I need to go ahead and purchase the transmission fluid and diff fluid so I can finish my winter drivetrain project for my 06 MT. I need to know the current belief on what is the best gear oil to use. Is it better to just get OEM fluid, Redline or something else. I need it to be dependable enough to stand up against hard fast runs through the dragon but also leisurely drives to dinner.

 

OEM ftw. I did both on my 03 DB Z with OEM. If you're not tracking/racing that's what I would stick with.

 

Two different fluids- the diff needs high pressure elements that would damage the tranny. For the tranny, I use Redline MT85 in both my street and race Zs. For the diff, I use Valvoline synthetic 75W-90.

 

I went with redline but only have a few miles on my swap...when I searched it almost seemed that people had good and bad experience with every brand...I would imagine that what this thread will turn into.

 

Synthetic GL4 for the trans and GL5 for the diff. Any brand will work fine, I use amsoil.

 

Redline in the trans and royal purple in the diff.

 

OK question about the weight of the oil for the tranny. Dealership says GL-4 in 75-90. The site says GL-4 75-85. Owners manual says I can use either. I live in Tennessee with 100 degree summers and 20 degree winters although car is rarely driven at either extreme. So should I use the GL-4 75-85 or the GL-4 75-90 or does it really just not matter.

 

Five points on the viscocity scale is not going to make much difference, particularly in your climate. If you had to choose, a 75-90W GL4-spec lubricant would make sense.

 

Redline in both. Will never go back to OEM. And I swapped in the fluid when the OEM tranny fluid was under 1k old so I literally went from new to new fluid and IMO Redline blew it away.

My only complaint about Redline is that it takes it takes longer to warm up. But once warmed up the shifts are like butter.

 

I only have experience with the 07-08 manual trannys and other cars, but I've tried quite a few different fluids in hopes of remedying some second gear issues when the the transmission is very cold, sub 32 degrees. So far the best by far has been OEM fluid. The OEM fluid makes going into second when very cold give a slight crunch very rarely. Everything else varied from essentially not even being able to get into second to a harsh crunch every single time I tried to go to second when very cold. For these reasons I've pretty much stopped ****ing around with any aftermarket transmission fluids for any car.

 

Best has been oem for me. Went from OEM to Redline and directly back to OEM.

 

OEM only for me. I tried Redline once, but saw no benefit.

 

Just my observation... I use Royal Purple Max Gear 75W-90 and the tranny is fine once warm but when cold 3rd and 5th grind. This is on a used CD009, my previous CD005 (factory 2003 Touring) ate 3rd gear so I had to do the swap. I'm in FL so "cold" isn't really cold at all. Still its very rough, notchy, stiff (whatever term you want) during the first few miles. Shifts fine after warm up, handles track abuse OK so far but I don't track in the heat of the summer. General option: meh. Might try Redline next.

 

Oem