How do you tell what gears you have in your rear end? - Ford Mustang Forum
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post #1 of 26 (permalink) Old 05-05-2008 Thread Starter
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How do you tell what gears you have in your rear end?

I recently bought my 1992 Mustang LX and it was completly stock with the exception of visible exhaust upgrades and a nitrous line still ran from the intake to the trunk. I've been talking to some people and they were telling me I probablly had different gears in my rear end (not stock) because my car would run about 3000 rpm at around 70mph in overdrive (4th gear)

My question is.. what rear end gears came stock in my car? And what gears would be best since I'm not going to be drag racing, but I'm getting rid of the AOD & installing a 5-speed. I would also like to run a shot of NOS every once and a blue moon just for adrenaline kicks!:nogrinner


Most people say 3.73 is what I need. What do you guys think? And is there any way I can tell what gears I have in the car now??... I will take it apart if I need to look inside!

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post #2 of 26 (permalink) Old 05-05-2008
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the stock gears that came in the car were 2.73's my oppinion is 3.73's are a little tall for daily driving. i like 3.27's and 3.55's. you can tell whats in there by popping the diferential cover off and divide the number of teeth on the ring gear by the number of teeth on the pinion gear
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post #3 of 26 (permalink) Old 05-05-2008 Thread Starter
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the stock gears that came in the car were 2.73's my oppinion is 3.73's are a little tall for daily driving. i like 3.27's and 3.55's. you can tell whats in there by popping the diferential cover off and divide the number of teeth on the ring gear by the number of teeth on the pinion gear
How do I tell which gear is the ring gear...and which gear is the pinion gear?.. Is there a diagram somewhere that might show me?

-1992 MUSTANG LX 5.0 Convertible
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post #4 of 26 (permalink) Old 05-05-2008
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How do I tell which gear is the ring gear...and which gear is the pinion gear?.. Is there a diagram somewhere that might show me?

ring is on the left ........pinion on the right
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Last edited by EagleAutosports; 05-06-2008 at 06:27 PM. Reason: merged 2 posts
post #5 of 26 (permalink) Old 05-05-2008
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figure what gears you have

lift the rear of the car and support it. spin the rear wheels exactly one full turn and count the number of times the drive shaft spins. if your rear wheels turn one full time and the drive shaft turns 3 3/4 turns ratio would be 3.73. if your rear wheels turn once and the shaft turns 4 1/8 turns, you have 4.10 etc. thats an easy way without removing anything.

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post #6 of 26 (permalink) Old 05-05-2008 Thread Starter
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lift the rear of the car and support it. spin the rear wheels exactly one full turn and count the number of times the drive shaft spins. if your rear wheels turn one full time and the drive shaft turns 3 3/4 turns ratio would be 3.73. if your rear wheels turn once and the shaft turns 4 1/8 turns, you have 4.10 etc. thats an easy way without removing anything.

Thanks for the help guys! I'm going to try this out and THEN if that doesn't work out... I'll just pull the cover off and count the teeth! :nogrinner

I actually think I have 4.10 gears because my car was hitting 3000 rpm in 4th gear/overdrive at just 70 mph. What's the advantage of 4.10 gears over 3.73 gears and whatnot?

-1992 MUSTANG LX 5.0 Convertible
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post #7 of 26 (permalink) Old 05-06-2008
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I can tell you there'll be a difference between 3:73 and 4:10's. I have 3:73's, AOD and a 2800 stall converter and at 70 mph I'm around 2500-2600. Definately sounds like 4:10's to me. They do well with the AOD, some say they're too much with the 5 speed but only one way to know... wait till you swap to a 5 speed and see. You might not have a problem with them, you might not like them.

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post #8 of 26 (permalink) Old 05-06-2008
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i had a set of 4.10's in mine with a 5 speed and really didn't like them. they are definitely fun but i was constantly in 5th gear around town
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post #9 of 26 (permalink) Old 05-06-2008
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yep 4:10s make ya shift alot, dont care for em in a daily driver 5spd. thats my .02






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post #10 of 26 (permalink) Old 05-06-2008 Thread Starter
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I should be able to figure it out tomorrow or the next day... I got MOST of my swap done today. The interior part is wrapped up and my manual pedal assembly is installed and ready to go!

Now I just have to pull the AOD off and bolt up the T-5. Tomorrow might be the day that my stang gets REBORN a 5-speed!!

I think I have 4.10 gears...what's that gonna do to my gas mileage and what ratio would be best for every day driving?

-1992 MUSTANG LX 5.0 Convertible
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Not to bring up an old thread but....

Quote:
Originally Posted by Duel Mustangs View Post
lift the rear of the car and support it. spin the rear wheels exactly one full turn and count the number of times the drive shaft spins. if your rear wheels turn one full time and the drive shaft turns 3 3/4 turns ratio would be 3.73. if your rear wheels turn once and the shaft turns 4 1/8 turns, you have 4.10 etc. thats an easy way without removing anything.
So if this is the case, if you spin the wheel one full turn and the driveshaft spins 3 1/2 times, does this mean 3.55s? Did they put 3.55s in 92 LXs at the factory?
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Quote:
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So if this is the case, if you spin the wheel one full turn and the driveshaft spins 3 1/2 times, does this mean 3.55s? Did they put 3.55s in 92 LXs at the factory?
The factory did not put those in but I have heard of Dealerships installing the better gear ratios. And yes tha would mean you have 3.55 if you counted right...
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The factory did not put those in but I have heard of Dealerships installing the better gear ratios. And yes tha would mean you have 3.55 if you counted right...
I counted a few times and i got the same thing 3 times...So, is it worth all the money to upgrade to 3.73s?
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I counted a few times and i got the same thing 3 times...So, is it worth all the money to upgrade to 3.73s?
IMO, no, it's not worth the money or work. I've got a 3.55 in my '93LX. Had an '88 GT with 3.73s. Not a HUGE amount of difference. Figure it on a percentage basis. 3.73 -3.55 = .18 / 3.55 = .05 or only 5 percent. So, with the .3.55 you will be turning 5 percent less RPM at a given speed than you would with the 3.73.

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The code on the door data tag will tell you what the car came with from the factory. It is under the heading of AX on the door tag. M=2.73's and E=3.27's. These were the only two gears available for an AOD.

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