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jdemaris
11-22-2003 15:48:00
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Re: Re: Re: 4020 hydraulics in reply to kevin, 11-22-2003 06:07:25
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If you've checked the obvious things, that it probably is your pump. I find it to be a fairly easy unit to rebuild, but getting it out is not easy. On 4020s, I pull the front end off and pull the pump out from the bottom. The most common wear item is the stroke-control valve which can be replaced without removing the pump (I was a field mechanic for John Deere and I've done many of them). 15-20 minute job when you're used to it. I also did their bench rebuiding for hydraulic pumps and fuel injection pumps). Complete pump rebuild, once on the bench, would take 2 hours and $120 in parts (on the average, back in 1989). Back to the point, when the stroke control valve gets wear along its seat, it will make a hammering or chattering noise. Usually, it will also make the tractor start hard. Very often starter motors are burnt out because of worn stroke control valves. Gets bad enough, you will lose all hydraulics. New valve and seat assembly used to cost around $35, but I haven't worked for a JD dealer since 1989. I fixed many of them by just pulling out the valve itself (not the seat), and stuck into a valve refacer, refaced it, and stuck it back in. Very often it worked fine although I'm sure such repairs are not sanctioned by John Deere. If you do so, you MUST readust the stand-by hydraulic pressure. There a adjuster on the outside of the pump for this. If you do remove the pump, it's not bad to work on. Has Timken style adjustable bearings, so bearing endplay must be adjusted with shims. You've got 8 pistons and springs to inspect, along with 8 discharge valves and 8 inlet valves that at least need to look at to make sure nothing is broken. As of course, as aforementioned, the stroke control valve is a MUST.
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