JCB 3C3 hydraulics

[roy.thomas]

We have a JCB 3C3 and are putting a JCB 3C clamp bucket on. We are using all the original pieces of the 3C, i.e. the control block, the front frame with the four hydraulic rams on it, and the clamp bucket with it's two rams, plus the flexible pipework, plus the 2 steel pipes that runs across the front of the outer bulkhead from left to right and right to left which operate the clamp bucket. We have not changed our hydraulic oil filter, but the only difference was a blank cap which we have put on our filter in the same position as the 3C. We have a problem with the hydraulic circuit. The JCB 3C3 has less hydraulic pipes than the 3C, but we put on the 3C control block and had the 2 extra pipes which we fitted according to the 3C hydraulic diagram. Now though, when the engine is started the front two hydraulic rams that tilt the bucket forwards or backwards operate, and the bucket starts to lift up. So we stopped the machine as soon as that happened.
Does anyone have any ideas where we have gone wrong please?

[philwheelton]

Does this start to tilt and lift without moving a lever? and are the valve blocks the same or is one 1 lever and the other a 3 lever block ?

[roy.thomas]

Yes it starts to lift and tilt without using a lever. it is immediately on starting the engine that the shovel rams start to operate.
The 3C3 had a 1 lever block, which we have replaced with the one taken off the machine with the clamp bucket which was a 3C
On pressing down the lever for the shovel rams that releases them back down to the floor again, but when it is going down it turns the engine over, as though hydraulic oil is being pushed backwards onto the hydraulic pump at the front of the engine.
Many thanks for sending an early response.

[essexpete]

Is it possible that the spool valves are opposite ways around between the two machines i.e. the inlet and outlets? Instead of flow back to tank you are turning the pump into a motor?

[roy.thomas]

That could be the problem, so I will try that out as soon as I get back home.
Thanks for your help - I'll let you know if I am successful.

[roy.thomas]

We changed the two hydraulic pipes around that went respectively to the chassis and to the pump, so now the pipe for the pump is at the top and the pipe for the chassis is at the bottom, as you can see on the diagram. This diagram is from a JCB manual for the machine that the clamp bucket came off. a JCB 3C. Our machine is a JCB 3C3.

It has cured the hydraulic problem in that you can now run the engine, you can rev. it and tick over and use all the excavator controls, and rear jack legs, with no problem.

However no matter what control is operated on the new control box, it instantly stalls the engine. We only do this procedure when the machine is on tick over. We have tried it just off tick over - it is not a slow tick over anyway.

The diagrams I have attached, if you look at the circuit diagram for the JCB 3C it shows the control block (shovel valve block) with two pipes at the left hand side of the block and one on the right had side, but on the loader valve daigram it shows the block exactly as it is on the one we have with one large pipe on the left and two on the right.

Hope someone is able to help with this as we are really confused.

[essexpete]

When you move a spool and the engine stalls do get any attempt at movement from any of the rams? This symptom is not unlike when you inadvertently plug into the wrong combinations of external services on an ag tractor. So effectively you are pushing oil out to a ram but the other side of the ram is locking up due to it being plumbed to a different spool. I guess you have probably thought of that.

[wiggy]

if it was me 1st thing id do is take all the hydraulic pipes of spool block that you have fitted
next id jerry rig up pipes that returned oil direct to tank of all fittings
warning hydraulic oil is dangorous and can kill you if it injects under skin so take extra care [color=#000000][/color]
yes im teaching you to suck eggs but ive seen it happen

take care staryt engine and operate lever see which pipe the oil comes out of mark it do in next postion mark it ect
till you have gone thru sequence on valve
that way you can work out what pipe goes were on what ram simples
if you find out oil isnt coming out of one or more pipes the problem is in ur spool block
ive known a blank cap to be left in or a stone bit of muck ect
you would be suprised what can stop oil flow

another thing to check is that you hydraulic pipes that are/you fitted did one or more get cruched again there can be no out side sign but it can and will stop oil flow

there is realy no easy solution
you literaly have to think what did you touch move replace or add on and it is a simple proses of alinanation


good luck

[roy.thomas]

Well today we have got nowhere. We have changed around all the hydraulic pipes in sections 1 2 and 3 of the the control block in case the flow was wrong, but still have same result. We swapped one section top to bottom, tried the machine, then did the same with section two, then section three. It still stalls the machine and no movement in any of the rams that operate the front bucket.

The control block was visually checked before we fitted it on, and it was working on the machine that it came off.

Lost the light now so will try something else tomorrow. Thanks to all for help given. Still struggling though.

[essexpete]

Made a mistake and cannot see how to delete post.