what rear gears? I'd run more gear with an overdrive before a stall converter.

Gears are stock from the orginal 289 C4 set up.
i think 280's

The motor is just a street toy for cruse night.
The AOD is for weekend coast runs on the interstates
 

As others have mentioned, gears would be a better choice.

You didn't mention what year model the AOD is. The better models are from 1988-1993. Models from '87 back to 1980 have various internal flaws from the factory, most notable, a lack of lubrication to the tail bushing. Lower gears (higher numerically) will make this problem worse if it's a pre-'88 model.

Regardless of automatic transmission type, one of the best and smartest things you can install is a transmission cooler --plumbed in series from the outlet of the cooling tank of the radiator to the fluid return line port on the transmission. Plate type coolers are superior to fin type.

I know this is a truck but this is an example of a Ford factory plate type transmission cooler I robbed from a 1992 F-150 and installed in my '69 F-100 with its stock C-4. Eventually, it'll cool the 4 R 70 W Ford 4-speed automatic overdrive transmission I have.

With the mention of 2.80 gears, that tells me you currently have an 8 - inch rear end under the car. The aftermarket has various rear gear ratios available.

Talking strictly Ford factory gears, and if you were looking for donor gears from a wrecking yard donor; lower gear sets (higher numerically) are not real common in vehicles with an 8 - inch rear end. In many cases, 3.00:1 is about as good as it gets. However, there were some vehicles that had 3.25, 3.40, 3.50, 3.55 or 3.80 gears in an 8-inch.

If donor gears are what you're after,  the best possibility to find a set of 3.40s or 3.55s would be to locate a '74-'78 Mustang I I or Pinto. Mavericks or Comets of that relative era may have them also. Some have Traction-Lok differentials, most do not. As an example, I have an 8-inch rear end assembly that came out of a '76 Mustang Cobra I I (302 V-8) with a 3.00:1 ratio but it does have a Traction-Lok differential. I also have an 8-inch 3rd member I pulled out of a '74 Mustang I I that had something less than a V-8 in it. It's a single track differential but does have 3.55:1 gears.

If you're looking for new aftermarket gears, there are some ratios available other than what came from the factory.

Great info guys.
So heres another question for ya.
What iif i just stay with the C4. and the 2.80 gears.

It just sounds like im not gaining alot for the investment.

And the AOD i have is a 89' fox body, but its been beat on. Its have way down on my bench and is defenatly burnt.
So id have to put a least $350 in it, and then all the conversion gagets $200.

When the C4 is fresh rebuild and new converter.


 

Yep thats what im going to do!
Ive been working on her for four years. Every nut and bolt and i mean every one.
You could eat off any part of her.
Im so close i can feel it.
Motor is running on a stand as is broke in.
She ready for it, everything done.
Motor in, mount fenders, hood, front grill, etc. Final paint, drive!
Ive kicking this around for to long, time to do something.
Thanks

MustangSteve wrote:

Do the math...  If you change to 3.70 gears with the AOD and a 0.76:1 overdrive, the car will have the equivalent of a 2.81:1 rear gear at highway cruise.  Basically a NET ZERO change at cruise RPM.
So, if final drive ratio and highway cruising is the goal, you could just as easily use the C-4 and gears you have.

Your car will be a dog with the 2.80 gear and overdrive, equivalent of that C-4 with a 2.13:1 final drive ratio.  If you add a stall converter, it will be slipping ALOT at the low RPM highway cruise and that generates extra heat and a shorter tranny life.

If you decide to go with the AOD, go with at LEAST a 3.25:1 ratio, preferably 3.50:1 or 3.70:1.  That last one would be my choice if you really want to wake up the car and have a decent cruise RPM also.  You will not BELIEVE the difference a 3.70:1 rear gear will make.  It is really the first step up to a performance gear.

 
OP mentioned a 2.80 ratio. That means the rear end is an 8-inch. The 3.70 ratio wasn't available in an 8-inch. That was a 9-inch only ratio. The closest 8-inch ratio to that would be a 3.80.

The AOD overdrive ratio would be .68:1 (.677:1) instead of .76:1. Final drive with AOD and 3.70 gears would be 2.52:1 instead of 2.81:1 but, since it's an 8-inch, the 3.70 ratio isn't an option.

If the rear ratio was 3.80, final drive with the AOD would be 2.60:1.

With a 3.25 rear gear it would be 2.21:1.

With a 3.40 rear gear it would be 2.31:1.

3.50 would be 2.38:1.

3.55 would be 2.41:1.

incredable information guys.
this prety much solves my delimma.
stock it shall be.
no need to invest the time and money for no gain.

besides, most of the driven will be cruse nights from red light to redlight anyway.
il just leave early and take my time if i decide to travel out of town.

Thanks