Changed my tranny fluid the other day, switched from GMSFM to Amsoil Synchromesh MTF. The shift quality has not been as good as the GMSFM.

I just realized that after I swapped fluids I didn't lower the car all the way before reinstalling the fill plug, just enough for the fluid to start pouring out.

I realize that my transmission might like the GMSFM better, but could a slight overfill cause shifting problems? (notchiness, feels rough and doesn't go into gears as easy)

 

A slight overfill should not, a larger overfill could cause the exact symptoms you described.

 

Really? Isn't the more fluid that is in the tranny the better?

 

No

 

I typically overfill my tranny by as much as 200cc on purpose. No biggie. It's not like the engine crankcase where you must worry about the "big end" slamming down onto the surface of the oil and making it foam. The tranny is used to being partially submerged in fluid. Another 1/4" or 1/2" higher level of fluid won't do any harm. I also overfill the rear diff, too.

 

I was around 150-200cc overfilled. Shifting felt slightly easier on the way to work, but it was too short of a drive to really tell if it was actually better or not.

 

I usually "tilt" the car on the side (slightly),to get as much fluid in,as I can (+-200 cc.).

 

The tranny likes a little more fluid.

I like AMSOIL but have not tried it in the tranny since the Honda and GM fluids seem to have a great track record and everything else is not up to par. I'll stick with the proven products and thank you for the feedback.

 

No problem, I love GMSFM but I want to find something that will last a little longer. After 100 miles or so, the amsoil feels a little better but the shift quality is not as good as GMSFM. Better than Honda MTF or Redline MTL though. I'll probably be changing back soon.

 

I overfill and I use Redline MT90.