JCB 3CII Removable Excavator Details

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JCB 3CII Removable Excavator Details

Post #1 by Baste » Mon Dec 27, 2021 1:11 am

Merry Christmas to everyone.
I have a JCB 3CII which has had the removable excavator frame welded in place (very poorly welded and keeps separating). I am trying to work out how the locking mechanism works but cannot find any diagrams for how it is meant to work. Can anybody shed any light on this for me, please? If possible, I would like to fix it properly rather than have it welded solid again. Thanks and best wishes, Ted


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Re: JCB 3CII Removable Excavator Details

Post #2 by Jeremy Rowland » Mon Dec 27, 2021 6:31 pm

Hi Ted and welcome :wave: there are a few JCB experts on here who should be able to point you in the right direction. :thumbup:

Jeremy


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Re: JCB 3CII Removable Excavator Details

Post #3 by Baste » Mon Dec 27, 2021 11:45 pm

Thanks Jeremy. I have managed to work out how to repair most of the issues I have had from reading your forum pages and the basic manuals I have found, but cannot find any details on how this assembly is meant to lock into position. Best wishes for a great new year and I look forward to receiving some advice from your members. :D :thumbup:
Ted


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Re: JCB 3CII Removable Excavator Details

Post #4 by MrF » Tue Dec 28, 2021 1:56 pm

Hi Ted, forgive me if I'm answering the wrong question but I'm not really understanding what you are asking, although Ive worked on a mk2 quite recently.
I think if it IS what I think it is, my mind is boggling at someone trying to weld a 50mm or so thick casting to steel rails with 4mm or so wall thickness.
So to confirm do you mean how does the sliding kingpost assembly lock to the H goalpost rails? The "goalpost" is welded solid onto the rear of the frame and part of the skid and has the stabilizer legs on its outermost parts.
If so, there are large bolts through thick plates on the inside of the goalpost that slide left and right with the kingpost, they are by default slack, but there are small hydraulic ring shaped rams on each bolt connected to a control inside the cab. When you "lock" the kingpost, you move a lever that allows hydraulic pressure into these hydraulic rings but not escape again, so they expand taking up the slackness of the large nut/bolt effectively tightening them until the kingpost locking lever is moved and the pressure released, and clamping the moving kingpost and heavy plate firmly to the H frame either side.
On a mk2, the lever is leftmost of the cab, sitting facing the main back acter hydraulics control. Its connected to Tee's on the main hydraulic lines, before they go off to the back acter control block proper.
Here's my 3c3 in the same area, the two models are very similar in this area and in this pic you can see the thinner hoses running to the hydraulics on the nuts.
Image

If you got really stuck and are missing all the parts, you could always source some of the heavy rear plates and bolts and just tighten/loosen them manually to shift the kingpost while you are hunting down the other parts.


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Re: JCB 3CII Removable Excavator Details

Post #5 by MrF » Tue Dec 28, 2021 2:17 pm

If you mean the H frame is removable, I've never seen a Mk2 like that, every mk2 I have encountered has been firmly welded to the rear of the skid, with heavy triangulation plates on the join because of the load its under. Someone else might know more, perhaps its a regional variant. Do you have some pics of the machine in question?


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Re: JCB 3CII Removable Excavator Details

Post #6 by Baste » Wed Dec 29, 2021 3:09 am

Hi Phil and thanks for your reply. Sorry, but I didn't explain things very well. The entire H Frame and excavator assembly is removable on my machine. It appears that there are pivot points at the bottom of the skid that the H Frame drops onto and the locking pins in the top of the H Frame which slide up into housings under the top side rails of the skid. The locking pins appear to be operated by a pedal on the right side (looking backwards) which rotates a shaft with cams on each end which lift and lower the locking pins. I would expect to see some mechanism for locking the pins in place once they are engaged, but I can't see anything. Hopefully the attached pictures will make sense. It appears that someone has welded a plate between the H Frame and the skid on each side, but it seems inadequate. If you could share photos of how your MKIII is welded, it would help greatly.

