Gearbox oil

[Kendo]

Ouch. Thanks for the warning. I was thinking more of running the new oil for N miles, then drain and refill. With synthetic that could get expensive.

[jbcollier]

Drive the car to get the transaxle oil warm.  Let it drain for an hour or two and then refill.  You'll be good.

Different oils can "leak" at different rates.  Monitor your oil level for a while to get an idea of what's up.

[Cheguava]

This is an old topic, but there is much useful info in it. I am planning to drain and refill my 336 gearbox, and have previously used Castrol Transmax Manual Multivehicle 75w-90 (under its former name of Syntrans 75w-90) in a Midget 1500 (Morris Marina) box, as that had yellow metal internals and a horrible gear change which the Castrol oil sorted out remarkably.  If I've understood the preceding posts correctly, despite the transaxle sharing fluid with the gearbox, the correct oil is still a gear oil, and Although Castrol say their modern equivalent is Transmax Manual EP80w, that's mineral based, and I was impressed by the effect the synthetic version had on the gearchange.

Is RedLine still the go to? Or are other oils being used? UK available oil particularly welcome. 

[cazman]

I posted this in another thread a while ago:

"I tried the Amsoil this summer and thought that my 5 speed shifted more harshly. Whatever was in there before was smoother. After reading a bunch of threads I ordered the Castrol Manual EP 80W Gear Oil. Seems to be the closest to spec, but not sold in the US. I ordered from DemonTweeks."

The Castrol worked well, so I am going to stick with it.

[TurboFource]

Redline is magic as far as I am concerned, we had a Jeep XJ that would not shift from first to second with out grinding and Redline changed that.

[BDA]

Is RedLine still the go to? Or are other oils being used? UK available oil particularly welcome. 

When I first got my car on the road, I had a rough 1 - 2 shift. I took my car to a shop I trusted and he swore Red Line would straighten it out. When I was racing and Red Line was new on the scene, I heard a lot of racers say that it was amazing and smoothed out their shifts. So it wasn’t new to me but I was still skeptical. I tried it and it did smooth my shifts! I now use Red Line for motor and tranny oil.

[314159td]

I am...skeptical that Redline is 100% of the improvements people are seeing, I'd wager 30-70% of it is just putting in new fluid.

That said, in the Corvair transaxle (same setup as the Europa with shared oil, and more aggressive final drive hypoid offset) I've regularly switched between StaLube 85w90 GL4 gear oil and redline 75w90NS, consistently noting the fresh redline seems better than the fresh straight gear oil.

[cazman]

If you want to go down a rat hole, join the Subaru boys:

Some have settled on this formula - Scotty's Cocktail

http://forums.nasioc.com/forums/showthread.php?t=920674&highlight=%22Uncle+Scotty%27s%22+cocktail