1964 Impala rear end swap - Impala Tech
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post #1 of 3 (permalink) Old 05-25-2020, 02:04 AM Thread Starter
Join Date: May 2020
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1964 Impala rear end swap

Hello all, i'm looking for information on putting a late model posi rear in my 64' impala. Any suggestions? Thanks.
miketilley is offline  
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post #2 of 3 (permalink) Old 05-25-2020, 07:50 AM
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Location: Coopersville, MI
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No 10 bolt, 12 bolt, or Ford 9" is a direct bolt in unless it has already been modified or is ordered from a company as a direct bolt in. With that said it would help to know why you need a posi-traction rear end? If it is for drag racing and such then yes you need a different rear end. If it is just a want and you are running a fairly standard HP engine in the car then you may just want to look to retrofit your existing rear end into a Posi. Drag racing then I would stay away from the ten bolt. The next question is how much torque and horse power are you going to put into the rear and what kind of transmission are you going to run? If your going over 800 hp then a standard is out of the question unless you go with a Lenko, but if your not doing something as far as tubbing to getting bigger meats on the rear you will never get 800 hp+ to hook with a tire that fits in a standard wheel well. A car 12 bolt and a ford 9" are about the same in strength with a little going to the ford 9", but also the ford 9" steals more power from the wheels due to the location the pinion gear rides on the ring gear. Ford 9" makes gear changes easier and comes standard with bolt in axles, but is slightly more expensive than a good car 12 bolt. 12 bolts can be built with bolt in axles and up to a 35 spline axle. The aftermarket though is flush with Ford 9" upgraded housings that can handle insane amounts of torque and horsepower.

The one rear end that seems to get over looked a lot is the Dana rear end. The housing is heavier, but in a stock housing it has the largest ring gear. They are only slightly more expensive than a 12 bolt to build and can handle brutal amounts of torque and horse power in a stock housing. I'm currently building a Pro Street 63 and am tossed between a 12 bolt and a Dana. Right now I'm only looking for HP numbers around 800 - 1000 which a built 12 bolt can handle, but if I get the bug for going faster the Dana would let me put more torque and horse power to the ground before breaking.

1963 Impala Convertible (Frame off resto-mod in progress)
1963 Impala 2 door hardtop (Pro Street build in progress)
1963 Impala 4 door hardtop (Parts car)
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post #3 of 3 (permalink) Old 05-25-2020, 09:46 AM
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Like you said can't go wrong with a Dana 60 rear end. NHRA made truck rear ends illegal in 1968 but the one loop hole was the Dana 60 because Chrysler used them as the stock rear end behind all of their high horse engines (426 Hemi and 440 max wedge). The rear end in stock trim has 31 spline axles same as the nine bolt: BUT it also offers 33 spline axles and 35 spline axles with a different differential and top of the heap is 45 spline axles that are only used with a spool.

12 bolt has 30 spline axles and the nine bolt in standard trim only 28 splines so the average nine inch is actually weaker than a 12 bolt. Moser also offers a modified side gear Eaton Positrac that accepts 31 spline axles (requires special bearings as well as the modified spur gears). It is the axles that usually break, not the ring and pinion in a Spicer style rear end (if you do you are a poor driver).

In your rear end it is the side gears that break first. If you replace them with modified side gears out of a MOPAR rear end then it becomes a toss up between the ring and pinion breaking due to housing flex or the axles being twisted in two from engine torque.You have to keep in mind that your Salisbury style rear end (a drop out style) was designed in 1939 for a 194 cubic inch six cylinder engine. It was replaced in 1965 with a Spicer rear end because the 348 or 409 engine could break one at will by just dumping the clutch.

Adding a an aftermarket posi to your old rear end will not make it that much stronger but quiet a bit more expensive. Better to put that money into a stronger replacement like an Olds-Pontiac rear out of a 1957-'64 that looks like yours but is four to five times stronger because Olds was the first to get an in line 8 cylinder that was winning races as it was bigger than the Caddy V8. Don Garlit's used one in his Swamp Rat IV dragster back when a 392 cube Hemi nitro motor only made 2,400 horsepower because they limited the nitro content and the volume of fuel. They still smoked their slicks from the start line to the finish line because the slider clutch hadn't been invented yet.

Big Dave
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