I've read many posts on the best lube for this trans but have a few questions. I had it rebuilt and the rebuilder recommended 10/40 engine oil stating it would lubricate better than atf. I used it but it was very notchy and difficult to shift in the morning with temps around 35 F. I drained it to get rid of the initial break-in material and put dex3-mercon in. It shifts better in the am but is still notchy. Trans otherwise is fine without any unusual noises.
Before wasting money on other fluids what's the consensus on pennzoil or valvoline synchromesh or redline mtl? Thanks

 

I put Napa Dexron-Mercon 3 in my '96 M5OD. I couldn't tell what kind of fluid was in it before, since I've only owned it two years. I will say that new fluid made a significant difference in shifting. It feels slicker for sure.

I've heard Redline is the best. FTE member SideWinder4.9l said in one thread that the syncromesh is the best, if you're willing to spend the money. I can't back that up, myself, and I'm hesitant to use anything other than what's recommended.

We'll see what others say when they chime in.

Paul

 

I would put the 10w40 back in and go to the trans guy. Have him drive and say WTF. Either YOUR rebuild is bad OR it has the wrong fluid in it(leave out how you put ATF in it) and see what he says. If he says ATF, put ATF in it and tell him his rebuild is bad and you want your money back. They are NOT notchy transmissions. he must have done something wrong, you do NOT need snake oils is a FRESHLY rebuilt trans

 

Diesel_Brad has the right idea. You can tell him that you read that it should have Dexron-Mercon 3 or better in it, but definitely don't tell him you put different fluid in it. Your transmission should last a very long time IF they rebuilt it the right way. You could even say you drove a friend's truck that's basically the same as yours, and it shifted better (even if that isn't what really happened).

Good luck and post back when you have more information.

 

I put schaeffers synthetic atf in it and it made a significant improvement. If it continues to shift like this I have no complaints.