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John Deere Tractors Discussion Forum

4620 hydraulics

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06-02-2020 18:14:09

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I've been chasing a problem on my 4620 hydraulic system and not getting anywhere with it. The tractor works almost perfect in winter time on feeder wagon when oil is cold. Most people wouldn't even notice an issue. But if I put it on my haygrinder and she warms up the hydraulics chatter terrible and the belt conveyor will speed and slow down, I even had it once quit totally and had to move hydraulic valve back and forth few times to get going. Now that it is warmer it is chattering all the time. Yes it is always full of oil. Gave it a full service on oil, filters screen. The screen was totally clear. Hydraulic pressure has been at 2400 psi no problem but if I start a second valve with hose routed within on the valve just so it flows my pressure drops to 500 psi and the priority valve is the culpert of the chatter. I checked the trans pump, plenty of pressure filled 5 gallon bucket in 25 seconds, checked at line going into pump, same, I thought well, the pump gives me pressure but no flow, possible problem inside, I replace the main hydraulic pump, problem not solved, I've inspected through the plug on back of rearend for leaks and have seen nothing with light. Steering and brakes all work fine, If I am flowing with the scv valve the pto will grind as it doesn't have enough pressure for the clutch. I obviously have a leak somewhere and am chasing but not much luck in finding, right now I have the priority valve off to inspect but it all looks good, there is three shim washers in it with the spring. I have felt lines but not really noticing heat but havn't really worked the tractor since in shop either. Also this tractor is a power shift

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06-05-2020 19:32:06

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 Re: 4620 hydraulics in reply to greenmachine59, 06-02-2020 18:14:09  
Im not a expert on P.S. so you know. Any way oil was warm up right 150 psi . The book I have is for a 4520. Books shows 160-180 psi I think your on low end . When you did the testing did you try PTO On & OFF did you notice a difference in Psi on gauge?? Where did put gauge to test trans psi ? @ clutch port ? If you look at LH side (sitting on tractor ) below floor board on side L.H. Trans look for a housing bolted to Tran case your clutch linkage will be there To . You may have to clean it off dirt& oil . Look it will have letters (clutch ) move back 4-5 inchs look PTO port check at PTO port see if you have same psi at both ports clutch&PTO. 2 gauges would be better . PTO will need To be in gauged to get psi . If your losing oil some where else that maybe way your trans pump low psi. You have I phone ? Send u photos of book ?? Everything else works right . Steering &brakes& 3 point hitch Shifting good not SLOW slipping in gear. Trying not to overload you w/ question &info. 10-4.

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06-05-2020 15:22:18

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 Re: 4620 hydraulics in reply to greenmachine59, 06-02-2020 18:14:09  
How is your priority valve behind the dash adjusted? Try taking couple shim washers out and see how it behaves. If it works better problem Is that priority valve is adjusted too high.

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06-04-2020 18:29:04

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 Re: 4620 hydraulics in reply to greenmachine59, 06-02-2020 18:14:09  
Trans pump approx 170-180 psi. You Need to put gauge on PTO (PORT) . Maybe have seal on (piston )clutch for PTO bad ??? . If gauge showing way below trans PSI Might be it?? Ill look to night I have a 4520 service manual . You do pull trans screen right.

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06-05-2020 10:50:05

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 Re: 4620 hydraulics in reply to widetrack, 06-04-2020 18:29:04  
just did pressure test on trans pump, and got 150 psi, is that enough, id think it would be

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06-03-2020 18:17:41

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 Re: 4620 hydraulics in reply to greenmachine59, 06-02-2020 18:14:09  
Green 59 can you provide more INFO . Hows it for shifting all gears ?? Shifting with PTO OFF& ON ?? Does PTO keep spinning when not used ?? Have you RUN pressure checks on clutch pack ?? Should be a port for PTO. Get some 300 psi gauges &hoses hook up watch & as you work PTO. I do not know if there is a PTO Brake port to tap in to gauge it to . Im thinking Maybe ??? bad seal PTO clutch pack would be in front 1/2 transmission. Need to do pressure check. Or your throwing a DART it the wall. There are other GUYS on here that know P.S. Somewhere on site theres info someone posted check list When you do PSI on each port w/gauges WRITE down and what port .I have book on P.S. Dont know how to load on site . To old to figure out!!

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06-04-2020 16:08:35

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 Re: 4620 hydraulics in reply to widetrack, 06-03-2020 18:17:41  
tractor shifts fine and has no slip. pto brake works fine and the problem is there while pto is engaged. I' m gonna back up and unhook low pressure side on pump and do a pressure test there after I get some fittings to adapt, When I took off I could not hold pressure and I thought it was adequate but I need numbers and I will work forward from there again. I have found some copper flakes in oil but not too many and am concerened if coming from pto clutch or where that is from.

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06-02-2020 20:21:48

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 Re: 4620 hydraulics in reply to greenmachine59, 06-02-2020 18:14:09  
I suspect the hydraulic system is running out of functional return oil back to hydraulic pump. Based off your description of problem, What work you have done, knowing this is a PS transmission and if you are not seeing oil leaking inside differential case the next most likely place for return oil to leak to sump would be the filter relief valve for the (rear) functional return hydraulic filter. This filter has its own filter relief valve located in the base of rear filer cavity. If this valve is caught open return oil from all rear hydraulic functions will be routed to sump causing a lack of return oil to supply main hydraulic pump. These systems must have all return oil for main hydraulic pump to meet it normal pumping capacity. Recommend to drain hydraulic oil from rear end, remove rear hydraulic filter, remove the three bolts retaining relief valve housing in back of filter cavity and inspect valves and springs in this housing / assembly. Good Luck, DW

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06-04-2020 16:14:19

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 Re: 4620 hydraulics in reply to WTW, 06-02-2020 20:21:48  
We checked the retaining relief valve and found little debris in it but was no fix the valve all functioned fine.

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