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Old 01-26-2008, 11:06 AM   #1
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Join Date: Jan 2008
Location: florida
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Car: Red T-Top 89 IROCZ
Engine: 400 / punched out 30
Transmission: 700R4 / 3500 stall
Axle/Gears: Ford 9" 390 gears

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Looking for 9" Ford Rear End

Does anyone have a 9" Ford Rear end for sale? Or do you know which Ford car has the best rear end size for the 89 IrocZ?
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Old 01-26-2008, 11:14 AM   #2
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Location: 51N 114W, 3500'
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Transmission: Powerglide
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Re: Looking for 9" Ford Rear End

Because of the third gen's torque arm suspension, there is no Ford factory differential that is a direct bolt in. Unless you plan on changing the rear suspension design, your best bet is to buy an aftermarket 9" designed to be a bolt in for a third gen.

My first junkyard 9" was out of a 1970 F100 but I installed ladder bars to eliminate the torque arm.
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Old 01-26-2008, 11:43 AM   #3
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Car: Red T-Top 89 IROCZ
Engine: 400 / punched out 30
Transmission: 700R4 / 3500 stall
Axle/Gears: Ford 9" 390 gears

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Re: Looking for 9" Ford Rear End

Thanks for getting back, I have a welder and was planning on doing a little welding to make it fit, but was unclear on the best ford axle to get. You think a 1970 F100 would be the best fit??. I have a 405 short block with a new 700r4 trans. what gears do you think will work best.
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Old 01-26-2008, 01:08 PM   #4
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Re: Looking for 9" Ford Rear End

The F100 differential is very close to the same width as a third gen but the pinion isn't centered. It's offset to the passenger side about 2" making both axle shafts the same length. A car diff like from an early Cougar or Mustang is a better choice. You'll also need to change the axles or have the wheel studs redrilled to a more common size. Ford truck bolt pattern is very big. I had aftermarket axles with the Ford 5 on 4-1/2 bolt pattern to easily use a Ford drum brake system. At the time, I was using Weld Draglite rims which have Ford and Chev bolt pattern.

With a 700R4 I wouldn't want anything deeper than about 3.55 gears. The 700's low first gear doesn't need a deep gear in the diff.

There's a lot more to using a junkyard diff than the width. You have to change over all the suspension mounting hardware from a third gen diff to the junkyard diff such as shock and spring mounts and the panhard bar mount. As I've already mentioned, there's no easy way to attach a torque arm. When I installed ladder bars, the front ladder bar mount is inside the car so I had to modify the floor. Then there's the brake system that needs to be addressed including park brake cable if you choose to use a park brake. Wheel bolt patterns since you can't put Chev rims on a Ford bolt pattern. You'll need a combination u-joint to hook up the driveshaft and "may" need a different length driveshaft.

By the time you're done fabricating and modifying, it can be cheaper to just buy an aftermarket bolt in diff.
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Old 01-26-2008, 01:19 PM   #5
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Re: Looking for 9" Ford Rear End

i used the junkyard 9 inch and had all the brackets cut off my 10 bolt and re-welded onto the 9 inch housing. I had it done though so i couldnt really tell you how hard it was, i know the guy that did had a jig built just for doing it, he also narrowed the housing, its slightly shorter than the stock 3rd gen housing. I bought a fully adjustable weld on torque arm mount from some company out of pennyslvania, i would have to look for the name of the place but have pics if you want or need them. I got an adjustable panard bar, and i havent yet ordered my axles thats next on the list. But i am using the ford explorer rear disc brake setup off ebay for 150 bucks.
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Old 01-28-2008, 09:19 PM   #6
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Car: Red T-Top 89 IROCZ
Engine: 400 / punched out 30
Transmission: 700R4 / 3500 stall
Axle/Gears: Ford 9" 390 gears

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Re: Looking for 9" Ford Rear End

Can anyone tell me if a 84 trans. rear end bolt up to my 89 IROCZ and do all the 84 Trans come stock 3,73 and posi.
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Old 01-28-2008, 09:38 PM   #7
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Re: Looking for 9" Ford Rear End

Yes. No. No.
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Old 02-12-2008, 09:51 PM   #8
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Re: Looking for 9" Ford Rear End

there are pictures of that torque arm mount i was talking about on this thread, im selling all my stuff and buying the bolt in housing. I gave up on trying to fab this one up the hard part is done already but i just dont want to mess with welding on the torque arm and trying to get all the angles right.


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