gear oil
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Freshman User
Joined: Feb 2002
Posts: 25
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From: Sullivan
gear oil
hello, I have a 78 3/4 ton and im getting ready to fill both the differentials and manuel transmission . Wondering if anyone had any favorite brands. I was thinking mystik jt-6 My rear end is not limited slip, so I guess regular gear oil will work?in a 5 gallon bucket
Post Fiend
Joined: Jan 2000
Posts: 5,860
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From: Metro Detroit (Redford)
I would go all synthetics for the manual tranny and differentials, mainly because they are in there a long time. For the crankcase I still stick with dead dino juice (rotted plants, animals, and I suspect a few dead people too
).
).
Postmaster
Joined: Mar 2001
Posts: 4,968
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From: So Cal
With the age of your truck I believe that regular gear lubes are what is specified.
I like Valvoline gear lubes just because. For hot climates I would probably go with 90W140 or something like that. For cooler climates probably 75W90 or similar.
If I wanted to baby things and not worry about the lube for a long time, I would use synthetic 75W90.
I have never had a gear train failure due to lubes so I do not know what doesn't work.
Just my opinion.
Jim Henderson
I like Valvoline gear lubes just because. For hot climates I would probably go with 90W140 or something like that. For cooler climates probably 75W90 or similar.
If I wanted to baby things and not worry about the lube for a long time, I would use synthetic 75W90.
I have never had a gear train failure due to lubes so I do not know what doesn't work.
Just my opinion.
Jim Henderson
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Mystik JT-6 is a grease. JT-7 is their gear oil. It is an EXCELLENT gear oil. I have read it is used and respected in the trucking industry, and I know that a lot of farmers use it. I also have heard from one of my relatives that is retired from John Deere that they use some Mystik products. So I say go for it. 
Elder User
Joined: Oct 2002
Posts: 743
Likes: 1
Mystic is good stuff, when it changes from red to black, it's time to change. Very easy to remember. I've run rear-ends to 300K miles on mystick changes once every 100K or so. The bearings usually wear out and fail before the gears. I don't think any other oil would do any better. If you have limited slip you just add the tube of stuff from ford or the additive you can get at most parts stores for L/S operation.
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