What type of transmission fluid to use?

Hey guys...doing a drop pan fluid and filter replacement on the 99 transmission, and need to know the type of tranny fluid to use and how many quarts for a simple pan drop fluid change.
What is recommended for the 99 4x4, and what are you guys using? Can I use Mobil 1 Dexron/Mercon, Valvoline Max Life Dex/Merc, or Royal Purple Max ATF? Or is it bad to mix the original Dex/MercIII stuff with the synthetic?
Thanks for the help and advice!

http://www.gmfullsize.com/forum/showthread.php?t=179148

This is how I flushed mine,that way you know what is in there and it is all the same.(this method is super easy).

I've had no problems after a year with an exchange of DexVI....

Trippers99hoe said:

http://www.gmfullsize.com/forum/showthread.php?t=179148

This is how I flushed mine,that way you know what is in there and it is all the same.(this method is super easy).

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HankHill said:

I've had no problems after a year with an exchange of DexVI....

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Thanks guys...but if I just do a pan drop fluid change, can I use the synthetic stuff, or should I stick with the DEX/MERC III fluid?
If I can...any recommendations on what to use and how much will I need?
I just want to be safe about this.
Thanks again.

I been using RP for over 2 years in mine with no problems.

as far as changing the fluid goes iv heard some guys say if its not acting up you dont need to bother changing it, any truth to that?

xanatost said:

I been using RP for over 2 years in mine with no problems.

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Thanks...so thats the MAX ATF kind?

Yukon420SEL said:

as far as changing the fluid goes iv heard some guys say if its not acting up you dont need to bother changing it, any truth to that?

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I'm no transmission expert. However, I would only abide by that if 1) the fluid is a perfect consistency (i.e. a slightly transparent bright red with the normal petroleumish smell), and 2) the tranny has a significant amount of original mileage, like 160k+. The purpose of the transmission fluid is to clean, cool and lubricate. With time, the introduction of small amounts of humidity and thus a certain bit of oxidation, along with the inevitable introduction of metallic particles into the fluid, means that the fluid loses some of all 3 of those properties. Heating and cooling takes its toll too.

Yukon420SEL said:

as far as changing the fluid goes iv heard some guys say if its not acting up you dont need to bother changing it, any truth to that?

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I've heard something similar. They say if it isn't acting up don't change it, then when it acts up they change it to fix it, then when it fails they blame the fluid change.

I think all automatic transmissions fail eventually. If you have close to 190k miles on a transmission and the fluid has not been changed on the recommended maintenance interval, you may hasten your next rebuild because the new slippery fluid will reveal that your friction surfaces are shot and it was the lower lubricity of the old fluid that kept you going.

If you've been changing fluid on schedule (highly unlikely given your question) it's probably safe to continue servicing the transmission. Or, save your money and save up for your rebuild.

So there is truth to your quote, but there is clearly no warranty expressed or implied by the makers.

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You can use either Dexron 3 or Dexron 6. I'd stick with what you have in it already unless you decide to flush it, then I'd go with Dexron 6. Don't go with the cheaper stuff. For example, Valvoline has told me they withhold some of the protective additives from the stuff they don't put in their bottles, hence I refuse to sell my companys private label Dexron 6. Capacity depends on which transmission you have. 4L60 = 5 quarts. 4L80 = 7.7 quarts.