Why a 9" over a 12 bolt?

[FasstGbody]

Originally Posted by ProdigyCustoms

Which if you ever had a Locker on the street, it is like driving a spool. UGH!

IMO its worse. i used to have a detroit in my dodge, (ramcharger) and it was downright scary. in the rain, wondering when it was going to ratchet in and out of full lock. sold it, got an open carrier and welded it.

[HRBS]

One thing not mentioned here yet is that the pinion or yoke location is "lower" on a 9" than that of a 12bolt. This helps when building a "low" ride height car because you wont have to modify the trans tunnel as much on a 9" than you would on say a 12 bolt. It "hangs" low instead of being located in the center of the ring gear as on a 12 bolt.
I prefer the old skool 12 bolt with 35 spline axles, big ford ends and a girdle cover. But have used both.

[deuce_454]

it makes no difference at all what you choose, the 12 bolt is marginally lighter and has the advantage of the slightly higher pinion and accepting gm brakes.. z06 and "ls1" brakes.. but a fab 9 housing weighs the same, costs the same and 9 inch carriers can be bought to accept both 12 bolt, ford 8.8, 9 and 9,5 inch difs and gears.. and can be spec.'ed to accept both ford and GM brakes, so its a matter of preference...

[chicane]

Lets get rid of some of the mis-conceptions.

1. The newer 12 bolt housings are from the KTRE molds. The center section is made of ductile iron and they use 3.00" dia 4130 tubes. The main cap webbing has been reinforced, they use 1/2" fastners and the main caps are larger to combat cap distortion. The main caps themsleves are constructed of nodular 65-45-12 iron material.

2. The housing ends are not Ford, (although you can special order it with various other housing ends.) The housing ends are GM midsize, offered to fit 58503, 504 or 505 in a sealed bearing cartridge or a 58506 tapered roller bearing. The housings also use either 3.062 or 3.250" bore components.

3. A 35 spline axle in a 12 bolt is a no-no... unless you use a Mark Williams spool with a specific 'high pressure angle'. Not to mention that when you use an axle larger than a 30 or a 33 spline, the carrier journels become so thin that even normal street driving will snap the bearing journels clean off the carrier housing.

4. The difference in pinion height is 0.75", which equates to about 3.5% in efficiency. This higher pinion location in the 12-bolt results in lower gear lubricant temperature, improved fuel economy, and best of all, more power delivered to the ground... and its 30 pounds lighter.

5. A "third member" design differential housing is stronger in many aspects. The most obvious is that it allows the tubes to flex without effecting the carrier bearing pre-load, which in effect opens up the pinion to ring gear mesh. You can even use a 12 bolt third member... in a 9" housing to get the best of both worlds.

6. What the hell is a center chunk ?? Is that like a hogs heads or a pigs snout ??

7. Ratio availability goes to Ford, hands down. As does the simplicity of changing the center section with a different differential device and/or gear ratio. Although, it takes the same amount of time to swap gears in a 9" or a 12 bolt... just having a pre assembled third member makes it a litter eaiser and a-lot less messy.

8. The axle hop is related to a combination of the IC angle, from the pinion angle difference, and the height of the axle tube above the spring. A taller spring perch yields a longer torque arm on the spring itself.

All in all... its a wash. For a heavy car that can actually hook up a-lot of power... a 9" has its advantages. In a moderate weight car that is used on street and track/road course... either. In a lighter chassis with a firmer suspension... a 12 bolt. You can however spend more on a 9" than a 12 bolt in a heartbeat.

[907rs]

As always, VERY good tech, Tom.

[Bowtieracing]

Thank you Chicane for professional input!! Wau!!

[HRBS]

Originally Posted by HRBS

I prefer the old skool 12 bolt with 35 spline axles, big ford ends and a girdle cover. But have used both.

I stand corrected... my Dana 60 has the 35 with a spool and my 12 bolt, 33 with a posi. Both have the Big Ford End upgrade.

[1969Crossram]

Originally Posted by chicane

Lets get rid of some of the mis-conceptions.

1. The newer 12 bolt housings are from the KTRE molds. The center section is made of ductile iron and they use 3.00" dia 4130 tubes. The main cap webbing has been reinforced, they use 1/2" fastners and the main caps are larger to combat cap distortion. The main caps themsleves are constructed of nodular 65-45-12 iron material.

2. The housing ends are not Ford, (although you can special order it with various other housing ends.) The housing ends are GM midsize, offered to fit 58503, 504 or 505 in a sealed bearing cartridge or a 58506 tapered roller bearing. The housings also use either 3.062 or 3.250" bore components.

3. A 35 spline axle in a 12 bolt is a no-no... unless you use a Mark Williams spool with a specific 'high pressure angle'. Not to mention that when you use an axle larger than a 30 or a 33 spline, the carrier journels become so thin that even normal street driving will snap the bearing journels clean off the carrier housing.

4. The difference in pinion height is 0.75", which equates to about 3.5% in efficiency. This higher pinion location in the 12-bolt results in lower gear lubricant temperature, improved fuel economy, and best of all, more power delivered to the ground... and its 30 pounds lighter.

5. A "third member" design differential housing is stronger in many aspects. The most obvious is that it allows the tubes to flex without effecting the carrier bearing pre-load, which in effect opens up the pinion to ring gear mesh. You can even use a 12 bolt third member... in a 9" housing to get the best of both worlds.

6. What the hell is a center chunk ?? Is that like a hogs heads or a pigs snout ??

7. Ratio availability goes to Ford, hands down. As does the simplicity of changing the center section with a different differential device and/or gear ratio. Although, it takes the same amount of time to swap gears in a 9" or a 12 bolt... just having a pre assembled third member makes it a litter eaiser and a-lot less messy.

8. The axle hop is related to a combination of the IC angle, from the pinion angle difference, and the height of the axle tube above the spring. A taller spring perch yields a longer torque arm on the spring itself.

All in all... its a wash. For a heavy car that can actually hook up a-lot of power... a 9" has its advantages. In a moderate weight car that is used on street and track/road course... either. In a lighter chassis with a firmer suspension... a 12 bolt. You can however spend more on a 9" than a 12 bolt in a heartbeat.

No they are not FORD, meaning a ford product. They are however referred to as ford housing ends.

[FasstGbody]

Originally Posted by chicane

6. What the hell is a center chunk ?? Is that like a hogs heads or a pigs snout ??

commonly reffered to as the center chunk, center section, pumpkin, etc. but you allready knew that.

[67rsconvert]

You can also get very good information from Mark Williams. I bought their 12 bolt modular setup for my car and am very happy with it. They walked me through the differences on all the different rears that would work for my car, both strengths and weaknesses.