I would like to rebuild the stock 10 bolt in my 85 Camaro to bulletproof specs and was wondering could I use positrac with an 8.5 ring and pinion? I talked to someone at Moser engineering and they said ALL 10 bolts are junk past 375HP, which sounded a bit off.

The diff in your car is a 7-1/2" 10 bolt. You can't put 8.5" parts in it any more than you can put Ford 9" parts into it. Ford 7-1/2" parts won't fit either.

There are no direct bolt in 8.5" 10 bolt diff housings for a third gen. Closest is the Dana 44 that was once offered directly from GM but good luck trying to find one.

You're stuck with a tiny ring and pinion diff unless you do a lot of fabrication to put some other diff under the car or buy an aftermarket direct bolt in diff such as a 12 bolt, 9" or Dana 60.

I really want to go with a 12 bolt but simply cannot afford the price tag ($2400 for just the rear alone not including brakes or labor!!!).

I want the rear to be able to stand UP TO 400 RWHP. This is gonna be a street 305 so in due time, I am going to be putting some serious work into it. Not saying I will actually hit 400 RWHP just would like the rear to be able to withstand UP TO that amount. What would you suggest?

And please don't tell me that a 305 is weak in to weak to achieve anywhere near those number beacuause while I realize It's not the most favorable engine around, with a little money and determination I'm sure at least 300 - 350 RWHP could be achieved.

Yes some years from now I do plan on slapping a supercharger on it ontop of the N/A mods.

If you can afford to build a high HP engine, the cost of an aftermarket diff is cheap. The entire driveline needs to be upgraded to handle the power produced by the engine.

Run what you currently have. If you manage to break it, then decide if an aftermarket diff is too expensive.

True, but here is the problem with that theory.

I buy one goodie for my car every month. So you see, when I do engine modifcations in intervals, new intake base here, new throttle body there. New heads here, new valvetrain there. All this seems pretty tolerable in moderation. $3500 all at once for a new rear end, suddenly seems not so cheap. I have more important things to worry about right now (getting the car painted and replacing the T-Top stripping and carpetting and rustproofing the floorboards. Car is in good shape, for now...) before I worry about being able to drag the car or get froggy. So while saving up for the rear would certainly be an option, it would take awhile...

Even with my mildly (for now) modded 305 making about 300 - 310 TQ at the flywheel, I know this rear will not hold up if I get froggy with the new torque converter and nitto drag radials getting put on next week. I absolutely hate that feeling when I know I have decent power I could really have a blast with, but I have to baby the whole thing because there is a single weaklink in the driveline that could immobalize the entire car.

As far as the 10 bolt goes, saying that I rebuilt the one in my car to max specs IE 28 spline axles, 3.73 positraction (I still have to do more research on ring and pinion before I can begin to sound like I know aht I'm talking about there) and a TA girdle cover, what could I expect from it?

I pushed a beefed up 10 bolt well into the 11's with over 500HP but no matter what you do to it, it still has a tiny ring and pinion. Street cars have broken the diff while driving on the street and others have made them survive on the dragstrip.

You can build up a 9" in stages. Buy the housing/axle package for around $1000. Slowly pick up a center section with posi/gears etc and brakes until you have a complete diff ready to bolt in. You can even pick up a complete center section from the local junk yard to get it on the road until you find a better gear set or a posi. The 9" housing package can use your factory brakes if you don't want to invest in something better.

If you're dead set on using a 12 bolt then you'll just have to budget for one.

You can spend about $1200 building the 10 bolt that you have now, and then you still have a weak 7.5 10 bolt. You can build the 9 inch a little at a time . The housing and axle package is $890 plus shipping. You can build the center a little at a time if you know how to assemble it and set the back lash, pinion depth and bearing preload. You can get brakes when you have the money and then swap the whole thing into the car when it is finished. You can also build a 12 bolt the same way. I'll have to look up the prices on the 12 bolt housing and axle package, but the complete rear end starts at about $2200.

Don't sink a bunch of money into the engine and then try to be cheap on the rer end. What good is 400 HP if you are sitting by the road with a pudle of gear oil under the back of the car?