Rear End upgrade

geostang351

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Mar 30, 2005

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Danb., CT

Dec 17, 2006

#1

• Dec 17, 2006

• #1

I currently have a 68 coupe wit AOD transmission and rear end with 3.00 open rear. I want to upgrade the rear to a traction loc. My question is should I go to 3.80 gears or 4.11 gears?

THis car has never and probably will never see the track (no tracks near here), just weekend cruising. What are your thoughts and ideas. :SNSign:

 

red65

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Apr 12, 2003

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Ann Arbor, MI

Dec 17, 2006

#2

• Dec 17, 2006

• #2

I've found 3.55 gears to be in about the right range on my '65 (blown 306 with a T-5). RPM at 75mph (with a 0.83 OD gear in the T-5 - higher than stock and probably higher than your AOD??) is about 2,700RPM and first gear is still usable. A numerically-higher ratio, like the 4.11 gears you're thinking of, would make the RPM rise through first gear so fast that it's hardly worth using it. Hope that helps.

 

geostang351

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Mar 30, 2005

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Danb., CT

Dec 17, 2006

#3

• Dec 17, 2006

• #3

red65 said:

I've found 3.55 gears to be in about the right range on my '65 (blown 306 with a T-5). RPM at 75mph (with a 0.83 OD gear in the T-5 - higher than stock and probably higher than your AOD??) is about 2,700RPM and first gear is still usable. A numerically-higher ratio, like the 4.11 gears you're thinking of, would make the RPM rise through first gear so fast that it's hardly worth using it. Hope that helps.

Click to expand...

Moving from 3.00 to 3.55 gears seems a waste. I'm not looking for fuel economy just some much needed pep. My AOD 4th gear I believe is somewhere around 0.68.

 

D

danny clemens

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May 4, 2005

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Dec 17, 2006

#4

• Dec 17, 2006

• #4

A lot of the new vehicles have 3.73 gears. They seem to work well in most vehicles that I've driven. I've never driven an older vehicle with an OD so I don't know how they would react to the gears. I would go with the 3.80's if it were me. It would be low enough for good take offs and high enough in the OD for good fuel milage and cruising.

 

rbohm

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Apr 12, 2002

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tucson,az

Dec 17, 2006

#5

• Dec 17, 2006

• #5

geostang351 said:

Moving from 3.00 to 3.55 gears seems a waste. I'm not looking for fuel economy just some much needed pep. My AOD 4th gear I believe is somewhere around 0.68.

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since you think going from 3.00 to 3.55 is a waste of time, in would go with a 3.89 gear.

 

67Dylan

New Member

May 11, 2006

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Phoenix, AZ

Dec 17, 2006

#6

• Dec 17, 2006

• #6

rbohm said:

since you think going from 3.00 to 3.55 is a waste of time, in would go with a 3.89 gear.

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I had an AOD equiped stang and would go nothing less than 4.10/.11's's, especially if you want pep. IMO 3.55's are nice, but nowhere near what the 4.10's/.11's will give you for 'pep'.

 

6

66forfun

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Feb 25, 2006

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Pittsburgh

Dec 17, 2006

#7

• Dec 17, 2006

• #7

I went 3.80 and auburn pro posi. need to wait till insurance is back on for a test drive. All the late model crowd seems to lean toward 4.11 for the aod unless huffing, then they like less gear. mine will see road trips and if its not enough gear for around town i will add more power.

 

Edbert

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Jul 13, 2002

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Austin TX

Dec 17, 2006

#8

• Dec 17, 2006

• #8

The 3.55s are about right for the C4/C6/Toploader guys, but for those with overdrive I'd say 3.73 is the lowest you want, and 4.11 is about the limit for "normal" use unless you just wanna bypass 1st a lot. I put 3.89s behind my AOD.

