John Deere 4520 CUT front axle breather

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I'm confused as heck. I've read about, and have experienced for myself, leaking front axles on John Deere 3 and 4 series tractors. I wanted to vent the front axle on my new-to-me 4520 and have seen after market dipsticks that have a vent (breather) in them.

I stopped in my JD dealership to inquire about these vented dipsticks, and he said the front axle already has a vent on it, even printed me a picture of it. Being as they had a 4520 on the lot, I walked out and looked for the vent, and couldn't find it. I've not seen one on my 4520 either (haven't looked again as it's at the farm), but I think I would have noticed.

So my question is: are there specific years they put these breathers on the front axles? Am I just not seeing it? Anyone have a service manual that references replacing or checking these breathers. I don't yet have a service manual, hoping someone on here can answer this for me.

Thanks

 

[msb1766]

Here are the parts for my homemade axle vent:

Amazon.com: uxcell Reducing Pipe Fitting Adapter M20X1.5 Male to 1/2 G Female, Stainless Steel for Water Oil Air Pressure Gauge: Home Improvement

https://smile.amazon.com/gp/product/B07D25TMNB/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

https://smile.amazon.com/gp/product/B00NF1SLT8/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

 

[shock]

Thank you for the info! Can i ask what model tractor you created this for?

 

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In addition to my above question - I've seen both M20 and 3/4" NPT male as the size for a JD axle dipstick and the diy breathers folks have created. Does anyone know for sure the correct size? Is it relative to the front axle that's being used on the different years/models? Thanks!