Drivetrain Rear Gears For An Automatic

Justin87 · Sep 20, 2017

Hey Guys

I know it's kind of a loaded question, but whats the consensus on the best rear gears for an automatic transmission? I had 3.73's in my previous 90GT 5/speed and I absolutely loved them but my new ride is an AOD.

The car is totally stock, it's NOT a daily driver and it never will be. I plan on using it as a weekend/fun hobby car with occasional trips to the drag strip. Currently the car is sitting on 16" pony wheels with 225/55r16's.

Future plans are budget minded and subject to change but I am thinking:

-Explorer intake
-GT40P heads
-Mild cam (e303 or something)
-Full exhaust
-Subframes
-lowered
-upper/lower control arms
-shift kit
-bigger stall converter
-17" SVE wheels (or a set of black Enkies if I can find one)
-All associated goodies for the set up

Eventually I'd like to put it under boost but that's like a million miles away.

My gut says 4.10's but I'm not sure how bad the RPM's are going to be.

So, now that I've rambled on, Please tell me what you think the best rear gears are for an automatic!

Thanks alot!

89ripper · Sep 20, 2017

I wouldn't worry about your rpms more than how different the car is going to drive. You'll have one less gear in an AOD, technically 2 less since you shouldn't be beating on the car in OD.
I have 373s and just passing over quarter mile close to redline in 3rd gear.

mikestang63 · Sep 21, 2017

3.73's only get Ford
you will - need to adjust your TV cable as your car will shift sooner and a speedo gear to compensate for the lower gear ratio
I would also recommend a trans cooler

Mustang5L5 · Sep 21, 2017

I'd say go 3.73's. You might need a slightly taller tire as I was crossing the traps in 3rd pretty much at redline in my car when it was an AOD.

Also, since you can't go WOT in OD, it make driving at higher speed a PITA. You basically do lose a gear, and top end driving is different now due to this. On a Daily driver, I found it to be annoying at times to drive on the highway. On a weekend fun car, probably not so much unless you want to drive an hour to/from car shows or the track.

If this was a trailered drag car...4.10's or 4.30/4.56. You'll just need to adjust tire size to make sure you don't run out of 3rd gear before the traps. This alone may limit you to 4.10's.

Justin87 · Sep 21, 2017

The idea of 4.10's really only appealed to the 16-year-old in me lol, but you guys have definitely confirmed that I won't be doing that.

I'm basically thinking that 3.73's are the way to go or (based on what you guys are saying) the 3.55s but only if it helps with the top end redline issue you guys had mentioned.

Mustang5L5 · Sep 21, 2017

It all depends on your use. I will say, 3.73's and a good sticky tire is fun in an AOD car. I went from 14.6's to 14.1's in my AOD LX with just a change to 3.73's in addition to pullies and a cobra intake and exhaust mods. A good 2-foot launch and i'd be out front of all my buddies and their stick cars and they would have to play chase. It woke the car up that much despite it's top end shortcomings which only became a factor as the top end of the track, and when I was on the highway driving 1hr+ or so.

If you said your use was DD mostly and an occasional drag strip pass, I'd say go 3.55's, but since this a weekend fun car, I'd go 3.73's.

But really...it;'s your call as you will be the one driving it.

I'd recommend adding a bigger trans cooler and bypassing the radiator cooler all together.

As quick as my car was with the AOD, I did eventually swap it to a 5-spd and haven't been back to a track since.

Drivetrain Rear Gears For An Automatic

Justin87

89ripper

mikestang63

Mustang5L5

That is…until I whipped out my Bissell

Justin87

Mustang5L5

That is…until I whipped out my Bissell

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Drivetrain Rear Gears For An Automatic

Justin87

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mikestang63

Mustang5L5

That is…until I whipped out my Bissell

Justin87

Mustang5L5

That is…until I whipped out my Bissell

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