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Gear oil recommendations?

Jorge6.5

Jorge6.5

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Location
Upstate New York
Looking for some ideas on what gear oil to run in the rear diff, full floater gov lock in my '96 I want to run amsoil synthetic but i just read on this site here that it can not be used pre 98 year cause of the seals. What the deal with that?
am i limited to using regular gear oil and should i use additive?
 
I've been using Amsoil Synthetic since the 90's sometime. No problems beyond normal with seals. Except for the cruddy new, garbage aftermarket seals they sell now. I've had more problems with seals in the last 5 years than ever.
I've worked on machinery my whole life and never had so many seals last such short times
I recomend Amsoil transmission and gear lube MTG05

Call Amsoil tech support and give them your application and then ask if the MTG will work also
 
No additive used in the Gov-Loc. There's some conflicting info out there (and lots of debates) but there is also a TSB direct from GM that says do not use "posi" or "limited slip" type additives in your gear oil if you have a Gov-Loc, unless you want trouble from it.

The Gov-Loc does have friction materials in it but nothing like a normal posi unit. It just uses straight-up gear oil.

Richard
 
My owners manual calls for regular gear oil.

The HD, 15000# gvw trucks call for a synthetic.
 
Looking through several of the owners' manuals, some of them don't reference the HD. My 1992 and 1995 manuals don't.

2000* C/K manual indicates 75W90 synthetic for the rear on regular models, 75W140 synthetic for the Dana 80 in the 3500HD's (*manual is from a GMT400 C2500, carryover C/K model, "classic")

1996 C/K manual indicates 80W90 GL5 for front/rear axles on regular models, 75W140 synthetic for the Dana 80 in the 3500HD's

1994 C/K manual indicates 80W90 for front/rear axles on regular models, 75W140 synthetic for the Dana 80 in the 3500HD's

It seems that whether they specify GL5 comes down to just whatever copyboy monkey was writing the manuals. GL5 would be the spec used for assemblies not containing any yellow metals, as the compounds in GL5 lubes will attack/corrode those metals. Some of the newer GL5 spec lubes claim they're safe for yellow metals but you know what? I'd rather play it safe and use the appropriate GL4 in those! A great example would be my old Mercedes Unimog; it was critical to use GL4 in the transmission, but you could use GL5 in the axles. I don't think I'd want to risk "yellow-metal-safe" GL5 in the transmission considering how costly it is to rebuild/replace and the fact that you have to take the BODY OFF to R&R the transmission.

Richard
 
Brooklyn Tow said:
Really!.....Anymore info on that?
Click to expand...

I looked into it Louis and it is the 3500HD with a DANA rear axle.

It recommends 3500 mile oil change intervals with regular 75-90 oil, with 75-140 synthetic oil the change interval is 30,000 miles.

It's in the Axle section of my manual, not in the lubrication or fluid section.
 
Koots said:
Sorry to threadjack, but I haven't seen your name pop up in forever, since you left or were banned from FSC!

How've ya been?
Click to expand...

Not banned. :D When I made a few tongue-in-cheek comments about things that could be improved on the site, I got a very snotty "You sure complain a lot about something you get for free" comment by the admins. When I considered that my answer to question ratio on most forums (and particularly FSC) is about a bazillion to one (meaning free help that others got, which is a contribution to a site that I sure as heck didn't get paid for), I decided they didn't need any more free help from me so I don't participate there anymore. :D I thought it was just pretty sorry of the admins to take that attitude with me when the overwhelming number of my posts are helping other people, not on there asking for help, or in their minds - "getting something for free."

Brooklyn Tow said:
So how do I know if I have a DANA rear axle?

My RPO code is GK9 - Rear Axle - 4.63 Ratio
Click to expand...

Just by year model, it's the Dana 80. All the 1991-2002 GMT4xx series 3500HD's used the Dana 80, except for a very rare few early ones that came with a Rockwell axle which is visibly very different, has a round housing. Now your truck being from up North, it may be hard to tell because of rust/scale on the housing but the Dana 80, as many Dana housings are marked this way, will have the 80 cast into the center section - and also has a long number either stamped into an axle tube (other models have it on a tag) that is the BOM number which can be used to look up the exact specs (and even year/model application) of the axle in Dana's catalog. (google search X510 dash 9 dot PDF - change the "dash" to a "-" and the "dot" to a ".", I didn't want to spell it out exactly and cause a false search hit for others)

Also the 4.63 ratio (as well as a 5.13) would be a Dana 80 giveaway as the 14 bolt full floater used in the 1 ton trucks didn't come in those ratios, not that you'd see the 14FF in an HD anyway.

Appearance is yet another giveaway as the Dana 80 has a unique look. Maybe not the best pic but here's the Dana 80 in my old '94:

35hd_172s.jpg


Richard
 
Well that thing is gonna have too get drained and refilled with synthetic.

Last summer my pinion seal needed to be changed (There was a plastic bag that got caught on the axle and worked it's way into the seal)

So I have no idea if they Changed/refilled and or what they used.

Thanks for the info Richard
 
NVW said:
I looked into it Louis and it is the 3500HD with a DANA rear axle.

It recommends 3500 mile oil change intervals with regular 75-90 oil, with 75-140 synthetic oil the change interval is 30,000 miles.

It's in the Axle section of my manual, not in the lubrication or fluid section.
Click to expand...

It's strange that they even give you the choice.....Who changes rear axle oil every 3500 miles?

Thanks,
Leo
 
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