Anyone know how to rebuild a charge pump for a 420?
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Thread: Anyone know how to rebuild a charge pump for a 420?

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    Anyone know how to rebuild a charge pump for a 420?

    I was starting to lose power/transmission slipping, so I took it in to the dealership. The first thing they did was (somehow) test the charge pump and told me it was shot. Replacement charge pump, rebuild kit, parts, replacement transmission - all LONG out of stock. They said that would need to be resolved before they could even think about looking at the transmission. I LOVE my old tractor! I bought a 1025R with the FEL and backhoe and a 60" mid-mount mower deck, but it's too big to fit under some of the stuff in my yard. Plus, the 420 was great for just hauling a trailer around the property. I'm fairly handy with mechanical stuff, I've just never worked on hydraulics that much. Anybody have any suggestions?

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    Sieden, I see only 4 options. Gonna be your call as to which one to use!

    1. Leave with dealer. He may eventually find parts for charge pump, move on to transmission repair/parts, and eventually have a running tractor again. Thinking maybe a few months (8-10??) and $3,000-$5,000.
    2. Find another 420 with bad engine or just a 420 hydro unit. Put hydro in your tractor or your motor in "new" tractor.
    3. Find parts and repair hydro your self.
    4. Scrap/sell your tractor "as is".

    If it was me, I'd look for parts and repair it myself. No "magic" in hydraulics, just a bunch of nuts, bolts, plates, and seals. Ya know, just mechanical stuff!
    There should be a plate on your hydro with manufacturer, model & serial number. Start there and locate parts. Also, if you din't have an account at jdparts.deere.com, create one! Check part numbers for 420 hydro and compare with others, 318, 322 etc. Other models may interchange. Find number for tech manual and get one, LOTS of useful info in them. Keep us posted on what your doing. Bob
    '80 317 w/18hp B&S and divert valve for rear hydraulics, 3 pt hitch, 5' york rake
    '82 314 w/rear PTO for tiller
    33 tiller
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    Mod 48 deck & Mod 462 TracVac

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    Used parts are probably going to be your best option. Dealerships typically shy away from using/installing used parts and won't warranty their work but they will do it. If not a JD dealership then usually some small shop tractor repair place will.

    Did a search for a 420 charge pump and they have several listed on Ebay for about 85 dollars so the parts are out there.

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    I think I have one in the shed. $50 would buy it. Shipping is probably fairly expensive though. I think it was $80 to ship one to ny state.

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    I wonder what makes the dealer believe the charge pump is "shot". I assume the only thing they did was check the charge pressure and found it was low. Low charge pressure doesn't necessarily mean the charge pump is shot.

    The charge pump is an integral part of the entire hydrostatic transmission.

    Has the hydraulic system been serviced regularly over the 1700 hours?

    Remove the spin on hydraulic oil filter, cut it apart and check for metal or brass.

    Possibly the charge pressure relief spring has broken.
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    Also check the relief valves for sticking/being stuck down. These are on the top of the unit and can be readily seen with the fender deck off. The pump can be rebuilt of course if you get a matched set of used parts or new parts. These are close tolerance pumps and do not mix old/new internal parts or parts from several units -- getting a complete pump used that is known good is the best way to go on a budget.

    Here is the section from the TM1590 that covers this transmission system:

    TM1590 section 50 - power train.pdf

    Chuck

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    I have to withdraw my offer. I found two older style, but not the 2 open frame I thought I had. They must be somewhere in the pile.

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