Hi !
What is the best oil for the gearbox and diff ???!
Synthetic or Mineral ?
Something like Castrol TAF-X (gearb) or SAF-XJ(diff) ??! Or original SHELL special for Subaru ??!

Thanks in advance :-)

GT555

 

GT555
The synthetic/semi synthetic preference is rather subjective. I have been using full synthetic 75w/90 but have found no benefit in improving the synchromesh performance. Castrol recommend their "Syntrax" for Japanese gearboxes, and I am about to give this a try. Dont forget that the rear differential requires limited slip compatable oil.
Cheers JohnD

 

I'm surprised at that, my MY00 owners manual states that GL5 hypoid oil is recommended for gearbox and diff, the LSD is a viscous type and is sealed for life, not affected by the oil in either.

 

Jim
Re-final drive oil - this was the recommendation of a well known Scooby service shop.
JohnD

 

If you want a really good gearchange theory says that you should use the worst oil you can find.The syncro hubs rely on friction to work so the less slippy the oil the better they work and the nicer the gearchange should be.

On the other hand if you want the best protection then use fully synthetic but in theory the gear change will be more notchy.

My gearbox was very notchy with new oil after its 30K service.

Cue all the people that have found the opposite
I did say it was theory

Andy

 

Andy
I aggree, What is needed is a compromise?
As Castrol Syntrax is recommended for Jap. G/boxes I am looking forward to detecting some (albeit small) difference. Mind you the recommendation might be based on its suitability for the gear tooth profiles favoured by Jap. power transmission designers and not synchromesh design!
JohnD