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redline88
03-16-2008, 12:33 PM
The car is an '81 TA and i'm changing rearends soon. I want to upgrade my 10 bolt. What are the advantages of a 9" rear vs a 12 bolt rear? My next engine will be in the 500 plus hp range. Mostly street driven and may visit the track about twice a year.

chicane67
03-16-2008, 12:39 PM
Try a search for this one. This topic has been beaten to death.

If it dosent yield any answers to your liking... come back and we'll hash it out all over again, one more time. :smoke:

redline88
03-16-2008, 01:03 PM
yeah kinda figured that.....just wondering if the 12 bolt will hold up over time with close to 6oo ft lbs of torque.

chicane67
03-16-2008, 01:19 PM
If you really question it... it may just be in your best interest to go with a 9".

I think that with your future power levels... I would be thinking 9" just for the options available, as the strength can be built beyond that of most 12bolts.

There have been many threads on this subject, on various sites. For the education you can get out of it, I would check out the numerous threads on LS1tech... as they of all sites have hashed it out more times than all other sites. There is a lot of good information to be had.

ProdigyCustoms
03-16-2008, 02:30 PM
I put 33 spline 12 bolts in 700HP and 800HP applications in NONE drag cars. This is not to say these cars will not be drag raced, but not every weekend either. The tires will break loose before the rear breaks.

We can sell you a Moser 9" or A 12 bolt, they are the same money. Either will work fine.

redline88
03-16-2008, 03:29 PM
ok so it looks like I should be fine ether way.

chicane67
03-16-2008, 03:30 PM
The only problem with that... is that a 33 spline axleshaft creates its own Achilles heel. The carrier bearing journal thickness become too thin and if a chassis hooks up (even once) it becomes the failure point.

Besides, if the peticular axleshaft manufacturer actually used better materials and actually paid attention do simple detail... there would be no use for a 33 spline axleshaft to begin with. I have put 30 spline axleshafts behind chassis' of that same power level (that actually do hook) through more abuse than any "single point cut" 33 spline axleshaft from that same peticular manufacturer.

aonghus
03-17-2008, 07:37 PM
I could be wrong, but I once read here on PT that the Ford 9" has a greater degree of parasitic drivetrain loss due to the offset pinion providing less mechanical advantage between the pinion & ring gear as compared to the 12-bolts more 'straight on' engagement point.

Not to menion, the 12 bolt is generally lighter, unless you build an all aluminum third member, pumpkin with 4130 tubes, can you say $$$.

But! It is generally easier to have a 9" serviced, as the third-member simply drops out of the housing, this is cool especially if you have the dough to swap out different ratio third members.

FWIW I went with a DTS Ford 9" and aluminium Strange center section, I'm sure at my power levels (400-450) I wont be worrying about it for a while.

redline88
03-18-2008, 03:16 AM
Will I be able to use my original brakes with the 9" rear? About how much heavier is the 9" compared to a 12 bolt?

aonghus
03-18-2008, 02:40 PM
No, you will not be able to re-use your original brakes with a 9" However there are a gaggle of aftermarket brake options availble at very reasonable prices.

The weight difference I don't know off hand unfortunately.

funcars
03-18-2008, 04:22 PM
Just the fact that 9" rears are more commonly used for all types of racing from drag racing to oval track to road racing means there are more options to choose from and they can be as bulletproof as you ever need. Just changing a pumpkin is a nice feature too.

shmoov69
03-18-2008, 08:01 PM
I went with a 9" for the only reason to be able to change gears (complete center sections) in about an hour or less.

chicane67
03-20-2008, 07:32 PM
I could be wrong, but I once read here on PT that the Ford 9" has a greater degree of parasitic drivetrain loss due to the offset pinion providing less mechanical advantage between the pinion & ring gear as compared to the 12-bolts more 'straight on' engagement point.

Not to mention, the 12 bolt is generally lighter, unless you build an all aluminum third member, pumpkin with 4130 tubes, can you say $$$.

But! It is generally easier to have a 9" serviced, as the third-member simply drops out of the housing, this is cool especially if you have the dough to swap out different ratio third members.

FWIW I went with a DTS Ford 9" and aluminum Strange center section, I'm sure at my power levels (400-450) I wont be worrying about it for a while.

It's typically... 3%.






You can build a 9" the same as or even a pound or three lighter than a 12bolt... with the right parts selection. And no... it doesn't cost too much more. It can be done for less than $3K... if you do your homework, and pay attention to your parts selection.

Typically... alloy third members are considered a no-no for street use. I for one... don't believe that for the most part. But it does come down to the third member itself. Your typical nodular iron center section weights in at roughly 29-30 pounds. The typical alloy center section comes in at 11-12 pounds. The reason that its not generally recommended to use an alloy center section is a few things, actually. The typical alloy housings don't have the strength that a nodular unit does... and the other big thing is growth and tolerance control.

Since then... "thru-bolt" center sections have come to the front. Over the last few years, alloy blends have come a long way and the new alloy center sections, because of their design, new materials and strengthening... are now even stronger than that of a nodular iron center section. And... it comes in at about half the weight of a nodular center section as well... at 16-17 pounds. So, only about four to five pounds heavier than a standard alloy center section... with the strength greater than nodular. To try and compare apples to apples... the difference between a 9" and a 12bolt (comparably optioned and considered closer to stock) is about 15-18 pounds. 22-25 pounds with HD housing's, nodular center sections and disk brakes.

Next is the cost question. The center sections that I am talking about... are right about $400 for the nodular, $440 for a standard alloy and $575 for the thru-bolt. So its not a huge difference. The high dollar items are the differential itself and axleshafts.