My 2nd cousin does brackets with a 54 Chevy coupe and a 406ci motor...he's a very knowledgable guy when it comes to differentials (he worked on them for his career). All he will EVER run is a 8.5, no 12-bolts, no Ford 9". He just runs a spool, Moser axles, and US gear ring and pinion. If they'll hold up in his car, they'll hold up in most others.
Why spend much more when you could put that dough to something else (like me!)?
The 8.5 should be plenty good for you. The 12 bolt is a little stronger, but the 8.5 can be built almost as strong. If you are going to build a 12 bolt or a 8.5, the cost would be the same, other than the cost of the core.
'69 RS/SS396 pro street
High Performance Drive Train Parts And Service www.lubedealer.com/biggearhead
Most of all the 67-69 platforms came with an 8.2' 10 bolt. 8.5 are not all that plentiful for the narrower F-body. There are very few 8.5's that will fit without modifications.
If I were to compare a Ford 8/9" to a GM 10 or 12 bolt, I would agree. The reason for this, is that the pinion is so much farther off ring gear center line....and that has basic mechanical theroy and application to back it up.
This is the only real change that would add/subtract a measureable amount of 'frictional' loss and its not really a frictional loss its mechanical, (being of a compound/hypoid type gear).
As for a 10 or 12 bolt, the ring and pinion's are on the same centers and are only a 1/4" different in diameter, not to mention that the surface contact aera on the two are almost the same. As for weight, the 10 bolt is a little lighter but only by a few pounds. So its not that much of a factor...
The weight is a factor, but really only if you run the times I mentioned earlier.
Some people gun-drill their axles for this very reason. The weight savings is small, but every ounce reduced in rotating mass is important when you run quick ETs.
Like I said before, in a street vehicle, it doesn't make a difference. I'm just trying
to cover all bases...
As far as ease to find one, yes it will be difficult to find a 8.5 or 8.875 that will fit w/o any modifications. You have to expect to do SOME modifications if you want to go cheap...either shorten the axle tubes, or weld on new spring pearches. Either of which is not a big deal.
A forum community dedicated to 1st generation Chevy Camaros owners and enthusiasts. Come join the discussion about performance, builds, restoration, modifications, classifieds, troubleshooting, reviews, and more!