Eventually I'm going to need to replace my 10 bolt for obvious reasons. There are plenty of companies making bolt-in 12 bolts and bolt-in 9" rears for our cars. The 12 bolts are available with the c-clip eliminators for about the same price as the 9", so price becomes a non issue in comparison. Here's what I've heard so far:

1. 9" has a less than ideal pinion angle which can suck up 1 or 2 mpg & a little horsepower.
2. 12 bolt seems to be notorious for leaks at the end of the axles.

So... on a semi-daily driven car that's going to make a few trips to the track a year, what would you choose and why? What are some other pros/cons that I'm not aware of?

 

Heavy duty axles, 31, 35 or 40 spline, are cheaper for the 9". There are more gear ratios available for the 9" and they all fit the same carrier.

Since price is about the same , it's up to you as to what you want under the car. The 9" is a better diff but the 12 bolt has better gears.

 

Since you guys have access to unlimited parts and options, the 12 bolt V 9inch is no problem. i would use the 9 inch as the whole thing is easier to work on,, if you want to go racing,just pull the axles,drop the prop shaft ,,undo the center,pull it out,and drop in a spare unit ,,, 4.1:1 or whatever,,,it takes 45 minutes,,,by yourself,,,,,or if you are going interstate,drop in an old galaxy 2.73:1 unit,,,,and get 20+mpg at good cruising speed, the 9 inch is indestructable as many early funny cars and dragsters,up till the late 70,s were using old 59 fairlane rearends, with the big axles,, with little or no mods,except gear ratios,,,the 12 bolt is great if you just want to put it in and drive it ,and be happy with the ratio,,and try and make it suite all driving aplications,,, ALSO remember tire height can be changed,if the exact ratio is unavailable,,,,, steve in Australia