Once thing you did not mention is what size tires you have, they can have a mjor effect on final gear ratio. You might also find this simple chart helpful...http://www.edbert.net/rpm_chart.htm

 

geostang351

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Mar 30, 2005

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Danb., CT

Dec 17, 2006

#9

• Dec 17, 2006

• #9

Edbert said:

The 3.55s are about right for the C4/C6/Toploader guys, but for those with overdrive I'd say 3.73 is the lowest you want, and 4.11 is about the limit for "normal" use unless you just wanna bypass 1st a lot. I put 3.89s behind my AOD.

Once thing you did not mention is what size tires you have, they can have a mjor effect on final gear ratio. You might also find this simple chart helpful...http://www.edbert.net/rpm_chart.htm

Click to expand...

My tire size is 225 60 15 (tire height I don't know how to figure). Right now I'm 80% leaning toward the 4.11's

 

Edbert

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#10

• Dec 17, 2006

• #10

Just measure them with a yardstick...LOL....really

 

ultrastang

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Feb 26, 2002

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Dec 17, 2006

#11

• Dec 17, 2006

• #11

http://www.ultrastang.com/Rearinfo.asp?Page_ID=3

 

F

Fang

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Jan 28, 2002

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Dec 28, 2006

#12

• Dec 28, 2006

• #12

Dude, don't go 4.11 in an older pushrod car. That's too much gear for a street car. Those gears are for an overhead cammer like my '99 cobra that likes to wind up. There is a HUGE difference between 3.00 and 3.55, definitely not a waste of time. Go 3.80 absolute max.

 

G

gsxrken

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Sep 12, 2005

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Weschester County, NY

Dec 28, 2006

#13

• Dec 28, 2006

• #13

I'd say go with either the 3.73 or the 3.90, depending on which way you want to err on.
4.11s get old after awhile (you're not ALWAYS blasting from a stop), and I agree you will find the 3.5s just a little too tall with the overdrive. You may find your cam doesn't like to lug at 2000 RPM on the highway.

 

ga289stocker

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May 23, 2006

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Sugar Hill, Ga

Dec 28, 2006

#14

• Dec 28, 2006

• #14

You'd be fine w/ 3.80's or better w/ the AOD, I switchfrom 3.55 open to3.80 trak loc and I have a 4sp. My rpms at 60 only went up about 200. I have 25" street tires, I will say if I were not racing the car I probably would have stayed w/ the 3.55's for the street, I did pick up 2/10's w/ added gearing though at the track and really like laying a nice posi patch from time to time on the street.

 

S-Car-Go

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Mar 25, 2003

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San Jose, CA

Dec 28, 2006

#15

• Dec 28, 2006

• #15

Edbert hit the nail on the head! You have to look at the gearing of the whole drivetrain. What is you first gear? What is your tire diameter? THEN figure what RPM you want at your freeway cruise. Only then will you get your rear nend ratio.

Example: I have a T5 with a 3.35 first gear and 3.40 gears. This is about the same as a T5Z with a 2.95 first gear and 3.80 rear end gears. .. Same thing just that 3.40 doesn't sound as cool as 3.80.

Tire size. My 68 with 3.40 gears and 25" tires has MORE RPM's at 75 mph than my 94 with 3.73 gears and 27.5" tall tires.

Most people would automaticly think the other way, but as Edbert said, tire size plays into it. 3.00 to 3.55 doesn't sound like much But.. Check your numbers.
3.00 x first gear = were you are now. 3.55 x first gear is a much bigger number. I don't know what gear you should have, but don't get caught up in the sound of what gear you should have. You'll get the biggest increase in first and second and the least in fourth.

 

ultrastang

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Dec 28, 2006

#16

• Dec 28, 2006

• #16

Comparrison of RPMs with varying ratios, tire heights, with and without overdrive transmissions;

http://www.ultrastang.com/Rearinfo.asp?Page_ID=3

 

67Dylan

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May 11, 2006

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Phoenix, AZ

Dec 28, 2006

#17

• Dec 28, 2006

• #17

W/the tire size you have I'd say you're in the neighborhood of 25.5" tall tires. You can now use ultrastangs link to help you figure RPM @ 60mph. I usually say 'don't fear the gear', but you want a weekend cruiser so maybe opt for less than the 4.11's, but more than the 3.55's.