# When to switch from conventional to synthetic ATF



## russ130 (Oct 29, 2002)

I rebuilt my tranny which is a th350 and has about 30k mi on it since rebuild. I have run regular ATF since the rebuild but I am considering switching to synthetic ATF when I change the filter in the next day or so. At 30k mi would the tranny be considered broken in enough to switch to synthetic? Are there any issues with the currently available synthetics like there was with the first synthetic oils? Is there any reason not to switch my tranny over to synthetic?


----------



## mnglocker (Dec 24, 2008)

30k sounds plenty broke in to me. 

I'm switching both my dodge's trannies to synthetic ATF+4 when they hit 6K on the fresh rebuild.


----------



## KSikkema (Oct 7, 2008)

transmissions should not require a break-in period the same way as engines do. that's part of the difference between engine oil and transmission fluid. synthetic oil too soon in an engine may cause the rings to not seat properly, transmissions should not have the same break in period. it should definately be okay to make the switch

mnglocker:

if your dodge transmissions require ATF+4 i am really suprised that anyone would even run the transmission with anything but that or equivalent synthetic, recently rebuilt or not. Chrysler has many special additives in ATF+4 that are absolutely required in their transmissions otherwise you will experience shift quality problems. I would not dream of running regular atf in dodge trannies.


----------



## mnglocker (Dec 24, 2008)

KSikkema;761074 said:


> mnglocker:
> 
> if your dodge transmissions require ATF+4 i am really suprised that anyone would even run the transmission with anything but that or equivalent synthetic, recently rebuilt or not. Chrysler has many special additives in ATF+4 that are absolutely required in their transmissions otherwise you will experience shift quality problems. I would not dream of running regular atf in dodge trannies.


When Daimler first released ATF+4 it was a conventional mineral based oil, now it's full synthetic.

Both of my trucks have 46RE's in them, both call for ATF+3 (no longer available as it is superceded by ATF+4) Napa branded ATF+4 is still available as a mineral based oil. That's what my trucks are filled with for the initial 6k, after that, the pans will be dropped, fillters changed and trannies refilled with sythetic base stock ATF+4.  :ubergeek:


----------



## SNOWPIMP (Dec 28, 2003)

I've got 3 auto's (no synthetic) in my ford powerstrokes and three with sticks. I gross sometimes 35,000lbs plus pulling the goosenecks. I can honestly say I've never even changed them my lowest mileage truck just turned 300,000 last week. Is this a chevy/dodge problem cause I haven't lost a trans yet (knocks on wood). I did do a clutch in my 3/4 ton at 375,000 miles But that was because I was making more power than the factory clutch would hold!


----------

