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View Full Version : 12 bolt or 9 inch. Which do you prefer?



MuscleRodz
11-09-2004, 04:34 PM
I almost hate asking this question but I am now in need of a new rear end for my Camaro. I do not like to crossbreed but at this point I am looking for exerpienced opinions. Which do you prefer and why?

Mike

ballistic69
11-09-2004, 05:18 PM
The Ford 9" is significantly stronger than the 12 bolt

baz67
11-09-2004, 06:23 PM
Kirt is correct but, the 9" is also heavier and has more friction internaly. Both cost HP. I am using a 9" on my car though.
Brian

parsonsj
11-09-2004, 06:35 PM
Nine inch here. (several jokes come to mind ...)

As Kirt and Brian have indicated, the 9 inch is considered to be a bit stronger, but it does cost you a few hp, due to the lower placement of the pinion on the ring gear.

Anyway, if you are starting from scratch, the 9 inch has a lot more aftermarket support, is usually less expensive for a comparable setup, and has more differential and ratio choices.

Good luck with your choice.

jp

ProdigyCustoms
11-09-2004, 07:31 PM
I will be in the minority, but I run a 12 bolt on 900HP, on slicks, with mid 1.30 short times, and ain't broke it in 5 years. This is not the first time trying this as we have others in the camp with similar set ups.
But a 9" is stronger.

73novaguy
11-09-2004, 07:41 PM
I run a Moser Engineering 12 Bolt. I have it behind a 502ci BB. They said it would handle 900 HP. Cost of rear end with Wilwood disc brakes and aluminum girdled rear-end cover was 2600. I think they sell just the rear end for 1800 or so. Just have them install the bigger axle housing ends so you can run the bigger Ford styled bearing. I love it. 3200 RPM trans brake launches with slicks and it is smooth as silk. I also have 33 spline axles and the Pro Gears. But at 1800. I like the GM name on it also!!!! :jump:

TurboLark
11-09-2004, 08:26 PM
Of those 2 choices, i'd use a 9", I want detroit lockers in everything and cant get one for the car 12 bolt. I will be using a dana 60 from Strange for my car though.

MuscleRodz
11-09-2004, 08:26 PM
Does the yoke actually sit lower in the pumkin on a 9". If so that may help due to the lowered stance and raised front subframe from channeling the floor pan.

Mike

parsonsj
11-10-2004, 06:50 AM
Yes, the yoke will be lower on the 9 inch.

jp

TurboLark
11-10-2004, 07:53 AM
Does the yoke actually sit lower in the pumkin on a 9". If so that may help due to the lowered stance and raised front subframe from channeling the floor pan.

Mike
Yup, it's lower. Thats the reason it takes more power to turn the 9".

gmachinz
11-11-2004, 06:10 AM
The Ford 9 inchers have much larger bearings than that of a 12-bolt to aid in absorbing more heat without having the bearing scorched to death but that is also a non-issue anymore if you are planning on using synthetic diff. fluid-so the bigger bearings theory is just more added weight at that this point. Also, info I have from a cirlce track dirt guy who is a master at setting up those cars to handle complains that running a 9" on dirt where you basically go in a circle causes the 9 inchers to break ring gears more often than 12-bolts due to the lower placement of the pinion on the ring gear. If this is an issue on dirt, it's definitely an issue that can come up on a road course. The positive is that on dirt, depending on track choice, it's easy to swap out the center section to swap gears. Dana's suck because you need special load seperating tools to "spread" the case to pull carriers in/out and everyone knows it's a pain trying to set backlash on a 10 or 12-bolt in a hurry, too. I like to set the rear-end up tight using an Auburn carrier, brace it wherever possible and use HD aftermarket axles like Strange or Mark Williams and since I light the weight savings, I prefer 10-bolt GM 8.5 rear diffs. I haven't broke one yet-though I have yet to put 600 or more HP in front of one, too. -Jabin

nancejd
11-11-2004, 05:46 PM
You could always get a hybrid. They make center sections that use 12 bolt GM internals for 9" cases. Easy to change, efficient like a 12 bolt, and about the same weight.

SDMAN
11-12-2004, 06:26 PM
9" here as well. In addition to the large bearings, there are locker units available that allow using 35 spline axles, a big improvement over 28 or 31. It is also very easy to put a full width back brace on a 9" housing.

ProdigyCustoms
11-12-2004, 06:40 PM
The 12 bolt pinion output will be better for you since you rasied everything else. A 9 inch is the ultimate over kill in this situation, and only steal HP. And a back brace is ONLY for show in this enviroment. Just lived this experiment, put a 9 inch with same gears in place of a 12 bolt. Did the 9 inch for ease of swaping chunks on a car that runs motor sometimes, nitrous other times. Slowed it nearly 2/10ths.
If I cannot break my original 69 SS 12 bolt rear, full stock length, no back brace, with a spool and axles, with street gears, on the street and the track, the way I abuse it leaving on the nitrous and dead hooking for years now, you will be just fine with a 12 bolt and retain some HP. And this is not the first time we have done this.

Bill Howell
11-12-2004, 11:53 PM
Even though I just bought a 9 inch for the malibu,I really am hard core gm. My 69 has a 12bolt and has taken alot of abuse(every time I drive it) with no problems. Unless you really plan on alot of hp I'd say the 12 bolt would be fine.

MuscleRodz
11-13-2004, 08:54 AM
Thanks for the replies. I am only planning around 400 rwhp. Should be enough for now. I think I will go ahead and run a 12 bolt still unless I come across a killer deal on a 9inch.

Mike

Autometer
11-23-2004, 09:42 PM
The reason I went with the 9 inch is because it already had large disc brakes and I can swap out with my extra 3rd member.