That small screw can be used to bleed excess diff fluid after assembly and if removed, you can use a small screwdriver as a lever to loosen that stuck sun gear.I'm finally going to shim all my diffs & started with my front diff on my V3 Kraton. I've built diffs before, but not Arrma diffs. I have the diff all clean and also fully understand how to shim them, so no problems there. However, I cannot remove the internal sun gear on the diff cup side. The other side (which has the large external crown gear) was easy to remove the sun gear. However, the sun gear is quite deep down in the diff cup side, and hard to get at, so very difficult to pull it off the pin/outdrive compared to the other side. I've even tried using needle nose vise grips (which should work), so not sure why I cannot remove the sun gear on the diff case side? I want to add a new bearing on this side, plus remove the o ring to lube with some green slime & most importantly, I need to add a 5x18 shim on the diff cup side. Also, what is the small set screw for on the side of the diff, as not one video addresses this?
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