Seeking 8" Posi Suggestions

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11-25-2010, 01:36 PM

#41

67mustang302

6th Gear Member

Join Date: Apr 2007

Location: California

Posts: 10,468

Quote:

Originally Posted by phutch11

67Mustang302 - You think the same way I do. Can you imagine that rear chunk with some fiberglass leaf springs. Probably lose 50-75 lbs of unsprung weight.

Nasty.

Which helps a lot to have better wheel rate in a leaf setup.

11-25-2010, 01:47 PM

#42

67mustang302

6th Gear Member

Join Date: Apr 2007

Location: California

Posts: 10,468

Quote:

Originally Posted by frdnut

If the 9 inch 28 spline axle rear end is no stronger than an 8 inch why would ford have made any?....I am not disagreeing that the 28 spline axles are a weak point but I do disagree that the two rear ends would fail at the same power level...The torque steer thing I think is more common with a spool type setup where one axle is locked and full power is constant regardless of what the other side is doing..

Because you actually have it backwards. Ford originally had the 9" rear, and developed the 8" later on. They realized there was no point in putting a larger, heavier, more expensive rear end in a car when they could get the same job done with a smaller, lighter, cheaper rear that had the same approximate strength.

The 8" suffers from a weaker pinion support setup, because it was a smaller, lighter case. So in the 8 you might break the axles, might break the carrier guts, or you might break the 3rd member case itself. In the 9 you're not going to break the pinion support, so it's either the carrier guts or axles.

That's why if you look at most of the 9" rears that grenade, they're usually 28s differential type units, and they break axles or the carrier guts.

Now, a 31s 9" rear with an upgunned carrier is substantially stronger than an 8". If you ran an 8" with a stock 3rd case, but forged axles and a heavy carrier unit....launch it on slicks and it's almost a guarantee you'll spit the pinion gear right out the front of the case. Especially with a heavy clutch.