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4620 looses hydraulics at low RPM

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Reaver

06-23-2001 07:26:05




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At low RPM's we loose hydraulics, steering, and most important (and dangerous) brakes!
Have change hytran and filter, hytran checks full.

Any ideas?
The tractor has not been ran a whole lot lately and we changed the hytran fluid and filter...could it be air in the lines? could using the tractor correct the problem?

Thanks!




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Don

06-27-2001 09:05:49




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 Re: 4620 looses hydraulics at low RPM in reply to Reaver, 06-23-2001 07:26:05  
Start the tractor and engage the pto. see if problem goes away . if the pto lever is not adjusted correctly this can cause the prob. also more frequently the valves in the remote control valves could be leaking. put your hand on them and see if they get hot right away.brake valves could be another possibility. I will bet on remote valves though. possible leak in the steering valve . you should be seeing other problems with this ,cyls creeping in or out steering eratic etc. just a few to look at. plug off the line to the rockshaft to see if it goes away ,that will isolate those valves (rockshaft and remotes).good luck.

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Paul

06-24-2001 10:46:25




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 Re: 4620 looses hydraulics at low RPM in reply to Reaver, 06-23-2001 07:26:05  
sounds to me like an internal leak( high pressure)along whith a destoking problem.your going to need a manual.



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twopop

06-23-2001 19:09:04




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 Re: 4620 looses hydraulics at low RPM in reply to Reaver, 06-23-2001 07:26:05  
there is a screen,located on the left side,just in front of the axle housing.it is under a large plug,about 2 inches in dia.remove the plug and then remove and clean the screen.drain the trans.fluid first.if it is clean you probably need to replace the trans.pump.there are also other possibilities depending on what transmission is in the 4620



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Reaver

06-24-2001 08:24:20




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 Re: Re: 4620 looses hydraulics at low RPM in reply to twopop, 06-23-2001 19:09:04  
When we changed the hy-tran and filter we did also clean the screen u r referring to...
How expensive is the trans. pump?
How hard to change?
It has the transmission on the dash with 8 gears.
Does that help?
Thanks, Reaver



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twopop

06-24-2001 09:17:25




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 Re: Re: Re: 4620 looses hydraulics at low RPM in reply to Reaver, 06-24-2001 08:24:20  
as i recall,they are not very expensive,as you can buy the parts you need.i believe the gears are about $150.in order to change it you have to remove the rockshaft housing,i would say you could change the pump in about 3 hours.there is a pipe that runs from the screen to the pump,if this pipe has a hole in it,then the pump could be getting air,which could cause your problem.you can make a simple check to see if the pump is the problem.remove the hyd.filter and put an empty bucket under the filter housing,start the tractor and see how much oil comes out of the housing.run the engine for about 30 seconds.you should get 2 1/2 to 3 gals of oil.if you get that amount ,you may have to look at the main hyd.pump

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G Taylor

06-23-2001 09:10:27




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 Re: 4620 looses hydraulics at low RPM in reply to Reaver, 06-23-2001 07:26:05  
Is there a de-stoke device for easier winter starting on that hydraulic pump? Maybe engaged a little? Don't have a service manual for a 4620 but they maybe a screen or filter in the system still requiring inspection/cleaning?



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jim

06-24-2001 18:18:34




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 Re: Re: 4620 looses hydraulics at low RPM in reply to G Taylor , 06-23-2001 09:10:27  
we just had one fixed for the vary same problem.
It ended up being an internal leak, bad gasket.
gasket was under seven dollars but labor was little over five hundred and ninty dollars.
the gasket is located down inside the trans, not for the beginner to attempt. also a common problem with this model. JD claims after it has been replaced we should not have any other prblems, all we can do is wait and see. Good Luck !

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mh malcolm

06-25-2001 19:12:46




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 Re: Re: Re: 4620 looses hydraulics at low RPM in reply to jim, 06-24-2001 18:18:34  
An internal leak in any of the sytems, be it steering, brakes, rockshaft, selective control valves, or internal leakage in the hydraulic pump itself can cause loss of hydraulics in any John Deere tractor with a closed center hydraulic system. Need to follow the diagnostic trouble shooting procedure in the John Deere technical manual to efficiently identify the problem area. This involves isolating the different systems so the leak can be isolated and identified. Need test gauges and assorted fittings to do this. Any John Deere ag dealership will have alot of experience doing this as it is a fairly common problem.

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jim

06-25-2001 20:41:11




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 Re: Re: Re: Re: 4620 looses hydraulics at low RPM in reply to mh malcolm, 06-25-2001 19:12:46  
yes I agree, I found that purchasing the needed equipment to isolate the systems would have been close to the cost of fixing the machine, I could not sell my father on the fact that we could use the equipment latter for future problems but as he stated in his fourty years of farming this is the first serious hydro problem he has encountered. I personaly don't think he could of handled seeing his "Baby" spreed all over the shop in Five different heeps, when I go breaking equipment into peices he gets nervious.
Thanks for the reply.

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