Fluids in diffs, transfer case, trans 99 'hoe

strad · Aug 3, 2011

I've discovered that my 99, with 115k miles on it, does not have records indicating that the trans fluid has been changed. I know it's due at 100k miles, so I've decided to take on the task. I am unsure which trans I have (4l60e or 4l80e). My truck has the heavy-duty 6800-lb towing package on the window sticker (yes, I did get the window sticker from the original owner-- yay!) and the 5.7 vortec.

Trans fluid is still red, but it does not smell new. I don't think it's in terrible condition but it definitely should be changed.

What fluids and amounts are specified for the front and rear diffs and transfer case, and what is the change interval? And where can I find diy's?

ezdaar · Aug 3, 2011

Heres how to tell diff between the trans by pan shape.

Heres how to with nice big perty pics how to flush trans. You will be advised to have a helper starting and running through the gears while you carefully watch for the bubbles...

If you have drain and fill plugs on Diff's Try this method.

If no fill plugs use this method

You want to change power steering fluid aswell..
Do you have a hydroboost setup? use this method.

Normal PS setup, use the turkey baster method described here

Sorry mods for the offsite links. but its a royal pain in the arse to wade through million posts about these same topics to find the OUR good threads...

strad · Aug 3, 2011

Thank you! I actually did find the specs for the fluids in my owner's manual -- the manual is kinda disorganized and has fluid specs all over the place rather than in one place (like I've gotten used to with other marques). So I didn't find it before the first post in the thread. It looks like my front diff has fill and drain plugs but the back one does not. Not sure about the transfer case. According to the manual the spec there is automatic transfer case fluid (mine is an electric transfer case).

edit: damn. I just counted the bolts on the pan, and mine has 16 bolts. I counted them like 3 times just to be sure. But it does not match the TH2004R example in terms of shape. So what might it be???

SunlitComet · Aug 3, 2011

5.7l has the 4l60e auto or a 5-speed manual 6.5l diesels had the 4l80e.

Unless you have been modded you should have 4l60e tranny and NVG 246-NP8 auto 4wd.

For the tranny use dexron 3

t-case autotrac II GM Part No. 12378508 fluid if auto 4wd other wise dexron 3 if standard e-shift

front case synthetic 75w-90 if auto 4wd otherwise gl-5 80w-90.

rear case gl-5 80w-90

rear case fill plug is on forward half of case. you drain by pulling the cover.

strad · Aug 6, 2011

Okay another question. Started off with the truck level (but transfer case is tilted towards the back of the truck) removed fill plug from tcase, and a significant amount of fluid came out.

Now, I'm used to putting fluid in gearboxes, rear ends etc with vehicle level. But I was thinking (based on the fact that fluid drained out of the fill hole with the truck level) maybe in this case the tcase should be level (back of truck should be raised to accomplish this). I went ahead and filled it this way, until fluid started coming out the fill hole. Is that correct?

Another thing. Fluid that was drained was not autotrack II blue. It was more like dirty dexron. I filled it with autotrack II, which I got by VIN. I have the 4hi, 4lo, 2hi and auto 4wd buttons on the dash. Is autotrack II correct?

Donnie Yukonie · Aug 7, 2011

i dont think ive ever changed the fluid in my transfer case lol i forgot fluid was in there :emotions122:

**** muds probaly the onlything holding it together

SunlitComet · Aug 7, 2011

The center of frame and the body lines should be relatively level even though the drivetrain is tilted back. a degree or 2 won't hurt anything.

There is something to keep in mind here the original autotrac fluid used to be red but the color was changed to light blue to distinguish the differences between the two. Primarily a better friction modifier. autotrac 2 is correct.

gpracer1 · Aug 7, 2011

strad said:
Okay another question. Started off with the truck level (but transfer case is tilted towards the back of the truck) removed fill plug from tcase, and a significant amount of fluid came out.

Now, I'm used to putting fluid in gearboxes, rear ends etc with vehicle level. But I was thinking (based on the fact that fluid drained out of the fill hole with the truck level) maybe in this case the tcase should be level (back of truck should be raised to accomplish this). I went ahead and filled it this way, until fluid started coming out the fill hole. Is that correct?

Another thing. Fluid that was drained was not autotrack II blue. It was more like dirty dexron. I filled it with autotrack II, which I got by VIN. I have the 4hi, 4lo, 2hi and auto 4wd buttons on the dash. Is autotrack II correct?

Are you sure you removed the fill plug and not the drain plug? The fill plug is a MAJOR pain in the ass to get to.
Drain plug is at the lowest point on the back of the tsfer case and the fill is about 5 inches above it right in the frikkin way of the cross member.....stupid ass engineers :emotions122:

I know because I just did the same last week.

Fluids in diffs, transfer case, trans 99 'hoe

strad

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ezdaar

Chat Troll

strad

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SunlitComet

OBS Jedi-Do Good

strad

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Donnie Yukonie

Yates Caretaker

SunlitComet

OBS Jedi-Do Good

gpracer1

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