So, i recently changed my transmission oil a few days ago and replaced it with redline heavy shockproof oil, what i always used to use when i owned an 240sx with an sr20det. i have been reading other threads with discussion about how gl-5 gear oil can ruin the brass syncros in the tranny, but i have always used it with great results in the sr20 transmission, which also has brass syncros. and i put about 50k miles on the sr20 with the heavy shockproof oil. i emailed redline to ask if the oil contains any sulphur that will damage the syncros, but i am curious to see what you all have to say.

 

It's the wrong fluid. If you want to use Redline, try one of their manual transmission fluids (MTL or MT-90).

 

The heavy duty was way to thick in my eclipse tranny... Even when just using a small amount

 

heavy shockproof will work but its a little much for these transmissions.

I have used light weight shock proof with good results.

 

If it's heavy, didn't you take significant hit on mileage?