I need to rebuild a hydraulic cylinder on a john deere 4300 with a 420 front end loader. the cylinder is for the bucket. how do i disassemble it

1. This cylinder is not to hard to disassemble.
2. Place upright in vise or suitable bracing.
3. Using a block or dowel of wood(maybe rubber mallet also), depress the top cap of the cylinder to relieve tension on the ring.
4. Use a small edged screw driver or pick and spin "retainer" in until the bent end comes to the opening.
5. Lift up and rotate the ring more to allow the ring to pass over the edge of the opening.
6. Once the retainer is started you can tap it with the wood and rubber mallet around the circumference of the cylinder to release the retainer from the groove.
7. If you havent done so by now the oil should be drained.
8. with the cylinder firm in vise(but not too firm to "distort the integrity of the cylinder.) Place the cylinder Sideways so you can pull out piston and rod assembly.*** Put hose or suitable drain on holes of cylinder***. With the motion of the piston the residual oil will tend to spray out.
9. Pull on the piston and position it to bottom out on the top gland(cap) ie:full extension
10. Place support under the rod to avoid damage. The gland is a tight tolerant fit with use of O-rings and backup rings. Too much offset can lead to damaging gland assembly, and jamming in the cylinder. You may be able to just hold with hand also depends on size, bore, stroke, pressure rating. Use due dilligence.
11. Now that its out you have the piston assembly with gland in hand..**if only the rod comes out there are more steps to take, and you need a new rod but sometimes its more cost effective to buy a new cylinder. If there is a farm supplier or hydraulic dealer near they can certifiably /replace repair the cylinder for you. Hydraulic pressure is kind of like lightening. If it strikes you under pressure it can kill you.*** Using the dead blow or rubber mallet try to pop the gland out by using the piston/rod assembly as the puller. You may not have to remove the top clevice or other end of the cylinder, so maybe you could tap on that.
12. The piston can be removed from the rod depending again on make. Usually a socket head cap screw or king nut holding it in place to the rod.
13. When the piston is removed you should be able to slide gland off also.
14. You'll need that pick and or the screwdriver to pick out the seals carefully. Let me know if you require more...WF Services

You'll have to use a spanner type of wrench and unscrew the end of the cylinder. Once it screws out, the ram will come out, and you will have access to all the seals to replace them.