Which tranny fluid do I need?

[EIB8400]

I am finishing the rebuild on my 4l65E tranny out of my Yukon. I want to use synthetic tranny fluid but, do I need to use regular atf to brake it in or can I just start out with synthetic fluid? How many miles should I put on it before I change the fluid?

 

[Greg Ducato]

You can start with any good synthetic meeting at least Dexron2/Mercon specifications which should be about all of them. No special break in fluid required.

 

[EIB8400]

Thank you .