I know for certain its a borg warner diff. Do you think it would be worth having someone rebuild the borg warner dropping the ratio to 3.7 or do the slight modification to fit a diff (stanza or bluebird) just to achieve the lower ratio.

I am going to try the G70 in the diff and gb first and hopefully i will get more life out of both of them but the thought of a correct ratio still lingers ide like to marry up the torque of the A15 with the correct ratio or a more suitable ratio.

G70 -- or any lube -- won't fix a grinding sound. It can reduce a whining sound. To fix grinding, you have to replace parts. It could just be the brake parts rubbing.

I wouldn't rebuild any diff when good used units are only $150 from the wreckers. Too many home rebuilds don't last, and if you pay a true expert to rebuild them it is $$$.

Best ratio for an A15 is 4.11. Nissan fitted 3.70 to them for fuel economy, not because it suited the engine any better. With the A15 they could use 3.70 and still have the same slow acceleration as an A12 with 4.11 gears, but it is not performance-oriented. As a compromise use 3.90.

4.11 was the factory ratio for Japan market B210 Twin Carb A14T. But with A12 only used 3.90.

oh ok thankyou ddzongal and all who have contributed.

I have spent so much time attending to the front end its definetly time to attack the rear so atleast i have a better understanding and idea of how to go about it.

Cheers

go for a 3.545 rear DD can get them and 4 speeds are still common