read end ratio
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Senior User
Joined: Jun 2003
Posts: 285
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From: Kannapolis NC
read end ratio
I have an aod in my 56 f100 , the rear end is (?) , But I did what I recently saw in another post and raised one wheel and rotated it 10 times which produce 13.75 revolutions of the pinion gear. Divided by 5 this gives me a ratio of 2.75. Is this the "rear end ratio or as Randyjack said the final ratio or is there a difference? Can someone tell me if this setup is going to result in an acceptable preformance as far as low end and a decent high speed cruise. BTW the truck will have a 351w in it. Thanks guys
Junior User
Joined: Dec 2004
Posts: 83
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From: Cedar Rapids, IA
Ford AOD (not wide ratio) gearing seems to be as follows
2.40, 1.47, 1.00, 0.67
With a rear end of 2.75, the final factor is going to be your wheel&tire diameter
Assuming a diameter of ~28" and a locked up torque converter you will be doing 70MPH (6160 ft/min) at ~1555 RPM (unless I messed up with the calculator somewhere)
BTW: wheel speed would be 844 RPM, driveshaft speed 2321 RPM
You ought to get decent mileage
2.40, 1.47, 1.00, 0.67
With a rear end of 2.75, the final factor is going to be your wheel&tire diameter
Assuming a diameter of ~28" and a locked up torque converter you will be doing 70MPH (6160 ft/min) at ~1555 RPM (unless I messed up with the calculator somewhere)
BTW: wheel speed would be 844 RPM, driveshaft speed 2321 RPM
You ought to get decent mileage
Logistics Pro
Joined: Oct 2002
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From: Valley Center, CA
IMHO, this seems a little tall. The AOD should handle your top end speed. I would think that most people will suggest 3.25 - 3.50 gears. But, I would try it out first and see how you like your take-off speed. Then, after you have driven it a while, change the ratio as necessary. Good luck, Jag
Posting Guru
Joined: Mar 2003
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From: Kansas City area
If you want low end performance you will probably need somewhere between 3.50 to 4.11 and with the AOD you should still get decent hiway rpms. I believe most newer autos run about 2200+/-rpm at 70mph with the AOD.
Fleet Mechanic
Joined: Sep 2002
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From: okla
I am using the original 3.92 rear end in my 53 with AOD/302. It performs well on enthusiastic starts, makes me happy with the 302. On leisurely starts, it seems to shift too early and "bogs". I am thinking 3.25 will be better, and am looking for replacement rear end. Joe
Fleet Mechanic
Joined: Sep 2002
Posts: 1,622
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From: okla
My rear tires are 30" and I am pretty sure that at 75 mph I was turning 1850 rpm. If I get a chance to drive it this week I will write it down. Joe
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Senior User
Joined: Jun 2003
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From: Kannapolis NC
I probably will try it as is but just wondering what is involved in changing this ratio, does it mean a new rear end or can the gears be changed? Thanks for all the good info,Jerry
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Posting Guru
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From: Kansas City area
You just have to change the center section(third member/ pumpkin), but you have to make sure your new third member takes the same axle spline as your current rearend. They are either 28 or 31 spline.
Hotshot
Joined: Oct 2004
Posts: 15,882
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From: Durham NC
You can just change the ring and pinion gear set in the center section, but you'll need someone who knows how to set the proper lash. Fortunately with all the racers running Ford 9" rears there's probably someone local with experience. Check at the closest speed shop or circle track. The popularity of the 9" also means you have one of the largest selections of ratios at reasonable prices available from high 1's to high 6's.
What's right for you is like asking what color should you paint your truck. What engine mods if any, what size tires, how much load you going to carry. Do you want to smoke the tires from gas station to gas station or are you going cross country interstate cruisin? Etc. etc etc.
What's right for you is like asking what color should you paint your truck. What engine mods if any, what size tires, how much load you going to carry. Do you want to smoke the tires from gas station to gas station or are you going cross country interstate cruisin? Etc. etc etc.
Last edited by AXracer; Aug 15, 2005 at 10:54 PM.
Logistics Pro
Joined: Oct 2002
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From: Valley Center, CA
I had a set of 3.50s in my 9" when I got it. I'm running a c-4, so the engine rpms were high on the freeway. Daryl sold me a good set of 3.00s for cheap ($25). I had them installed by the local rearend guru as I was not sure that I could get the proper setting. It runs great on the freeway and will still burn the tiresmam little on takeoff. 
Jag
Jag
Postmaster
Joined: Jun 2004
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From: Riverside, So Cal
Jerry -
Try this website. It lets you change ratios, etc to find out what rpm you'll be running. Use 0.67:1 as the final drive ratio of the AOD, then plug in the various rear end ratios, tire size.
Might answer your questions...kinda cool.
http://www.car-videos.com/tools/speedrpm.asp
Try this website. It lets you change ratios, etc to find out what rpm you'll be running. Use 0.67:1 as the final drive ratio of the AOD, then plug in the various rear end ratios, tire size.
Might answer your questions...kinda cool.
http://www.car-videos.com/tools/speedrpm.asp