Thanks and best regards, Ted

P.S. Sorry, the attached photos didn't come out in a logical order and I can't work out how to put them in sequence, but hopefully it will make some sense. :dizzy: :D
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Re: JCB 3CII Removable Excavator Details

Post #7 by MrF » Wed Dec 29, 2021 1:32 pm

Thanks for posting that, it all makes sense and your original description was fine. I was confused because I didn't know the 3c2 came in a detachable backhoe variant, the mk2 frame I have here is firmly welded in place and I've never seen a detachable variant or even knew they existed.

But in the JCB 2B, 3, 3C, 3D, 4C MK2 1968-77 Operators Handbook here :- JCB 2B, 3, 3C, 3D, 4C MK2 1968-77 Operators Handbook and on page 26-28 it details the attach/detach sequence and how the shafts lock with a pin etc for the detachable variant if that helps at all. There doesn't appear to be any extra coverage in the service manual apart from a mention of a odd shaped hydraulic coupler.

Also, someone here might yet have one and could take some photo's of the area for you to help clear things up. I think you have a rare variant there that's worth saving.
I can take some shots of how the factory welded frame is connected in that area on a old 3c2 chassis I have out behind the barn, but it won't really be applicable to yours.


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Re: JCB 3CII Removable Excavator Details

Post #8 by Baste » Wed Dec 29, 2021 11:56 pm

Thanks Phil. I found a diagram on page 52 of the JCB 2, 3, 3C, 4C Parts Manual MK1 ?-1967 download which shows a similar configuration for a 2B Frame. It shows the pins as being operated by springs, but the actuation setup is different, having separate levers on each side and a different cam arrangement. This fits with my feeling that the pins would be spring loaded to "click" into place when the frame is pushed in as described by the operators document you mentioned. Unfortunately, I cannot see how the springs would locate without detaching the entire excavator assembly, which I am reluctant to do as I have been unable to centralise the kingpost while the frame is not attached. Maybe I will get someone to weld it back together for now and look at it further in the future. The welds can always be ground away later to return it to original. :think: :)
Thanks and happy new year, Ted


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Re: JCB 3CII Removable Excavator Details

Post #9 by MrF » Thu Dec 30, 2021 2:38 pm

Hi Ted,
I totally get that, its a big heavy lump to manipulate back in place. If you have another machine you can call on it makes life safer & easier so maybe you have a neighbor you can bribe with scotch to appear with the farm's telehander like I did mine.
Here's some pictures of the jcb 3c2 frame hopefully showing the reinforcing, it might give you some inspiration on how the factory tackled
it. I can see why they offered a detachable version as it would make the machine multi purpose as the back acter assembly is really heavy on its own and makes the machine more prone to getting bogged down when on other duties, but on the normal 3c2 they glued it on in such a way that you know they meant business :)

The 3c2 frame is upside down. Its eventually being re-purposed as a cnc plasma table frame, as it was leaking hydraulic oil from cracks in the main frame after the machine itself was rolled & had various fatigue cracks as evident in one of the pictures at least.
H frame from above, if you look at the long row of slag on the tube/crosspiece this is where a substantial (1/4 plate) long brace was cut off. In fact I think it joins the rear lower floor to the back frame also.
jcb3c2_frame.jpg

Side through H cut.
jcb3c2_frame2.jpg

Bit closer and different angle of H
jcb3c2_frame3.jpg


Finally I took 2 photos of the connection area on my 3c3, its the same in layout but more difficult to see the internal bracing etc because of covers.
Lower frame rail connection area
jcb3c3_frame1.jpg


Upper frame->H join area.
jcb3c3_frame2.jpg


Have a happy new year also :)
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Re: JCB 3CII Removable Excavator Details

Post #10 by essexpete » Fri Dec 31, 2021 12:37 am

I think, but I am not sure, that this machine is unusual. The removable back actor/hoe was usually found on the 2B or possibly 2D models.
The 384 part probably refers to the Leyland 384 tractor skid. They were built between 1969 and 1972.

There is a little here and perhaps someone can be contacted for some help/info?

Anyone got a JCB 2BII?


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