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Discussion Starter · #1 ·
Started to take apart JD 420 tonight. The "little once in a while drip drip leak" has turned into a steady stream. At about $20 a gallon for fluid, it is too expensive to not fix. Do not know exact cause of leak yet, except... I bought it dirt cheap-great motor, great deck, great tires, barely 1000 hours, AND a leak. Was fixed by PO with some goop on the joint between to two halves of the differential. Probably cracked, but at what I bought it for VS what I see them going for on E-something and Craigs I have room to spend on repairs. Such a nice starting, running and mowing machine. Can't promise I will have and post a lot of photos of the overall procedure, but I will try.


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Couple tips to help out. Put the tires back on and support the frame with jack stands just infront of the diff/pump where the wheel just are off the ground. Loosen the driveshaft bolts, unhook the diif lock and shift linkage from the diff, remove the 4 axle to frame bolts, remove the back nut on each brake rod, remove the two hydro lines for the pump, unbolt direction control linkage and unbolt the two bolts for the front diff cross brace.

Have the rolling jack on the front of the diff with a little pressure. Once everything is unboltded lower down some to clear things and use the jack and wheels to roll out the back of the frame.

Stand whole unit on one tire, pull the top tire, then the axle, Then the pump. Now would be a good time to clean and reseal the diff as well-if so pull the other axle bolts off and lift diff off as well.

Reseal input/output shaft and trunion seals as well as gasket for the pump halfs and the oring on the front of the charge pump (input seal) and the oring between pump and diff. Inspect shaft for where at the needle bearings.

Diff-replace both axle seals and the shifter/diff lock seals and case gasket.

Now is the time to also replace the suction hose. Look at the hose also going from the pump to the steering valve. The swival often starts to leak.

Look at the direction control linkage-often work and causes creep and speed changes.

Look at the frame near the axle mounts and cross brace as well as the steer cylinder mounts for cracks-fix as needed.

Assembly is reverse of what I said.

Good time to also check your fuel tank pickup screen that likely has the hose broken. Use 3 inches of 1/4 inch Tygon hose-resists chemicals better.

Can be done in a full days work for not very much money and you aren't going back to fix the next leak becuase the seal is almost ready to leak. Doing this you are good for years to come.
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