JCB 3CX - Only one movement at a time, is my pump shot? - Now with pics!

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the_jcb_boy
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Re: JCB 3CX - Only one movement at a time, is my pump shot? - Now with pics!

Post #11 by the_jcb_boy » Fri Mar 07, 2014 12:04 pm

Nice machine. That looks like 2 m3 of timber, should weigh about 1.5 tons if wet. Shouldn't be a problem for your back actor. Lifting your machine is a very nice test to see if it lacks power and if everything is sealed nicely (if not the machine will drop by itself slowly to the ground in about few minutes, what is more it's not a crucial leak).

Don't forget to open and inspect the tank when you do the oil change.

"It could still be a restriction to flow somewhere meaning the back actor actions happen sequentially, I imagine the flow taking the path of least resistance first, then when that ram is fully retracted/extended it goes to the next etc. It can do both back legs at the same time but they are smaller bore pipes so i'm guessing take less flow?"

That is exactly my thinking. The same thing happens to me when i open too many valves to full at the same time (lift boom, extend dipper, lover arm and move the actor to side). Some actions stall out others due to the lack of oil quantity. But this happens only, when you open 4 valves to max. If i open all 4 to a degree or add throttle so that i increase the pump speed and so doing the oil flow, it all gets done the same time. If your stabilizer legs can lift you normally, than your second section of the pump is doing it's job. The little oil around the place where the shaft connects is not a big concern.

Like you said you are an electronic engineer, so you got voltage (pressure) in your system, you need to find what's limiting your current (flow).

Is this a new problem or was the machine always like this? If the machine was always like this than check the ARV's (auxiliary release valves). No need to check your MRV due to the fact your front loader is working normally. ARV's are under the back actors valve block.

So that you know what you are aiming at: The back actor should be able to lift your machine (7 tons) of the ground easily, should be able to lift twice that timber load (3 tons) vertically with no problem before the release valves kick in. It actually can exert more hydraulic force than the body of the digger and the rams can handle it, that's why there are release valves, so you don't tear your digger apart.

Does your hydraulics jerk a bit? Are the motions smooth or do they go-stop-go-stop, because that's the sign of air in your hydraulics system. When you finish with the oil change, don't forget to force all the air out of your system. You do that by running the machine and doing all actions with your hydraulic system from one maximum position to the other few times (until the motion is smooth), just like if you ever had to bleed your servo steering on your car, you turned on the car and went left-right to the max with your steering wheel a few times.

Hope you find the root of your problem and fix it soon, i see you got a lot of work to do.

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darklegend
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Re: JCB 3CX - Only one movement at a time, is my pump shot? - Now with pics!

Post #12 by darklegend » Tue Mar 25, 2014 12:29 am

the_jcb_boy wrote:
Is this a new problem or was the machine always like this? If the machine was always like this than check the ARV's

Does your hydraulics jerk a bit? Are the motions smooth or do they go-stop-go-stop, because that's the sign of air in your hydraulics system.

Hope you find the root of your problem and fix it soon, i see you got a lot of work to do.


Hi thanks for the reply. It's always been a problem since we've had the machine but we've only had it a few weeks. I'll check the ARVs after my oil change, how do you know they are set correctly? Am I looking at fitting a gauge somewhere?

The motions are sometimes a little jerky, it's not bad though.

Been thinking about how to flush the system, i've started another thread about that.

There's many a job waiting for her when we finish getting her right!

Thx


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