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Old 01-22-2006, 03:14 PM
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Ford 9" rear axle

I have a 77 Ford short box pick up that originally had a 302 with 4 speed manual trans. When I got it the trans had been switched to a C4. How do I tell what gearing is in the rear. The tag is gone. Do I have to pull it apart. I'm new at this, so any help is appreciated. I also have an 82 Crown Vic with a 351W that I am planning to use parts from. I'm thinking of pulling the body off the truck and put it on the Crown Vic frame. Any thoughts?

Thanks

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Old 01-22-2006, 04:11 PM
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There should be a plate/sticker on the drivers door that will contain the VIN (serial number) paint, trim, trans codes...

Find me the "AXLE" or "AX" (pretty sure that's what it says) code, and I'll decode it for you when I return to work on Monday ... if time permits.

Try these sites as well:
http://www.medicine.wisc.edu/~mrm/bronco/ftvin.cgi
http://www.clubfte.com/users/mil1ion...ruckCodes.html
http://home.comcast.net/~petebre/mav...rear_ends.html
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Old 01-22-2006, 10:41 PM
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Nuts, some one in the past put a different drivers door on the truck, so that's no good. The only thing I know is it's pretty low geared for the transmission, I think, because it seems to be revving pretty high on the highway. I'm planning on using the AOD trans out of the 82 Crown Vic, which how has 2.73 gears (have the tag) I think, so don't mind if the existing axle is kind of low geared. I'm pretty sure the axle in the truck is a 9", going from the shape of the case and the bolts. Any ideas? Thanks for any help.
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Old 01-22-2006, 11:34 PM
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OK...
There are at least a couple of methods that you can use without resorting to tearing the diff carrier out and doing a tooth count. (Doing a tooth count on both the crown and the pinion WILL tell you exactly)

1.) Use wheel chocks or some other method to make sure the truck won't fall on you!
2.) Trans in Neutral, park brake off.
3.) Raise one rear wheel, and set a jackstand under the frame.
4.) Using a tire crayon, make a mark on both the tire and the driveshaft.
5.) Rotate the wheel slowly and count (estimate) the rotations of the driveshaft. 3-1/2 turns would approximate a 3.50:1 ratio.

Based on your "it seems to be revving pretty high on the highway" comment I'd imagine it to be 3.50:1 which is pretty low gearing by today's standards. It was also a pretty popular ratio for 6-bangers and small v8's.

The other method is to calculate the gear ratio by speed/rpm.

You'd have to run the truck thru one of those odometer test sections or otherwise verifiy that the speed displayed on the speedometer is accurate.
You'd also have to have (or install) a tachometer.
Next you'd measure your tire diameter.
Finally... you'd go here to use their handy-dandy calculator.
http://ring-pinion.com/content/calculators/RPM.asp

Just for fun ... I "plugged in" some assumed numbers:
225/70R15 tires = 27.4" OD
3.50:1 gears
Auto trans (not overdrive)

At a speed of 60 MPH, your engine RPM would be 2644.

HTH,
Don

PS.
As far as verifying that it IS a 9" (which I'm quite sure it will be) ...
Check here http://www.kevinstang.com/Ninecase.htm
for some ID methods and other info.

Last edited by 66GMC; 01-22-2006 at 11:47 PM.
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Old 01-23-2006, 08:19 PM
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Thanks for the help! I'm sure the speedos way out, so I'll do the tire and driveshaft count. Eventually I'll have to pull the rear end, because I also need to know if its a worn out posi or not. Unless there's a way to tell from the outside? I do know that I can't get it out of my driveway (short steep uphill) when it's wet (90% of the time in the winter here). Is it difficult/expensive to change it to posi if not? Again, thanks for the help. It's great to finally find a site that isn't just commercials.
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Old 01-24-2006, 06:25 PM
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Rear End

Quote:
Originally Posted by 66GMC
There should be a plate/sticker on the drivers door that will contain the VIN (serial number) paint, trim, trans codes...

Find me the "AXLE" or "AX" (pretty sure that's what it says) code, and I'll decode it for you when I return to work on Monday ... if time permits.

Try these sites as well:
http://www.medicine.wisc.edu/~mrm/bronco/ftvin.cgi
http://www.clubfte.com/users/mil1ion...ruckCodes.html
http://home.comcast.net/~petebre/mav...rear_ends.html
I have a resr end and the plate # is gbx-g1 9" any idear what i have it is supposed to be a granada

oldrod
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