The Classic Machinery Network

Howdy,
As the title suggests I have a JCB 3CX Black Cab serial number 321109 and she has stopped slewing the backhoe.

When you attempt to slew it seems like it will engage in one direction but no movement. You can swing the boom by hand.

I have read some of the forums and think it might be the kingpin has sheared but just looking for as many possible causes as I can get.

Cheers,
EG

Hi Erris and welcome to the site there is plenty of knowledge on here, sometimes it takes a few days for people to get back but generally they do.

Jeremy

Hi Erris,If you prise off the plastic cover on the top of the king post you'll likely see the shaft turning instead of the arm slewing. It's most likely that the outer splines will have worn away at the bottom of the king post carriage. There is a splined boss available to refit but the carriage has to be machined out first. The answer is to replace the carriage,bushes and king post.(By carriage,I mean the bit that slides across the rails and is held in place with the 4 hydraclamps.)
Since you are in ROI,Francis Charles....FC Spares,Longford is likely the best man to speak to.

Cheers Jeremy.

Agrimax, thanks for your reply.
It turns out that someone had left the slew gear box filler bolt out and it has been sitting for years with nothing covering it (not my machine just trying to get it running again). I pulled off the plate under the king post carriage where there was a lot of black rotten oil obviously spoiled by water. I’ve taken the gear out and cleaned it.
While it was off I actuated the slew and you can see the teeth moving back and forth so I think it may be that there was most likely a big build up of muck inside. Ive put some oil in to clean it out overnight and will try and run it tomorrow and see.
Failing that working will have to come back for advice!

I'm trying to get the gear back into the slew gearbox and the saw teeth is stopping the planet gear from slotting into place (if that makes sense)

Would anyone be able to tell me if i need to do something first to take the forward pressure off the saw tooth so that the gear can slot into place. I've tried putting a fair bit of pressure on to it and moving the slew level back and forth to see if it finds its own happy place but no joy.

Cheers,
EG

Splines will have gone Vicery plant spares or FC Spares will sort you out

JCB4CX, cheers for the reply.
The splines on the Inner gear and the bottom of the kingpin seem fine.

The issue I have is with the teeth on the outer gear fitting back into the teeth on the “saw” that moves back and forth inside the cylinders to slew the king post.

You said above you can slew the boom by hand. That's still a sure sign that the splines are gone at the bottom of the king post. Above the splines that the big gear goes onto. I may be wrong but something tells me there is a master spline on the gear too. You'll likely need the slew pots removed so you can turn the rack and wiggle it about to get the gear back up in again. You'll also need to centralise the rack in relation to the boom position as it'll want to pull through when you remove the pots...........

Thanks Agrimax,
Yeah there still probably is an issue of bigger proportions considering what you’ve said about the boom moving by hand.

How can I tell if the master splines are shredded? Or is it a given that if you can move the boom by hand that it has to be that?

I know there is a post about replacing the kingpin on the forum elsewhere but do you know the best place to get the kit including new pin?

I was thinking that’s what I might have to do. I’ll pull off the slew pots and see if that works out...

Either FC Spares in Longford or Vicary Plant in England know these things inside out.
If the splines in the carriage are gone,when you slew,the kingpin can be seen turning inside the top of the carriage but the boom won't move. With the large gear off you can see what the splines are like inside it and also the ones that it pushes up on to.BTW,there are two sets of splines in the kingpost.....those that mesh inside the carriage and those that mesh inside the big gear..

Here's a kit from either of the above.....