JCB 803 Super

[Agrimax]

Hello folks,Wonder if anybody can help? Major hydraulics problem with the above machine.
Very little power while tracking. 2 speed tracking is switching on and off as it should.
Dozer blade is slower than normal to lift and has no power pushing down. Will not lift the machine of the ground.
No downward force on boom,dipper and bucket rams,but it will lift them up and reach ok.
Slew hasn't a lot of power.
However,if the breaker pedal is depressed while operating any other function all services work as they should.Both in power and speed. Likewise if the dozer blade is lifted to the end of the ram travel and held,other functions work fine.
This one has a piston pump with two outlets and a gear pump on the end. Pumps are providing pressure and flow as per the shop manual.With a gauge on the servo pressure maintenance valve test point,again the correct pressure is maintained.Haven't went any further yet and thought it would be worth asking the experts if there are
any common known issues with these or any pointers as to how to find and fix the problem?

 

[CPS]

Pretty sure @jd6820 was able to help a guy on here with a similar problem

 

[Mick-the-fitter]

Sounds like you have a relief valve stuck open in the spool block, when the breaker pedal is operated it takes oil from both pumps, and would be less obvious that a valve is stuck open, does it straight track?

 

[Agrimax]

It does track straight but has little power tracking unless dead ending another service at the same time.
Have searched and found the thread containing a similar problem,that jd6280 was so helpful on as mentioned above. Gives me something to go on.More pressure testing to do as well.

 

[jd6820]

The Servo pressure maintenance valve would be a good shout, especially as it also has the fast track solenoid attached to the same block. The shuttle valves can break up and they determine fluid path. I'd guess that dead ending the services brings P1 up to full pressure and the system works correctly. A broken shuttle can do weird things to P1 pressure which supplies the pressure maintenance valve. At low swash it'll not be generating the flow required I'd guess until you hit a dead end. Be interesting to know if the other services dead ended have the same effect?

 

[Agrimax]

I'll maybe get another run through it tomorrow,but although the dozer blade has no power,I'm nearly sure if it's dead ended after lifting it up, full power returns to the boom ram which will then lift the machine off the ground no bother. Thanks again jd.

 

[Agrimax]

Folks...Meant to come back a lot sooner and say that the problem was sorted! In the pressure maintenance valve block,one of the two shuttle valves had unscrewed and allowed the ball bearing to rattle about in the orifice. Servo pressure was always correct but pump pressure was always well under half max at the pmv test point.
So @jd6820 ,you were on the ball. Thanks for that.

 

[jamiespc1]

I am having similar issues. I have the JCB 803 and it has lack of power and the hydraulics system gets hot. I did notice psi at the Pmv block shows about 1600psi and have already replaced the two valves there and made adjustments on them too and still can’t get any higher. You think it’s the pump?

 

[jamiespc1]

I also noticed if I take out that spring behind that plug I can lift the machine off the ground still at 1600 psi and gets hot even quicker.

 

[dclt]

Good day, writing from Canada, i have this issue on my JCB 803 as well. Power / flow slows down and requires a second function selected to bring movement back to normal. I have had this machine in two different shops and still have not found the root cause. I had to replace the pump a few years back due to a crack in the housing and all testing so far on that pump shows no issue. My oil also heats up fairly quickly. Reading these comments looks like i need to look at some relief values, but without photos or diagrams it is hard to understand what is talked about and were to look. I have just purchased pressure testing kit, so will be able to get value myself. My machine has the 3 stack pump set up. Hoping someone can help me debug this unit. I only use it here on my small farm and it only gets about 50 hours a year on it.
Further to the above, i tested the operating temperatures of the three pumps after working the machine for 1/2 hour, and the two outside pumps were about 48 to 55C, but the pump closest to the engine was well over 90C, so that make me think, any problem is in that oil circuit.

 

[V8Druid]

oil heating up rapidly would usually indicate it's being 'forced' through small orifices, like PRVs/reducers