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Author Topic: Jd 640 grapple skidder with hydraulic issues  (Read 2497 times)

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Offline lumberjack1981

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Jd 640 grapple skidder with hydraulic issues
« on: August 13, 2014, 10:10:37 PM »
I have always been a clark and timberjack man but decided to take the plunge and buy an older 640 grapple skidder that i thought was in good shape.  I'm doing some pretty long skids and thought the skidder would help.  My arch shakes like a congressmen who's asked to tell the truth and the hydraulics are often slow to respond and weak.   I did a pressure check on the hydraulic pump and got 1500psi on the high pressure which i know is low but my low pressure reading was low too.  I'm not sure about the gauge i used for the low pressure side and will buy another gauge and test that before buying a new pump as they're not cheap.  Is there a way to check the trans pressure?  I was told this could also be the problem.  I replaced all the hydraulic filters and trans filter and the suction screen did have a couple of pieces of clutch disk in them(small though). I'm no expert at all and know this isn't a good sign.  I'm hoping the trans isn't the problem as that's a bill i'm not looking forward to or could swing at the moment. Any advice or trouble shutting tips would be greatly appreciated

Offline sshier

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #1 on: August 14, 2014, 06:21:35 AM »
Just a thought but we had same problem with our 548 but as we worked it got worse about two hours in to the day everyone thought it was the relief valve on the pump we finally got tired of chasing the problem and took pump in and it was the pump 1200 to total rebuild now we're back at 3000 psi.

Offline sshier

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #2 on: August 14, 2014, 06:31:39 AM »
Lost train of thought you may want to pull the relief and check it out first don't take much to hold them open a little

Offline tj240

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #3 on: August 14, 2014, 06:50:11 AM »
i ran one and the main hyd line going to the grapple controls was crushed flat. it ran down the side off the belly pan good luck
work with my father[jwilly] and my son. we have a 240 tj 160 barko[old] works great three generations working together

Offline lumberjack1981

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #4 on: August 14, 2014, 03:28:49 PM »
Filters and fluid changed....psi on pump still 1500and now steering doesnt not work....what is going on? I can't find a manual online and to be honest I'm no Jd expert. I don't even know where to look for a relief valve.  Any help would be greatly appreciated.   I may be reached by phone at 5184235947 if anyone has some time and could help out and I will be checking this site often too. Eitherway I thank you all for your time and wish you guys better luck than me lol.  On a side note I miss my old Clark 666 and my timber jack 450....they ran.  I'm hoping it's just the learning curve that's hurting me and not jd

Offline SliverPicker

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #5 on: August 14, 2014, 05:32:06 PM »
I have a friend with a 1978 640.  He bought it used in 1980 and has used it for his sole source of income ever since..  He has over 32,000 hours (honestly) on it and has never had to replace the transmission.  He has resealed it and replaced clutch packs, but that's it as far as the transmission. 

Keep at it.
Yooper by trade.

Offline thecfarm

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #6 on: August 14, 2014, 06:23:58 PM »
lumberjack1981,sorry to hear of your troubles,but welcome to the forum.
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Offline jd540b

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #7 on: August 14, 2014, 08:42:31 PM »
Could be charge pump on the transmission ?? I had a 540 and a 440 that would loose hyd pressure when warm.  Both ended up being trans charge pumps.

Offline tj240

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #8 on: August 14, 2014, 09:24:16 PM »
if its an older jd the pump should be in front of the radiator they arent that bad to change. call nortrax and talk to someone in sevrvice the usually help alot around here
work with my father[jwilly] and my son. we have a 240 tj 160 barko[old] works great three generations working together

Offline lumberjack1981

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Re: Jd 640 grapple skidder with hydraulic issues
« Reply #9 on: August 16, 2014, 02:32:49 PM »
Got an increase in pressure on the high side on hydraulic pump to 2000psi.  Thelow side on the pump was fine at first but got worse as the mmachine warmed up.  Come to find out the tec left the plug in the return line from the pump to the Trans so we are wondering if that was the reason for the increase in pressure.  At this point we're about to put the hydraulic pump back together.  Had one bad spring in it.  On a side not the Trans pressure on the charge pump was 180psi.  At this point probably going to put the hydraulic pump back together and start taking the motor out to get to the Trans pump.  Any suggestions would be a great help as i am lost lol


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