Hydraulics problem

I have a mid 70s Case CK780 backhoe. The thing had seen lots of abuse before I bought it and I have used it pretty hard since. The power of
the hydraulics has gotten weaker over the years. I used to be able to kill the engine by trying to push or pull too hard. Now this doesn't happen. So I'm thinking that the pump has a lot of wear. Over 30 years ago I used to repair gear pumps in a lumbermill I worked in by grinding the end plates of the pumps to remove scoring. But I don't know how much more pressure the pumps put out after this repair, it was just what I was told to do and I did it a lot. Considering the age of the tractor I'm wondering if I might just be better off buying a new pump and also if there is somwhere else I should look for the lowered power of the hydraulics. The power loss has been gradual over the years so I'm thinking it's probably the pump. Thanks, Eric
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snipped-for-privacy@whidbey.com fired this volley in

It could be. It could also be bypass leakage in cylinders, or a weakening spring in a pressure relief valve.
You can check all that with a pressure gauge and some judicious tapping/re- routing of a few lines.
Lloyd
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snipped-for-privacy@whidbey.com wrote:

Is it open or closed center hydraulics? Better machines will be closed center and they will have variable displacement pumps, not basic gear pumps. Step one is figure out what type of system you have, step two is install a pressure gauge in the system and see what pressure you are operating at. In an open center system you will only have pressure when you operate an axis to it's limit, on a closed center system you will have pressure all the time. An open center system will have a relief valve that limits the max pressure and they can certainly develop weak springs, debris causing leakage, etc. On a closed center system the pressure setting is controlled in the pumps displacement control which causes it to go out of stroke when the pressure limit is reached. Factory manuals are a good thing to have, particularly on the more complicated closed center systems.
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wrote:

Greetings Pete, I don't know if the thing is open or closed center. I'll try to find out soon. I don't have a repair manual but I do have an operator manual (I think) and some sort of parts manual. Eric
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On Thu, 12 Jun 2014 11:00:51 -0500, "Pete C."

FYI http://www.coincollectorkings.com/tag/780ck http://www.ebookily.org/pdf/allis-chalmers-wd-service-manual-download http://us.aolsearch.com/search?s_pt=aolsem&s_it=aolsem&s_chn &qÊse%20service%20manuals
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I bought a new pump from Bailey after fussing too long with the wrong size of old Danfoss pump, which I had to regrind like you. http://www.baileynet.com/#prodcat/Hydraulic-Pumps-and-Accessories/type/Gear-Pump Second on the pressure gauge, glycerin filled to damp the needle and located where you can see but not break it. 4000 PSI should cover the possibilities but not be too hard to read at half scale. I think common pressures run around 2500 - 3000 or you could check the hose rating.
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I forgot to mention that the tee and adapters to add it must be rated for hydraulics. Water pipe fittings aren't strong enough. -jsw
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On Thu, 12 Jun 2014 08:42:50 -0700, snipped-for-privacy@whidbey.com wrote:

Ya, a guage wouldn't hurt to verify what you already know, the pump is wore out. beware old Case parts must have thick gold plating on them, judging by what they ask for them. Repairing an old hoe can be a money pit, BTDT. it might be time to send this one on down the road and shop for another. that's what I'm doing right now, looking for a ford 555 (triple nickle)
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On Thu, 12 Jun 2014 13:04:55 -0500, Karl Townsend

I was talking to a friend of mine a few minutes ago and he said grinding the end plates flat works pretty well to raise the pressure some. But there will also be some wear around the periphery of the gears that I can't fix. If I can figure out which pump the thing uses I'm hoping to find one surplus. As far as the hoe being a money pit I really haven't had to spend too much on it beyond the 5 grand I paid for it. So three hundred to fix the hydraulics is probably OK. I bought it to install my own septic system and saved about 9 grand over the lowest bid I got for installing one. The County said it was one of the best installations they had seen, they were actually talking about me at the health dept. I had never even sat on a backhoe before I bought it so that's why I don't know if it is closed or open center. Eric
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wrote:

No wonder they are priced so low and easier to find. Is this printed on calfskin vellum? http://www.yesterdaystractors.com/CAP780CKTLB_2393.htm
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On 6/12/2014 2:18 PM, Jim Wilkins wrote: ...

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Lower power output of pumps does happen due to wear. Pay to have it rebuilt.
i

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On Thu, 12 Jun 2014 14:49:13 -0500, Ignoramus32163

If oil is leaking past the gears then the pressure should drop, right? Danfoss, who make hydraulic gear pumps agree with me. They say if the pump pressure plates wear the pressure output will bw lower. And lower pressure is the problem I am having. Eric

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wrote:

This gives 2050 PSI: http://www.casece.com/en_us/Gallery/Downloads/xPM_LB_780/cce_LB_Historic_780_specs_06-26-2009_1.pdf
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I recall reading a certain talmudic tome on hydraulics and they say that neither having a high pressure, or high flow, alone, indicates that the pump is not worn. Only loss of "power", which is pressure multiplied by flow, is a good indicator that the pump is worn.
You have a hydraulic pressure gauge on your machine, right? Easy to add one temporarily and see what the pressure does when the pump is pumping a lot of fluid.
i
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On Thu, 12 Jun 2014 19:30:23 -0500, Ignoramus32163

Some pumps, when worn, will not even produce rated pressure against a closed valve, much less into a functioning system.
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On Thu, 12 Jun 2014 19:30:23 -0500, Ignoramus32163

I have lost power. The cylinders don't move as fast or pull as hard as they used to. The machine does not have a pressure gauge for the hydraulics that operate the how and loader. I think I know where to put one now. But of course it's pissing down rain here and I don't have a place big enough to drive the backhoe into to work on it. Maybe tomorrow I can fit a pressure gauge and see. Eric
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snipped-for-privacy@whidbey.com wrote:

Those EZ-Up tents are handy for working on stuff like tractors and backhoes if you don't have a shop that can fit them. Put down a tarp, drive the item onto it and then pop up the tent over the top.
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On Thu, 12 Jun 2014 08:42:50 -0700, snipped-for-privacy@whidbey.com wrote:

Don't overlook the pressure regulator, Eric. Maybe try a new spring there to see if it puts the Oomph! back into it.
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Larry Jaques wrote:

The Case uses a two stage pump, one stage for the front bucket and one for the hoe. An easy way to check the pump is to curl the hoe see what the engine does. If the rpm holds with little extra stress and the govenor not cutting in too much you most likely have a bad pump. Do this on both the how and the front bucket to check each section of the pump. Also get the hydraulic oil tested and that will tell you if the pump is worn out. It costa about15 bucks.
John
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