1983 JCB3CX slew speed problem

[sotted]

Good afternoon all,
I own a 1983 JCB3CX, when you slew in the left direction the machine operates correctly, when you slew right the arm moves extreemly slow and will not move with any load. If you extend or retracted the boom or bucket to a point where it is bypassing at the valve (and hold it bypassing) then the slew will function correctly. I have swapped the bypass spools ( i think they call them ARVs?) between the left and right direction, but nothing has changed. i have increased the distance that the control lever pushes into the valve block, no difference? has anyone ever had this problem or can anyone point me in the right direction or at the correct post? Any help would be much appreciated. Apologies if you read this post on another forum. Been looking for answers without a great deal of success.
Thank you

[hubert]

Had this problem on an old MK1 3c. From memory there was a problem with a relief valve. Might only be a piece of dirt lodged in the relief valve not allowing it to seat properly.

[essexpete]

If you like I'll post this up on the farming forum. Somewhere there is a pressure/flow drop on that side (internal leak?) and by blowing the relief valve with another service the flow/pressure increases. But why? Oddly I have a similar thing with an old telehandler. If overloaded with large bucket of gravel it will lift if the crowd is selected at the same time as the boom raise.

[essexpete]

A reply from a knowledgeable (I believe) guy with the handle TP on the British Farming Forum:



As a short term diagnostic test swop the pipes for the slew with another service and use the lever for that to test the slew, if the fault remains in the slew then it's a ram related fault or as I suspect it will go away your fault is in the spool block. The slew function has a special anti-cavitation feature built into the valves or the arv's so it's important not to use the other lever long term as you could drive along the road with the dipper flopping left to right and wipe someone out. How this works is there is some backpressure deliberately held on the return pipe from the spools and a check valve allows a cavitating cylinder to suck oil from it so it is always full of oil both sides of the piston and never able to flop around especially dangerous travelling. This is to cater for a scenario where there is insufficient oil from the pump to fill the backside of a piston as fast as gravity or other force pushes it out of the other side. It's a sort of re-generation. You might well have a broken poppet or spring on the ant-cavitation side of things. Unfortunately there are many different spool blocks/arv's etc used so it's hard to be more precise on the location of the bits and bobs. Later machines tend to have anti-cavitation fitted to all the cylinders whereas in the early days it was only on the critical functions like slew. Sometimes the bits are inside a hollow spool rod itself. If you are really lucky it might just be a chunk of seal that has wedged a poppet open, the reason it works when you activate another valve is probably related to creating a dead end beyond the spool with the fault when you pull the second lever so the escaping oil from the first function cannot return to tank and has to extend it's rod......certainly some ideas there for you to think about/try.

[sotted]

Thankyou for the replies, i will look at swapping the control valves to see if the fault remains or moves. Much Appreciated everyone