I have just completed a ratio swap on my GV and thought I would share my findings.
To stat with my car is a manual 99 GV that had 4.3 ratio diff gears and I have swapped them with the gears from a 99 Automatic GV. This has given me roughly a 13% reduction of gearing.
Front
No issues. The crown wheel and pinion swapped straight over as expected.
Installed a CV support from Bruce while I was at it.
Rear
For starters if you are planning on doing this swap make sure you get the complete rear carrier assembly(third member) i will explain why.
Get this whole bit
The inside diameter of the crown wheel is 10mm larger from the 4.3 to the 4.8. With the 4.8 having the larger ID. The 4.3 is on the left and 4.8 right.
So this means you cannot use the 4.3 diff case with the 4.8 gears.
The 4.3 Carrier assembly(third member) has a difference too.
The gear end pinion bearing cup is machined 4mm deeper into the 4.3 housing to allow for the taller height of the 4.3 pinion gear. This also means that the crush spacer for the 4.3 is different as the distance between the bearings is 4mm closer. The 4.8 uses the same spacer as the front where as the 4.3 has it's own rear specific spacer. The pink arrow shows the location of what I am talking about.
So overall it would have been easier to just change the complete thing but it was good to find out exactly why you can't so others can learn. Hope it helps.
Cheers
Greg
