JCB 526-56 boom crashes down, crowd+lift then tip.

[Water Wheel]

The boom on our JCB 526 56 Loadall goes into freefall dropping down with no resistance.

This follows- crowd and lift at the same time, then tipping……… crash ! Can be scary.

All other operations seem fine.

Any suggestions where to start to cure it, I guess there is a valve not operating correctly somewhere.

First reaction from main dealer , “Never seen this before ,no idea, I’ll go away and have a think.”

 

[Skintagain]

I have noticed on old loadalls that they lift slightly when you tip which is to do with the small ram at the back then when you stop tipping/crowding they fall back slightly but not as much as you are seeing. Maybe a place to start. Have seen a couple knackered loadalls with this small ram removed too for whatever reason and they don’t do the lift action whatsoever.

 

[DaveGrohl]

Think you might need to speak to a different dealer?

 

[PostHarvest]

I've seen this happen in 2014 on a client's brand new 531-70. The main dealer said it couldn't happen. Luckily the client has a big construction business as well as his farm and so had some pull with JCB. They got the dealer's MD, JCB's sales manager and product designer out on the farm and it almost crushed the design engineer when the boom crashed down. I believe that it was a software problem. Yes JCB do know of the fault.

 

[8100]

Sounds like a valve problem somewhere .That can not be very nice when it happens at all.
Don't go messing with valves though i heard of a fitter loosing his hand on one @ACEngineering

 

[roscoe erf]

thats the self levelling ram I believe its very noticeable on my 530-70 but not so much on the older 525-67 will have to keep an eye on this one

 

[ACEngineering]

Sounds like a valve problem somewhere .That can not be very nice when it happens at all.
Don't go messing with valves though i heard of a fitter loosing his hand on one @ACEngineering

often get a very vague description of problem IMO so not the same as actually seeing it in person. i would expect lift ram seals and or its check valve or very worn pins and bushes.

It'll only be happening when the OP puts the machine in my pet hate situation where but the tilt has been bottomed out one way or the other and then the boom i lifted or lowered. there no other way the self level ram can take weight off the boom lift ram otherwise. (with the exception of some JCB have a small pipe linked in to the lift ram in to the self level ram with a one way valve in it but i only seen this on a few models mostly the bigger construction ones, even if that one way valve is faulty it would' cause this problem anyway.

OP need to watch the ram and see if its the rod pulling out or wear in the pins.

It could even be the piston inside the ram come off the rod i guess!

 

[essexpete]

Am i missing something here? The self levelling ram is linked to the crowd ram so should not, in theory, be anything to do with the OP's original symptoms. The other thing the burst hose valve/check valve should prevent oil roaring out of the ram and require hydraulic pressure to release. Somehow the function of the burst hose valve is being bypassed. If the piston head has detached from the rod would it not more likely allow free movement in the ram extending direction?

 

[ACEngineering]

Am i missing something here? The self levelling ram is linked to the crowd ram so should not, in theory, be anything to do with the OP's original symptoms. The other thing the burst hose valve/check valve should prevent oil roaring out of the ram and require hydraulic pressure to release. Somehow the function of the burst hose valve is being bypassed. If the piston head has detached from the rod would it not more likely allow free movement in the ram extending direction?

i was thinking if he was powering the tilt circuit with tilt ram dead ended boom would go up pulling rod out of lift ram leaving piston behind. soon as you dump the tilt the lift ram crashes to the level of oil that was in it before.

 

[essexpete]

i was thinking if he was powering the tilt circuit with tilt ram dead ended boom would go up pulling rod out of lift ram leaving piston behind. soon as you dump the tilt the lift ram crashes to the level of oil that was in it before.

So do you mean the compensating ram is effectively lifting the boom?

 

[Water Wheel]

often get a very vague description of problem IMO so not the same as actually seeing it in person. i would expect lift ram seals and or its check valve or very worn pins and bushes.

It'll only be happening when the OP puts the machine in my pet hate situation where but the tilt has been bottomed out one way or the other and then the boom i lifted or lowered. there no other way the self level ram can take weight off the boom lift ram otherwise. (with the exception of some JCB have a small pipe linked in to the lift ram in to the self level ram with a one way valve in it but i only seen this on a few models mostly the bigger construction ones, even if that one way valve is faulty it would' cause this problem anyway.

OP need to watch the ram and see if its the rod pulling out or wear in the pins.

It could even be the piston inside the ram come off the rod i guess!

Struggling to get my head round exactly what s happening.
Just had a play.
Full crowd and lift then tilt - drops to point at which lift started,if I then crowd again ( no lift ) it lifts back up to point at which I droped from.
Only dare to try it over a limited distance / lift of a couple of feet or so for fear of doing damage.
Could well have been doing this since new, now 3000 hrs 2013 machine, but its become an issue with one guy here ( understandably)

My interpritation is its lifting on the small ram leaving the big ram empty ??

