Boom has trouble returning

[Woodman777]

Hello all, hope I can receive some help with my backhoe. The backhoe specs are; JCB backhoe/loader model # 301260, manufactured 29 April 1983, serial # 14/N/2/09/301260, engine #880807/K,gearbox #13027/383/1165, T/C #11888 and rear axle #01147.

When I first purchased the backhoe the main boom cylinder was leaking a small dribble of hydraulic oil. Pulling the main boom control back, the boom hesitated and would come back in small incrememnts. Let the control go back to neutral and then pull back another small increment.

At this point to correct the leak I pulled out the main boom cylinder and sent it to the repair shop where the seal was repaired on the cylinder.

With the refurbished cylinder back in place and no hydraulic leaks, the problem was still there but not as bad. There is no problem with the boom going down but bringing the boom back up just would not happen on its own. I have to help the boom return by extending the Extending Dipper. Once the boom gets back to within 15 degrees vertical it works perfectly.

It is like there is not enought hydraulic pressure because of the weight of the whole backhoe assembly. I have looked at the hydraulic drawings and especially at spool 4B. It looks like this main boom cylinder circuit has a restrictor (diagram photo item E in the circuit). The question is, Does this sound familiar to enyone and could blockage to the restrictor cause the condition that I am seeing. Again thank you for letting me join this forum and I hope that I can get some great advice on what the experts think the problem is. Dave.

[essexpete]

I thought the dipper has a restricting port so as the ram fully opens it does not slam into it's end?
Do all the other services and front loader work normally?
Can you get at the spool block to see that the spool for the poor service is actually travelling the whole way when selected?
Was the repair shop a hydraulic specialist?

[FOWLER MAN]

Hi,
I'm pretty sure, from what you describe, that the fault is in the ARV, (service line relief valve), in the boom hoist circuit. A pressure test is the only way to be sure.
It may be simply a bit of O ring or seal lodged in the valve.
As you probably know the ARVs are housed in the spool block, two for each service, to prevent overloading and damaging the system.
A test rig and hand pump are normaly required to set the ARVs and this is done with the valve removed from the machine. It would probably be easier to fit a new or reconditioned / exchange valve which has been pre-set if you can get hold of one.

Fred

[essexpete]

Ever tactful Fred for those with much lesser knowledge!

[Woodman777]

UPDATE, Thanks for the suggestions. Essexpete - Yes all of the other cylinders work perfectly and yes the main cylinder was taken to a registered hydraulic shop for a reseal. Fowler - I think it is a pressure problem also.
I moved on in the machines problems. The tachometer/speedometer did not work. I found that the inner cable had broken. I removed the inner cable and it was a clean break. I was quoted a price of $260.00 CAN for a new one. I set up a rig for alignment and brazed the cable back together. A little bit of filing to bring the diameter to the same consistency and slid the cable back into the outer sheath. The engine was started and the tachometer is now operational. I advanced the lever to full throttle and the tachometer read 1600 RPM. So now I need to know what the full throttle RPM should be. I released some tension on the throttle pull back spring and the RPM advanced to about 2000 RPM. The spring does not look like the original spring, maybe someone else's quick fix. The boom cylinder now seems to operate quite a bit better. At least I can get it to the upright lock position. I haven't tried to dig under load yet until I get the fuel rack problem sorted out. All help fully appreciated. Dave