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Gear oil for a Truetrac

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2K views 13 replies 8 participants last post by  fartsinpublic 
#1 ·
I learned a long time ago not to debate oil on a forum. In 2004, we almost had a war on the factory five forum about what oil to use and I swear a couple people left the forum over their outrage!

I searched this forum and Google looking for my answer, but then decided to just bite the bullet and straight up ask. What’s the worst that could happen? I run Redline MT90 (75w90 GL4) in my Series III in every case, okay except the 300TDI. I planned to do the same in the TC, swivels and diffs in my LS equipped 90, but then noticed that Eaton says not to use synthetic or FM with the Truetrac. Most other gear oils are GL5 and contain FM.

So, what is the correct answer?
 
#2 · (Edited)
When I fitted mine I asked GBR Bill and he said plain old gear oil. So I run 90 weight.
The eye-ties are also very passionate with oil weights and brands.
 
#4 ·
It does not matter. You are just wasting money using synthetic in the axles. Nothing in the axles ever wears as long as the oil is kept clean. Bulk 80W-90 in 5 gallon pails is the easiest way to go.
 
#7 ·
Man, I’m liking these answers!

How about the GL5 issue? Should I look for GL4 or is that only a TC/tranny concern?

I will admit to f’ing up on the 109. After carefully rebuilding the front axle and installing disk brakes to manage the 300tdi, I should have gone with a heavier weight non-synthetic. One swivel has a slight drip. Live and learn.
 
#9 ·
GL 5 is ok for the diffs but I been using 4 as I get by the drum, is the oil coming from the ball/seal or from behind the seal? You did use sealant and not rtv? I like to put a thin coat of of permanent on the outer edge before offerING it up.
 

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#10 · (Edited)
I use synth in the LT230 and regular in the diffs. I replace the diff fluidss after any large water usage. Not wading, but getting stuck wading... then I might replace it. I change all my fluids every year or so---it just seems intuitively smart to run clean fluids.

I think I just run 75/90 Valvoline in the diffs--whatever was cheapest.

I'd love to see your conversion. Are you planning to come up to CO or Utah for some wheeling in 2018? Just looked at a map, and a little longer than I originally thought (I don't know Texas well and everyplace is more miles than expected) but if you do, drop me a line. Fun to plan some camping/wheeling. I have to start thinking about what I want to hit next year now that I am done with mine...
 
#12 ·
I'd love to see your conversion. Are you planning to come up to CO or Utah for some wheeling in 2018? Just looked at a map, and a little longer than I originally thought (I don't know Texas well and everyplace is more miles than expected) but if you do, drop me a line. Fun to plan some camping/wheeling. I have to start thinking about what I want to hit next year now that I am done with mine...
Chris, my best friend (old navy buddy) lives in Greeley and I’m up there several times a year. He and his wife are avid campers, but they’ve now reverted from a more primitive approach to a large 5th wheel trailer. I plan on driving up in the Spring. The wife will probably stay behind as she still refers to my truck as the Offender. That’s probably my fault as I apply the “easier to get forgiveness than permission” approach in my car/truck dealings. Where are you located?
 
#14 ·
I learned a long time ago not to debate oil on a forum.
Nor ask whether to run oil vs grease for the wheel bearings.

Everyone knows the answer is grease but there are some out there who think otherwise... :rolleyes

Been running that same diff up front since 1997ish on straight mineral 90wt or 85/90 or whatever is closest to hand. Same-same, day in, day out. No fancy/exotic name, no small batch artisanal production either.
 
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