[loggerhead]

Street driven 1976 Trans Am. Up to but never intending (and I mean never)
to exceed 600HP. 5-Speed TKO600. May not ever see the track. I am considering the following:

1) GM 12 Bolt
2) Ford 9"
3) Dana 60

Which ever one I choose, it will be from a company such as Moser, Strange,
or Currie. Other words, these rears should be stronger than stock.
I am leaning towards the 12 Bolt but what do you guys think? Ratio will be 3.73 if that makes a difference.

Thanks,
David

P.s.---I do not care about being able to swap gear ratios. (i.e. Ford 9")

[WDCreech]

As far as strength goes, you have them listed in order of the least, of the three, to the strongest. A Moser 12 bolt will be plenty strong for your application, but if you want the covenience of gear changability, the 9" would be the best. The Dana 60 is almost inistructable, but it is the heaviest.

[Billy177]

the 9 inch is stronger and cheaper then the 12 bolt

[Karch]

Originally Posted by Billy177

the 9 inch is stronger and cheaper then the 12 bolt

Is the 9" cheaper than the others when purchased as a new package?

[HWYSTR455]

Keep in mind rear brake options when choosing, since some only work with certain axle flanges. You can have Ford big bearing ends put on the 12 bolt and avoid the need for c-clip eliminators. That obviously requires you to use brakes (brackets) for Ford rears, but there's a big selection, so no worries. Check too about using c-clip eliminators, because most rear disc kits won't work with them.

I've seen where when using some 9" housing that the rear sway bar may make contact. Think this is less of an issue these day with the new stampings, etc. Think there's more of a chance with a 60.

When selecting perches, use single leaf perches, and eliminate the upper pad. (Or the pads all together). This avoids any unwanted movement, and no, does not make for a noticeably harsher ride.

Keep in mind, never say never! Who knows, in 5 years you might get a bug and want to throw slicks on it, or even street stickies. That, with a mild shot of N2O, and 600hp you've past. If your going through it, for a couple extra, the added insurance is more than worth it.

12 bolt is fine, and so is the 9. Both are about the same money, maybe like a $250 diff, depending on your options. One thing to keep in mind is that there are more ratios available for the 12 bolt, and you can get closer to your target for shift points/RPM. 373 is fine, but might make 1st kind of worthless. It your running a 455 or bigger, you may want to go to a 323-342. The closer you go to the 300 mark, the bigger dip your going to have on the 4-5 shift, depending on your OD (64/82). If you don't have the torque, you may find yourself downshifting on steep grades. (Or detonating). Your displacement & cam selection should help you chose as well....

[HWYSTR455]

Another thing I should add is that the differential selection is different too. If your driving on the street mostly, forget the locker in the 9". I say the Truetrac is the way to go, then the Auburn Pro....

The only 'real' benefit I've found over the years of the 9 as compared to the 12 is that you can rebuild the rear leaving the housing in the car. Sure, you can TAKE your car somewhere to have it done (rebuild rear), but you have to leave the car. Of course they have to test drive it after! Yeah, you can do it at home on stands in the garage, but convince me doing a crush sleeve on your back is fun? (Yes I know there's alternatives)....

[Billy177]

yes if I recall ordering both from moser the 9 inch is around a few hundred dollars cheaper

[mrtonegto]

Actually you can put Ford type weld-on ends on a 12 bolt that have the original 12 bolt pattern. I have them on mine and run Caddy discs.
Got mine from Tom's Differentials.