ziggy89

I have not decided wich direction i want to go with on my 91 Firebird. In the near future i have a engine swap planed however the power i want to put to the rear end will destroy it. So which is better the GM 12 bolt or a ford 9 inch. I know what the 9 inch can hold but i dont know about the 12 bolt.
The only reason i am leaning towards the 12 Bolt is because im hopeing somebody makes a direct bolt in for one but if i fabricate it i will go the the 9 inch i have

Any advice would be helpful, thanks

sofakingdom

iTrader: (1)

They are both available as a somewhat direct bolt-in. The 12-bolt is more nearly direct, but the chassis-specific 9" isn't too far from it.

The main advantages of the 9" are no C-clips, MASSIVE racing aftermarket support, and easier gear changes (you can keep chunks in stock with different gears on them, and do the swap in a half-hour or so).

The main advantages of the 12" are a better fit and somewhat lower losses. You can get it with C-clip eliminators but they're famous for leaking.

Depending on what you're doing that you're just "so sure" you're going to tear up your existing rear, you might want to just run it until it dies, and deal with it then. People with LS1 cars are getting deep into the 12s and 1.7x short times before it becomes a problem, especially with auto trans. Meanwhile, there's things you can do to strengthen your 10-bolt; weld the axle tubes, a girdle cover, better axles.

I would not recommend "fabricating" a 9". Stock ones are a total POS with only a few rare exceptions, little IF ANY better than your 10-bolt. The advantage of the 9" doesn't come from its being some kind of a bulletproof thing from the factory. Rather, it's because it's such a common PLATFORM, for which all manner of aftermarket goodies are available. If you buy a racing 9", odds are there will be NOT ONE SINGLE PART off of a factory 9" in it. EVERY PIECE - center section, housing, bearing support, axles, carrier, and so on - will be aftermarket. You won't get that with some old junkyard POS.

xpndbl3

iTrader: (5)

I went moser 9" with several upgrades. Really nice piece, lighter than a 12 bolt with all the aluminum center section and spool. Not cheap by any means, but it will get the job done and like stated above, not one single piece is off a "factory" type 9".

cooltc2004

iTrader: (4)

May I ask what exceptions in the 9"? Just wondering.

sofakingdom

iTrader: (1)

The ones with the nodular iron center section. Which, since they haven't been made since the 70s sometime, are getting REAL TOUGH to find. Just to put it into perspective, I knew somebody whose truck (about a 71 model ¾ ton) got stolen about 20 years ago, and when they found it, all that was gone was.....

the nodular iron center section.

AlkyIROC

I don't even use a nodular case in my car. The case is just a junkyard C7AW-E. 4.56 gears of unknown brand. A 31 spline Strange spool and 31 spine aftermarket axles. My old 9" had Strange axles. My new narrowed diff has Moser axles.

ziggy89

The moser 9in is what i was looking at in summit and i have seen the abuse my dads takes in his mustang so if it works well and its lighter then thats waht im looking for.

rjt76

I have a 12 bolt moser setup with no c clips or leaks in 12,000 miles. I hope this helps.. by the way the fabrication on this rear end is high quality. well worth the cash in my opion. go with either one you will be happy im sure.

Drac0nic

You can do a 12 bolt with Ford ends as well I believe, I've got a "stock" 9 inch housing under my van; I got 11 inch drums out of it, 31 spline axles (that make a 7.5's axles look like a tooth pick) ford ends so it won't spit an axle out and quick gear changes. Most of all it's not hemmoraging gear lube into the drums. Stock for stock I'd still think a "grey" case would be less of a time bomb then your typical 7.5, even with some minimal mods like a large bearing pinion support. At the very least if you had a stock third member and it fragged you'd have a decent case to upgrade. The big advantages of a new case IMHO is that the tubes are a smaller size, both for weight reasons and getting anything in the 3 1/8th inch tubes is a PITA.

erictheviking

The Moser 9" does use a factory part, the centre of the housing is a used one which is cleaned up with new tubes welded in. At least it is on my car and 1 more I know of. I have a nodular case but might get a strange one, and a Quaife diff. Expensive at $895 but the best you can get for an unbreakable very streetable smooth operating diff. Its a good job its a long term project or the wife would have thrown me out for spending the dough on the car and not the house

Dr. Pepper

That was true a number of years ago. Somewhere around 2000 they ran out of old axles to retube. They switched over to buying new stamped housings to tube. Coincidentally, this is the same time they switched to 3" tubing instead of 3.25" tubing, but both are 0.25" thick instead of the factory 0.188" or thinner. This all doesn't really matter since the "heavy duty" housing used in the later 9" axles is pretty strong and all it seems the new ones are is a reproduction piece. The only difference I have seen in my limited experience is that it looks like the new reproduction pieces can't hold a 3.25" axle tube.

All of this is beyond the needs of a street machine, and a good number of race cars.



I would stay away from the Moser 12 bolt myself. There have been way too many reports of problems with the Moser 12 bolt. The Strange 12 bolt seems to have fewer reports of problems. If there is no need to change gear sets to multi-purpose the car then there is really minimal difference between the 12 bolt and 9". I would recommend the 12 bolt just because it is a GM design and I consider the posi design in the 12 bolt superior.