JCB Mk3 - Lost digging power!

[rocky_robin]

Hi all.

I've just lost all digging power virtually overnight.
There is no hydraulic leaks, fluid level is fine and all rams work fully in and out at the same speed as before.
The problem occurs when the bucket meets the ground and starts to 'dig'.

It seems to have no power and the functions will just stop until you wiggle the bucket enough for it to break through softer ground. It was digging though the same ground a week ago with no problems.

I've raised the engine speed and makes no difference other than speeds up the functions whilst in the air.

Any ideas? Is there a by-pass in the manifold that could be bypassing earlier than it should?

Trust this to happen when I've hired help on site!!!!!!

Thanks,
Robin

[rocky_robin]

May I also add that the front rams will pick up the front of the machine and the stabilising jacks will pick the rear tyres off the ground no probs, so it seems to be a problem with the backhoe.

Thanks.

[Jeremy Rowland]

Robin I am no expert here but would guess that there could be a problem with one of the spool valves for the back actor, I am sure somebody on here will point you in the right direction.

Jeremy

[essexpete]

Robin I am no expert here but would guess that there could be a problem with one of the spool valves for the back actor, I am sure somebody on here will point you in the right direction.

Jeremy

Relief valve stuck with some dirt??

[nux]

Hi Robin

I have a JCB 3 which done the same thing, hopefully by now you have found the problem, mine turned out to be a pressure relief valve in the spool valve block, it was a while ago now, but I believe it is to the R/H side of the block as you look at the levers. Just needed a clean and she was fine again.

Pete

[martyn williams]

It seems to point to a pressure relief valve problem, may have picked up something in the hydraulic system like fragments from an internally disintegrating hose.sticking the valve open
Martyn

[FOWLER MAN]

HI,
if all services are affected equaly it points to the MLRV, (main line releif valve).
If I remember rightly this is situated in the front loader valve block and controls all services front and back. It is not adjustable but it may just want cleaning as Martyn suggests.
Before you attempt to remove the valve for cleaning, be sure to place all arms and legs on the ground and then opperate all controls to release pressure after stopping the engine.
If you have a guage pressure should be 2,000 Lbs or 138 Bars.
Fred

[philwheelton]

if you have a single lever front valve block you can adjust the MRV if it is a 3 lever block it is pre set

[rocky_robin]

Thanks for the replies.
I'm trying to hunt down this illusive PRV.

All I can see is 4 caps which require a Allen key to remove.
I took out two of them and saw a cone shape dome looking up wards. They both had holes in them but could not remove either of them.
Are these the prv's??

If they are, any ideas how to get them out? I've tried all sorts of tools. Grrrrrrr!!!

I've attached a pic of my manifold at the rhs.

Thanks,
Robin

[rocky_robin]

I've managed to get the cone shaped fitting out (wanted to really suck back in)
I had to count the number of turns the screw was into the body.
Upon cleaning, rebuild and installation of all valves, its made no difference what so ever. No crud found either.

I have read the workshop manual and that says that they are Aux relief valves.
Has anyone played with the pilot setting?