# Replacing Rack gear on G4003G



## epanzella (Feb 24, 2019)

I need to replace the gear that contacts the rack on my Grizzly g4003G 12x36 lathe. Can anyone give me a general idea of how to do this? It looks like the feed and lead screws may have to come off but I'm hoping there's a more efficient way to do this!


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## markba633csi (Feb 24, 2019)

Is the gear damaged? Broken tooth? 
Mark


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## epanzella (Feb 24, 2019)

markba633csi said:


> Is the gear damaged? Broken tooth?
> Mark



I was turning a long gun barrel and ran the carriage nearly to the end. I couldn't see anything that the carriage hit but it stopped about 2 inches from the end and pulling the feed lever back to neutral took about double the normal effort. Now when I traverse the carriage with the handwheel it
has tight spots intermittantly. Looking in with a lite I can see the trailing edges of some of the teeth are malformed. The shaft may be bent too but I can't tell.


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## Cadillac (Feb 24, 2019)

Without pictures you will have to remove the lower apron from the saddle. Then the leadscrew will need to be disconnected and unbolted from bearing support on tail end. Then it can come off as one unit.


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## markba633csi (Feb 25, 2019)

Agree with Cadillac, in fact you may end up removing the entire carriage if there isn't enough working room to extract the gear


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## sixball (Feb 25, 2019)

I found and downloaded a manual for a Grizzly G1003 on line, the Grizzly site I think. I tells how to disassemble the lathe. It is very similar to yours but I bet there is a manual for the G4003G there too. It is a pain but really not that complicated. My lathe is a Shenwai.


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## psgflier (Feb 25, 2019)

I just did that with mine a few weeks ago. Running the carriage back toward the tail stock with the lead screw to distribute oil after cleaning. It came to an abrupt stop about 4" before contacting the tail stock and was rough moving under power after that. I got to looking and the shaft for the change levers was bent. I think one of the other shafts in the change gear box was bent also, causing the gear train to bind up in some positions. The gears were all fine. I ordered all three new shafts, one is on back-order.
I'm pretty sure the hole in the rear bearing block is misaligned for the lead screw and caused it to bind when it got near the end.


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## epanzella (Feb 27, 2019)

I ordered the 11T gear that contacts the rack and it comes with the shaft so hopefully that's all I need. I can see the distorted teeth with a lite. There seems to be some sort of plug on the opposite end of the shaft along with another gear. I don't know if that plug is threaded, pressed in, or what?   Here's some pix showing the plug and the small rack gear that's chowed.


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## Cadillac (Feb 27, 2019)

I have a jet 10x24 that the apron looks very similar. When I got it 10yrs ago I replaced the gear in question along with some others and the worm gear. Everything is exposed once the apron is taken off the machine. One tip is block the bottom off the apron so when unbolted from the saddle it doesn’t drop away. I also shimmed the worm gear to a tighter fit. This is what drives the carriage when auto feeding is engaged and should be a nice fit in part 466 of diagram. 
Alignment of the apron to the saddle and leadscrew is the technical part make alignment marks before you separate the apron. The screw I used a magbase on the cross slide and traveled back and fourth till perfect then tighten bearing support end.


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## epanzella (Feb 27, 2019)

Thanks for the info.  My one complaint about the G4003G was the lack of a feed clutch! It took 6 years but it finally came back to bite me.


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## derf (Feb 27, 2019)

Doesn't it have a brass shear pin on the power feed shaft?


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## epanzella (Feb 27, 2019)

derf said:


> Doesn't it have a brass shear pin on the power feed shaft?


I think it does but in any event it didn't let go. The power feed and the lead screw still work fine. I'm assuming the "tight" spots are still there under power but there's not enough resistance to cause any obvious problem. With the feed in neutral and the half nuts open I can feel the intermittant resistance in the hand wheel but I can still turn it. It was smooth as glass before the incident.


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## epanzella (Feb 28, 2019)

Grizzly just got back to me with step by step instructions for this job. Unfortunately  all the parts I was hoping wouldn't have to come off actually have to come off. The gear and shaft are scheduled to arrive tuesday. Thx to all for the help.


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