955L no controls

[Pralhad Birdi]

Update:
So I got the o ring from Mantrac, fitted it and again, the machine worked for about 5 minutes and blew the o ring again. What could be causing this?

 

[Dave Neubert]

have you checked pressure maybe the relief valve is stuck

 

[Nige]

I'd suspect there are no pressure gauges on site. Maybe just better to disassemble the relief valve and inspect/clean it

 

[Pralhad Birdi]

Yep no pressure gauges on site unfortunately. Let me give it a shot, as when I replaced the o ring I only went as far as removing the pilot valve and the dump valve spring, but from the diagrams, the dump valve has another o ring right at the end. So could it be a case of that o ring having failed, which led to this one failing? Unfortunately I've already come back from the site, and I dont really trust anyone there to do this, so it'll mean another trip back down. Oh well.

 

[Welder Dave]

If one O-ring was bad it's likely the other one is too.

 

[Pralhad Birdi]

Update: I disassembled the entire control valve assembly, checked all the valves and the o rings, replaced the relief valve o ring and put the assembly back in the tank. The machine worked perfectly for about half a day, then I get a call saying no controls again! What could be causing the relief valve to behave like this?

 

[AllDodge]

I think the valve assembly while it looks good, it has to much wear so the O rings keep blowing.

 

[Pralhad Birdi]

Yes the machine has done a fair bit of work over the past few years so I wouldn't rule out wear.
Another thing I noticed was the clamp for the master valve actuating rod on the tilt cylinder is broken off, so the actuating rod is no longer there. Just changed operators a couple of months back, so no one can tell me how long its been that way. Could that be an issue, or somehow related?

 

[Welder Dave]

Are you talking about the return-to-dig rod? It shouldn't matter as long as the bucket stays where it's set manually.

 

[Pralhad Birdi]

Yes that's the one. Okay fair enough just wanted to rule that out, thanks.

 

[Pralhad Birdi]

Update: Took the relief valve out, turns out it was stuck open. Freed it up, cleaned it and put it back in. Machine's been working for about the last half hour or so without any issues. Question is, what could cause the relief valve to keep getting stuck open? The o ring fitted earlier was fine, but it was just stuck open.

 

[Nige]

Any signs of scoring on either the relief valve body or the plunger itself.?
Did the plunger feel "sloppy" in the bore.? I'm wondering if there is wear that is allowing the plunger to "cock" sideways and jam in the bore.
Did you take any photos of the parts when you had it disassembled.? Photos are always good. I understand the difficulties of uploading them when you are out in the field but they could be uploaded later when you reach a location with better internet.

 

[Pralhad Birdi]

Unfortunately no photos, as I didn't really expect it to work to be honest, it was just one last shot out of exasperation. I left the site and the machine did a good whole day's work, and now its started acting up again. I cant even go back as they've banned inter city travel here cos of the virus. I did however manage to get hold of a complete tank off of a scrapped 955L. It's plumbed for a ripper and multi purpose bucket as well, which mine doesn't have. So the plan is to blank off the outlet ports for the accessories and send the entire tank to site to be fitted (if I can get a lorry through the lockdown roadblocks). Hopefully this sorts out the issue, and once the machine comes back to the yard, I'll bolt on a ripper and fabricate a multi purpose bucket out of an old dozer blade I have. I think the jamming must be due to wear, although I can't say it felt sloppy in the bore. I've asked the Mechanic on site to try and free it up again, so that way at least we'll get a bit more work out of the machine before I can get the replacement tank to site. Btw Mantrac quoted me $3200 + 1 month waiting time for a new relief valve.