Quote:
Originally Posted by Ol' Ron
Why the 9"?? Plan on running an LS??The weight of the rear axle determines the ride quality of the Vehicle. Usr a Spicer/Dana 35 from a Grand Cherokee. Very light good foe 300 hp comes with disk brakes/ posi and is very inexpensive as nobody uses them Usr a 49 up stock for trans with OD 3.73 gears in the rear and have a very nice riding car. The only down side is the 5 on 4.5 wheel bolt pattern. Convert the front brakes to disk and there are millions of wheels available to you. When taking on a project as big as this, it pays to plan ahead.
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There's an awful lot that can be said FOR, and AGAINST using a Ford 9" rear end, especially in a street-driven "hot rod", as with this sort of mod, we ain't talking 'STOCK' any more.
No doubt, the 9" axle is likely among the heaviest of the common automotive rears out there. How much heavier is it? The only REAL reason we need to discuss what they weigh is when considering "UNSPRUNG WEIGHT". Hell, the AVERAGE back-yard builder/driver, after considering the different possibilities available for brake types, wheel/tire combinations, spring types and rates, as well as shock types and valving likely couldn't tell the difference between a '40 Ford with a 9", and a similar '40 Ford with a Chevy 12-bolt, or even your Grand Cherokee rear. And one minor side-note about your Grand Cherokee rears....my in-laws' Grand Cherokee and an ex-boss' Grand Cherokee both required dealer rear end replacements not too long after warranty expired because of pinion bearing disasters. Wimpy, ill-engineered, cheap-a*s, little throw-away rear ends. And NOBODY needs disc brakes on the REAR end of a street-driven, 3,200 pound "hot rod"....the FRONTS do the majority of the braking! There is NOT another rear end going today that has MORE selection of rear end ratios than a 9" Ford, and parts can almost be found under nearly any tree in the neighborhood.
But the main thing here is that old idea about the big Ford rear eating horsepower, or is less efficient than other rears. This is an effect that is actually substantiated by the hypoid offset angle of the Ford pinion. The offset on the 9" Ford is 2.250", whereas the offset on a 12-bolt Chevy is only 1.5". The greater offset of the Ford DOES cause more friction because of the increased contact area of ring and pinion teeth. This factor also dictates why the 9" is probably the strongest of all of the stock automotive rears out there. Dyno runs have shown that the Ford 9" lost 2.6% efficiency over the Chevy 12-bolt, both running the same engine turning at 5,800 RPMs when tied to a Ford 9", and then tied to a 12-bolt Chevy rear, both being equipped with similar gear ratios. Does anyone think that the AVERAGE guy can feel that 2.6% difference? I surely doubt that I could! And you can have just about any standard bolt pattern you want besides the stock 4-1/2" pattern. You can get 5-1/2" pattern stock on the old Bronco axles, and I have a 4-3/4" bolt circle on the axles in the '57 Ford 9" in my '40 Coupe. There ain't nothin' wrong with a 9", just like there ain't nothin' wrong with a flathead engine! Our '40 with 9" pictured below! DD
