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

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

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

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.

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.

The ute diff is not a direct bolt-in for a 120Y. The shock mounting points needs modification and perhaps the hand brake cable.

Ideally you would replace a 120Y diff with another 120Y diff. The 120Y diffs (either kind) are strong lasting for long term A15 torque. The exception is the 1974 120Y diff which is too weak and will eventually break behind an A15.

Being a 120Y it can have either a borg warner diff (Plate on back) or a h150 in Australia as they came with either,The Lift out bolt in Diff centre H series is best.

If it is a borg warner then you will need a whole diff assembly and that means ideally a 1200 Ute complete diff,then you can find either a 3.9 or the more common 3.7 out of either a stanza (3.9) or Bluebird series one (3.7) and all of these are the stronger H165 and desireable for long term A 15 Power.

Try G70 in the diff too. Its designed to quieten both GB and diff

BeeJJ i am in brisbane at the moment and weekend1000 has mentioned he has a 5 speed spare at what seems like a reasonable but i decided i will have to do something with the diff because its just about gone anyway its making horrible grinding noises. I figure this new 4 speed is doing fine so i may as put the money into something that really needs attention.
Thanks for the tip though i will probly give the G70 ago ide like this gbox to last as long as possible.

Thanks ddgonzal atleast i know where and what im looking for now so i can id what gbox i have.

4-speed is perfectly fine, returns better acceleration than a 5-speed and still provides a 150 kph top speed.

A15 gearboxes are the 60-series. They have '60' cast into the right side and are smooth-case boxes.

56A will last behind an A15
56L (early 1200) will break behind an A15, the gears will literally chip off.

56L has no marking.
56A will be cast into the right side.

Early 56A - will last if easily driven



Late 56A 4-speed - super strong.