running, they pump about double or maybe 3 times the volume.

With everything connected, wheels off ground, engine running, turn wheel until I reach the stops, the system hydraulics are releasing at 1400psi. (same for both directions)


So, I think the priority valve is working. I think the steering box is working as it is supposed to with no power. My question is: Does the increased flow for the power assist sound about right? If it is, the steering cylinder must be by-passing internally?

 

[RonMar]

The steering "gear" is a rotary vane pump. As you turn the pump, the vanes pump fluid to the steering cylinder. when you turn the wheel and reach a stop, does it get harder to turn the steering wheel? If I recall you mentioned in the other thread that it was hard to steer with the wheels on the ground. What does power steering do? It makes it easier to steer right? If the cylinder was bypassing, the steering wheel would steer easy, the front wheels just wouldn't turn very well.

The priority valve has a small port that sends fluid down to the rotary vane steering pump. I think this is called pilot flow? But no fluid flows this way as it cannot pass thru the non rotating pump. As you turn the wheel this fluid can now flow from the diverter to the steering and puts pressure on the backside of the vanes you are rotating. As it starts to flow, this flow opens the piston in the diverter trying to maintain pressure down that line and diverts fluid flow from the 3PH to the steering to provide the power assist. You stop turning, the flow stops and the diverter reverts to feeding the 3PH.

Quick check of the diverter, very slowly lift the 3PH and try and turn the wheel at the same time(this is easier with a load on the 3PH). If the diverter is working the 3PH should slow/stop while you are turning the wheel as the steering is stealing the fluid via the diverter. You may discover that the steering gets easier while you are trying to lift the 3PH which would be because of the added pressure in the system feeding down thru that little bit of pilot flow. Because it is such a little bit of flow though you will probably be able to out-turn its little bit of assistance with the steering wheel...

The added flow you are seeing with the hoses disconnected is probably the pilot flow thru the diverter...

 

[Tim Berframe]

Thanks for the detailed description. There is definitely no part of this where turning the wheel gets easier. It is a workout to try to bucket dirt. It takes two hands to turn if moving in less than third gear

I was trying to rationalize why the pressure relief trips at the steering stops. I was thinking there had to be fluid moving in abundance and therefore the priority valve was working
I was trying to rationalize why the steering is identical with and without the extra little fluid. Your explanation handles that

I'll do your suggested tests in the morning.

 

[RonMar]

Also if you are tripping at 1400 PSI, that is a little low IMO. I don't know the spec for the 354, but if I recall correctly the spec for my 284 is around 2700 PSI...

 

[quicksandfarmer]

My vote is for diverter valve as well. If you're seeing 1400 PSI when the steering is against the stops then the cylinder isn't bypassing. If the steering is hard rather than soft then the steering control seems to be fine.

You can verify that the cylinder isn't bypassing with the engine off. Disconnect one hose from the cylinder and turn the wheel in the direction that makes oil flow out of that hose. If the cylinder is bypassing you'll be able to keep pumping oil out even after the cylinder is extended all the way.

My understanding of how the steering works: the steering wheel operates a pump. Turning it one way pumps fluid into one side of the steering cylinder causing it to move in one direction, and turning it the other way pumps it into the other side making it move in the other direction. This could be a closed system and would work just fine. The diverter valve senses what you're trying to do and assists it. The way that it senses is that it is connected to the steering hoses, it detects the flow of fluid and if fluid is flowing in one direction it provides additional fluid in that direction ("diverts" it from the main hydraulic fluid flow path, hence the name).

What is making the diagnosis tough is that you don't seem to have a complete failure. The diverter valve is doing something: your test with the hoses disconnected shows that when you turn the wheel more fluid flows with the engine running than without, which is exactly what the diverter valve should be doing. And the fact that your PRV releases with 1400 PSI when the steering is turned against the stops shows that something is happening.

But the fluid doesn't seem to be getting to the cylinder, at least not enough to help with the steering. My suspicion is that the diverter valve is partially obstructed and lets a little bit of oil through, enough that when the steering cylinder is fully extended it creates back pressure, but not enough to do any useful work. Cleaning the diverter valve may be the solution. My understanding is there isn't a rebuild kit, it needs to be replaced if faulty.

 

[Tim Berframe]

My day job and the rain kept me from this project. I took the diverter valve apart today. The pictures show what is inside. There were chunks of rubber seal in the inlet side on the end of the piston. The piston pushed out with little effort although it is a very tight fit. The piston has signs of wear but it is immeasurable with my calipers.View attachment 515515

View attachment 515516

The piston is 20mm diameter with 3 Oring grooves. They are 1mm wide with a bottom diameter of 18.9mm. There were no O rings present. I assume there should be rings and that the chunky bits of pump seals went through the system and tore them out of there to be relocated somewhere further downstream (in the steering box, the steering cylinder, the 3pt cylinder or the sump). The only thing I could get locally were 18mm X 16mm X 1mm O rings. They are actually 0.75mm thick and 0.95 mm wide. So, they fit in the grooves but 18.9mm + 0.75mm + 0.75mm = 20.4mm. There is no way I could get the piston back in the bore. I suppose I need 20mmX19mmX1mm rings?


I had to cut them to get back off. The piston will not go back in the bore without them! WTF? I'm stumped. I took it out with little effort but there is no way that will push back in.

 

[Tim Berframe]

Should have mentioned:

valve model FLD - F6 - something unreadable
# 06-02-569

8mPa ( which I think is about 1160 psi)

 

[Bob Rooks]

You don't use O-rings on hydraulic spool valves. The grooves you see on the spool are to soften the inrush of oil when the port opens. It provides for a feathering effect and also lubricates the valve body. And btw, the spools are a lap fit to the body - no seals needed except for dust and dirt, and those are wipers.

 

[RonMar]

What Bob said...

 

[Bob Rooks]

The piston has signs of wear but it is immeasurable with my calipers.View attachment 515515

View attachment 515516

This is what I get when I try to view your attachments.
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