Backhoe Hydraulics problem

[KJM]

I'm hoping someone has had this problem and fixed it!

Problem: Tried to use the BH this morning. No hydraulic power . Pump spins fine on the PTO, plenty of oil in the tank, no input restrictions. Disconnected the pump pressure feed from the valve stack - plenty of oil at high velocity! The outward symptom looks to me (I'm not a hydraulics guru) like there is a blockage in the valve stack or the pressure relief valve is almost 100% bypassing. There is a tiny bit of very jerky hydraulic power getting there, enough to slowly shudder the stabiliser rams up an inch and down an inch but nothing near enough to make the main boom or dipper stick even think about moving .

I have taken the top of the relief valve assembly off but there is no obvious chunk of grot stopping it closing. If I rev the engine I can feel the hydraulic lines "pulsating" somewhat - makes me think it really is the relief valve. I have never seen a stack of spools disassembled, but clearly there must be pressure galleries that line up, exhaust ports that line up etc etc. I'd rather not try to take the thing to bits on a Saturday and am hoping there is a simple technique for dealing with this!

Any suggestions? I'm thinking I need to "reverse flow" the valve stack to flush whatever entrained crud is in there out - but I don't know if there is some kind of one-way mechanism in there. H E L P!!

/Kevin

 

[john_bud]

Tractor? backhoe - company, model, year ??

(I have never heard of this total failure before - sorry!)

jb

 

[KJM]

Tractor? backhoe - company, model, year ??

(I have never heard of this total failure before - sorry!)

jb

OOPS. Mea culpa

Tiny Kubota B7100 (mid 80's model) and unknown backhoe. (Although it did have a Kubota sticker on it, it has no model #'s or anything useful to identify it). Certainly seems to be a model not sold in the US, from the total lack of pictures I've seen. It is nothing particularly special - the problem seems to lie in the valve stack which looks basically the same as all the backhoes I've ever seen. I suspect the valves are cessna - the pump certainly is - but there is no marking on the castings that I've yet found..

/Kevin

 

[KJM]

I've found the problem, but haven't as yet fixed it. Oh boy, this one is mega-embarrassing!

My original posting claimed I had plenty of oil being pumped. Well, quite true. But only if there is no-load on the pump. The pump is a PTO pump with a 16mm (5/8") round shaft and is coupled via an adaptor. The adaptor has a 1/4" keyway in it and the pump has an (approx) 4mm keyway. "Approx" because there is no key and the keyway is, well, a bit secondhand looking right now! The key that was in there has been turned into its constituent atoms... Grrrrrrr....

The "pulsation" was clearly the coupling grabbing on the pump shaft and giving it a bit of a whirl.

SO: big question! Clearly, the same sized keyway should be on both fittings. Given that I need to get this going and it is not something I use every day - is it OK to use a dremel and make the pump shaft have a 1/4" keyway? Or do I really need to dis-assemble and take to someone who has a mill? (Obviously the preferred engineering solution, but I don't have a mill and I don't want to remove the pump - draining oil, O-rings etc etc).

Sorry to get people's grey matter engaged on a problem that actually had a simple solution. BTW - the only way I found this was by playing with the manual pump on the backhoe and noticing that it "seemed to work"....

/Kevin

 

[BTDT]

Any pics? I think someone mentioned something made by Loctite to attatch shafts to couplers. Maybe some of this with a key would be sufficient. I think it was mentioned in a post to Poohbear on his cement mixer build.

 

[MJPetersen]

I had the situation one time that the key way on the drive shafts for a Cat 14E motor grader was wallowed out. I welded up the slot on the shaft and cut a new keyway with a carbide bit and die grinder. This lasted for as long as we owned the machine. They finally upgraded to a G model with hydraulics.

The point is it can be done. It is not easy and may actually be more time consuming than taking it somewhere to have it done right.

If you do that make sure you wear protective clothing as I recall the bits cut out by the carbide bit were as sharp as needles.

Mike

 

[KJM]

BTDT: It's called shaft fit (in Australia, at least). The clearance is a bit too much for it to be effective. I'll certainly be using it to firm the key in my (cough) machined keyway though...

MJPetersen: Thanks for that. Read your post and thought I'd give it a go. The shaft isn't as hard as I thought it would be... This looks like it'll work just fine. I've opened the keyway on the pump shaft to 1/4" (or thereabouts - doing it by hand). Thought I'd check how it fits - do you think I can find the 1/4" key stock in the shed . Nothing seems to be working for me today.

So, it looks like I'll have it all going again tomorrow (Sunday). No doubt I'll buy a new length of 1/4" key steel and then find the one I know I have, but I think it'll be a goer tomorrow!

Thanks to all! Will post the outcome tomorrow, hopefully..

/Kevin

 

[KJM]

Thanks to all! Will post the outcome tomorrow, hopefully..

Well, its now "tomorrow" and I'm happy to report that it works just fine. "Machining" the keyway with a dremel isn't a joyful experience however. Took most of this morning to do it!

The pump shaft is a bit bent, I've just noticed. One of those things that I wished I'd not seen!! Ah the joys of old and poorly maintained second hand equipment!

Again - thanks to all. Very happy it works again!

/Kevin

 

[MJPetersen]

Glad it worked for you. Happy digging.

I actually spent a year in Australia. But never made it to Adelaide. Lived near Melbourne, and saw Sydney, and Canberra, but unfortunately never made it to the far south.

Mike

 

[KJM]

Well, South Australia is just the same only drier and flatter Except the bit I live in - my property is steep!

The thing works OK now, I have dug the bits I need to dig (it is FINALLY going to rain again tomorrow) so now I have 5Tonne of "blue metal" (dolomite rubble) arriving in the next 1/2 hour to spread and even out the pad for the new shed before it turns into a quagmire tomorrow.

Ahh the joys of tractor ownership! Again, thanks for the input - the concept of hand machining a keyway with a dremel seemed to me to be the ravings of a madman. But it actually worked out pretty well - except that you can't mill the end closest to the pump nicely. But that's OK too...

Cheers
/Kevin