Skyline GTT (automanual) rear differential oil

[joufher]

Can anyone recommend rear differential oil for '98 Skyline R34 GTT (automanual transmission)? 75w80 or 80w90 or 75w140? What is good for racing or extreme performance.

GTT have LSD? 

Thank you in advance. I live in Sicily, Italy and hard to find real help so I do my research and work on my R34 I use mostly for drag racing and time attack.

[Kinkstaah]

...automanual?

The Auto And Manual Turbo diffs are the same (well they have a VERY slightly different ratio).

They use the same oil, though. At least standard, which is generally considered pretty shit, as people then update the diff to some other center.

Use whatever oil that center wants ?

[joufher]

Automanual, I meant automatic with manual mode. 

[KiwiRS4T]

if you have an open diff or viscous LSD (effectively the same) use any  75W 140

If you have a mechanical LSD use Motul Gear Competition 75W 140

[GTSBoy]

Any good diff oil will do for the standard LSD, which is not a real LSD so does not need LSD oil.

 

edit. Kiwi beat me to the details.

Edited July 30, 2020 by GTSBoy

[joufher]

Thank you. How much differential oil? I use Motul and Royal Purple.

[GTSBoy]

Fill it until it starts to dribble out of the fill point (with the car level, of course).

[joufher]

2 liters should be enough?

[joufher]

1 hour ago, KiwiRS4T said:

if you have an open diff or viscous LSD (effectively the same) use any  75W 140

If you have a mechanical LSD use Motul Gear Competition 75W 140

Is it not effective to use Motul gear competition 75w140 on viscous LSD? 

[Kinkstaah]

It's not that it's not effective, its that LSD specific oil (the competition stuff) has stuff for the clutches in it.

The Viscous LSD has no clutches
The Helical LSD has no clutches
The Open diff has no clutches

Generally stock diffs in skylines aren't very good anymore, (worn out) so people replace them with aftermarket plate style clutches. These need "LSD" diff oil.

[GTSBoy]

Viscous LSD is not a mechanical LSD. The "LSD" part of it is a viscous coupling which is a sealed unit with its own silicone fill fluid inside it. Every mechanical gear part of a VLSD is just the same as a normal diff, so you do not need to use LSD oil in them.

The reason you need to use special oil for mechanical LSDs is that they rely on friction to do their thing. Oils are kinda all about not doing the friction thing. So you need different friction modifiers in LSD oils.

Mechanical LSDs work.

Viscous LSDs do not.

Edited July 31, 2020 by GTSBoy

[joufher]

Thanks all for the info.