450C Final Drives / 80w-90 Gear Oil or Hygard Hydraulic?

[Farmboy]

I just changed out my fluids and filters.
The book calls for hydraulic fluid in the finals but what came out was heavier than hydraulic, so I put in 80w-90 gear oil. I talked with an experienced mechanic who said they always used to run the gear oil because the hydraulic just doesn't seem heavy enough.
Now I'm having second thoughts, mainly because I'm wondering if there is any potential for cross contamination of the transmission fluids. I know the trans and steering clutches share a common sump.
Does anyone have experience / knowledge on this?
Help much appreciated!
Thanks.

[KenP]

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[Farmboy]

No offense meant but, I understand what is specified.
I also know that there are compromises made in specifications - for example the benefit of just going with one lubricant for entire machine (no need for user to stock multiple products) when another might be slightly better in a given location.
Not talking about putting in a "snake oil" product.
Looks like basically a drive gear, driven gear, bearings and seals.
My question is really to those with direct experience on if it is done and either the benefit or if it is (or could somehow be) harmful.
I've got $30 of new oil in there now. Would prefer not to waste it..... but I'm not willing to be the test case either!
I do appreciate the response though so thanks!
Bill

[Lavoy]

Hy-gard is used in the trans and differentials of the highest HP tractors Deere manufactures today, so I doubt the theory that it is insufficient for the final drives on a 450. Plus, on a C model, doesn't the oil in the clutch housings somehow circulate or mix with the finals anyhow?
$30 thrown away is a lot cheaper than damage to related components from improper oil.
Lavoy

[CatD8RII]

If the 450 C is anything like the 350 C, then the oil from your final is shared with the steering clutch housing oil. Using gear oil would concern me most on the brake drums/bands and the steering clutches. They count on a certain viscosity of oil to be properly lubed.

[gerald]

I argee 100% change it . On my 350 I used gear oil in the finals it is a sealed unit by its self gears an bearings. If it leaks in the dry clutchs there ruined but any oil will do that in the older dry clutch units.

[Farmboy]

Thanks for the responses.
I've been looking at the parts book and I don't believe the final shares oil with anything else. The trans and steering clutches share the same sump but that is it. If anything, it looks like a leak would let oil from the steering clutches migrate to the finals as they are lower.
However, I've not heard anyone here say they've done it with no problems, and I'm not about to risk it. Also, the fact that the big dozers all use the same hydraulic oil in their finals says a lot.
I'm going to drain, flush with diesel and put in the hydraulic.
Appreciate the input.