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Restoration & Repair Tips Board

JD 420 hyd. pump damage- run dry?

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11-13-2013 09:21:57

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Hello all-
Recently revived my 1956 JD 420W after other complications in life had caused me to (regrettably) leave it sitting for a spell of a few years. The good news is that with some minor tuning up, it runs every bit as well as it ever did (it has great compression, good oil pressure, and quiet gears). The bad news is that, like most Dubuques, the hydraulics leak- but it turns out that they leak worse than I'd have ever guessed- and- I raised the rear 3 point to drive it to a different spot to work on it (and the 3point raised normally), left the 3pt raised raised, left it running for quite a while (45 min- an hour), and then went to raise the front end loader- and found that the hydraulic system had totally lost prime and there was nothing flowing to run the loader, or, after I lowered the 3 point, to even raise the 3 point. I then added a lot of fluid to the Touch-o-Matic fill port, and after a lot of burping, the 3 point came back to life, and after more fluid and more burping, the flow to the loader (which is plumbed en route between the engine driven hydraulic pump and the pressure inlet to the Touch-o-Matic) came back. BUT the loader moves upward only with a pulsating jerky surging. I do have a high pressure fine filtration Donaldson Hyd. filter in the lines after the loader and before the Touch-o-Matic, so if I've got nasties circulating, it should be filtering them. I don't really have time or funds right now to pull open the engine driven hyd. gear pump to see if it was running dry or what damage could have occurred- but also don't want to worsen any damage by continuing to run it, if that will make a bad situation worse. I welcome and appreciate suggestions from folks who may have 'been there done that' with a Dubuque hyd. system that inadvertently had the engine running with low/ little fluid for some interval (probably about 45-60 minutes). Thanks!

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11-14-2013 16:11:12

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 Re: JD 420 hyd. pump damage- run dry? in reply to kd1yt, 11-13-2013 09:21:57  
I'm sure it didn't do it any good. Your pump is probably worn, but if it has oil in it now will be alright to use it. I have used 20X50 Valvoline and a can of STP in a worn out MT.

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11-15-2013 17:04:41

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 Re: JD 420 hyd. pump damage- run dry? in reply to VicS, 11-14-2013 16:11:12  

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11-13-2013 12:14:47

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 Re: JD 420 hyd. pump damage- run dry? in reply to kd1yt, 11-13-2013 09:21:57  
The filter is good for 1200psi ?

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11-15-2013 17:03:20

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 Re: JD 420 hyd. pump damage- run dry? in reply to buickanddeere, 11-13-2013 12:14:47  
Yes, the filter IS good for over 1200 PSI; it's a Donaldson Industrial filter sourced from Applied Industrial. When I got this loader its history was unknown and it was a bit scruffy, and I didn't want any scuz in the loader's system passing into my tractor's hydraulics, so went to the extra trouble of a filter that could go in a high pressure line (due to the nature of a 56 420's simple hydraulics, the loader is in line between the pump and the remainder of the machine's hydraulics).

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