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I recently had a loud noise coming from the gear case on my 2007 X720 mower deck. I found that the lower bearing in the gear case was the culprit and it was not a part I could get through JD. Only thing I could get was a complete gear case which was about $650.00 after taxes and shipping. One point, not sure why JD used a deep groove bearing on the lower part of the shaft since this has most of the load on it. From inspection, all other bearings in the case are roller bearings which hold up a lot better than deep groove bearings. Anyhow, below are the steps used to replace the lower vertical shaft bearing on a JD AM136330 mower deck gear case.



1. Remove deck.

2. Release idler tension spring.

3. Loosen the four bolts that attach the gear case bracket to the mower deck.
This will make it easier when you finally remove the gear case.

4. Remove the two bolts from the input side of the gear case then the four
four bolts on the back. Some newer models only have two on the back.
Mine had four.

5. Un-loosen the bolt on the drive shaft attached to the input shaft of the
gear case and remove the drive shaft.

6. Once you have the gear case out, remove the fill plug and drain the oil
and dispose it according to your local regulations. Mine had little metal
particles in it probably from the failed bearing and some gear wear.

7. Remove the output shaft pulley. **CAUTION** this is a left hand thread
so turn it clock-wise to remove it otherwise you may damage the vertical
shaft trying to remove it. I used an air impact wrench so it came off quite

8. Remove the lower oil seal. This will be damaged during the removal process
and should be replace for a complete repair.

9. Remove the spring clip bearing retainer. This may require a special tool to
remove it. I modified an old pair of mini needle nose pliers to fit in the
holes of the retainer to remove it.

10. Remove the lower bearing shim.

11. Turn the case over and remove the four bolts holding the top access cover

12. Remove the access cover. There will be a gasket here that will need to be
replaced as well.

13. Remove top bearing shim.

14. Using something smaller than the splines on the top of the shaft, drive
the vertical shaft out through the bottom of the case being careful not
to damage the splines of the top bearing. You should now have the
vertical shaft and lower bearing out of the gear case. This is the bearing
that failed in my case. Remove the bearing from the shaft.

At this point my dis-assembling was complete. Depending on what your problem may be, you may have to dig deeper. I completely inspected everything else and everything checked out good. Just spinning the lower bearing in my hand, it made a noise and felt "gritty".

Here is a list of parts for the repair:

1. New bearing: part# 6005 (was printed on old bearing) $20

2. New lower oil seal: 25X47X8 (dimensions you will use to get new one
and was stamped on old seal) $5

3. Sheet of 1/64 gasket material: $2

4. New 80W90 gear oil: $8

5. Couple of cans of brake/parts cleaner: $7

Total cost was around $40 opposed to the $650 wanted for a new gear case!

Once everything was removed, I gave it a good cleaning with the brake cleaner to remove old oil and foreign matter from the gear case. If you have a parts washer this would be good to use also.

Now just reverse the steps for re-assembly. I went to a local garage and they pressed the new bearing on the shaft for no charge since I use them for my car repairs. As for the gasket on the top access cover, just use the cover as a template and cut it out. Take notice of the under-side of the cover. You will notice a small cutout in the metal to allow for oil to reach the top bearing. Make sure you don't cover this with the new gasket material. If you have any concerns or questions, feel free to PM me.
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