 

[ACEngineering]

Struggling to get my head round exactly what s happening.
Just had a play.
Full crowd and lift then tilt - drops to point at which lift started,if I then crowd again ( no lift ) it lifts back up to point at which I droped from.
Only dare to try it over a limited distance / lift of a couple of feet or so for fear of doing damage.
Could well have been doing this since new, now 3000 hrs 2013 machine, but its become an issue with one guy here ( understandably)

My interpritation is its lifting on the small ram leaving the big ram empty ??

you need to find out if its got that one way valve and pipe linked from lift ram to self level ram. Look on the pipe work of the main lift ram and see if there is a small 1/4 pipe teeing off it. on a 14metre machine the boom is far to heavy for the self level rams to lift so that might be why i didnt get this problem, other wise it has to be a lift ram problem, either piston loose or seals knackered or the check valve in the ram.

Worn pins will account for maybe 5 inches or so lift if really bad but not feet!

 

[sulky]

The boom on our JCB 526 56 Loadall goes into freefall dropping down with no resistance.

This follows- crowd and lift at the same time, then tipping……… crash ! Can be scary.

All other operations seem fine.

Any suggestions where to start to cure it, I guess there is a valve not operating correctly somewhere.

First reaction from main dealer , “Never seen this before ,no idea, I’ll go away and have a think.”

i dont know much about loadalls but i had this on a digger (case 580) problem turned out to be the return to dig switch , do loadalls have this feature ? after tip or crowd on bucket arms would drop

 

[essexpete]

Does the machine have soft ride facility with an accumulator?

 

[Water Wheel]

Does the machine have soft ride facility with an accumulator?
No.
No small pipe from main lift ram.

 

[ACEngineering]

Problem with ram then. Pull it apart. If looks ok reseal it and fit new lock out valve.

 

[Water Wheel]

Problem with ram then. Pull it apart. If looks ok reseal it and fit new lock out valve.

Thanks for your replies.

Just had another play while no one around to mither me, one guy is making an issue over it.
Only crowd at the limit causes it to happen, Lift + crowd without reaching the limit of crowd and it does not happen.
Think (not 100% sure) it only happens with a light attachment, put empty bale spike on it happens, put bale on spike it dosen't.
Over the years we have had loadall, while I have been aware it could happen, it did not seem to be a problem, because when you crowd there tends to be weight on it?
I would still like to get to the bottomof it and stop it happening.

 

[Mur Huwcun]

Thanks for your replies.

Just had another play while no one around to mither me, one guy is making an issue over it.
Only crowd at the limit causes it to happen, Lift + crowd without reaching the limit of crowd and it does not happen.
Think (not 100% sure) it only happens with a light attachment, put empty bale spike on it happens, put bale on spike it dosen't.
Over the years we have had loadall, while I have been aware it could happen, it did not seem to be a problem, because when you crowd there tends to be weight on it?
I would still like to get to the bottomof it and stop it happening.

My take on this then is that with the bale on the compensator ram is not strong enough to lift the boom so it doesn’t happen but it it putting extreme pressure and stress on the compensator ram and pins. Hopefully the PRV is doing it’s work but with very worn linkages it wont and can rip the ram or pins or mountings to pieces on other machines. No idea if this happens on JCBs though but seen it on ACEs favourites machines and a lot if front end loaders!!!

 

[Water Wheel]

My take on this then is that with the bale on the compensator ram is not strong enough to lift the boom so it doesn’t happen but it it putting extreme pressure and stress on the compensator ram and pins. Hopefully the PRV is doing it’s work but with very worn linkages it wont and can rip the ram or pins or mountings to pieces on other machines. No idea if this happens on JCBs though but seen it on ACEs favourites machines and a lot if front end loaders!!!

Not sure why it only happens when crowd has maxed out.
Headstock and boom has fair wear for a 3000 hr machine but not excessive, its well greased.

 

[ACEngineering]

Not sure why it only happens when crowd has maxed out.
Headstock and boom has fair wear for a 3000 hr machine but not excessive, its well greased.

because once the tilt ram has reached its full travel the oil has to go some where else! the relief valves for it are set above main pressure often around 20bar higher. There fore if the oil cant get in the tilt ram it has to go somewhere else like the self level rams or blow the relief valve off if the boom is loaded enough to get enough pressure.

At no point should the self level rams be able to do any more than take the slack/wear out of the main lift ram pins, if they start pulling the rod out then you have a loose piston on the lift ram rod, knackered ram seals or faulty lock out/check valve on the ram body.

I dont know how i can make it any clearer than that!